WorldWideScience

Sample records for advanced wavefront measurement

  1. Advanced wavefront measurement and analysis of laser system modeling

    Energy Technology Data Exchange (ETDEWEB)

    Wolfe, C.R.; Auerback, J.M. [Lawrence Livermore National Lab., CA (United States)

    1994-11-15

    High spatial resolution measurements of the reflected or transmitted wavefronts of large aperture optical components used in high peak power laser systems is now possible. These measurements are produced by phase shifting interferometry. The wavefront data is in the form of 3-D phase maps that reconstruct the wavefront shape. The emphasis of this work is on the characterization of wavefront features in the mid-spatial wavelength range (from 0.1 to 10.0 mm) and has been accomplished for the first time. Wavefront structure from optical components with spatial wavelengths in this range are of concern because their effects in high peak power laser systems. At high peak power, this phase modulation can convert to large magnitude intensity modulation by non-linear processes. This can lead to optical damage. We have developed software to input the measured phase map data into beam propagation codes in order to model this conversion process. We are analyzing this data to: (1) Characterize the wavefront structure produced by current optical components, (2) Refine our understanding of laser system performance, (3) Develop a database from which future optical component specifications can be derived.

  2. Advanced Wavefront Control Techniques

    Energy Technology Data Exchange (ETDEWEB)

    Olivier, S S; Brase, J M; Avicola, K; Thompson, C A; Kartz, M W; Winters, S; Hartley, R; Wihelmsen, J; Dowla, F V; Carrano, C J; Bauman, B J; Pennington, D M; Lande, D; Sawvel, R M; Silva, D A; Cooke, J B; Brown, C G

    2001-02-21

    this project, work was performed in four areas (1) advanced modeling tools for deformable mirrors (2) low-order wavefront correctors with Alvarez lenses, (3) a direct phase measuring heterdyne wavefront sensor, and (4) high-spatial-frequency wavefront control using spatial light modulators.

  3. Wavefront Measurement in Ophthalmology

    Science.gov (United States)

    Molebny, Vasyl

    Wavefront sensing or aberration measurement in the eye is a key problem in refractive surgery and vision correction with laser. The accuracy of these measurements is critical for the outcome of the surgery. Practically all clinical methods use laser as a source of light. To better understand the background, we analyze the pre-laser techniques developed over centuries. They allowed new discoveries of the nature of the optical system of the eye, and many served as prototypes for laser-based wavefront sensing technologies. Hartmann's test was strengthened by Platt's lenslet matrix and the CCD two-dimensional photodetector acquired a new life as a Hartmann-Shack sensor in Heidelberg. Tscherning's aberroscope, invented in France, was transformed into a laser device known as a Dresden aberrometer, having seen its reincarnation in Germany with Seiler's help. The clinical ray tracing technique was brought to life by Molebny in Ukraine, and skiascopy was created by Fujieda in Japan. With the maturation of these technologies, new demands now arise for their wider implementation in optometry and vision correction with customized contact and intraocular lenses.

  4. Curvature sensor for ocular wavefront measurement.

    Science.gov (United States)

    Díaz-Doutón, Fernando; Pujol, Jaume; Arjona, Montserrat; Luque, Sergio O

    2006-08-01

    We describe a new wavefront sensor for ocular aberration determination, based on the curvature sensing principle, which adapts the classical system used in astronomy for the living eye's measurements. The actual experimental setup is presented and designed following a process guided by computer simulations to adjust the design parameters for optimal performance. We present results for artificial and real young eyes, compared with the Hartmann-Shack estimations. Both methods show a similar performance for these cases. This system will allow for the measurement of higher order aberrations than the currently used wavefront sensors in situations in which they are supposed to be significant, such as postsurgery eyes.

  5. Improved wavefront reconstruction algorithm from slope measurements

    Science.gov (United States)

    Phuc, Phan Huy; Manh, Nguyen The; Rhee, Hyug-Gyo; Ghim, Young-Sik; Yang, Ho-Soon; Lee, Yun-Woo

    2017-03-01

    In this paper, we propose a wavefront reconstruction algorithm from slope measurements based on a zonal method. In this algorithm, the slope measurement sampling geometry used is the Southwell geometry, in which the phase values and the slope data are measured at the same nodes. The proposed algorithm estimates the phase value at a node point using the slope measurements of eight points around the node, as doing so is believed to result in better accuracy with regard to the wavefront. For optimization of the processing time, a successive over-relaxation method is applied to iteration loops. We use a trial-and-error method to determine the best relaxation factor for each type of wavefront in order to optimize the iteration time and, thus, the processing time of the algorithm. Specifically, for a circularly symmetric wavefront, the convergence rate of the algorithm can be improved by using the result of a Fourier Transform as an initial value for the iteration. Various simulations are presented to demonstrate the improvements realized when using the proposed algorithm. Several experimental measurements of deflectometry are also processed by using the proposed algorithm.

  6. Advanced Imaging Optics Utilizing Wavefront Coding.

    Energy Technology Data Exchange (ETDEWEB)

    Scrymgeour, David [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Boye, Robert [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Adelsberger, Kathleen [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

    2015-06-01

    Image processing offers a potential to simplify an optical system by shifting some of the imaging burden from lenses to the more cost effective electronics. Wavefront coding using a cubic phase plate combined with image processing can extend the system's depth of focus, reducing many of the focus-related aberrations as well as material related chromatic aberrations. However, the optimal design process and physical limitations of wavefront coding systems with respect to first-order optical parameters and noise are not well documented. We examined image quality of simulated and experimental wavefront coded images before and after reconstruction in the presence of noise. Challenges in the implementation of cubic phase in an optical system are discussed. In particular, we found that limitations must be placed on system noise, aperture, field of view and bandwidth to develop a robust wavefront coded system.

  7. Measuring optical transmission matrices by wavefront shaping

    CERN Document Server

    Yoon, Jonghee; Park, Jongchan; Park, YongKeun

    2015-01-01

    We introduce a simple but practical method to measure the optical transmission matrix (TM) of complex media. The optical TM of a complex medium is obtained by modulating the wavefront of a beam impinging on the complex medium and imaging the transmitted full-field speckle intensity patterns. Using the retrieved TM, we demonstrate the generation and linear combination of multiple foci on demand through the complex medium. This method will be used as a versatile tool for coherence control of waves through turbid media.

  8. Gaussian weighting of ocular wave-front measurements.

    Science.gov (United States)

    Schwiegerling, Jim

    2004-11-01

    The measurement of ocular wave-front error gives insight into the optical performance of the eye and possibly a means for assessing visual performance. The visual system responds not only to the quality of the optical image formed on the retina but also to the processing that occurs in the retina and the brain. To develop a metric of visual performance based on wave-front error measurements, these latter processes must somehow be incorporated. In representing the wave-front error in terms of Zernike polynomials, it appears that terms with lower angular frequency have a greater deleterious effect on visual performance than higher-angular-frequency terms. A technique for weighting the pupil function of the eye with a Gaussian filter is demonstrated. It is further demonstrated that the variance of the Gaussian-weighted wave-front error is well correlated with visual performance.

  9. Wavefront measurement of plastic lenses for mobile-phone applications

    Science.gov (United States)

    Huang, Li-Ting; Cheng, Yuan-Chieh; Wang, Chung-Yen; Wang, Pei-Jen

    2016-08-01

    In camera lenses for mobile-phone applications, all lens elements have been designed with aspheric surfaces because of the requirements in minimal total track length of the lenses. Due to the diffraction-limited optics design with precision assembly procedures, element inspection and lens performance measurement have become cumbersome in the production of mobile-phone cameras. Recently, wavefront measurements based on Shack-Hartmann sensors have been successfully implemented on injection-molded plastic lens with aspheric surfaces. However, the applications of wavefront measurement on small-sized plastic lenses have yet to be studied both theoretically and experimentally. In this paper, both an in-house-built and a commercial wavefront measurement system configured on two optics structures have been investigated with measurement of wavefront aberrations on two lens elements from a mobile-phone camera. First, the wet-cell method has been employed for verifications of aberrations due to residual birefringence in an injection-molded lens. Then, two lens elements of a mobile-phone camera with large positive and negative power have been measured with aberrations expressed in Zernike polynomial to illustrate the effectiveness in wavefront measurement for troubleshooting defects in optical performance.

  10. Wavefront sensing with all-digital Stokes measurements

    CSIR Research Space (South Africa)

    Dudley, Angela L

    2014-09-25

    Full Text Available . INTRODUCTION The quest for efficient and precise measurement techniques of the phase (or wavefront) of an optical field has led to some conventional, state-of-the-art methods, ranging from ray tracing [1], pyramid sensors [2], interferometers [3, 4...] on our SLM, to construct an adjustment-free, computer-controlled measurement scheme. We illustrate the robustness of our technique by measuring the wavefront of a variety of static and propagating optical fields such as vortex, Bessel, Airy and speckle...

  11. Relative optical wavefront measurement in displacement measuring interferometer systems with sub-nm precision

    NARCIS (Netherlands)

    Meskers, A.J.H.; Voigt, D.; Spronck, J.W.

    2013-01-01

    Many error sources can affect the accuracy of displacement measuring interferometer systems. In heterodyne interferometry two laser source frequencies constitute the finally detected wavefront. When the wavefronts of these source frequencies are non-ideal and one of them walks off the detector, the

  12. Common-Path Wavefront Sensing for Advanced Coronagraphs

    Science.gov (United States)

    Wallace, J. Kent; Serabyn, Eugene; Mawet, Dimitri

    2012-01-01

    Imaging of faint companions around nearby stars is not limited by either intrinsic resolution of a coronagraph/telescope system, nor is it strictly photon limited. Typically, it is both the magnitude and temporal variation of small phase and amplitude errors imparted to the electric field by elements in the optical system which will limit ultimate performance. Adaptive optics systems, particularly those with multiple deformable mirrors, can remove these errors, but they need to be sensed in the final image plane. If the sensing system is before the final image plane, which is typical for most systems, then the non-common path optics between the wavefront sensor and science image plane will lead to un-sensed errors. However, a new generation of high-performance coronagraphs naturally lend themselves to wavefront sensing in the final image plane. These coronagraphs and the wavefront sensing will be discussed, as well as plans for demonstrating this with a high-contrast system on the ground. Such a system will be a key system-level proof for a future space-based coronagraph mission, which will also be discussed.

  13. Near infrared reflective shearing point diffraction interferometer for dynamic wavefront measurement

    Science.gov (United States)

    Zhu, Wenhua; Chen, Lei; Zheng, Donghui

    2016-09-01

    A near infrared reflective shearing point diffraction interferometer (NIRSPDI) is designed for large-aperture dynamic wave-front measurement. The PDI is integrated on the small substrate with properly designed thin film. The wave-front under test is reflected by the front and rear surfaces of the substrate respectively to generate an interferogram with high linear-carrier frequency, which is used to reconstruct the wave-front by means of the Fourier transform algorithm. In this article, the system error and the major parameters of NIRSPDI are discussed. In addition, we give an effective method to adjust NIRSPDI for fast measurement. Experimentally NIRSPDI was calibrated by a standard spherical surface and then it was applied to the dynamic wave-front with a diameter of 400mm. The measured results show the error of whole system which verifies that the proposed NIRSPDI is a powerful tool for large-aperture dynamic wave-front measurement.

  14. Wavefront-sensor-based electron density measurements for laser-plasma accelerators

    Energy Technology Data Exchange (ETDEWEB)

    Plateau, Guillaume; Matlis, Nicholas; Geddes, Cameron; Gonsalves, Anthony; Shiraishi, Satomi; Lin, Chen; van Mourik, Reinier; Leemans, Wim

    2010-02-20

    Characterization of the electron density in laser produced plasmas is presented using direct wavefront analysis of a probe laser beam. The performance of a laser-driven plasma-wakefield accelerator depends on the plasma wavelength, hence on the electron density. Density measurements using a conventional folded-wave interferometer and using a commercial wavefront sensor are compared for different regimes of the laser-plasma accelerator. It is shown that direct wavefront measurements agree with interferometric measurements and, because of the robustness of the compact commercial device, have greater phase sensitivity, straightforward analysis, improving shot-to-shot plasma-density diagnostics.

  15. Telescope Alignment From Sparsely Sampled Wavefront Measurements Over Pupil Subapertures

    Science.gov (United States)

    Bloemhof, Eric E.; An, Xin; Kuan, Gary M.; Moore, Douglas M.; OShay, Joseph F.; Tang, Hong; Page, Norman A.

    2012-01-01

    Alignment of two-element telescopes is a classic problem. During recent integration and test of the Space Interferometry Mission s (SIM s) Astrometric Beam Combiner (ABC), the innovators were faced with aligning two such telescope subsystems in the presence of a further complication: only two small subapertures in each telescope s pupil were accessible for measuring the wavefront with a Fizeau interferometer. This meant that the familiar aberrations that might be interpreted to infer system misalignments could be viewed only over small sub-regions of the pupil, making them hard to recognize. Further, there was no contiguous surface of the pupil connecting these two subapertures, so relative phase piston information was lost; the underlying full-aperture aberrations therefore had an additional degree of ambiguity. The solution presented here is to recognize that, in the absence of phase piston, the Zygo measurements primarily provide phase tilt in the subaperture windows of interest. Because these windows are small and situated far from the center of the (inaccessible) unobscured full aperture, any aberrations that are higher-order than tilt will be extremely high-order on the full aperture, and so not necessary or helpful to the alignment. Knowledge of the telescope s optical prescription allows straightforward evaluation of sensitivities (subap mode strength per unit full-aperture aberration), and these can be used in a predictive matrix approach to move with assurance to an aligned state. The technique is novel in every operational way compared to the standard approach of alignment based on full-aperture aberrations or searching for best rms wavefront. This approach is closely grounded in the observable quantities most appropriate to the problem. It is also more intuitive than inverting full phase maps (or subaperture Zernike spectra) with a ray-tracing program, which must certainly work in principle, but in practice met with limited success. Even if such

  16. Pupil phase discontinuity measurement: comparison of different wavefront sensing concepts

    Science.gov (United States)

    El Hadi, K.; Sauvage, J.-F.; Dohlen, K.; Fusco, T.; Neichel, B.; Marchis, F.; N'Diaye, M.

    2016-07-01

    The Laboratoire d'Astrophysique de Marseille is involved in the preparation of the E-ELT instrumentation framework: In particular, an ESO-EELT M1 mirror segment (1.5 m) has been demonstrated and different wavefront sensing (WFS) concepts among which Pyramid, Zernike phase mask sensor (ZELDA), Phase diversity or still NL Curvature) are also investigated. Segmented mirrors are widely used today in diverse domains: fiber coupling, laser beam shaping, microscopy or retina imaging. If, these mirrors offer a solution to realize important monolithic sizes for giant telescopes in astronomy, they also raise the problem of segments cophasing and measurement of phase discontinuities. In this work, we aim to investigate a suitable WFS approach for pupil phase discontinuity measurement. Coupling a segmented PTT mirror (Iris AO) with four different WFS (Shack-Hartmann, Quadriwave Lateral Shearing Interferometer, Pyramid and Zernike Phase Mask), we study their sensitivity to segmented pupil: in particular, segment phasing, stability, saturation, flat, or still the addressing mode are then performed and compared.

  17. The construction of individual eye model based on eye's wavefront aberration measurement

    Science.gov (United States)

    Wang, Zhao-Qi; Guo, Huan-Qing

    2005-08-01

    Based on the widely used Gullstrand-Le Grand eye model, the individual human eye model has been established here, which has individual corneal data, anterior chamber depth and the eyeball depth. Furthermore the foremost thing is that the wavefront aberration calculated from the individual eye model is equal to the eye's wavefront aberration measured with the Hartmann-shack wavefront sensor. There were four main steps to build the model. Firstly, the corneal topography instrument was used to measure the corneal surfaces and depth. And in order to input cornea into the optical model, high order aspheric surface-Zernike Fringe Sag surface was chosen to fit the corneal surfaces. Secondly, the Hartmann-shack wavefront sensor, which can offer the Zernike polynomials to describe the wavefront aberration, was built to measure the wavefront aberration of the eye. Thirdly, the eye's axial lengths among every part were measured with A-ultrasonic technology. Then the data were input into the optical design software -ZEMAX and the crystalline lens's shapes were optimized with the aberration as the merit function. The individual eye model, which has the same wavefront aberrations with the real eye, is established.

  18. Broadband Interferometer for Measuring Transmitted Wavefronts of Optical Bandpass Filters for HST (ACS)

    Science.gov (United States)

    Boucarut, R. A.; Leviton, D. B.

    1998-01-01

    The transmitted wavefronts of optical filters for the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) are characterized using the Wildly and Openly Modified Broadband Achromatic Twyman Green (WOMBAT) Interferometer developed in the NASA/GSFC Optics Branch's Diffraction Grating Evaluation Facility (DGEF). Because only four of thirty-three of ACS's optical bandpass filters transmit the 633 nm light of most commercial interferometers, a broadband interferometer is required to verify specified transmitted wavefront of ACS filters. WOMBAT's design is a hybrid of the BAT interferometer developed by JPL used for HST Wide Field and Planetary Camera 2 (WFPC-2) filters and a WYKO 400 phase shifting interferometer. It includes a broadband light source, monochromator, off-axis, parabolic collimating and camera mirrors, an aluminum-coated fused silica beam splitter, flat retroreflecting mirrors for the test and reference arms, and a LTV-sensitive CCD camera. An outboarded, piezo-electric phase shifter holds the flat mirror in the interferometer's reference arm. The interferometer is calibrated through interaction between the WYKO system's software and WONMAT hardware for the test wavelength of light entering the beam splitter. Phase-shifted interferograms of the filter mounted in the test arm are analyzed using WYKO's Vision' software. Filters as large as 90 mm in diameter have been measured over a wavelength range from 200 to 1100 nm with a sensitivity of lambda/200 rms at lambda = 633 nm. Results of transmitted wavefront measurements are shown for ACS fixed band pass and spatially-variable bandpass filters for a variety of wavelengths.

  19. Broadband Interferometer for Measuring Transmitted Wavefronts of Optical Bandpass Filters for HST (ACS)

    Science.gov (United States)

    Boucarut, R. A.; Leviton, D. B.

    1998-01-01

    The transmitted wavefronts of optical filters for the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) are characterized using the Wildly and Openly Modified Broadband Achromatic Twyman Green (WOMBAT) Interferometer developed in the NASA/GSFC Optics Branch's Diffraction Grating Evaluation Facility (DGEF). Because only four of thirty-three of ACS's optical bandpass filters transmit the 633 nm light of most commercial interferometers, a broadband interferometer is required to verify specified transmitted wavefront of ACS filters. WOMBAT's design is a hybrid of the BAT interferometer developed by JPL used for HST Wide Field and Planetary Camera 2 (WFPC-2) filters and a WYKO 400 phase shifting interferometer. It includes a broadband light source, monochromator, off-axis, parabolic collimating and camera mirrors, an aluminum-coated fused silica beam splitter, flat retroreflecting mirrors for the test and reference arms, and a LTV-sensitive CCD camera. An outboarded, piezo-electric phase shifter holds the flat mirror in the interferometer's reference arm. The interferometer is calibrated through interaction between the WYKO system's software and WONMAT hardware for the test wavelength of light entering the beam splitter. Phase-shifted interferograms of the filter mounted in the test arm are analyzed using WYKO's Vision' software. Filters as large as 90 mm in diameter have been measured over a wavelength range from 200 to 1100 nm with a sensitivity of lambda/200 rms at lambda = 633 nm. Results of transmitted wavefront measurements are shown for ACS fixed band pass and spatially-variable bandpass filters for a variety of wavelengths.

  20. Specification and Measurement of Mid-Frequency Wavefront Errors

    Institute of Scientific and Technical Information of China (English)

    XUAN Bin; XIE Jing-jiang

    2006-01-01

    Mid-frequency wavefront errors can be of the most importance for some optical components, but they're not explicitly covered by corresponding international standards such as ISO 10110. The testing methods for the errors also have a lot of aspects to be improved. This paper gives an overview of the specifications especially of PSD. NIF,developed by America, and XMM, developed by Europe, have both discovered some new testing methods.

  1. Study on the modification of measured wavefront aberration data for customized visual correction

    Science.gov (United States)

    Liu, Ming; Zhang, Yong; Zhang, Zhidong; Quan, Wei; An, Li

    2008-12-01

    Wavefront aberration of human eye is an important foundation for customized vision correction. In most current aberrometers, near infrared light is used to measure ocular wavefront aberration, whereas for customized visual correction, wavefront aberration data in visible range are required. With the measured wavefront aberration, corneal topography and eye's axial lengths data, individual eye models for twenty normal human eyes are constructed with the optical design software ZEMAX. Changing the incidence light wavelength and the refractive indexes of eye models, the values of defocus, astigmatism, higher-order aberrations in the measuring wavelength (833nm) and at the most sensitive wavelength of human eye (555nm) are obtained. Average focus shift between 833nm and 555nm is found to be about 0.94D, and different slightly for different individuals; the differences of astigmatism and higher-order aberrations between 833nm and 555nm are quite slight. For customized visual correction, the measured defocus value should be modified, whereas the measured astigmatism and higher-order aberrations could be used directly for the current correction precision. Individual eye model is a useful tool for accurate transformation of the measured wavefront aberration data into the data for visible spectrum.

  2. The shape of the radio wavefront of extensive air showers as measured with LOFAR

    CERN Document Server

    Corstanje, A; Nelles, A; Buitink, S; Enriquez, J E; Falcke, H; Frieswijk, W; Hörandel, J R; Krause, M; Rachen, J P; Scholten, O; ter Veen, S; Thoudam, S; Trinh, G; Akker, M van den; Alexov, A; Anderson, J; Avruch, I M; Bell, M E; Bentum, M J; Bernardi, G; Best, P; Bonafede, A; Breitling, F; Broderick, J; Butcher, H R; Ciardi, B; de Gasperin, F; de Geus, E; de Vos, M; Duscha, S; Eislöffel, J; Engels, D; Fallows, R A; Ferrari, C; Garrett, M A; Griessmeier, J; Gunst, A W; Hamaker, J P; Hoeft, M; Horneffer, A; Iacobelli, M; Juette, E; Karastergiou, A; Kohler, J; Kondratiev, V I; Kuniyoshi, M; Kuper, G; Maat, P; Mann, G; McFadden, R; McKay-Bukowski, D; Mevius, M; Munk, H; Norden, M J; Orru, E; Paas, H; Pandey-Pommier, M; Pandey, V N; Pizzo, R; Polatidis, A G; Reich, W; Röttgering, H; Scaife, A M M; Schwarz, D; Smirnov, O; Stewart, A; Swinbank, J; Tagger, M; Tang, Y; Tasse, C; Toribio, C; Vermeulen, R; Vocks, C; van Weeren, R J; Wijnholds, S J; Wucknitz, O; Yatawatta, S; Zarka, P

    2014-01-01

    Extensive air showers, induced by high energy cosmic rays impinging on the Earth's atmosphere, produce radio emission that is measured with the LOFAR radio telescope. As the emission comes from a finite distance of a few kilometers, the incident wavefront is non-planar. A spherical or conical shape of the wavefront has been proposed, but measurements of individual air showers have been inconclusive so far. For a selected high-quality sample of 161 measured extensive air showers, we have reconstructed the wavefront by measuring pulse arrival times to sub-nanosecond accuracy in 200 to 350 individual antennas. For each measured air shower, we have fitted a conical, spherical, and hyperboloid shape to the arrival times. The fit quality and a likelihood analysis show that a hyperboloid is the best parametrization. Using a non-planar wavefront shape gives an improved angular resolution, when reconstructing the shower arrival direction. Furthermore, a dependence of the wavefront shape on the shower geometry can be s...

  3. Estimating the point spread function of an imaging system using wavefront measurement

    Science.gov (United States)

    Mao, Hongjun; Liang, Yonghui; Huang, Zongfu; Liu, Jin; Jiang, Pengzhi

    2016-10-01

    An imaging system is constructed by atmosphere turbulence and ground-based telescope when the latter is used to observe a space object. The wavefront measurement produced by adaptive optics system can be used to estimate the point spread function (PSF) of the imaging system since it contains the wavefront aberration information of the light from the object. But the detector noise of the wavefront sensor (WFS) will inevitably bring estimation error. Based on the statistical theory, a method is presented to improve the PSF estimation accuracy by eliminating the noise error from the wavefront measurement. The numerical simulation shows that the estimation error of this method could be lower than 10%. It also indicates that the higher the signal-noise ratio (SNR) of the WFS is, the more frames of the wavefront measurements are used, and the bigger the Fried constant is, the more accurate the estimation will be. The work in this paper can be applied to performance evaluation of imaging system, deconvolution of AO images, as well as photometric analysis of space object.

  4. Wavefront shaping for imaging-based flow velocity measurements through distortions using a Fresnel guide star.

    Science.gov (United States)

    Koukourakis, Nektarios; Fregin, Bob; König, Jörg; Büttner, Lars; Czarske, Jürgen W

    2016-09-19

    Imaging-based flow measurement techniques, like particle image velocimetry (PIV), are vulnerable to time-varying distortions like refractive index inhomogeneities or fluctuating phase boundaries. Such distortions strongly increase the velocity error, as the position assignment of the tracer particles and the decrease of image contrast exhibit significant uncertainties. We demonstrate that wavefront shaping based on spatially distributed guide stars has the potential to significantly reduce the measurement uncertainty. Proof of concept experiments show an improvement by more than one order of magnitude. Possible applications for the wavefront shaping PIV range from measurements in jets and film flows to biomedical applications.

  5. The shape of the radio wavefront of extensive air showers as measured with LOFAR

    NARCIS (Netherlands)

    Corstanje, A.; et al., [Unknown; Swinbank, J.

    2015-01-01

    Extensive air showers, induced by high energy cosmic rays impinging on the Earth’s atmosphere, produce radio emission that is measured with the LOFAR radio telescope. As the emission comes from a finite distance of a few kilometers, the incident wavefront is non-planar. A spherical, conical or hyper

  6. Spatial-frequency analysis algorithm for in-situ measurement of wavefront

    Science.gov (United States)

    Liu, Qian; Wang, Yang; Ji, Fang; He, Jianguo

    2015-05-01

    To apply phase-shifting interferometry (PSI) to in-situ measurement, we have proposed an algorithm to detect and suppress phase-shifting error and contrast fluctuation. The phase shift and contrast are analyzed in spatial-frequency domain. The strength of baseband and sideband implies the pattern contrast. The position and phase angle of the sideband indicates the tilt gradients and translational value of phase shift. Thus, the phase shift error and contrast fluctuation could be extracted. A contrast-compensated equation is established to calculate the wavefront phase. The proposed algorithm was applied to the interferograms subjecting to vibration and wavefront phase was calculated. The experimental results show that, under vibration of one micron amplitude and 60Hz frequency, the error of wavefront PV value is less than 0.01wave and the 2σ repeatability is less than 0.01wave. For no hardware is required, the proposed algorithm provides a cost-effective method for wavefront in-situ measurement with PSI.

  7. Wave-front analysis of personal eye protection.

    Science.gov (United States)

    Eppig, Timo; Zoric, Katja; Speck, Alexis; Zelzer, Benedikt; Götzelmann, Jens; Nagengast, Dieter; Langenbucher, Achim

    2012-07-30

    Shack-Hartmann wave-front sensing has been successfully applied to many fields of optical testing including the human eye itself. We propose wave-front measurement for testing protective eye wear for production control and investigation of aberrations. Refractive power data is derived from the wave-front data and compared to a subjective measurement technique based on a focimeter. Additional image quality classification was performed with a multivariate model using objective parameters to resample a subjectively determined visual quality. Wave-front measurement advances optical testing of protective eye wear and may be used for objective quality control.

  8. More Zernike modes' open-loop measurement in the sub-aperture of the Shack-Hartmann wavefront sensor.

    Science.gov (United States)

    Zhu, Zhaoyi; Mu, Quanquan; Li, Dayu; Yang, Chengliang; Cao, Zhaoliang; Hu, Lifa; Xuan, Li

    2016-10-17

    The centroid-based Shack-Hartmann wavefront sensor (SHWFS) treats the sampled wavefronts in the sub-apertures as planes, and the slopes of the sub-wavefronts are used to reconstruct the whole pupil wavefront. The problem is that the centroid method may fail to sense the high-order modes for strong turbulences, decreasing the precision of the whole pupil wavefront reconstruction. To solve this problem, we propose a sub-wavefront estimation method for SHWFS based on the focal plane sensing technique, by which more Zernike modes than the two slopes can be sensed in each sub-aperture. In this paper, the effects on the sub-wavefront estimation method of the related parameters, such as the spot size, the phase offset with its set amplitude and the pixels number in each sub-aperture, are analyzed and these parameters are optimized to achieve high efficiency. After the optimization, open-loop measurement is realized. For the sub-wavefront sensing, we achieve a large linearity range of 3.0 rad RMS for Zernike modes Z2 and Z3, and 2.0 rad RMS for Zernike modes Z4 to Z6 when the pixel number does not exceed 8 × 8 in each sub-aperture. The whole pupil wavefront reconstruction with the modified SHWFS is realized to analyze the improvements brought by the optimized sub-wavefront estimation method. Sixty-five Zernike modes can be reconstructed with a modified SHWFS containing only 7 × 7 sub-apertures, which could reconstruct only 35 modes by the centroid method, and the mean RMS errors of the residual phases are less than 0.2 rad2, which is lower than the 0.35 rad2 by the centroid method.

  9. Sparse aperture differential piston measurements using the pyramid wave-front sensor

    CERN Document Server

    Arcidiacono, Carmelo; Yan, Zhaojun; Zheng, Lixin; Agapito, Guido; Wang, Chaoyan; Zhu, Nenghong; Zhu, Liyun; Cai, Jianqing; Tang, Zhenghong

    2016-01-01

    In this paper we report on the laboratory experiment we settled in the Shanghai Astronomical Observatory (SHAO) to investigate the pyramid wavefront sensor (WFS) ability to measure the differential piston on a sparse aperture. The ultimate goal is to verify the ability of the pyramid WFS work in closed loop to perform the phasing of the primary mirrors of a sparse Fizeau imaging telescope. In the experiment we installed on the optical bench we performed various test checking the ability to flat the wave-front using a deformable mirror and to measure the signal of the differential piston on a two pupils setup. These steps represent the background from which we start to perform full closed loop operation on multiple apertures. These steps were also useful to characterize the achromatic double pyramids (double prisms) manufactured in the SHAO optical workshop.

  10. Wavefront metrology measurements at SACLA by means of X-ray grating interferometry.

    Science.gov (United States)

    Kayser, Yves; Rutishauser, Simon; Katayama, Tetsuo; Ohashi, Haruhiko; Kameshima, Takashi; Flechsig, Uwe; Yabashi, Makina; David, Christian

    2014-04-21

    The knowledge of the X-ray wavefront is of importance for many experiments at synchrotron sources and hard X-ray free-electron lasers. We will report on metrology measurements performed at the SACLA X-ray Free Electron Laser by means of grating interferometry which allows for an at-wavelength, in-situ, and single-shot characterization of the X-ray wavefront. At SACLA the grating interferometry technique was used for the study of the X-ray optics installed upstream of the end station, two off-set mirror systems and a double crystal monochromator. The excellent quality of the optical components was confirmed by the experimental results. Consequently grating interferometry presents the ability to support further technical progresses in X-ray mirror manufacturing and mounting.

  11. Customized schematic eye model for refraction correction design based on ocular wavefront and corneal topography measurements

    Science.gov (United States)

    Curatu, Eugene O.; Pettit, George H.; Campin, John A.

    2002-06-01

    The subject of this paper relates to the ocular optical design and vision analysis of refractive correction of the eye. After the purpose statement and the assumption list, the concept of the schematic eye matching a particular (measured) wavefront is introduced. This concept is based on the fact that the ocular wavefront, together with the corneal topography, can be seen as the mathematical global representation of the eye working in monochromatic light and having a foveal vision. The discussed design technique, including an iterative optimization method, could be applied in any ocular correction that utilizes cornea topography and/or ocular wavefront, e.g. contact lens or intra-corneal implant. However, the application this paper refers to is the ocular refractive correction by a procedure using the LADARVISION. It consists of surgical removal and subsequent replacement of a corneal flap on a stromal surface whose shape has been changed by laser ablation of the tissue. Subsequent sections of this paper are dedicated to establishing the limits of possible refractive correction, the influences of the flap and corneal topography into the refractive correction calculation. Finally a realistic evaluation of the results and a list of possible developments of this new optical design method are discussed.

  12. Single-Shot Wavefront Measurement of an Injection-seeded Plasma-based Soft X-Ray Laser

    Science.gov (United States)

    Wang, S.; Li, L.; Wang, Y.; Oliva, E.; Yin, L.; Luther, B.; Maynard, G.; Ros, D.; Rocca, J. J.; Zeitoun, Ph.

    2013-10-01

    The wavefront of a λ = 18.9 nm soft x-ray beam from an injection-seeded plasma amplifier created by irradiation of a solid target was measured using a Hartmann wavefront sensor with an accuracy of λ/32 in a single shot. A significant improvement in wavefront aberrations from 0.51 +/- 0.06 λ rms of high harmonic seed to 0.23 +/- 0.01 λ rms for the amplified seeded beam was observed. The variation of wavefront characteristic as a function of time delay between the injection of the seed and peak of soft x-ray amplifier pump was studied. The wavefront sensor allows for the independent measurement of the different aberrations. The strongest improvement of the wavefront as it exits the amplifier is observed for coma, with values improve by more than a factor of 2, from 0.4l λ to 0.18 λ rms. The measurements were used to reconstruct the soft x-ray source and confirm its high peak brightness of about 1 ×1026 photons/(s.mm2.mrad2. 0.01 % bandwidth). Work supported by AMOS program, Office of Basic Energy Sciences of the US DoE, and the NSF ERC Program with equipment developed under NSF Award MRI-ARRA 09-561, and by LASERLAB3-INREX European project and SHYLAX plus CIBORG RTRA `Triangle de la Physique.'

  13. Measurement of corneal topography through Hartmann-Shack wave-front sensor

    Science.gov (United States)

    Yang, Jinsheng; Rao, Xuejun; Rao, Changhui

    2008-12-01

    A corneal topography based on Hartmann-Shack Sensor is presented in this paper. In the system, the focus of an objective lens is precisely positioned on cornea's curve center. Wave-front of the reflecting beam can be measured by the Hartmann-Shack sensor which is conjugate to the cornea plane. If the corneal surface is a perfect sphere, wave-front detected by the Hartmann-Shack sensor is a plane. As a result, data measured by Hartmann-Shacks sensor is the deviation between the sphere and the real cornea surface. This paper describes a methodology for designing instrument based on Hartmann-Shack sensor. Then, applying this method, an instrument is developed for accurate measurement of corneal topography. In addition, measuring principle of Hartmann-Shack sensor which determined system parameters is also introduced. Repeatability is demonstrated by a series of data. The instrument was able to accurately measure simulative cornea's reflective aberrations, from which corneal topography and corneal refractive aberrations were derived.

  14. The Infrared Imaging Spectrograph (IRIS) for TMT: multi-tiered wavefront measurements and novel mechanical design

    Science.gov (United States)

    Dunn, Jennifer; Andersen, David; Chapin, Edward; Reshetov, Vlad; Wierzbicki, Ramunas; Herriot, Glen; Chalmer, Dean; Isbrucker, Victor; Larkin, James E.; Moore, Anna M.; Suzuki, Ryuji

    2016-08-01

    The InfraRed Imaging Spectrograph (IRIS) will be the first light adaptive optics instrument on the Thirty Meter Telescope (TMT). IRIS is being built by a collaboration between Caltech, the University of California, NAOJ and NRC Herzberg. In this paper we present novel aspects of the Support Structure, Rotator and On-Instrument Wavefront Sensor systems being developed at NRC Herzberg. IRIS is suspended from the bottom port of the Narrow Field Infrared Adaptive Optics System (NFIRAOS), and provides its own image de-rotation to compensate for sidereal rotation of the focal plane. This arrangement is a challenge because NFIRAOS is designed to host two other science instruments, which imposes strict mass requirements on IRIS. As the mechanical design of all elements has progressed, we have been tasked with keeping the instrument mass under seven tonnes. This requirement has resulted in a mass reduction of 30 percent for the support structure and rotator compared to the most recent IRIS designs. To accomplish this goal, while still being able to withstand earthquakes, we developed a new design with composite materials. As IRIS is a client instrument of NFIRAOS, it benefits from NFIRAOS's superior AO correction. IRIS plays an important role in providing this correction by sensing low-order aberrations with three On-Instrument Wavefront Sensors (OIWFS). The OIWFS consists of three independently positioned natural guide star wavefront sensor probe arms that patrol a 2-arcminute field of view. We expect tip-tilt measurements from faint stars within the IRIS imager focal plane will further stabilize the delivered image quality. We describe how the use of On-Detector Guide Windows (ODGWs) in the IRIS imaging detector can be incorporated into the AO correction. In this paper, we present our strategies for acquiring and tracking sources with this complex AO system, and for mitigating and measuring the various potential sources of image blur and misalignment due to properties of

  15. Measuring aberrations in the rat brain by a new coherence-gated wavefront sensor using a Linnik interferometer

    Science.gov (United States)

    Wang, Jinyu; Leger, Jean-Francois; Binding, Jonas; Boccara, Claude; Gigan, Sylvain; Bourdieu, Laurent

    2012-03-01

    Wavefront distortions due to refractive index mismatch and tissue inhomogeneity may limit the resolution, contrast, signal strength and achievable imaging depth of microscope. Traditional Shack-Hartmann wavefront sensors can't be used in strongly scattering biological samples since there is no selection of the ballistic photons originating from the reference point in the sample amongst all the backscattered photons. In contrast, coherence-gated wavefront sensing (CGWS) allows the fast measurement of aberrations in scattering samples and therefore should permit adaptive corrections. We have implemented a new CGWS scheme based on a Linnik interferometer with Super Luminescent Emission Diode as low temporal coherence light source. Compared to the previously described CGWS system based on a femtosecond laser, its main advantages are the automatic compensation of dispersion between the two arms and its easy implementation on any microscope. The configuration of virtual Shack-Hartmann wavefront sensor for wavefront reconstruction was optimized, and the measurement precision was analyzed when multiple scattering was not negligible. In fresh rat brain slices, we successfully measured up to about 400 μm depth a known defocus aberration, obtained by axially displacing the coherence gate with respect to the actual focus in the sample.

  16. Measuring aberrations in the rat brain by coherence-gated wavefront sensing using a Linnik interferometer.

    Science.gov (United States)

    Wang, Jinyu; Léger, Jean-François; Binding, Jonas; Boccara, A Claude; Gigan, Sylvain; Bourdieu, Laurent

    2012-10-01

    Aberrations limit the resolution, signal intensity and achievable imaging depth in microscopy. Coherence-gated wavefront sensing (CGWS) allows the fast measurement of aberrations in scattering samples and therefore the implementation of adaptive corrections. However, CGWS has been demonstrated so far only in weakly scattering samples. We designed a new CGWS scheme based on a Linnik interferometer and a SLED light source, which is able to compensate dispersion automatically and can be implemented on any microscope. In the highly scattering rat brain tissue, where multiply scattered photons falling within the temporal gate of the CGWS can no longer be neglected, we have measured known defocus and spherical aberrations up to a depth of 400 µm.

  17. Directional property of the retinal reflection measured with optical coherence tomography and wavefront sensing

    Science.gov (United States)

    Gao, Weihua

    The last thirty years have experienced tremendous advancement in our understanding of light-tissue interactions in the human retina. Nevertheless, major gaps remain, and our modeling of light return from the back of the eye continues to evolve. The objective of this thesis is to investigate one of these gaps, specifically that related to the directional property (angular dependence) of the retinal reflection and in particular that of cone photoreceptors. Directionality of cones is commonly referred to as the optical Stiles-Crawford effect (SCE). While cone directionality is well known to originate from their waveguide properties, considerable uncertainty remains as to which reflections are waveguided. Since normal directionality of the photoreceptor requires normal morphology, the optical SCE has significant clinical interest. The research presented in this thesis contains three main objectives. First, I evaluated the potential of spectral-domain optical coherence tomography (SD-OCT) to study the optical SCE. Second, motivated by these first results, I developed a custom high-resolution SD-OCT that was designed specifically for directional reflectance measurements. This allowed a more complete study to be performed and extended the analysis from photoreceptors to several other major layers of the retina. Directional properties were measured for the retinal pigment epithelium (RPE), two principle reflections of the photoreceptor layer (inner/outer segment (IS/OS) and posterior tips of outer segment (PTOS), Henle's fiber layer (HFL), retinal nerve fiber layer (RNFL), and finally the sum of all the layers considered (overall directionality). Reflectance of the IS/OS and PTOS were found highly sensitive to illumination angle regardless of retinal eccentricity. In contrast, the reflectance of the RPE showed little directionality. The reflectance of HFL and RNFL showed directional dependence, but unlike that of the photoreceptors, depended strongly on pupil meridian and

  18. Extracting hysteresis from nonlinear measurement of wavefront-sensorless adaptive optics system

    NARCIS (Netherlands)

    Song, H.; Vdovin, G.; Fraanje, R.; Schitter, G.; Verhaegen, M.

    2008-01-01

    In many scientific and medical applications wavefront-sensorless adaptive optics (AO) systems are used to correct the wavefront aberration by optimizing a certain target parameter, which is nonlinear with respect to the control signal to the deformable mirror (DM). Hysteresis is the most common nonl

  19. Design and verifications of an eye model fitted with contact lenses for wavefront measurement systems

    Science.gov (United States)

    Cheng, Yuan-Chieh; Chen, Jia-Hong; Chang, Rong-Jie; Wang, Chung-Yen; Hsu, Wei-Yao; Wang, Pei-Jen

    2015-09-01

    Contact lenses are typically measured by the wet-box method because of the high optical power resulting from the anterior central curvature of cornea, even though the back vertex power of the lenses are small. In this study, an optical measurement system based on the Shack-Hartmann wavefront principle was established to investigate the aberrations of soft contact lenses. Fitting conditions were micmicked to study the optical design of an eye model with various topographical shapes in the anterior cornea. Initially, the contact lenses were measured by the wet-box method, and then by fitting the various topographical shapes of cornea to the eye model. In addition, an optics simulation program was employed to determine the sources of errors and assess the accuracy of the system. Finally, samples of soft contact lenses with various Diopters were measured; and, both simulations and experimental results were compared for resolving the controversies of fitting contact lenses to an eye model for optical measurements. More importantly, the results show that the proposed system can be employed for study of primary aberrations in contact lenses.

  20. Measurement of M²-Curve for Asymmetric Beams by Self-Referencing Interferometer Wavefront Sensor.

    Science.gov (United States)

    Du, Yongzhao

    2016-11-29

    For asymmetric laser beams, the values of beam quality factor M x 2 and M y 2 are inconsistent if one selects a different coordinate system or measures beam quality with different experimental conditionals, even when analyzing the same beam. To overcome this non-uniqueness, a new beam quality characterization method named as M²-curve is developed. The M²-curve not only contains the beam quality factor M x 2 and M y 2 in the x-direction and y-direction, respectively; but also introduces a curve of M x α 2 versus rotation angle α of coordinate axis. Moreover, we also present a real-time measurement method to demonstrate beam propagation factor M²-curve with a modified self-referencing Mach-Zehnder interferometer based-wavefront sensor (henceforth SRI-WFS). The feasibility of the proposed method is demonstrated with the theoretical analysis and experiment in multimode beams. The experimental results showed that the proposed measurement method is simple, fast, and a single-shot measurement procedure without movable parts.

  1. Measurement of M2-Curve for Asymmetric Beams by Self-Referencing Interferometer Wavefront Sensor

    Directory of Open Access Journals (Sweden)

    Yongzhao Du

    2016-11-01

    Full Text Available For asymmetric laser beams, the values of beam quality factor M x 2 and M y 2 are inconsistent if one selects a different coordinate system or measures beam quality with different experimental conditionals, even when analyzing the same beam. To overcome this non-uniqueness, a new beam quality characterization method named as M2-curve is developed. The M2-curve not only contains the beam quality factor M x 2 and M y 2 in the x-direction and y-direction, respectively; but also introduces a curve of M x α 2 versus rotation angle α of coordinate axis. Moreover, we also present a real-time measurement method to demonstrate beam propagation factor M2-curve with a modified self-referencing Mach-Zehnder interferometer based-wavefront sensor (henceforth SRI-WFS. The feasibility of the proposed method is demonstrated with the theoretical analysis and experiment in multimode beams. The experimental results showed that the proposed measurement method is simple, fast, and a single-shot measurement procedure without movable parts.

  2. Investigation of the radio wavefront of air showers with LOPES measurements and CoREAS simulations (ARENA 2014)

    CERN Document Server

    Schröder, F G; Arteaga-Velazquez, J C; Bähren, L; Bekk, K; Bertaina, M; Biermann, P L; Blümer, J; Bozdog, H; Brancus, I M; Cantoni, E; Chiavassa, A; Daumiller, K; de Souza, V; Di Pierro, F; Doll, P; Engel, R; Falcke, H; Fuchs, B; Fuhrmann, D; Gemmeke, H; Grupen, C; Haungs, A; Heck, D; Hörandel, J R; Horneffer, A; Huber, D; Huege, T; Isar, P G; Kampert, K -H; Kang, D; Krömer, O; Kuijpers, J; Link, K; Luczak, P; Ludwig, M; Mathes, H J; Melissas, M; Morello, C; Oehlschläger, J; Palmieri, N; Pierog, T; Rautenberg, J; Rebel, H; Roth, M; Rühle, C; Saftoiu, A; Schieler, H; Schmidt, A; Schoo, S; Sima, O; Toma, G; Trinchero, G C; Weindl, A; Wochele, J; Zabierowski, J; Zensus, J A

    2015-01-01

    We investigated the radio wavefront of cosmic-ray air showers with LOPES measurements and CoREAS simulations: the wavefront is of approximately hyperbolic shape and its steepness is sensitive to the shower maximum. For this study we used 316 events with an energy above 0.1 EeV and zenith angles below $45^\\circ$ measured by the LOPES experiment. LOPES was a digital radio interferometer consisting of up to 30 antennas on an area of approximately 200 m x 200 m at an altitude of 110 m above sea level. Triggered by KASCADE-Grande, LOPES measured the radio emission between 43 and 74 MHz, and our analysis might strictly hold only for such conditions. Moreover, we used CoREAS simulations made for each event, which show much clearer results than the measurements suffering from high background. A detailed description of our result is available in our recent paper published in JCAP09(2014)025. The present proceeding contains a summary and focuses on some additional aspects, e.g., the asymmetry of the wavefront: Accordin...

  3. Extracting hysteresis from nonlinear measurement of wavefront-sensorless adaptive optics system.

    Science.gov (United States)

    Song, H; Vdovin, G; Fraanje, R; Schitter, G; Verhaegen, M

    2009-01-01

    In many scientific and medical applications wavefront-sensorless adaptive optics (AO) systems are used to correct the wavefront aberration by optimizing a certain target parameter, which is nonlinear with respect to the control signal to the deformable mirror (DM). Hysteresis is the most common nonlinearity of DMs, which can be corrected if the information about the hysteresis behavior is present. We report a general approach to extract hysteresis from the nonlinear behavior of the adaptive optical system, with the illustration of a Foucault knife test, where the voltage-intensity relationship consists of both hysteresis and some memoryless nonlinearity. The hysteresis extracted here can be used for modeling and linearization of the AO system.

  4. Effect of Single Administration of Coffee on Pupil Size and Ocular Wavefront Aberration Measurements in Healthy Subjects

    Directory of Open Access Journals (Sweden)

    Handan Bardak

    2016-01-01

    Full Text Available No study has so far evaluated the impact of coffee drinking on ocular wavefront aberration (OWA measurements. This study presents novel findings regarding the OWA of the eye following coffee intake. We aimed to evaluate the acute changes in pupil size and OWA of the eye after single administration of coffee. A total of 30 otherwise healthy participants were included in this prospective study. All subjects drank a cup of coffee containing 57 mg caffeine. Measurements of pupil size, total coma (TC, total trefoil (TF, total spherical aberration (TSA, and total higher order aberration (HOA were performed before and at 5 minutes, at 30 minutes, and at 4 hours after coffee drinking using a wavefront aberrometer device (Irx3, Imagine Eyes, Orsay, France. The mean age of the study population was 20.30 ± 2.74 years. Pupil size did not show a significant change during the measurements (p>0.05. A significant increase was observed in TF and HOA measurements following coffee intake (p=0.029 and p=0.009, resp.. Single administration of coffee results in significant increase in TF and total HOAs in healthy subjects without any effect on pupil diameter. Ultrastructural changes in the cornea following coffee intake might be of relevance to the alterations in ocular aberrations in healthy subjects.

  5. Advanced Ceramics Property Measurements

    Science.gov (United States)

    Salem, Jonathan; Helfinstine, John; Quinn, George; Gonczy, Stephen

    2013-01-01

    Mechanical and physical properties of ceramic bodies can be difficult to measure correctly unless the proper techniques are used. The Advanced Ceramics Committee of ASTM, C-28, has developed dozens of consensus test standards and practices to measure various properties of a ceramic monolith, composite, or coating. The standards give the "what, how, how not, and why" for measurement of many mechanical, physical, thermal, and performance properties. Using these standards will provide accurate, reliable, and complete data for rigorous comparisons with other test results from your test lab, or another. The C-28 Committee has involved academics, producers, and users of ceramics to write and continually update more than 45 standards since the committee's inception in 1986. Included in this poster is a pictogram of the C-28 standards and information on how to obtain individual copies with full details or the complete collection of standards in one volume.

  6. Fast algorithms for calculating laser wavefront phase compensation given noisy measurements of phase gradient

    Science.gov (United States)

    Gavel, Don

    1989-09-01

    Laser light propagating through atmosphere will become distorted as a result of the changing index of refraction along the light path. Wavefront distortions can be actively compensated using adaptive optic systems, which sense the wavefront aberations and compensate by changing the shape of a reflecting surface. Corrections must be done rapidly in order to keep up with the variations in the atmosphere. Numerically, the calculation of the correcting surface is a least-squares fit problem. However, since a typical adaptive optic system has a large number of actuators and sensors, the ordinary solution methods, such as Gaussian elimination, are infeasible for real time application. Instead, advantage must be taken of the structure and sparseness of the equations in order to speed up the calculation. The algorithm proposed requires only O(nq) calculation steps and uses only O(n) memory storage, where n is the total number of actuators and q is the influence width of a single actuator. The derivation of the proposed algorithm, proofs of convergence, and results of several test runs are presented. The algorithm was incorporated into Y division's ORACLE simulation code where it is used to calculate the phase conjugate surfaces necessary to precompensate a high powered laser beam for atmospheric propagation.

  7. Wavefront sensing reveals optical coherence.

    Science.gov (United States)

    Stoklasa, B; Motka, L; Rehacek, J; Hradil, Z; Sánchez-Soto, L L

    2014-01-01

    Wavefront sensing is a set of techniques providing efficient means to ascertain the shape of an optical wavefront or its deviation from an ideal reference. Owing to its wide dynamical range and high optical efficiency, the Shack-Hartmann wavefront sensor is nowadays the most widely used of these sensors. Here we show that it actually performs a simultaneous measurement of position and angular spectrum of the incident radiation and, therefore, when combined with tomographic techniques previously developed for quantum information processing, the Shack-Hartmann wavefront sensor can be instrumental in reconstructing the complete coherence properties of the signal. We confirm these predictions with an experimental characterization of partially coherent vortex beams, a case that cannot be treated with the standard tools. This seems to indicate that classical methods employed hitherto do not fully exploit the potential of the registered data.

  8. The Infrared Imaging Spectrograph (IRIS) for TMT: Multi-tiered Wavefront Measurements and Novel Mechanical Design

    CERN Document Server

    Dunn, Jennifer; Chapin, Edward; Reshetov, Vlad; Wierzbicki, Ramunas; Herriot, Glen; Chalmers, Dean; Isbrucker, Victor; Larkin, James E; Moore, Anna M; Suzuki, Ryuji

    2016-01-01

    The InfraRed Imaging Spectrograph (IRIS) will be the first light adaptive optics instrument on the Thirty Meter Telescope (TMT). IRIS is being built by a collaboration between Caltech, the University of California, NAOJ and NRC Herzberg. We present novel aspects of the Support Structure, Rotator and On-Instrument Wavefront Sensor systems being developed at NRC Herzberg. IRIS is suspended from the bottom port of the Narrow Field Infrared Adaptive Optics System (NFIRAOS), and provides its own image de-rotation to compensate for sidereal rotation of the focal plane. This arrangement is a challenge because NFIRAOS is designed to host two other science instruments, which imposes strict mass requirements on IRIS. We have been tasked with keeping the instrument mass under seven tonnes which has resulted in a mass reduction of 30 percent for the support structure and rotator compared to the most recent IRIS designs. To accomplish this goal, while still being able to withstand earthquakes, we developed a new design wi...

  9. Compressive wavefront sensing with weak values.

    Science.gov (United States)

    Howland, Gregory A; Lum, Daniel J; Howell, John C

    2014-08-11

    We demonstrate a wavefront sensor that unites weak measurement and the compressive-sensing, single-pixel camera. Using a high-resolution spatial light modulator (SLM) as a variable waveplate, we weakly couple an optical field's transverse-position and polarization degrees of freedom. By placing random, binary patterns on the SLM, polarization serves as a meter for directly measuring random projections of the wavefront's real and imaginary components. Compressive-sensing optimization techniques can then recover the wavefront. We acquire high quality, 256 × 256 pixel images of the wavefront from only 10,000 projections. Photon-counting detectors give sub-picowatt sensitivity.

  10. Fiber coupler end face wavefront surface metrology

    Science.gov (United States)

    Compertore, David C.; Ignatovich, Filipp V.; Marcus, Michael A.

    2015-09-01

    Despite significant technological advances in the field of fiber optic communications, one area remains surprisingly `low-tech': fiber termination. In many instances it involves manual labor and subjective visual inspection. At the same time, high quality fiber connections are one of the most critical parameters in constructing an efficient communication link. The shape and finish of the fiber end faces determines the efficiency of a connection comprised of coupled fiber end faces. The importance of fiber end face quality becomes even more critical for fiber connection arrays and for in the field applications. In this article we propose and demonstrate a quantitative inspection method for the fiber connectors using reflected wavefront technology. The manufactured and polished fiber tip is illuminated by a collimated light from a microscope objective. The reflected light is collected by the objective and is directed to a Shack-Hartmann wavefront sensor. A set of lenses is used to create the image of the fiber tip on the surface of the sensor. The wavefront is analyzed by the sensor, and the measured parameters are used to obtain surface properties of the fiber tip, and estimate connection loss. For example, defocus components in the reflected light indicate the presence of bow in the fiber end face. This inspection method provides a contact-free approach for quantitative inspection of fiber end faces and for estimating the connection loss, and can potentially be integrated into a feedback system for automated inspection and polishing of fiber tips and fiber tip arrays.

  11. On-sky demonstration of matched filters for wavefront measurements using ELT-scale elongated laser guide stars

    Science.gov (United States)

    Basden, A. G.; Bardou, L.; Calia, D. Bonaccini; Buey, T.; Centrone, M.; Chemla, F.; Gach, J. L.; Gendron, E.; Gratadour, D.; Guidolin, I.; Jenkins, D. R.; Marchetti, E.; Morris, T. J.; Myers, R. M.; Osborn, J.; Reeves, A. P.; Reyes, M.; Rousset, G.; Stangalini, M.; Townson, M. J.; Vidal, F.

    2017-01-01

    The performance of adaptive optics systems is partially dependant on the algorithms used within the real-time control system to compute wavefront slope measurements. We demonstrate use of a matched filter algorithm for the processing of elongated laser guide star (LGS) Shack-Hartmann images, using the CANARY adaptive optics instrument on the 4.2 m William Herschel Telescope and the European Southern Observatory Wendelstein LGS Unit placed 40m away. This algorithm has been selected for use with the forthcoming Thirty Meter Telescope, but until now had not been demonstrated on-sky. From the results of a first observing run, we show that the use of matched filtering improves our adaptive optics system performance, with increases in on-sky H-band Strehl measured up to about a factor of 1.1 with respect to a conventional centre of gravity approach. We describe the algorithm used, and the methods that we implemented to enable on-sky demonstration.

  12. Deconvolution of differential OTF (dOTF) to measure high-resolution wavefront structure

    Science.gov (United States)

    Knight, Justin M.; Rodack, Alexander T.; Codona, Johanan L.; Miller, Kelsey L.; Guyon, Olivier

    2015-09-01

    Differential OTF uses two images taken with a telescope pupil modification between them to measure the complex field over most of the pupil. If the pupil modification involves a non-negligible region of the pupil, the dOTF field is blurred by convolution with the complex conjugate of the pupil field change. In some cases, the convolution kernel, or difference field, can cause significant blurring. We explore using deconvolution to recover a highresolution measurement of the complex pupil field. In particular, by assuming we know something about the area and nature of the difference field, we can construct a Wiener filter that increases the resolution of the complex pupil field estimate in the presence of noise. By introducing a controllable pupil modification, such as actuating a telescope primary mirror segment in piston-tip-tilt to make the measurement, we explain added features to the difference field which can be used to increase the signal-to-noise ratio for information in arbitrary ranges of spatial frequency. We will present theory and numerical simulations to discuss key features of the difference field which lead to its utility for deconvolution of dOTF measurements.

  13. Wavefront reconstruction by modal decomposition

    CSIR Research Space (South Africa)

    Schulze, C

    2012-08-01

    Full Text Available We propose a new method to determine the wavefront of a laser beam based on modal decomposition by computer-generated holograms. The hologram is encoded with a transmission function suitable for measuring the amplitudes and phases of the modes...

  14. Individual eye model based on wavefront aberration

    Science.gov (United States)

    Guo, Huanqing; Wang, Zhaoqi; Zhao, Qiuling; Quan, Wei; Wang, Yan

    2005-03-01

    Based on the widely used Gullstrand-Le Grand eye model, the individual human eye model has been established here, which has individual corneal data, anterior chamber depth and the eyeball depth. Furthermore, the foremost thing is that the wavefront aberration calculated from the individual eye model is equal to the eye's wavefront aberration measured with the Hartmann-shack wavefront sensor. There are four main steps to build the model. Firstly, the corneal topography instrument was used to measure the corneal surfaces and depth. And in order to input cornea into the optical model, high-order aspheric surface-Zernike Fringe Sag surface was chosen to fit the corneal surfaces. Secondly, the Hartmann-shack wavefront sensor, which can offer the Zernike polynomials to describe the wavefront aberration, was built to measure the wavefront aberration of the eye. Thirdly, the eye's axial lengths among every part were measured with A-ultrasonic technology. Then the data were input into the optical design software-ZEMAX and the crystalline lens's shapes were optimized with the aberration as the merit function. The individual eye model, which has the same wavefront aberrations with the real eye, is established.

  15. Measurement of wave-front aberration in a small telescope remote imaging system using scene-based wave-front sensing

    Energy Technology Data Exchange (ETDEWEB)

    Poyneer, Lisa A; Bauman, Brian J

    2015-03-31

    Reference-free compensated imaging makes an estimation of the Fourier phase of a series of images of a target. The Fourier magnitude of the series of images is obtained by dividing the power spectral density of the series of images by an estimate of the power spectral density of atmospheric turbulence from a series of scene based wave front sensor (SBWFS) measurements of the target. A high-resolution image of the target is recovered from the Fourier phase and the Fourier magnitude.

  16. Optical wavefront distortion due to supersonic flow fields

    Institute of Scientific and Technical Information of China (English)

    CHEN ZhiQiang; FU Song

    2009-01-01

    The optical wavefront distortion caused by a supersonic flow field around a half model of blunt nose cone was studied in a wind tunnel. A Shack-Hartmann wavefront sensor was used to measure the dis-totted optical wavefront. Interesting optical parameters including the peak variation (PV), root of mean square (RMS) and Strehl ratio were obtained under different test conditions during the experiment. During the establishing process of the flow field in the wind tunnel test section, the wavefront shape was unstable. However after the flow field reached the steady flow state, the wavefront shape kept sta-ble, and the relative error of wavefront aberration was found small. The Shack-Hartmann wavefront sensor developed was proved to be credible in measuring quantitatively the optical phase change of light traveling through the flow field around model window.

  17. A modified phase diversity wavefront sensor with a diffraction grating

    Institute of Scientific and Technical Information of China (English)

    Luo Qun; Huang Lin-Hai; Gu Nai-Ting; Rao Chang-Hui

    2012-01-01

    The phase diversity wavefront sensor is one of the tools used to estimate wavefront aberration,and it is often used as a wavefront sensor in adaptive optics systems.However,the performance of the traditional phase diversity wavefront sensor is limited by the accuracy and dynamic ranges of the intensity distribution at the focus and defocus positions of the CCD camera.In this paper,a modified phase diversity wavefront sensor based on a diffraction grating is proposed to improve the ability to measure the wavefront aberration with larger amplitude and higher spatial frequency.The basic principle and the optics construction of the proposed method are also described in detail.The noise propagation property of the proposed method is also analysed by using the numerical simulation method,and comparison between the diffraction grating phase diversity wavefront sensor and the traditional phase diversity wavefront sensor is also made.The simulation results show that the diffraction grating phase diversity wavefront sensor can obviously improve the ability to measure the wavefront aberration,especially the wavefront aberration with larger amplitude and higher spatial frequency.

  18. Direct measurement of wave-front distortion induced during second-harmonic generation: application to breakup-integral compensation.

    Science.gov (United States)

    Caumes, Jean Pascal; Videau, Laurent; Rouyer, Claude; Freysz, Eric

    2004-04-15

    The wave-front distortion of femtosecond laser pulses recorded with a Shack-Hartmann analyzer makes it possible to retrieve the nonlinear index of refraction of different glasses and the nonlinear phase shift induced during second-harmonic generation in beta-barium borate (BBO) crystal versus the phase mismatch. It is shown that the nonlinear phase shift induced in a 2-mm-thick BBO crystal allows compensation for up to a 2pi breakup-integral induced in a 4-cm fused-silica glass. The stability of the compensation is reported to be from 10 to 100 GW cm(-2).

  19. ZELDA, a Zernike wavefront sensor for the fine measurement of quasi-static aberrations in coronagraphic systems: concept studies and results with VLT/SPHERE

    Science.gov (United States)

    N'Diaye, M.; Vigan, A.; Dohlen, K.; Sauvage, J.-F.; Caillat, A.; Costille, A.; Girard, J. H. V.; Beuzit, J.-L.; Fusco, T.; Blanchard, P.; Le Merrer, J.; Le Mignant, D.; Madec, F.; Moreaux, G.; Mouillet, D.; Puget, P.; Zins, G.

    2016-07-01

    The high-contrast imaging instruments VLT/SPHERE and GPI have been routinely observing gas giant planets, brown dwarfs, and debris disks around nearby stars since 2013-2014. In these facilities, low-wind effects or differential aberrations between the extreme Adaptive Optics sensing path and the science path represent critical limitations for the observation of exoplanets orbiting their host star with a contrast ratio larger than 106 at small separations. To circumvent this problem, we proposed ZELDA, a Zernike wavefront sensor to measure these quasistatic aberrations at a nanometric level. A prototype was installed on VLT/SPHERE during its integration in Chile. We recently performed measurements on an internal source with ZELDA in the presence of Zernike or Fourier modes introduced with the deformable mirror of the instrument. In this communication, we present the results of our experiment and report on the contrast gain obtained with a first ZELDA-based wavefront correction. We finally discuss the suitability of such a solution for a possible upgrade of VLT/SPHERE and for its use with future E-ELT instruments or space missions with high-contrast capabilities (e.g. WFIRST-AFTA, HDST).

  20. All-digital wavefront sensing for structured light beams.

    Science.gov (United States)

    Dudley, Angela; Milione, Giovanni; Alfano, Robert R; Forbes, Andrew

    2014-06-02

    We present a new all-digital technique to extract the wavefront of a structured light beam. Our method employs non-homogeneous polarization optics together with dynamic, digital holograms written to a spatial light modulator to measure the phase relationship between orthogonal polarization states in real-time, thereby accessing the wavefront information. Importantly, we show how this can be applied to measuring the wavefront of propagating light fields, over extended distances, without any moving components. We illustrate the versatility of the tool by measuring propagating optical vortices, Bessel, Airy and speckle fields. The comparison of the extracted and programmed wavefronts yields excellent agreement.

  1. Advancing the measurement of participation.

    Science.gov (United States)

    Whiteneck, Gale G; Bogner, Jennifer A; Heinemann, Allen W

    2011-04-01

    The authors of 3 articles in this issue have collaborated in an effort to advance the conceptualization and measurement of participation. These articles offer (1) a new tool for measuring participation, the Participation Assessment with Recombined Tools-Objective (PART-O), which combines items from widely used instruments in traumatic brain injury rehabilitation research; (2) 2 methods of scoring 17 items of PART-O, assessing relatively objective social role performance and yielding 3 subscale scores, as well as 2 alternative total scores (including 1 incorporating the concept of balance among types of participation), and (3) 19 enfranchisement items assessing the degree to which people with disability perceive they have the freedom to engage in social roles of their choosing while being accepted and valued by others.

  2. Integrated Wavefront Corrector Project

    Data.gov (United States)

    National Aeronautics and Space Administration — One of the critical issues for NASA missions requiring high contrast astrophysical imaging such as Terrestrial Planet Finder (TPF) is wavefront control. Without use...

  3. Extension of the modal wave-front reconstruction algorithm to non-uniform illumination.

    Science.gov (United States)

    Ma, Xiaoyu; Mu, Jie; Rao, ChangHui; Yang, Jinsheng; Rao, XueJun; Tian, Yu

    2014-06-30

    Attempts are made to eliminate the effects of non-uniform illumination on the precision of wave-front measurement. To achieve this, the relationship between the wave-front slope at a single sub-aperture and the distributions of the phase and light intensity of the wave-front were first analyzed to obtain the relevant theoretical formulae. Then, based on the principle of modal wave-front reconstruction, the influence of the light intensity distribution on the wave-front slope is introduced into the calculation of the reconstruction matrix. Experiments were conducted to prove that the corrected modal wave-front reconstruction algorithm improved the accuracy of wave-front reconstruction. Moreover, the correction is conducive to high-precision wave-front measurement using a Hartmann wave-front sensor in the presence of non-uniform illumination.

  4. Coded Shack-Hartmann Wavefront Sensor

    KAUST Repository

    Wang, Congli

    2016-12-01

    Wavefront sensing is an old yet fundamental problem in adaptive optics. Traditional wavefront sensors are limited to time-consuming measurements, complicated and expensive setup, or low theoretically achievable resolution. In this thesis, we introduce an optically encoded and computationally decodable novel approach to the wavefront sensing problem: the Coded Shack-Hartmann. Our proposed Coded Shack-Hartmann wavefront sensor is inexpensive, easy to fabricate and calibrate, highly sensitive, accurate, and with high resolution. Most importantly, using simple optical flow tracking combined with phase smoothness prior, with the help of modern optimization technique, the computational part is split, efficient, and parallelized, hence real time performance has been achieved on Graphics Processing Unit (GPU), with high accuracy as well. This is validated by experimental results. We also show how optical flow intensity consistency term can be derived, using rigor scalar diffraction theory with proper approximation. This is the true physical law behind our model. Based on this insight, Coded Shack-Hartmann can be interpreted as an illumination post-modulated wavefront sensor. This offers a new theoretical approach for wavefront sensor design.

  5. X-ray pulse wavefront metrology using speckle tracking

    Energy Technology Data Exchange (ETDEWEB)

    Berujon, Sebastien, E-mail: berujon@esrf.eu; Ziegler, Eric; Cloetens, Peter [European Synchrotron Radiation Facility, BP-220, F-38043 Grenoble (France)

    2015-05-09

    The theoretical description and experimental implementation of a speckle-tracking-based instrument which permits the characterisation of X-ray pulse wavefronts. An instrument allowing the quantitative analysis of X-ray pulsed wavefronts is presented and its processing method explained. The system relies on the X-ray speckle tracking principle to accurately measure the phase gradient of the X-ray beam from which beam optical aberrations can be deduced. The key component of this instrument, a semi-transparent scintillator emitting visible light while transmitting X-rays, allows simultaneous recording of two speckle images at two different propagation distances from the X-ray source. The speckle tracking procedure for a reference-less metrology mode is described with a detailed account on the advanced processing schemes used. A method to characterize and compensate for the imaging detector distortion, whose principle is also based on speckle, is included. The presented instrument is expected to find interest at synchrotrons and at the new X-ray free-electron laser sources under development worldwide where successful exploitation of beams relies on the availability of an accurate wavefront metrology.

  6. Bit-efficient sub-millisecond wavefront measurement using a lock-in camera for time-reversal based optical focusing inside scattering media (Conference Presentation)

    Science.gov (United States)

    Liu, Yan; Ma, Cheng; Shen, Yuecheng; Wang, Lihong V.

    2016-03-01

    Optical focusing plays a central role in biomedical optical imaging, manipulation, and therapy. However, in scattering media, direct optical focusing becomes infeasible beyond ~10 mean free paths. To break this limit, time-reversed ultrasonically encoded (TRUE) optical focusing phase-conjugates ultrasonically tagged diffuse light back to the ultrasonic focus, thus forming a focus deep inside scattering media. In previous works, the speed of wavefront measurement was limited by the low frame rate of the camera used to record the four images required for phase-shifting holography. Moreover, most of the bits of a pixel value were used to represent an informationless background caused by the large amount of untagged light, increasing the amount of data to transfer and necessitating the use of costly high-resolution analog-to-digital converters (ADCs). Here, we developed a digital TRUE focusing system based on a lock-in camera (300×300 pixels), in which each pixel performs analog lock-in detection on chip. Since only the information of the signal, not that of the background, is digitized, the lock-in camera reduces the amount of data to transfer, and enables the use of cheap low-resolution ADCs. Using this lock-in camera, we were able to measure the wavefront of ultrasonically tagged light in less than 0.3 ms, and to achieve TRUE focusing in between two ground glass diffusers. Even when the signal-to-background ratio dropped to 6.32×10^-4, a phase sensitivity as low as 0.51 rad could still be realized, which is more than enough for digital optical phase conjugation.

  7. Correlations between corneal and total wavefront aberrations

    Science.gov (United States)

    Mrochen, Michael; Jankov, Mirko; Bueeler, Michael; Seiler, Theo

    2002-06-01

    Purpose: Corneal topography data expressed as corneal aberrations are frequently used to report corneal laser surgery results. However, the optical image quality at the retina depends on all optical elements of the eye such as the human lens. Thus, the aim of this study was to investigate the correlations between the corneal and total wavefront aberrations and to discuss the importance of corneal aberrations for representing corneal laser surgery results. Methods: Thirty three eyes of 22 myopic subjects were measured with a corneal topography system and a Tschernig-type wavefront analyzer after the pupils were dilated to at least 6 mm in diameter. All measurements were centered with respect to the line of sight. Corneal and total wavefront aberrations were calculated up to the 6th Zernike order in the same reference plane. Results: Statistically significant correlations (p corneal and total wavefront aberrations were found for the astigmatism (C3,C5) and all 3rd Zernike order coefficients such as coma (C7,C8). No statistically significant correlations were found for all 4th to 6th order Zernike coefficients except for the 5th order horizontal coma C18 (p equals 0.003). On average, all Zernike coefficients for the corneal aberrations were found to be larger compared to Zernike coefficients for the total wavefront aberrations. Conclusions: Corneal aberrations are only of limited use for representing the optical quality of the human eye after corneal laser surgery. This is due to the lack of correlation between corneal and total wavefront aberrations in most of the higher order aberrations. Besides this, the data present in this study yield towards an aberration balancing between corneal aberrations and the optical elements within the eye that reduces the aberration from the cornea by a certain degree. Consequently, ideal customized ablations have to take both, corneal and total wavefront aberrations, into consideration.

  8. Improving active space telescope wavefront control using predictive thermal modeling

    Science.gov (United States)

    Gersh-Range, Jessica; Perrin, Marshall D.

    2015-01-01

    Active control algorithms for space telescopes are less mature than those for large ground telescopes due to differences in the wavefront control problems. Active wavefront control for space telescopes at L2, such as the James Webb Space Telescope (JWST), requires weighing control costs against the benefits of correcting wavefront perturbations that are a predictable byproduct of the observing schedule, which is known and determined in advance. To improve the control algorithms for these telescopes, we have developed a model that calculates the temperature and wavefront evolution during a hypothetical mission, assuming the dominant wavefront perturbations are due to changes in the spacecraft attitude with respect to the sun. Using this model, we show that the wavefront can be controlled passively by introducing scheduling constraints that limit the allowable attitudes for an observation based on the observation duration and the mean telescope temperature. We also describe the implementation of a predictive controller designed to prevent the wavefront error (WFE) from exceeding a desired threshold. This controller outperforms simpler algorithms even with substantial model error, achieving a lower WFE without requiring significantly more corrections. Consequently, predictive wavefront control based on known spacecraft attitude plans is a promising approach for JWST and other future active space observatories.

  9. Wavefront coding with adaptive optics

    Science.gov (United States)

    Agbana, Temitope E.; Soloviev, Oleg; Bezzubik, Vitalii; Patlan, Vsevolod; Verhaegen, Michel; Vdovin, Gleb

    2015-03-01

    We have implemented an extended depth of field optical system by wavefront coding with a micromachined membrane deformable mirror. This approach provides a versatile extension to standard wavefront coding based on fixed phase mask. First experimental results validate the feasibility of the use of adaptive optics for variable depth wavefront coding in imaging optical systems.

  10. Measurement of advanced electromagnetic radiation

    OpenAIRE

    Bajlo, Darko

    2017-01-01

    For the purpose of detecting advanced electromagnetic radiation predicted by Wheeler-Feynman absorber theory for the case of incomplete absorption of retarded electromagnetic radiation, pulses in duration of 6 ns to 24 ns, wavelength from 91 cm to 200 cm where supplied to three different transmitting antennas. Detection was done with a λ/20 monopole antenna in the advanced time window at a time 2r/c before the arrival of the center of the retarded pulse. At distances ranging from 430 cm to 18...

  11. Method and apparatus for wavefront sensing

    Science.gov (United States)

    Bahk, Seung-Whan

    2016-08-23

    A method of measuring characteristics of a wavefront of an incident beam includes obtaining an interferogram associated with the incident beam passing through a transmission mask and Fourier transforming the interferogram to provide a frequency domain interferogram. The method also includes selecting a subset of harmonics from the frequency domain interferogram, individually inverse Fourier transforming each of the subset of harmonics to provide a set of spatial domain harmonics, and extracting a phase profile from each of the set of spatial domain harmonics. The method further includes removing phase discontinuities in the phase profile, rotating the phase profile, and reconstructing a phase front of the wavefront of the incident beam.

  12. SEG Advances in Rotational Seismic Measurements

    Energy Technology Data Exchange (ETDEWEB)

    Pierson, Robert; Laughlin, Darren; Brune, Bob

    2016-10-17

    Significant advancements in the development of sensors to enable rotational seismic measurements have been achieved. Prototypes are available now to support experiments that help validate the utility of rotational seismic measurements.

  13. Advanced in-flight measurement techniques

    CERN Document Server

    Lawson, Nicholas; Jentink, Henk; Kompenhans, Jürgen

    2013-01-01

    The book presents a synopsis of the main results achieved during the 3 year EU-project "Advanced Inflight Measurement Techniques (AIM)" which applied advanced image based measurement techniques to industrial flight testing. The book is intended to be not only an overview on the AIM activities but also a guide on the application of advanced optical measurement techniques for future flight testing. Furthermore it is a useful guide for engineers in the field of experimental methods and flight testing who face the challenge of a future requirement for the development of highly accurate non-intrusive in-flight measurement techniques.

  14. Fast & Furious focal-plane wavefront sensing

    NARCIS (Netherlands)

    Korkiakoski, V.A.; Keller, C.U.; Doelman, N.; Kenworthy, M.; Otten, G.; Verhaegen, M.H.G.

    2014-01-01

    We present two complementary algorithms suitable for using focal-plane measurements to control a wavefront corrector with an extremely high-spatial resolution. The algorithms use linear approximations to iteratively minimize the aberrations seen by the focal-plane camera. The first algorithm, Fast &

  15. Implementation of a Wavefront-Sensing Algorithm

    Science.gov (United States)

    Smith, Jeffrey S.; Dean, Bruce; Aronstein, David

    2013-01-01

    A computer program has been written as a unique implementation of an image-based wavefront-sensing algorithm reported in "Iterative-Transform Phase Retrieval Using Adaptive Diversity" (GSC-14879-1), NASA Tech Briefs, Vol. 31, No. 4 (April 2007), page 32. This software was originally intended for application to the James Webb Space Telescope, but is also applicable to other segmented-mirror telescopes. The software is capable of determining optical-wavefront information using, as input, a variable number of irradiance measurements collected in defocus planes about the best focal position. The software also uses input of the geometrical definition of the telescope exit pupil (otherwise denoted the pupil mask) to identify the locations of the segments of the primary telescope mirror. From the irradiance data and mask information, the software calculates an estimate of the optical wavefront (a measure of performance) of the telescope generally and across each primary mirror segment specifically. The software is capable of generating irradiance data, wavefront estimates, and basis functions for the full telescope and for each primary-mirror segment. Optionally, each of these pieces of information can be measured or computed outside of the software and incorporated during execution of the software.

  16. Focal plane wave-front sensin8 algorithm for high-contrast imaging

    Institute of Scientific and Technical Information of China (English)

    DOU JiangPei; REN DeQing; ZHU YongTian; ZHANG Xi

    2009-01-01

    High-contrast imaging provided by a coronagraph is critical for the direction imaging of the Earth-like planet orbiting its bright parent star. A major limitation for such direct imaging is the speckle noise that is induced from the wave-front error of an optical system. We derive an algorithm for the wave-front measurement directly from 3 focal plane images. The 3 images are achieved through a deformable mirror to provide specific phases for the optics system. We introduce an extra amplitude modulation on one deformable mirror configuration to create an uncorrelated wave-front, which is a critical procedure for wave-front sensing. The simulation shows that the reconstructed wave-front is consistent with the original wave-front theoretically, which indicates that such an algorithm is a promising technique for the wave-front measurement for the high-contrast imaging.

  17. The Asymmetric Pupil Fourier Wavefront Sensor

    CERN Document Server

    Martinache, Frantz

    2013-01-01

    This paper introduces a novel wavefront sensing approach that relies on the Fourier analysis of a single conventional direct image. In the high Strehl ratio regime, the relation between the phase measured in the Fourier plane and the wavefront errors in the pupil can be linearized, as was shown in a previous work that introduced the notion of generalized closure-phase, or kernel-phase. The technique, to be usable as presented requires two conditions to be met: (1) the wavefront errors must be kept small (of the order of one radian or less) and (2) the pupil must include some asymmetry, that can be introduced with a mask, for the problem to become solvable. Simulations show that this asymmetric pupil Fourier wavefront sensing or APF-WFS technique can improve the Strehl ratio from 50 to over 90 % in just a few iterations, with excellent photon noise sensitivity properties, suggesting that on-sky close loop APF-WFS is possible with an extreme adaptive optics system.

  18. Fast & Furious focal-plane wavefront sensing

    CERN Document Server

    Korkiakoski, Visa; Doelman, Niek; Kenworthy, Matthew; Otten, Gilles; Verhaegen, Michel

    2014-01-01

    We present two complementary algorithms suitable for using focal-plane measurements to control a wavefront corrector with an extremely high spatial resolution. The algorithms use linear approximations to iteratively minimize the aberrations seen by the focal-plane camera. The first algorithm, Fast & Furious (FF), uses a weak-aberration assumption and pupil symmetries to achieve fast wavefront reconstruction. The second algorithm, an extension to FF, can deal with an arbitrary pupil shape; it uses a Gerchberg-Saxton style error reduction to determine the pupil amplitudes. Simulations and experimental results are shown for a spatial light modulator controlling the wavefront with a resolution of 170 x 170 pixels. The algorithms increase the Strehl ratio from ~0.75 to 0.98-0.99, and the intensity of the scattered light is reduced throughout the whole recorded image of 320 x 320 pixels. The remaining wavefront rms error is estimated to be ~0.15 rad with FF and ~0.10 rad with FF-GS.

  19. Telescope Multi-Field Wavefront Control with a Kalman Filter

    Science.gov (United States)

    Lou, John Z.; Redding, David; Sigrist, Norbert; Basinger, Scott

    2008-01-01

    An effective multi-field wavefront control (WFC) approach is demonstrated for an actuated, segmented space telescope using wavefront measurements at the exit pupil, and the optical and computational implications of this approach are discussed. The integration of a Kalman Filter as an optical state estimator into the wavefront control process to further improve the robustness of the optical alignment of the telescope will also be discussed. Through a comparison of WFC performances between on-orbit and ground-test optical system configurations, the connection (and a possible disconnection) between WFC and optical system alignment under these circumstances are analyzed. Our MACOS-based computer simulation results will be presented and discussed.

  20. Advances in Measurement Technology at NIST's Physical Measurement Laboratory

    Science.gov (United States)

    Dehmer, Joseph

    2014-03-01

    The NIST mission is to promote U.S. innovation and industrial competitiveness by advancing measurement science, standards, and technology. The Physical Measurement Laboratory (PML) has responsibility for maintaining national standards for two dozen physical quantities needed for international trade; and, importantly, it carries out advanced research at the frontiers of measurement science to enable extending innovation into new realms and new markets. This talk will highlight advances being made across several sectors of technology; and it will describe how PML interacts with its many collaborators and clients in industry, government, and academe.

  1. Conditionally sampled two-dimensional optical wavefront measurements in the near-nozzle region of a heated axisymmetric jet

    Science.gov (United States)

    Hugo, Ronald J.; McMackin, Lenore J.

    1996-10-01

    The time-evolution of optical degradation in the near nozzle region of a heated axisymmetric jet is measured using conditional sampling techniques. A novel linearized stability experiment is performed in order to identify the flowfield states most applicable for conditional sampling techniques. The results of the conditional sampling experiment exhibit a condition where two distinct flowfield states are evident. Potential explanations for the observance of these two distinct states are proposed, with the most probable explanation being due to pi-jumps that can arise between the phase of the excitation signal and the phase of the flowfield events.

  2. X-ray pulse wavefront metrology using speckle tracking.

    Science.gov (United States)

    Berujon, Sebastien; Ziegler, Eric; Cloetens, Peter

    2015-07-01

    An instrument allowing the quantitative analysis of X-ray pulsed wavefronts is presented and its processing method explained. The system relies on the X-ray speckle tracking principle to accurately measure the phase gradient of the X-ray beam from which beam optical aberrations can be deduced. The key component of this instrument, a semi-transparent scintillator emitting visible light while transmitting X-rays, allows simultaneous recording of two speckle images at two different propagation distances from the X-ray source. The speckle tracking procedure for a reference-less metrology mode is described with a detailed account on the advanced processing schemes used. A method to characterize and compensate for the imaging detector distortion, whose principle is also based on speckle, is included. The presented instrument is expected to find interest at synchrotrons and at the new X-ray free-electron laser sources under development worldwide where successful exploitation of beams relies on the availability of an accurate wavefront metrology.

  3. Tracking of Wavefronts

    CERN Document Server

    Bahrdt, J

    2005-01-01

    The design of beamlines for VUV and x-ray FEL facilities requires a detailed knowledge of the coherent radiation source. Time dependent simulations with FEL codes like GENESIS provide the electric field distribution at the end of the FEL which represents the complete information. Ray tracing codes used to transform the light from the source to the sample are generally based on geometrical optics and do not include directly the coherent properties of the FEL radiation. On the other hand Fourier optic techniques are usually applied to the propagation across normal incidence optics. We present an algorithm based on physical optics which permits the propagation of wavefronts across grazing incidence optics including interference effects, diffraction, polarization variation and pulse lengthening. Some examples are given for the proposed BESSY soft x-ray FEL.

  4. Wavefront reconstruction using computer-generated holograms

    Science.gov (United States)

    Schulze, Christian; Flamm, Daniel; Schmidt, Oliver A.; Duparré, Michael

    2012-02-01

    We propose a new method to determine the wavefront of a laser beam, based on modal decomposition using computer-generated holograms (CGHs). Thereby the beam under test illuminates the CGH with a specific, inscribed transmission function that enables the measurement of modal amplitudes and phases by evaluating the first diffraction order of the hologram. Since we use an angular multiplexing technique, our method is innately capable of real-time measurements of amplitude and phase, yielding the complete information about the optical field. A measurement of the Stokes parameters, respectively of the polarization state, provides the possibility to calculate the Poynting vector. Two wavefront reconstruction possibilities are outlined: reconstruction from the phase for scalar beams and reconstruction from the Poynting vector for inhomogeneously polarized beams. To quantify single aberrations, the reconstructed wavefront is decomposed into Zernike polynomials. Our technique is applied to beams emerging from different kinds of multimode optical fibers, such as step-index, photonic crystal and multicore fibers, whereas in this work results are exemplarily shown for a step-index fiber and compared to a Shack-Hartmann measurement that serves as a reference.

  5. Optical differentiation wavefront sensing with binary pixelated transmission filters.

    Science.gov (United States)

    Qiao, J; Mulhollan, Z; Dorrer, C

    2016-05-02

    Sensors measuring the spatial phase of optical waves are widely used in optics. The optical differentiation wavefront sensor (ODWS) reconstructs the wavefront of an optical wave from wavefront slope measurements obtained by inducing linear field-transmission gradients in the far-field. Its dynamic range and sensitivity can be adjusted simply by changing the gradient slope. We numerically and experimentally demonstrate the possibility of implementing the spatially varying transmission gradient using distributions of small pixels that are either transparent or opaque. Binary pixelated filters are achromatic and can be fabricated with high accuracy at relatively low cost using commercial lithography techniques. We study the impact of the noise resulting from pixelation and binarization of the far-field filter for various test wavefronts and sensor parameters. The induced wavefront error is approximately inversely proportional to the pixel size. For an ODWS with dynamic range of 100 rad/mm over a 1-cm pupil, the error is smaller than λ/15 for a wide range of test wavefronts when using 2.5-μm pixels. We experimentally demonstrate the accuracy and consistency of a first-generation ODWS based on binary pixelated filters.

  6. Propofol effects on atrial fibrillation wavefront delays.

    Science.gov (United States)

    Cervigón, Raquel; Moreno, Javier; Millet, José; Pérez-Villacastín, Julián; Castells, Francisco

    2010-08-01

    Since the cardiac activity during atrial fibrillation (AF) may be influenced by autonomic modulations, in this study, a novel method to quantify the effects of the most common anesthetic agent (propofol) in AF ablation procedures is introduced. This study has two main objectives: first, to assess whether the sedation earlier to radio frequency ablation affects the arrhythmia itself, and second, to provide new information that contributes to a better understanding of the influence of the autonomic nervous system on AF. The methodology presented is based on the measurement of synchronization and delay indexes between two atrial activations at adjacent intracavitary electrodes. These parameters aim to estimate whether two activations at different sites may be caused by the same propagating wavefront, or otherwise, are the consequence of independent wavefronts. The results showed that the mentioned indexes have a different behavior at both atria: the right atrium becomes more synchronized with propofol administration, whereas the synchronization index decreases at the left atrium.

  7. Focal plane wave-front sensing algorithm for high-contrast imaging

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    High-contrast imaging provided by a coronagraph is critical for the direction imaging of the Earth-like planet orbiting its bright parent star.A major limitation for such direct imaging is the speckle noise that is induced from the wave-front error of an optical system.We derive an algorithm for the wave-front measurement directly from 3 focal plane images.The 3 images are achieved through a deformable mirror to provide specific phases for the optics system.We introduce an extra amplitude modulation on one deformable mirror configuration to create an uncorrelated wave-front,which is a critical procedure for wave-front sensing.The simulation shows that the reconstructed wave-front is consistent with the original wave-front theoretically,which indicates that such an algorithm is a promising technique for the wave-front measurement for the high-contrast imaging.

  8. Refractive error sensing from wavefront slopes.

    Science.gov (United States)

    Navarro, Rafael

    2010-01-01

    The problem of measuring the objective refractive error with an aberrometer has shown to be more elusive than expected. Here, the formalism of differential geometry is applied to develop a theoretical framework of refractive error sensing. At each point of the pupil, the local refractive error is given by the wavefront curvature, which is a 2 × 2 symmetric matrix, whose elements are directly related to sphere, cylinder, and axis. Aberrometers usually measure the local gradient of the wavefront. Then refractive error sensing consists of differentiating the gradient, instead of integrating as in wavefront sensing. A statistical approach is proposed to pass from the local to the global (clinically meaningful) refractive error, in which the best correction is assumed to be the maximum likelihood estimation. In the practical implementation, this corresponds to the mode of the joint histogram of the 3 different elements of the curvature matrix. Results obtained both in computer simulations and with real data provide a close agreement and consistency with the main optical image quality metrics such as the Strehl ratio.

  9. Phase-Controlled Magnetic Mirror for Wavefront Correction

    Science.gov (United States)

    Hagopian, John; Wollack, Edward

    2011-01-01

    Typically, light interacts with matter via the electric field and interaction with weakly bound electrons. In a magnetic mirror, a patterned nanowire is fabricated over a metallic layer with a dielectric layer in between. Oscillation of the electrons in the nanowires in response to the magnetic field of incident photons causes a re-emission of photons and operation as a "magnetic mirror." By controlling the index of refraction in the dielectric layer using a local applied voltage, the phase of the emitted radiation can be controlled. This allows electrical modification of the reflected wavefront, resulting in a deformable mirror that can be used for wavefront control. Certain applications require wavefront quality in the few-nanometer regime, which is a major challenge for optical fabrication and alignment of mirrors or lenses. The use of a deformable magnetic mirror allows for a device with no moving parts that can modify the phase of incident light over many spatial scales, potentially with higher resolution than current approaches. Current deformable mirrors modify the incident wavefront by using nano-actuation of a substrate to physically bend the mirror to a desired shape. The purpose of the innovation is to modify the incident wavefront for the purpose of correction of fabrication and alignment-induced wavefront errors at the system level. The advanced degree of precision required for some applications such as gravity wave detection (LISA - Laser Interferometer Space Antenna) or planet finding (FKSI - Fourier-Kelvin Stellar Interferometer) requires wavefront control at the limits of the current state of the art. All the steps required to fabricate a magnetic mirror have been demonstrated. The modification is to apply a bias voltage to the dielectric layer so as to change the index of refraction and modify the phase of the reflected radiation. Light is reflected off the device and collected by a phase-sensing interferometer. The interferometer determines the

  10. The Wavefront Control System for the National Ignition Facility

    Energy Technology Data Exchange (ETDEWEB)

    Van Atta, L; Perez, M; Zacharias, R; Rivera, W

    2001-10-15

    The National Ignition Facility (NIF) requires that pulses from each of the 192 laser beams be positioned on target with an accuracy of 50 {micro}m rms. Beam quality must be sufficient to focus a total of 1.8 MJ of 0.351-{micro}m light into a 600-{micro}m-diameter volume. An optimally flat beam wavefront can achieve this pointing and focusing accuracy. The control system corrects wavefront aberrations by performing closed-loop compensation during laser alignment to correct for gas density variations. Static compensation of flashlamp-induced thermal distortion is established just prior to the laser shot. The control system compensates each laser beam at 10 Hz by measuring the wavefront with a 77-lenslet Hartmann sensor and applying corrections with a 39-actuator deformable mirror. The distributed architecture utilizes SPARC AXi computers running Solaris to perform real-time image processing of sensor data and PowerPC-based computers running VxWorks to compute mirror commands. A single pair of SPARC and PowerPC processors accomplishes wavefront control for a group of eight beams. The software design uses proven adaptive optic control algorithms that are implemented in a multi-tasking environment to economically control the beam wavefronts in parallel. Prototype tests have achieved a closed-loop residual error of 0.03 waves rms. aberrations, the spot size requirement and goal could not be met without a wavefront control system.

  11. Algorithm study of wavefront reconstruction based on the cyclic radial shear interferometer

    CERN Document Server

    Li Da Hai; Chen Huai Xin; Chen Zhen Pei; Chen Bo Fei; Jing Feng

    2002-01-01

    The author presents a new algorithm of wavefront reconstruction based on the cyclic radial shear interferometer. The algorithm is a technique that the actual wavefront can be reconstructed directly and accurately from the distribution of phase difference which is obtained from the radial shearing pattern by Fourier transform. It can help to measure accurately the distorted wavefront of ICF in-process. An experiment is presented to test the algorithm

  12. Measuring Combustion Advance in Solid Propellants

    Science.gov (United States)

    Yang, L. C.

    1986-01-01

    Set of gauges on solid-propellant rocket motor with electrically insulating case measures advance of combustion front and local erosion rates of propellant and insulation. Data furnished by gauges aid in motor design, failure analysis, and performance prediction. Technique useful in determining propellant uniformity and electrical properties of exhaust plum. Gauges used both in flight and on ground. Foilgauge technique also useful in basic research on pulsed plasmas or combustion of solids.

  13. Simulation of wavefront reconstruction in beam reshaping system for rectangular laser beam

    Science.gov (United States)

    Zhou, Qiong; Liu, Wenguang; Jiang, Zongfu

    2014-05-01

    A new method to calculating the wavefront of slap laser is studied in this paper. The method is based on the ray trace theory of geometrical optics. By using the Zemax simulation software and Matlab calculation software, the wavefront of rectangular beam in beam reshaping system is reconstructed. Firstly, with the x- and y-slope measurement of reshaping beam the direction cosine of wavefront can be calculated. Then, the inverse beam path of beam reshaping system is built by using Zemax simulation software and the direction cosine of rectangular beam can be given, too. Finally, Southwell zonal model is used to reconstruct the wavefront of rectangular beam in computer simulation. Once the wavefront is received, the aberration of laser can be eliminated by using the proper configuration of beam reshaping system. It is shown that this method to reconstruct the wavefront of rectangular beam can evidently reduce the negative influence of additional aberration induced by beam reshaping system.

  14. Advances in near-infrared measurements

    CERN Document Server

    Patonay, Gabor

    1991-01-01

    Advances in Near-Infrared Measurements, Volume 1 provides an overview of near-infrared spectroscopy. The book is comprised of six chapters that tackle various areas of near-infrared measurement. Chapter 1 discusses remote monitoring techniques in near-infrared spectroscopy with an emphasis on fiber optics. Chapter 2 covers the applications of fibers using Raman techniques, and Chapter 3 tackles the difficulties associated with near-infrared data analysis. The subsequent chapters present examples of the capabilities of near-infrared spectroscopy from various research groups. The text wi

  15. Wavefront sensing based on phase contrast theory and coherent optical processing

    Science.gov (United States)

    Lei, Huang; Qi, Bian; Chenlu, Zhou; Tenghao, Li; Mali, Gong

    2016-07-01

    A novel wavefront sensing method based on phase contrast theory and coherent optical processing is proposed. The wavefront gradient field in the object plane is modulated into intensity distribution in a gang of patterns, making high-density detection available. By applying the method, we have also designed a wavefront sensor. It consists of a classical coherent optical processing system, a CCD detector array, two pieces of orthogonal composite sinusoidal gratings, and a mechanical structure that can perform real-time linear positioning. The simulation results prove and demonstrate the validity of the method and the sensor in high-precision measurement of the wavefront gradient field.

  16. Partial coherence and imperfect optics at a synchrotron radiation source modeled by wavefront propagation

    Science.gov (United States)

    Laundy, David; Alcock, Simon G.; Alianelli, Lucia; Sutter, John P.; Sawhney, Kawal J. S.; Chubar, Oleg

    2014-09-01

    A full wave propagation of X-rays from source to sample at a storage ring beamline requires simulation of the electron beam source and optical elements in the beamline. The finite emittance source causes the appearance of partial coherence in the wave field. Consequently, the wavefront cannot be treated exactly with fully coherent wave propagation or fully incoherent ray tracing. We have used the wavefront code Synchrotron Radiation Workshop (SRW) to perform partially coherent wavefront propagation using a parallel computing cluster at the Diamond Light Source. Measured mirror profiles have been used to correct the wavefront for surface errors.

  17. Correcting the wavefront aberration of membrane mirror based on liquid crystal spatial light modulator

    Science.gov (United States)

    Yang, Bin; Wei, Yin; Chen, Xinhua; Tang, Minxue

    2014-11-01

    Membrane mirror with flexible polymer film substrate is a new-concept ultra lightweight mirror for space applications. Compared with traditional mirrors, membrane mirror has the advantages of lightweight, folding and deployable, low cost and etc. Due to the surface shape of flexible membrane mirror is easy to deviate from the design surface shape, it will bring wavefront aberration to the optical system. In order to solve this problem, a method of membrane mirror wavefront aberration correction based on the liquid crystal spatial light modulator (LCSLM) will be studied in this paper. The wavefront aberration correction principle of LCSLM is described and the phase modulation property of a LCSLM is measured and analyzed firstly. Then the membrane mirror wavefront aberration correction system is designed and established according to the optical properties of a membrane mirror. The LCSLM and a Hartmann-Shack sensor are used as a wavefront corrector and a wavefront detector, respectively. The detected wavefront aberration is calculated and converted into voltage value on LCSLM for the mirror wavefront aberration correction by programming in Matlab. When in experiment, the wavefront aberration of a glass plane mirror with a diameter of 70 mm is measured and corrected for verifying the feasibility of the experiment system and the correctness of the program. The PV value and RMS value of distorted wavefront are reduced and near diffraction limited optical performance is achieved. On this basis, the wavefront aberration of the aperture center Φ25 mm in a membrane mirror with a diameter of 200 mm is corrected and the errors are analyzed. It provides a means of correcting the wavefront aberration of membrane mirror.

  18. Non-iterative adaptive optical microscopy using wavefront sensing

    Science.gov (United States)

    Tao, X.; Azucena, O.; Kubby, J.

    2016-03-01

    This paper will review the development of wide-field and confocal microscopes with wavefront sensing and adaptive optics for correcting refractive aberrations and compensating scattering when imaging through thick tissues (Drosophila embryos and mouse brain tissue). To make wavefront measurements in biological specimens we have modified the laser guide-star techniques used in astronomy for measuring wavefront aberrations that occur as star light passes through Earth's turbulent atmosphere. Here sodium atoms in Earth's mesosphere, at an altitude of 95 km, are excited to fluoresce at resonance by a high-power sodium laser. The fluorescent light creates a guide-star reference beacon at the top of the atmosphere that can be used for measuring wavefront aberrations that occur as the light passes through the atmosphere. We have developed a related approach for making wavefront measurements in biological specimens using cellular structures labeled with fluorescent proteins as laser guide-stars. An example is a fluorescently labeled centrosome in a fruit fly embryo or neurons and dendrites in mouse brains. Using adaptive optical microscopy we show that the Strehl ratio, the ratio of the peak intensity of an aberrated point source relative to the diffraction limited image, can be improved by an order of magnitude when imaging deeply into live dynamic specimens, enabling near diffraction limited deep tissue imaging.

  19. Modeling on Bessel beam guide star beacon for wavefront sensing

    Science.gov (United States)

    Sun, Quan; Luo, Ruiyao; Yang, Yi; Wu, Wuming; Du, Shaojun; Ning, Yu

    2017-06-01

    Bessel beam has the advantages of reducing scattering artefacts and increasing the quality of the image and penetration. This paper proposed to generate a guide star by Bessel beam with vortex phase, and to use the beacon with special spot structure to measure the atmosphere turbulence aberrations. With the matching algorithm of measured characteristic spot in each subaperture, the detection accuracy of Hartmann wavefront sensor can be improved. Based on wave optics theory, the modeling of Bessel beam guide star and wavefront sensing system was built. The laser guide star beacon generated by Bessel beam with vortex phase and beacon echo wave measured by Hartmann sensor were both simulated. Compared with the results measured by echo wave from Gauss beam generated guide star beacon, this novel method can reduce the error of wavefront detection and increase the detection accuracy of Hartmann sensor.

  20. Advanced Ceramics Property and Performance Measurements

    Science.gov (United States)

    Jenkins, Michael; Salem, Jonathan; Helfinstine, John; Quinn, George; Gonczy, Stephen

    2015-01-01

    Mechanical and physical properties of ceramic bodies can be difficult to measure correctly unless the proper techniques are used. The Advanced Ceramics Committee of ASTM, C-28, has developed dozens of consensus test standards and practices to measure various properties of a ceramic monolith, composite, or coating. The standards give the what, how, how not, and why for measurement of many mechanical, physical, thermal, and performance properties. Using these standards will provide accurate, reliable, and complete data for rigorous comparisons with other test results from your test lab, or another. The C-28 Committee has involved academics, producers, and users of ceramics to write and continually update more than 45 standards since the committees inception in 1986. Included in this poster is a pictogram of the C-28 standards and information on how to obtain individual copies with full details or the complete collection of all of the standards in one volume.

  1. Real-time wavefront-shaping through scattering media by all optical feedback

    CERN Document Server

    Nixon, Micha; Small, Eran; Bromberg, Yaron; Friesem, Asher A; Silberberg, Yaron; Davidson, Nir

    2013-01-01

    Focusing light through dynamically varying heterogeneous media is a sought-after goal with important applications ranging from free-space communication to nano-surgery. The underlying challenge is to control the optical wavefront with a large number of degrees-of-freedom (DOF) at timescales shorter than the medium dynamics. Recently, many advancements have been reported following the demonstration of focusing through turbid samples by wavefront-shaping, using spatial light modulators (SLMs) having >1000 DOF. Unfortunately, SLM-based wavefront-shaping requires feedback from a detector/camera and is limited to slowly-varying samples. Here, we demonstrate a novel approach for wavefront-shaping using all-optical feedback. We show that the complex wavefront required to focus through highly scattering samples, including thin biological tissues, can be generated at sub-microsecond timescales by the process of field self-organization inside a multimode laser cavity, without requiring electronic feedback or SLMs. This...

  2. Spatial Light Modulator for wavefront correction

    CERN Document Server

    Vyas, Akondi; Banyal, Ravinder Kumar; Prasad, B Raghavendra

    2009-01-01

    We present a liquid crystal method of correcting the phase of an aberrated wavefront using a spatial light modulator. A simple and efficient lab model has been demonstrated for wavefront correction. The crux of a wavefront correcting system in an adaptive optics system lies in the speed and the image quality that can be achieved. The speeds and the accuracy of wavefront representation using Zernike polynomials have been presented using a very fast method of computation.

  3. Zernike aberration coefficients transformed to and from Fourier series coefficients for wavefront representation.

    Science.gov (United States)

    Dai, Guang-Ming

    2006-02-15

    The set of Fourier series is discussed following some discussion of Zernike polynomials. Fourier transforms of Zernike polynomials are derived that allow for relating Fourier series expansion coefficients to Zernike polynomial expansion coefficients. With iterative Fourier reconstruction, Zernike representations of wavefront aberrations can easily be obtained from wavefront derivative measurements.

  4. Wavefront Sensing via High Speed DSP

    Science.gov (United States)

    Smith, J. Scott; Dean, Bruce

    2004-01-01

    Future light-weighted and segmented primary mirror systems require active optical control to maintain mirror positioning and figure to within nanometer tolerances. Current image-based wavefront sensing approaches rely on post-processing techniques to return an estimate of the aberrated optical wavefront with accuracies to the nanometer level. But the lag times between wavefront sensing, and then control, contributes to a significant latency in the wavefront sensing implementation. In this analysis we demonstrate accelerated image-based wavefront sensing performance using multiple digital signal processors (DSP's). The computational architecture is discussed as well as the heritage leading to the approach.

  5. Wavefront-error evaluation by mathematical analysis of experimental Foucault-test data

    Science.gov (United States)

    Wilson, R. G.

    1975-01-01

    The diffraction theory of the Foucault test provides an integral formula expressing the complex amplitude and irradiance distribution in the Foucault pattern of a test mirror (lens) as a function of wavefront error. Recent literature presents methods of inverting this formula to express wavefront error in terms of irradiance in the Foucault pattern. The present paper describes a study in which the inversion formulation was applied to photometric Foucault-test measurements on a nearly diffraction-limited mirror to determine wavefront errors for direct comparison with ones determined from scatter-plate interferometer measurements. The results affirm the practicability of the Foucault test for quantitative wavefront analysis of very small errors, and they reveal the fallacy of the prevalent belief that the test is limited to qualitative use only. Implications of the results with regard to optical testing and the potential use of the Foucault test for wavefront analysis in orbital space telescopes are discussed.

  6. Hartmann wavefront sensors and their application at FLASH.

    Science.gov (United States)

    Keitel, Barbara; Plönjes, Elke; Kreis, Svea; Kuhlmann, Marion; Tiedtke, Kai; Mey, Tobias; Schäfer, Bernd; Mann, Klaus

    2016-01-01

    Different types of Hartmann wavefront sensors are presented which are usable for a variety of applications in the soft X-ray spectral region at FLASH, the free-electron laser (FEL) in Hamburg. As a typical application, online measurements of photon beam parameters during mirror alignment are reported on. A compact Hartmann sensor, operating in the wavelength range from 4 to 38 nm, was used to determine the wavefront quality as well as aberrations of individual FEL pulses during the alignment procedure. Beam characterization and alignment of the focusing optics of the FLASH beamline BL3 were performed with λ(13.5 nm)/116 accuracy for wavefront r.m.s. (w(rms)) repeatability, resulting in a reduction of w(rms) by 33% during alignment.

  7. 11 A METHOD FOR WAVEFRONT CURVATURE RANGING OF ...

    African Journals Online (AJOL)

    algorithm estimates the curvature of the incident wavefront of the source with ... A narrow-band (NB) filter is used to increase the SNR of the measured signal ..... oCher-scua:s cootn'bute to the varimce about this mean. This property forms the ...

  8. All-digital wavefront sensing for structured light beams

    CSIR Research Space (South Africa)

    Dudley, Angela L

    2014-01-01

    Full Text Available We present a new all-digital technique to extract the wavefront of a structured light beam. Our method employs non-homogeneous polarization optics together with dynamic, digital holograms written to a spatial light modulator to measure the phase...

  9. Modal liquid crystal wavefront corrector.

    Science.gov (United States)

    Kotova, S; Kvashnin, M; Rakhmatulin, M; Zayakin, O; Guralnik, I; Klimov, N; Clark, P; Love, Gordon; Naumov, A; Saunter, C; Loktev, M; Vdovin, G; Toporkova, L

    2002-11-04

    Results are presented of the properties of a liquid crystal wavefront corrector for adaptive optics. The device is controlled using modal addressing in which case the device behaves more like a continuous facesheet deformable mirror than a segmented one. Furthermore, the width and shape of the influence functions are electrically controllable. We describe the construction of the device, the optical properties, and we show experimental results of low order aberration generation.

  10. Wavefront Compensation Segmented Mirror Sensing and Control

    Science.gov (United States)

    Redding, David C.; Lou, John Z.; Kissil, Andrew; Bradford, Charles M.; Woody, David; Padin, Stephen

    2012-01-01

    The primary mirror of very large submillimeter-wave telescopes will necessarily be segmented into many separate mirror panels. These panels must be continuously co-phased to keep the telescope wavefront error less than a small fraction of a wavelength, to ten microns RMS (root mean square) or less. This performance must be maintained continuously across the full aperture of the telescope, in all pointing conditions, and in a variable thermal environment. A wavefront compensation segmented mirror sensing and control system, consisting of optical edge sensors, Wavefront Compensation Estimator/Controller Soft ware, and segment position actuators is proposed. Optical edge sensors are placed two per each segment-to-segment edge to continuously measure changes in segment state. Segment position actuators (three per segment) are used to move the panels. A computer control system uses the edge sensor measurements to estimate the state of all of the segments and to predict the wavefront error; segment actuator commands are computed that minimize the wavefront error. Translational or rotational motions of one segment relative to the other cause lateral displacement of the light beam, which is measured by the imaging sensor. For high accuracy, the collimator uses a shaped mask, such as one or more slits, so that the light beam forms a pattern on the sensor that permits sensing accuracy of better than 0.1 micron in two axes: in the z or local surface normal direction, and in the y direction parallel to the mirror surface and perpendicular to the beam direction. Using a co-aligned pair of sensors, with the location of the detector and collimated light source interchanged, four degrees of freedom can be sensed: transverse x and y displacements, as well as two bending angles (pitch and yaw). In this approach, each optical edge sensor head has a collimator and an imager, placing one sensor head on each side of a segment gap, with two parallel light beams crossing the gap. Two sets

  11. Broadband, Common-path, Interferometric Wavefront Sensor

    Science.gov (United States)

    Wallace, James Kent (Inventor)

    2015-01-01

    Hybrid sensors comprising Shack-Hartmann Wavefront Sensor (S-HWFS) and Zernike Wavefront Sensor (Z-WFS) capabilities are presented. The hybrid sensor includes a Z-WFS optically arranged in-line with a S-HWFS such that the combined wavefront sensor operates across a wide dynamic range and noise conditions. The Z-WFS may include the ability to introduce a dynamic phase shift in both transmissive and reflective modes.

  12. Subaperture test of wavefront error of large telescopes: error sources and stitching performance simulations

    Science.gov (United States)

    Chen, Shanyong; Li, Shengyi; Wang, Guilin

    2014-11-01

    The wavefront error of large telescopes requires to be measured to check the system quality and also estimate the misalignment of the telescope optics including the primary, the secondary and so on. It is usually realized by a focal plane interferometer and an autocollimator flat (ACF) of the same aperture with the telescope. However, it is challenging for meter class telescopes due to high cost and technological challenges in producing the large ACF. Subaperture test with a smaller ACF is hence proposed in combination with advanced stitching algorithms. Major error sources include the surface error of the ACF, misalignment of the ACF and measurement noises. Different error sources have different impacts on the wavefront error. Basically the surface error of the ACF behaves like systematic error and the astigmatism will be cumulated and enlarged if the azimuth of subapertures remains fixed. It is difficult to accurately calibrate the ACF because it suffers considerable deformation induced by gravity or mechanical clamping force. Therefore a selfcalibrated stitching algorithm is employed to separate the ACF surface error from the subaperture wavefront error. We suggest the ACF be rotated around the optical axis of the telescope for subaperture test. The algorithm is also able to correct the subaperture tip-tilt based on the overlapping consistency. Since all subaperture measurements are obtained in the same imaging plane, lateral shift of the subapertures is always known and the real overlapping points can be recognized in this plane. Therefore lateral positioning error of subapertures has no impact on the stitched wavefront. In contrast, the angular positioning error changes the azimuth of the ACF and finally changes the systematic error. We propose an angularly uneven layout of subapertures to minimize the stitching error, which is very different from our knowledge. At last, measurement noises could never be corrected but be suppressed by means of averaging and

  13. Measure for Measure: Advancement's Role in Assessments of Institutional Quality.

    Science.gov (United States)

    Wedekind, Annie; Pollack, Rachel H.

    2002-01-01

    Explores how accreditation, bond ratings, and magazine rankings--including advancement's role in these assessments--continue to be incomplete and controversial indicators of educational quality. Asserts that advancement officers should work to demonstrate the importance of their efforts, such as increasing endowments and alumni support, within the…

  14. Differential OTF Wavefront Sensing

    CERN Document Server

    Codona, Johanan L

    2013-01-01

    An image-based technique for measuring the complex field in the pupil of an imaging system is presented. Two point source images, one with a small modification introduced in the pupil, are combined using a simple and non-iterative algorithm. The non-interferometric method is based on the change in the optical transfer function (OTF), giving a differential OTF (dOTF). The dOTF includes two images of the complex pupil field, conjugated and reflected about the position of the pupil modification, leaving an overlap that obscures some the the pupil. The overlap can be minimized by introducing the modification near the edge of the pupil. The overlap region can be eliminated altogether by using a second modification and a third point source image. The pupil field is convolved by the change in the pupil field, so smaller modification areas are preferred. The non-monochromatic light, but the result incurs a proportional radial blurring determined by the fractional bandwidth. We include some simple demonstration experi...

  15. CMOS-based Integrated Wavefront Sensor

    NARCIS (Netherlands)

    De Lima Monteiro, D.W.

    2002-01-01

    This thesis addresses the design, implementation and performance of an integrated Hartmann-Shack wavefront sensor suitable for real-time operation and compatible with a standard technology. A wavefront sensor can be used for the detection of distortions in the profile of a light beam or of an optica

  16. Single-Grating Talbot Imaging for Wavefront Sensing and X-Ray Metrology

    Energy Technology Data Exchange (ETDEWEB)

    Grizolli, Walan; Shi, Xianbo; Kolodziej, Tomasz; Shvyd' ko, Yuri; Assoufid, Lahsen

    2017-01-01

    Single-grating Talbot imaging relies on high-spatial-resolution detectors to perform accurate measurements of X-ray beam wavefronts. The wavefront can be retrieved with a single image, and a typical measurement and data analysis can be performed in few seconds. These qualities make it an ideal tool for synchrotron beamline diagnostics and in-situ metrology. The wavefront measurement can be used both to obtain a phase contrast image of an object and to characterize an X-ray beam. In this work, we explore the concept in two cases: at-wavelength metrology of 2D parabolic beryllium lenses and a wavefront sensor using a diamond crystal beam splitter.

  17. Performance of wavefront-sensorless adaptive optics using modal and zonal correction

    Science.gov (United States)

    Anzuola, Esdras; Segel, Max; Gladysz, Szymon; Stein, Karin

    2016-10-01

    Unconventional wavefront sensing strategies are being developed to provide alternatives for measuring the wavefront deformation of a laser beam propagating through strong turbulence and/or along a horizontal-path. In this paper we present results from two "wavefront-sensorless" approaches: stochastic parallel gradient descent (SPGD) and its modal version (M-SPGD). We compare the performance of both algorithms through experimental measurements under emulated dynamic atmospheric turbulence by using the coupling efficiency in a single mode fiber as performance metric. We estimate probability density function of coupling efficiency for free-space optical links using adaptive optics (AO) as a function of key parameters such us turbulence strength and AO loop rate. We demonstrate faster convergence rate of the M-SPGD algorithm as compared to the traditional SPGD, although classic SPGD achieves higher correction. Additionally, we constrain the main temporal requirements of an AO system using wavefront-sensorless architectures.

  18. Telescope interferometers: an alternative to classical wavefront sensors

    CERN Document Server

    Henault, Francois

    2008-01-01

    Several types of Wavefront Sensors (WFS) are nowadays available in the field of Adaptive Optics (AO). Generally speaking, their basic principle consists in measuring slopes or curvatures of Wavefront Errors (WFE) transmitted by a telescope, subsequently reconstructing WFEs digitally. Such process, however, does not seem to be well suited for evaluating co-phasing or piston errors of future large segmented telescopes in quasi real-time. This communication presents an original, recently proposed technique for direct WFE sensing. The principle of the device, which is named "Telescope-Interferometer" (TI), is based on the addition of a reference optical arm into the telescope pupil plane. Then incident WFEs are deduced from Point Spread Function (PSF) measurements at the telescope focal plane. Herein are described two different types of TIs, and their performance are discussed in terms of intrinsic measurement accuracy and spatial resolution. Various error sources are studied by means of numerical simulations, am...

  19. Advanced adhesion and friction measurement system

    Science.gov (United States)

    Li, Meng; Huang, Wei; Wang, Xiaolei

    2017-03-01

    An advanced micro-force tester for investigating the micromechanical behavior of various patterned surfaces in dry and wet conditions is presented in this paper. The parallel slice-beam configuration of the tester not only eliminates the large load-dependent slope and tangential displacement at the free end that is found in a single beam system, but also performs a trans-scale deflection with high sensitivity and linearity for force sensing. Meanwhile, the simple structure is characterized by low cost, high efficiency, and ease of fabrication. An integrated nano- and micro-stage comprise the mobile table to produce a large stroke with high resolution, which is specifically required in wet adhesion testing because of the formation of a long liquid bridge. Preliminary experiments of adhesion and friction conducted using PDMS pillars with a plano-convex lens validated the feasibility of this setup.

  20. Revisiting static modulation in pyramid wavefront sensing

    Science.gov (United States)

    Marafatto, L.; Ragazzoni, R.; Vassallo, D.; Bergomi, M.; Biondi, F.; Farinato, J.; Greggio, D.; Magrin, D.; Viotto, V.

    2016-07-01

    The Pyramid Sensor (PS) is based on the Focault knife-edge test, yielding then, in geometrical approximation, only the sign of the wavefront slope. To provide linear measurements of the wavefront slopes the PS relies on a technique known as modulation, which also plays a central role to improve the linear range of the pyramid WFS, very small in the nonmodulated case. In the main PS using modulation so far, this task is achieved by moving optical components in the WFS, increasing the complexity of the system. An attractive idea to simplify the optical and mechanical design of a pyramid WFS is to work without any dynamic modulation. This concept was only merely described and functionally tested in the framework of MAD, and subsequently, with a holographic diffuser. The latter produce a sort of random distribution of the light coming out from the pupil plane, leading to sort of inefficient modulation, as most of the rays are focused in the central region of the light diffused by such device. The bi-dimensional original grating is, in contrast, producing a well defined deterministic distribution of the light onto a specifically shaped pattern. A crude option has been already discussed as a possibility, and it is here generalized to holographic plates leading to various distribution of lights, including a circle whose diameter would match the required modulation pattern, or more cost effective approaches like the one of a square pattern. These holographic diffusers would exhibit also zero-th and high order patterns and the actual size of the equivalent modulation would be linearly wavelength dependent, leading to colour effects that requires a careful handling in order to properly choose the right amount of equivalent modulation.

  1. Multidirectional mobilities: Advanced measurement techniques and applications

    Science.gov (United States)

    Ivarsson, Lars Holger

    Today high noise-and-vibration comfort has become a quality sign of products in sectors such as the automotive industry, aircraft, components, households and manufacturing. Consequently, already in the design phase of products, tools are required to predict the final vibration and noise levels. These tools have to be applicable over a wide frequency range with sufficient accuracy. During recent decades a variety of tools have been developed such as transfer path analysis (TPA), input force estimation, substructuring, coupling by frequency response functions (FRF) and hybrid modelling. While these methods have a well-developed theoretical basis, their application combined with experimental data often suffers from a lack of information concerning rotational DOFs. In order to measure response in all 6 DOFs (including rotation), a sensor has been developed, whose special features are discussed in the thesis. This transducer simplifies the response measurements, although in practice the excitation of moments appears to be more difficult. Several excitation techniques have been developed to enable measurement of multidirectional mobilities. For rapid and simple measurement of the loaded mobility matrix, a MIMO (Multiple Input Multiple Output) technique is used. The technique has been tested and validated on several structures of different complexity. A second technique for measuring the loaded 6-by-6 mobility matrix has been developed. This technique employs a model of the excitation set-up, and with this model the mobility matrix is determined from sequential measurements. Measurements on ``real'' structures show that both techniques give results of similar quality, and both are recommended for practical use. As a further step, a technique for measuring the unloaded mobilities is presented. It employs the measured loaded mobility matrix in order to calculate compensation forces and moments, which are later applied in order to compensate for the loading of the

  2. Loeb measures in practice recent advances

    CERN Document Server

    Cutland, Nigel J

    2000-01-01

    This expanded version of the 1997 European Mathematical Society Lectures given by the author in Helsinki, begins with a self-contained introduction to nonstandard analysis (NSA) and the construction of Loeb Measures, which are rich measures discovered in 1975 by Peter Loeb, using techniques from NSA. Subsequent chapters sketch a range of recent applications of Loeb measures due to the author and his collaborators, in such diverse fields as (stochastic) fluid mechanics, stochastic calculus of variations ("Malliavin" calculus) and the mathematical finance theory. The exposition is designed for a general audience, and no previous knowledge of either NSA or the various fields of applications is assumed.

  3. 3D imaging and wavefront sensing with a plenoptic objective

    Science.gov (United States)

    Rodríguez-Ramos, J. M.; Lüke, J. P.; López, R.; Marichal-Hernández, J. G.; Montilla, I.; Trujillo-Sevilla, J.; Femenía, B.; Puga, M.; López, M.; Fernández-Valdivia, J. J.; Rosa, F.; Dominguez-Conde, C.; Sanluis, J. C.; Rodríguez-Ramos, L. F.

    2011-06-01

    Plenoptic cameras have been developed over the last years as a passive method for 3d scanning. Several superresolution algorithms have been proposed in order to increase the resolution decrease associated with lightfield acquisition with a microlenses array. A number of multiview stereo algorithms have also been applied in order to extract depth information from plenoptic frames. Real time systems have been implemented using specialized hardware as Graphical Processing Units (GPUs) and Field Programmable Gates Arrays (FPGAs). In this paper, we will present our own implementations related with the aforementioned aspects but also two new developments consisting of a portable plenoptic objective to transform every conventional 2d camera in a 3D CAFADIS plenoptic camera, and the novel use of a plenoptic camera as a wavefront phase sensor for adaptive optics (OA). The terrestrial atmosphere degrades the telescope images due to the diffraction index changes associated with the turbulence. These changes require a high speed processing that justify the use of GPUs and FPGAs. Na artificial Laser Guide Stars (Na-LGS, 90km high) must be used to obtain the reference wavefront phase and the Optical Transfer Function of the system, but they are affected by defocus because of the finite distance to the telescope. Using the telescope as a plenoptic camera allows us to correct the defocus and to recover the wavefront phase tomographically. These advances significantly increase the versatility of the plenoptic camera, and provides a new contribution to relate the wave optics and computer vision fields, as many authors claim.

  4. Digital pyramid wavefront sensor with tunable modulation.

    Science.gov (United States)

    Akondi, Vyas; Castillo, Sara; Vohnsen, Brian

    2013-07-29

    The pyramid wavefront sensor is known for its high sensitivity and dynamic range that can be tuned by mechanically altering its modulation amplitude. Here, a novel modulating digital scheme employing a reflecting phase only spatial light modulator is demonstrated. The use of the modulator allows an easy reconfigurable pyramid with digital control of the apex angle and modulation geometry without the need of any mechanically moving parts. Aberrations introduced by a 140-actuator deformable mirror were simultaneously sensed with the help of a commercial Hartmann-Shack wavefront sensor. The wavefronts reconstructed using the digital pyramid wavefront sensor matched very closely with those sensed by the Hartmann-Shack. It is noted that a tunable modulation is necessary to operate the wavefront sensor in the linear regime and to accurately sense aberrations. Through simulations, it is shown that the wavefront sensor can be extended to astronomical applications as well. This novel digital pyramid wavefront sensor has the potential to become an attractive option in both open and closed loop adaptive optics systems.

  5. Hartmann-Shack test with random masks for modal wavefront reconstruction.

    Science.gov (United States)

    Soloviev, Oleg; Vdovin, Gleb

    2005-11-14

    The paper discusses the influence of the geometry of a Hartmann-(Shack) wavefront sensor on the total error of modal wavefront reconstruction. A mathematical model is proposed, which describes the modal wavefront reconstruction in terms of linear operators. The model covers the most general case and is not limited by the orthogonality of decomposition basis or by the method chosen for decomposition. The total reconstruction error is calculated for any given statistics of the wavefront to be measured. Based on this estimate, the total reconstruction error is calculated for regular and randomised Hartmann masks. The calculations demonstrate that random masks with non-regular Fourier spectra provide absolute minimum error and allow to double the number of decomposition modes.

  6. Calibrating the interaction matrix for the LINC-NIRVANA high layer wavefront sensor.

    Science.gov (United States)

    Zhang, Xianyu; Arcidiacono, Carmelo; Conrad, Albert R; Herbst, Thomas M; Gaessler, Wolfgang; Bertram, Thomas; Ragazzoni, Roberto; Schreiber, Laura; Diolaiti, Emiliano; Kuerster, Martin; Bizenberger, Peter; Meschke, Daniel; Rix, Hans-Walter; Rao, Changhui; Mohr, Lars; Briegel, Florian; Kittmann, Frank; Berwein, Juergen; Trowitzsch, Jan

    2012-03-26

    LINC-NIRVANA is a near-infrared Fizeau interferometric imager that will operate at the Large Binocular Telescope. In preparation for the commissioning of this instrument, we conducted experiments for calibrating the high-layer wavefront sensor of the layer-oriented multi-conjugate adaptive optics system. For calibrating the multi-pyramid wavefront sensor, four light sources were used to simulate guide stars. Using this setup, we developed the push-pull method for calibrating the interaction matrix. The benefits of this method over the traditional push-only method are quantified, and also the effects of varying the number of push-pull frames over which aberrations are averaged is reported. Finally, we discuss a method for measuring mis-conjugation between the deformable mirror and the wavefront sensor, and the proper positioning of the wavefront sensor detector with respect to the four pupil positions.

  7. Advanced, Analytic, Automated (AAA) Measurement of Engagement during Learning

    Science.gov (United States)

    D'Mello, Sidney; Dieterle, Ed; Duckworth, Angela

    2017-01-01

    It is generally acknowledged that engagement plays a critical role in learning. Unfortunately, the study of engagement has been stymied by a lack of valid and efficient measures. We introduce the advanced, analytic, and automated (AAA) approach to measure engagement at fine-grained temporal resolutions. The AAA measurement approach is grounded in…

  8. FOCAL PLANE WAVEFRONT SENSING USING RESIDUAL ADAPTIVE OPTICS SPECKLES

    Energy Technology Data Exchange (ETDEWEB)

    Codona, Johanan L.; Kenworthy, Matthew, E-mail: jlcodona@gmail.com [Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States)

    2013-04-20

    Optical imperfections, misalignments, aberrations, and even dust can significantly limit sensitivity in high-contrast imaging systems such as coronagraphs. An upstream deformable mirror (DM) in the pupil can be used to correct or compensate for these flaws, either to enhance the Strehl ratio or suppress the residual coronagraphic halo. Measurement of the phase and amplitude of the starlight halo at the science camera is essential for determining the DM shape that compensates for any non-common-path (NCP) wavefront errors. Using DM displacement ripples to create a series of probe and anti-halo speckles in the focal plane has been proposed for space-based coronagraphs and successfully demonstrated in the lab. We present the theory and first on-sky demonstration of a technique to measure the complex halo using the rapidly changing residual atmospheric speckles at the 6.5 m MMT telescope using the Clio mid-IR camera. The AO system's wavefront sensor measurements are used to estimate the residual wavefront, allowing us to approximately compute the rapidly evolving phase and amplitude of speckle halo. When combined with relatively short, synchronized science camera images, the complex speckle estimates can be used to interferometrically analyze the images, leading to an estimate of the static diffraction halo with NCP effects included. In an operational system, this information could be collected continuously and used to iteratively correct quasi-static NCP errors or suppress imperfect coronagraphic halos.

  9. Focal Plane Wavefront Sensing using Residual Adaptive Optics Speckles

    CERN Document Server

    Codona, Johanan L

    2013-01-01

    Optical imperfections, misalignments, aberrations, and even dust can significantly limit sensitivity in high-contrast imaging systems such as coronagraphs. An upstream deformable mirror (DM) in the pupil can be used to correct or compensate for these flaws, either to enhance Strehl ratio or suppress residual coronagraphic halo. Measurement of the phase and amplitude of the starlight halo at the science camera is essential for determining the DM shape that compensates for any non-common-path (NCP) wavefront errors. Using DM displacement ripples to create a series of probe and anti-halo speckles in the focal plane has been proposed for space-based coronagraphs and successfully demonstrated in the lab. We present the theory and first on-sky demonstration of a technique to measure the complex halo using the rapidly-changing residual atmospheric speckles at the 6.5m MMT telescope using the Clio mid-IR camera. The AO system's wavefront sensor (WFS) measurements are used to estimate the residual wavefront, allowing ...

  10. Advanced (Measurement) Applications of Curriculum-Based Measurement in Reading

    Science.gov (United States)

    Petscher, Yaacov; Cummings, Kelli Dawn; Biancarosa, Gina; Fien, Hank

    2013-01-01

    The purpose of this article is to provide a commentary on the current state of several measurement issues pertaining to curriculum-based measures of reading (R-CBM). We begin by providing an overview of the utility of R-CBM, followed by a presentation of five specific measurements considerations: (a) the reliability of R-CBM oral reading fluency…

  11. X-ray grating interferometer for in situ and at-wavelength wavefront metrology.

    Science.gov (United States)

    Kayser, Yves; David, Christian; Flechsig, Uwe; Krempasky, Juraj; Schlott, Volker; Abela, Rafael

    2017-01-01

    A wavefront metrology setup based on the X-ray grating interferometry technique for spatially resolved, quantitative, in situ and at-wavelength measurements of the wavefront at synchrotron radiation and hard X-ray free-electron laser beamlines is reported. Indeed, the ever-increasing demands on the optical components to preserve the wavefront shape and the coherence of the delivered X-ray beam call for more and more sensitive diagnostic instruments. Thanks to its angular sensitivity, X-ray grating interferometry has been established in recent years as an adequate wavefront-sensing technique for quantitatively assessing the quality of the X-ray wavefront under working conditions and hence for the in situ investigation of X-ray optical elements. In order to characterize the optical elements at any given beamline by measuring the aberrations introduced in the wavefront, a transportable X-ray grating interferometry setup was realised at the Swiss Light Source (SLS). The instrument, which is expected to be a valuable tool for investigating the quality of the X-ray beam delivered at an endstation, will be described hereafter in terms of the hardware setup and the related data analysis procedure. Several exemplary experiments performed at the X05DA Optics beamline of the SLS will be presented.

  12. Wavefront Control for Extreme Adaptive Optics

    Energy Technology Data Exchange (ETDEWEB)

    Poyneer, L A

    2003-07-16

    Current plans for Extreme Adaptive Optics systems place challenging requirements on wave-front control. This paper focuses on control system dynamics, wave-front sensing and wave-front correction device characteristics. It may be necessary to run an ExAO system after a slower, low-order AO system. Running two independent systems can result in very good temporal performance, provided specific design constraints are followed. The spatially-filtered wave-front sensor, which prevents aliasing and improves PSF sensitivity, is summarized. Different models of continuous and segmented deformable mirrors are studied. In a noise-free case, a piston-tip-tilt segmented MEMS device can achieve nearly equivalent performance to a continuous-sheet DM in compensating for a static phase aberration with use of spatial filtering.

  13. Broadband Phase Retrieval for Image-Based Wavefront Sensing

    Science.gov (United States)

    Dean, Bruce H.

    2007-01-01

    A focus-diverse phase-retrieval algorithm has been shown to perform adequately for the purpose of image-based wavefront sensing when (1) broadband light (typically spanning the visible spectrum) is used in forming the images by use of an optical system under test and (2) the assumption of monochromaticity is applied to the broadband image data. Heretofore, it had been assumed that in order to obtain adequate performance, it is necessary to use narrowband or monochromatic light. Some background information, including definitions of terms and a brief description of pertinent aspects of image-based phase retrieval, is prerequisite to a meaningful summary of the present development. Phase retrieval is a general term used in optics to denote estimation of optical imperfections or aberrations of an optical system under test. The term image-based wavefront sensing refers to a general class of algorithms that recover optical phase information, and phase-retrieval algorithms constitute a subset of this class. In phase retrieval, one utilizes the measured response of the optical system under test to produce a phase estimate. The optical response of the system is defined as the image of a point-source object, which could be a star or a laboratory point source. The phase-retrieval problem is characterized as image-based in the sense that a charge-coupled-device camera, preferably of scientific imaging quality, is used to collect image data where the optical system would normally form an image. In a variant of phase retrieval, denoted phase-diverse phase retrieval [which can include focus-diverse phase retrieval (in which various defocus planes are used)], an additional known aberration (or an equivalent diversity function) is superimposed as an aid in estimating unknown aberrations by use of an image-based wavefront-sensing algorithm. Image-based phase-retrieval differs from such other wavefront-sensing methods, such as interferometry, shearing interferometry, curvature

  14. Synchronous phase-demodulation of concentric-rings Placido mires in corneal topography and wavefront aberrometry (theoretical considerations)

    CERN Document Server

    Servin, Manuel

    2012-01-01

    This paper presents a digital interferometric method to demodulate Placido fringe patterns. This method uses a computer-stored conic-wavefront as reference carrier. Even though, Placido mires are widely used in corneal topographers. This is not however a paper on corneal topography and/or its clinical use. This paper focuses on the theoretical aspects to phase-demodulate Placido mires using synchronous interferometric techniques. Placido patterns may also be applied to test optical wavefronts using a Placido-Hartmann opaque plate with periodic annular apertures. This test is sensitive to the radial slope of the measuring wavefront. Another wavefront testing approach may use a Placido-Hartmann-Shack screen with a periodic array of toroidal lenslets. This periodic screen is sensitive to the wavefront's radial-slope at the focal plane of the lenslets. In brief, digital interferometric methods are herein applied for the first time to demodulate conic-carrier Placido images. Finally it should be mentioned that thi...

  15. 10 um wavefront spatial filtering first results with chalcogenide fibers

    CERN Document Server

    Bordé, P J; Nguyen, T; Amy-Klein, A; Daussy, C; Raynal, P; Léger, A; Mazé, G; Borde, Pascal; Perrin, Guy; Nguyen, Thanh; Amy-Klein, Anne; Daussy, Christophe; Raynal, Pierre-Ivan; Leger, Alain; Maze, Gwenael

    2003-01-01

    Wavefront cleaning by single-mode fibers has proved to be efficient in optical-infrared interferometry to improve calibration quality. For instance, the FLUOR instrument has demonstrated the capability of fluoride glass single-mode fibers in this respect in the K and L bands. New interferometric instruments developped for the mid-infrared require the same capability for the 8-12 um range. We have initiated a program to develop single-mode fibers in the prospect of the VLTI mid-infrared instrument MIDI and of the ESA/DARWIN and NASA/TPF missions that require excellent wavefront quality. In order to characterize the performances of chalcogenide fibers we are developping, we have set up an experiment to measure the far-field pattern radiated at 10 um. In this paper, we report the first and promising results obtained with this new component.

  16. Coronagraph-Integrated Wavefront Sensing with a Sparse Aperture Mask

    CERN Document Server

    Subedi, Hari; Kasdin, N Jeremy; Cavanagh, Kathleen; Riggs, A J Eldorado

    2015-01-01

    Stellar coronagraph performance is highly sensitive to optical aberrations. In order to effectively suppress starlight for exoplanet imaging applications, low-order wavefront aberrations entering a coronagraph such as tip-tilt, defocus and coma must be determined and compensated. Previous authors have established the utility of pupil-plane masks (both non-redundant/sparse-aperture and generally asymmetric aperture masks) for wavefront sensing. Here we show how a sparse aperture mask (SAM) can be integrated with a coronagraph to measure low-order, differential phase aberrations. Starlight rejected by the coronagraph's focal plane stop is collimated to a relay pupil, where the mask forms an interference fringe pattern on a subsequent detector. Our numerical Fourier propagation models show that the information encoded in the fringe intensity distortions is sufficient to accurately discriminate and estimate Zernike phase modes extending from tip-tilt up to radial degree $n=5$, with amplitude up to $\\lambda/20$ RM...

  17. Wavefronts and Light Cones for Kerr Spacetimes

    CERN Document Server

    Frutos-Alfaro, Francisco; Mueller, Thomas; Adis, Daria

    2014-01-01

    We investigate the light propagation by means of simulations of wavefronts and light cones for Kerr spacetimes. Simulations of this kind give us a new insight to better understand the light propagation in presence of massive rotating black holes. A relevant result is that wavefronts are back scattered with winding around the black hole. To generate these visualizations, an interactive computer program with a graphical user interface, called JWFront, was written in Java.

  18. Advances in deuterium dioxide concentration measurement

    Energy Technology Data Exchange (ETDEWEB)

    Shon, Woojung [University of Science & Technology, Daejeon (Korea, Republic of); Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Yim, Sung Paal, E-mail: nspyim@kaeri.re.kr [University of Science & Technology, Daejeon (Korea, Republic of); Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Lee, Lim; Park, Hyunmin [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Kim, Kwang Rag; Chung, Hongsuk [University of Science & Technology, Daejeon (Korea, Republic of); Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Lee, Cheo Kyung [Handong Global University, Pohang (Korea, Republic of)

    2016-11-01

    Highlights: • Heavy water (D{sub 2}O) with a high purity level is necessary for nuclear fusion application. • D{sub 2}O purity is analyzed using Fourier Transform infrared (FT-IR) spectroscopy and newly introduced off-axis integrated cavity output spectroscopy (OA-ICOS). • OA-ICOS has advantages in terms of analysis of D{sub 2}O vapor. • OA-ICOS is expected that it can be used for accurate isotopic analyses in the future. - Abstract: The deuterium–tritium (D–T) reaction has been identified as the most efficient reaction for fusion devices. Deuterium can be obtained by heavy water electrolysis. Heavy water (D{sub 2}O) with a high purity level is necessary for nuclear fusion application. A D{sub 2}O isotopic analysis is thus very important. A system for a heavy water analysis was built and a newly designed isotopic analysis experiment was carried out. We tried to analyze the D{sub 2}O purity using Fourier Transform infrared (FT-IR) spectroscopy and newly introduced off-axis integrated cavity output spectroscopy (OA-ICOS). We found that the OA-ICOS based on measurement via laser absorption spectroscopy shows very high sensitivity. We ameliorated the sensitivity by an order of magnitude of more than 10{sup 3}–10{sup 5}. We could make the apparatus smaller by employing very tiny diode laser and fiber optics elements of a DFB (Distributed Feedback) type. Consequently, our device has advantages in terms of maintainability and mobility even in a radioactive environment. This new method could be used for an accurate isotopic analysis in the future.

  19. Analysis of wavefront reconstruction in 8 meter ring solar telescope

    Science.gov (United States)

    Dai, Yichun; Jin, Zhenyu

    2016-07-01

    Chinese Giant Solar Telescope (CGST) is the next generation infrared and optical solar telescope of China, which is proposed and pushed by the solar astronomy community of China and listed into the National Plans of Major Science and Technology Infrastructures. CGST is currently proposed to be an 8 meter Ring Solar Telescope (RST) with width of 1 meter, the hollow and symmetric structure of such an annular aperture facilitates the thermal control and high precision magnetic field measurement for a solar telescope. Adaptive optics (AO) is an indispensable tool of RST to obtain diffraction limited observations. How to realize AO involved wavefront sensing and correcting, and the degree of compensating in a narrow annular aperture is the primary problem of AO implementation of RST. Wavefront reconstruction involved problems of RST are first investigated and discussed in this paper using end to end simulation based on Shack-Hartmann wavefront sensing (SHWFS). The simulation results show that performance of zonal reconstruction with measurement noise no more than 0.05 arc sec can meets the requirement of RST for diffraction-limited imaging at wavelength of 1μm, which satisfies most science cases of RST in near infrared waveband.

  20. The wavefront of the radio signal emitted by cosmic ray air showers

    Energy Technology Data Exchange (ETDEWEB)

    Apel, W.D.; Bekk, K.; Blümer, J.; Bozdog, H.; Daumiller, K.; Doll, P.; Engel, R. [Institut für Kernphysik, Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany); Arteaga-Velázquez, J.C. [Instituto de Física y Matemáticas, Universidad Michoacana, Edificio C-3, Cd. Universitaria, C.P. 58040 Morelia, Michoacán (Mexico); Bähren, L.; Falcke, H. [ASTRON, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo (Netherlands); Bertaina, M.; Cantoni, E.; Chiavassa, A.; Pierro, F. Di [Dipartimento di Fisica, Università degli Studi di Torino, Via Giuria 1, 10125 Torino (Italy); Biermann, P.L. [Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn (Germany); Brancus, I.M. [National Institute of Physics and Nuclear Engineering, Str. Reactorului no. 30, P.O. Box MG-6, Bucharest-Magurele (Romania); De Souza, V. [Instituto de Física de São Carlos, Universidade de São Paulo, Av. Trabalhador São-Carlense 400, Pq. Arnold Schmidt, São Carlos (Brazil); Fuchs, B. [Institut für Experimentelle Kernphysik, Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany); Gemmeke, H. [Institut für Prozessdatenverarbeitung und Elektronik, Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany); Grupen, C., E-mail: frank.schroeder@kit.edu [Faculty of Natural Sciences and Engineering, Universität Siegen, Walter-Flex-Straße 3, 57072 Siegen (Germany); and others

    2014-09-01

    Analyzing measurements of the LOPES antenna array together with corresponding CoREAS simulations for more than 300 measured events with energy above 10{sup 17} eV and zenith angles smaller than 45{sup o}, we find that the radio wavefront of cosmic-ray air showers is of approximately hyperbolic shape. The simulations predict a slightly steeper wavefront towards East than towards West, but this asymmetry is negligible against the measurement uncertainties of LOPES. At axis distances ∼> 50 m, the wavefront can be approximated by a simple cone. According to the simulations, the cone angle is clearly correlated with the shower maximum. Thus, we confirm earlier predictions that arrival time measurements can be used to study the longitudinal shower development, but now using a realistic wavefront. Moreover, we show that the hyperbolic wavefront is compatible with our measurement, and we present several experimental indications that the cone angle is indeed sensitive to the shower development. Consequently, the wavefront can be used to statistically study the primary composition of ultra-high energy cosmic rays. At LOPES, the experimentally achieved precision for the shower maximum is limited by measurement uncertainties to approximately 140 g/c {sup 2}. But the simulations indicate that under better conditions this method might yield an accuracy for the atmospheric depth of the shower maximum, X{sub max}, better than 30 g/c {sup 2}. This would be competitive with the established air-fluorescence and air-Cherenkov techniques, where the radio technique offers the advantage of a significantly higher duty-cycle. Finally, the hyperbolic wavefront can be used to reconstruct the shower geometry more accurately, which potentially allows a better reconstruction of all other shower parameters, too.

  1. Large field-of-view wavefront control for deep brain imaging (Conference Presentation)

    Science.gov (United States)

    Park, Jung-Hoon; Cui, Meng

    2016-03-01

    The biggest obstacle for deep tissue imaging is the scattering of light due to the heterogeneous distribution of biological tissue. In this respect, multiphoton microscopy has an inherent advantage as the scattering is significantly reduced by the use of longer excitation wavelengths. However, as we go deeper into the brain, effects of scattering still accumulate resulting in a loss of resolution and increased background noise. Adaptive optics is an ideal tool of choice to correct for such distortions of the excitation wavefront; the incident light can be tuned to cancel out the wavefront distortion experienced while propagating into greater depths resulting in a diffraction limited focus at the depth of interest. However, the biggest limitation of adaptive optics for in vivo brain imaging is its limited corrected field-of-view (FOV). For typical multiphoton laser scanning microscopes, the wavefront corrector for adaptive optics is placed at the pupil plane. This means that a single correction wavefront is applied to the entire scanned FOV which results in inefficient correction as the correction is averaged over the entire FOV. In this work, we demonstrate a novel approach to measure and display different correction wavefronts over different segments of the FOV. The application of the different correction wavefronts for each segment is realized in parallel resulting in fast aberration corrected imaging over a large FOV for high resolution in vivo brain imaging.

  2. A demonstration of wavefront sensing and mirror phasing from the image domain

    Science.gov (United States)

    Pope, Benjamin; Cvetojevic, Nick; Cheetham, Anthony; Martinache, Frantz; Norris, Barnaby; Tuthill, Peter

    2014-05-01

    In astronomy and microscopy, distortions in the wavefront affect the dynamic range of a high-contrast imaging system. These aberrations are either imposed by a turbulent medium such as the atmosphere, by static or thermal aberrations in the optical path, or by imperfectly phased subapertures in a segmented mirror. Active and adaptive optics (AO), consisting of a wavefront sensor and a deformable mirror, are employed to address this problem. Nevertheless, the non-common-path between the wavefront sensor and the science camera leads to persistent quasi-static speckles that are difficult to calibrate and which impose a floor on the image contrast. In this paper, we present the first experimental demonstration of a novel wavefront sensor requiring only a minor asymmetric obscuration of the pupil, using the science camera itself to detect high-order wavefront errors from the speckle pattern produced. We apply this to correct errors imposed on a deformable microelectromechanical segmented mirror in a closed loop, restoring a high-quality point spread function and residual wavefront errors of the order of ˜10 nm using 1600 nm light, from a starting point of ˜300 nm in piston and ˜0.3 mrad in tip-tilt. We recommend this as a method for measuring the non-common-path error in AO-equipped ground based telescopes, as well as an approach to phasing difficult segmented mirrors such as on the James Webb Space Telescope primary and as a future direction for extreme AO.

  3. Closed-loop focal plane wavefront control with the SCExAO instrument

    Science.gov (United States)

    Martinache, Frantz; Jovanovic, Nemanja; Guyon, Olivier

    2016-09-01

    Aims: This article describes the implementation of a focal plane based wavefront control loop on the high-contrast imaging instrument SCExAO (Subaru Coronagraphic Extreme Adaptive Optics). The sensor relies on the Fourier analysis of conventional focal-plane images acquired after an asymmetric mask is introduced in the pupil of the instrument. Methods: This absolute sensor is used here in a closed-loop to compensate for the non-common path errors that normally affects any imaging system relying on an upstream adaptive optics system.This specific implementation was used to control low-order modes corresponding to eight zernike modes (from focus to spherical). Results: This loop was successfully run on-sky at the Subaru Telescope and is used to offset the SCExAO deformable mirror shape used as a zero-point by the high-order wavefront sensor. The paper details the range of errors this wavefront-sensing approach can operate within and explores the impact of saturation of the data and how it can be bypassed, at a cost in performance. Conclusions: Beyond this application, because of its low hardware impact, the asymmetric pupil Fourier wavefront sensor (APF-WFS) can easily be ported in a wide variety of wavefront sensing contexts, for ground- as well space-borne telescopes, and for telescope pupils that can be continuous, segmented or even sparse. The technique is powerful because it measures the wavefront where it really matters, at the level of the science detector.

  4. Design of Optical Systems with Extended Depth of Field: An Educational Approach to Wavefront Coding Techniques

    Science.gov (United States)

    Ferran, C.; Bosch, S.; Carnicer, A.

    2012-01-01

    A practical activity designed to introduce wavefront coding techniques as a method to extend the depth of field in optical systems is presented. The activity is suitable for advanced undergraduate students since it combines different topics in optical engineering such as optical system design, aberration theory, Fourier optics, and digital image…

  5. Study of the wavefront aberrations in children with amblyopia

    Institute of Scientific and Technical Information of China (English)

    ZHAO Peng-fei; ZHOU Yue-hua; WANG Ning-li; ZHANG Jing

    2010-01-01

    Background Amblyopia is a common ophthalmological condition and the wavefront aberrometer is a relatively new diagnostic tool used globally to measure optical characteristics of human eyes as well as to study refractive errors in amblyopic eyes. We studied the wavefront aberration of the amblyopic children's eyes and analyzed the mechanism of the wavefront aberration in the formation of the amblyopia, try to investigate the new evidence of the treatment of the amblyopia, especially in the refractory amblyopia.Methods The WaveScan Wavefront System (VISX, USA) aberrometer was used to investigate four groups of children under dark accommodation and cilliary muscle paralysis. There were 45 cases in the metropic group, 87 in the amblyopic group, 92 in the corrected-amblyopic group and 38 in the refractory amblyopic group. One-way analysis of variance (ANOVA), t-test and multivariate linear regression were used to analyze all the data.Results Third order to 6th order aberrations showed a decreasing trend whereas in the higher order aberrations the main ones were 3rd order coma (Z3-1-Z31), trefoil (Z3-3-Z33) and 4th order aberration (Z40); and 3rd order coma represented the highest percentage of all three main aberrations. Within 3rd order coma, vertical coma (Z3-1) accounted for a greater percentage than horizontal coma (Z31). Significant differences of vertical coma were found among all clinical groups of children: vertical coma in the amblyopic group (0.17±0.15) was significantly higher than in the metropic group (0.11±0.13, P0.05).Conclusions Although lower order aberrations such as defocus (myopia and hyperopia) and astigmatism are major factors determining the quality of the retinal image, higher order aberrations also need to be considered in amblyopic eyes as their effects are significant.

  6. Wavefront measurement of single-mode quantum cascade laser beam for seed application in laser-produced plasma extreme ultraviolet system.

    Science.gov (United States)

    Nowak, Krzysztof M; Ohta, Takeshi; Suganuma, Takashi; Yokotsuka, Toshio; Fujimoto, Junichi; Mizoguchi, Hakaru

    2012-12-01

    Quantum cascade laser (QCL) is a very attractive seed source for a multikilowatt pulsed CO2 lasers applied for driving extreme ultraviolet emitting plasmas. In this Letter, we investigate output beam properties of a QCL designed to address P18 and P20 lines of 10.6 micron band of CO2 molecule. In particular, output beam quality and stability are investigated for the first time. A well-defined linear polarization and a single-mode operation enabled a use of phase retrieval method for full description of QCL output beam. A direct, multi-image numerical phase retrieval technique was developed and successfully applied to the measured intensity patterns of a QCL beam. Very good agreement between the measured and reconstructed beam profiles was observed at distances ranging from QCL aperture to infinity, proving a good understanding of the beam propagation. The results also confirm a high spatial coherence and high stability of the beam parameters, the features expected from an excellent seed source.

  7. Wavefront-Error Performance Characterization for the James Webb Space Telescope (JWST) Integrated Science Instrument Module (ISIM) Science Instruments

    Science.gov (United States)

    Aronstein, David L.; Smith, J. Scott; Zielinski, Thomas P.; Telfer, Randal; Tournois, Severine C.; Moore, Dustin B.; Fienup, James R.

    2016-01-01

    The science instruments (SIs) comprising the James Webb Space Telescope (JWST) Integrated Science Instrument Module (ISIM) were tested in three cryogenic-vacuum test campaigns in the NASA Goddard Space Flight Center (GSFC)'s Space Environment Simulator (SES) test chamber. In this paper, we describe the results of optical wavefront-error performance characterization of the SIs. The wavefront error is determined using image-based wavefront sensing, and the primary data used by this process are focus sweeps, a series of images recorded by the instrument under test in its as-used configuration, in which the focal plane is systematically changed from one image to the next. High-precision determination of the wavefront error also requires several sources of secondary data, including 1) spectrum, apodization, and wavefront-error characterization of the optical ground-support equipment (OGSE) illumination module, called the OTE Simulator (OSIM), 2) F-number and pupil-distortion measurements made using a pseudo-nonredundant mask (PNRM), and 3) pupil geometry predictions as a function of SI and field point, which are complicated because of a tricontagon-shaped outer perimeter and small holes that appear in the exit pupil due to the way that different light sources are injected into the optical path by the OGSE. One set of wavefront-error tests, for the coronagraphic channel of the Near-Infrared Camera (NIRCam) Longwave instruments, was performed using data from transverse translation diversity sweeps instead of focus sweeps, in which a sub-aperture is translated and/or rotated across the exit pupil of the system. Several optical-performance requirements that were verified during this ISIM-level testing are levied on the uncertainties of various wavefront-error-related quantities rather than on the wavefront errors themselves. This paper also describes the methodology, based on Monte Carlo simulations of the wavefront-sensing analysis of focus-sweep data, used to establish

  8. Wavefront analysis and modulation transfer function of three multifocal intraocular lenses

    Directory of Open Access Journals (Sweden)

    Santhiago Marcony

    2010-01-01

    Full Text Available Purpose: To evaluate wavefront performance and modulation transfer function (MTF in the human eye after the implantation of diffractive or refractive multifocal intraocular lenses (IOLs. Materials and Methods: This was a prospective, interventional, comparative, nonrandomized clinical study. Uncorrected distance and near visual acuity, and wavefront analysis including MTF curves (iTrace aberrometer, Tracey Technologies, Houston, TX, USA were measured in 60 patients after bilateral IOL implantation with 6 months of follow-up. Forty eyes received the diffractive ReSTOR (Alcon, 40 eyes received the refractive ReZoom (Advanced Medical Optics and 40 eyes, the Tecnis ZM900 (Advanced Medical Optics. The comparison of MTF and aberration between the intraocular lenses was performed using analysis of variance (ANOVA, followed by the Dunn test when necessary. Results: The mean uncorrected distance visual acuity was similar in all three groups of multifocal IOLs. The ReSTOR group provided better uncorrected near visual acuity than the ReZoom group ( P < 0.001, but similar to the Tecnis group. Spherical aberration was significantly higher in the ReZoom group ( P = 0.007. Similar MTF curves were found for the aspheric multifocal IOL Tecnis and the spheric multifocal IOL ReSTOR, and both performed better than the multifocal IOL ReZoom in a 5 mm pupil ( P < 0.001 at all spatial frequencies. Conclusions: Diffractive IOLs studied presented similar MTF curves for a 5 mm pupil diameter. Both diffractive IOLs showed similar spherical aberration, which was significantly better with the full-diffractive IOL Tecnis than with the refractive IOL ReZoom.

  9. Wavefront Control and Image Restoration with Less Computing

    Science.gov (United States)

    Lyon, Richard G.

    2010-01-01

    PseudoDiversity is a method of recovering the wavefront in a sparse- or segmented- aperture optical system typified by an interferometer or a telescope equipped with an adaptive primary mirror consisting of controllably slightly moveable segments. (PseudoDiversity should not be confused with a radio-antenna-arraying method called pseudodiversity.) As in the cases of other wavefront- recovery methods, the streams of wavefront data generated by means of PseudoDiversity are used as feedback signals for controlling electromechanical actuators of the various segments so as to correct wavefront errors and thereby, for example, obtain a clearer, steadier image of a distant object in the presence of atmospheric turbulence. There are numerous potential applications in astronomy, remote sensing from aircraft and spacecraft, targeting missiles, sighting military targets, and medical imaging (including microscopy) through such intervening media as cells or water. In comparison with prior wavefront-recovery methods used in adaptive optics, PseudoDiversity involves considerably simpler equipment and procedures and less computation. For PseudoDiversity, there is no need to install separate metrological equipment or to use any optomechanical components beyond those that are already parts of the optical system to which the method is applied. In Pseudo- Diversity, the actuators of a subset of the segments or subapertures are driven to make the segments dither in the piston, tilt, and tip degrees of freedom. Each aperture is dithered at a unique frequency at an amplitude of a half wavelength of light. During the dithering, images on the focal plane are detected and digitized at a rate of at least four samples per dither period. In the processing of the image samples, the use of different dither frequencies makes it possible to determine the separate effects of the various dithered segments or apertures. The digitized image-detector outputs are processed in the spatial

  10. Advanced Measuring (Instrumentation Methods for Nuclear Installations: A Review

    Directory of Open Access Journals (Sweden)

    Wang Qiu-kuan

    2012-01-01

    Full Text Available The nuclear technology has been widely used in the world. The research of measurement in nuclear installations involves many aspects, such as nuclear reactors, nuclear fuel cycle, safety and security, nuclear accident, after action, analysis, and environmental applications. In last decades, many advanced measuring devices and techniques have been widely applied in nuclear installations. This paper mainly introduces the development of the measuring (instrumentation methods for nuclear installations and the applications of these instruments and methods.

  11. Wavefront sensors for adaptive optical systems

    Science.gov (United States)

    Lukin, V. P.; Botygina, N. N.; Emaleev, O. N.; Konyaev, P. A.

    2010-10-01

    A high precision Shack-Hartmann wavefront (WF) sensor has been developed on the basis of a low-aperture off-axis diffraction lens array. The device is capable of measuring WF slopes at array sub-apertures of size 640x640 μm with an error not exceeding 4.80 arcsec (0.15 pixel), which corresponds to the standard deviation equal to 0.017λ at the reconstructed WF with wavelength λ . Also the modification of this sensor for adaptive system of solar telescope using extended scenes as tracking objects, such as sunspot, pores, solar granulation and limb, is presented. The software package developed for the proposed WF sensors includes three algorithms of local WF slopes estimation (modified centroids, normalized cross-correlation and fast Fourier-demodulation), as well as three methods of WF reconstruction (modal Zernike polynomials expansion, deformable mirror response functions expansion and phase unwrapping), that can be selected during operation with accordance to the application.

  12. First tests of wavefront sensing with a constellation of laser guide beacons

    CERN Document Server

    Lloyd-Hart, M; Milton, N M; Stalcup, T; Snyder, M; Putnam, N; Angel, J R P

    2005-01-01

    Adaptive optics to correct current telescopes over wide fields, or future very large telescopes over even narrow fields, will require real-time wavefront measurements made with a constellation of laser beacons. Here we report the first such measurements, made at the 6.5 m MMT with five Rayleigh beacons in a 2 arcmin pentagon. Each beacon is made with a pulsed beam at 532 nm, of 4 W at the exit pupil of the projector. The return is range-gated from 20-29 km and recorded at 53 Hz by a 36-element Shack-Hartmann sensor. Wavefronts derived from the beacons are compared with simultaneous wavefronts obtained for individual natural stars within or near the constellation. Observations were made in seeing averaging 1.0 arcsec with 2/3 of the aberration measured to be from a ground layer of mean height 380 m. Under these conditions, subtraction of the simple instantaneous average of the five beacon wavefronts from the stellar wavefronts yielded a 40% rms reduction in the measured modes of the distortion over a 2 arcmin ...

  13. The wavefront of the radio signal emitted by cosmic ray air showers

    CERN Document Server

    Apel, W D; Bähren, L; Bekk, K; Bertaina, M; Biermann, P L; Blümer, J; Bozdog, H; Brancus, I M; Cantoni, E; Chiavassa, A; Daumiller, K; de Souza, V; Di Pierro, F; Doll, P; Engel, R; Falcke, H; Fuchs, B; Gemmeke, H; Grupen, C; Haungs, A; Heck, D; Hörandel, J R; Horneffer, A; Huber, D; Huege, T; Isar, P G; Kampert, K -H; Kang, D; Krömer, O; Kuijpers, J; Link, K; Luczak, P; Ludwig, M; Mathes, H J; Melissas, M; Morello, C; Oehlschläger, J; Palmieri, N; Pierog, T; Rautenberg, J; Rebel, H; Roth, M; Rühle, C; Saftoiu, A; Schieler, H; Schmidt, A; Schröder, F G; Sima, O; Toma, G; Trinchero, G C; Weindl, A; Wochele, J; Zabierowski, J; Zensus, J A

    2014-01-01

    Analyzing measurements of the LOPES antenna array together with corresponding CoREAS simulations for more than 300 measured events with energy above $10^{17}$eV and zenith angles smaller than $45^\\circ$, we find that the radio wavefront of cosmic-ray air showers is of hyperbolic shape. At axis distances $\\gtrsim 50$m, the wavefront can be approximated by a simple cone. According to the simulations, the cone angle is clearly correlated with the shower maximum. Thus, we confirm earlier predictions that arrival time measurements can be used to study the longitudinal shower development, but now using a realistic wavefront. Moreover, we show that the hyperbolic wavefront is compatible with our measurement, and we present several experimental indications that the cone angle is indeed sensitive to the shower development. Consequently, the wavefront can be used to statistically study the primary composition of ultra-high energy cosmic rays. At LOPES, the experimentally achieved precision for the shower maximum is lim...

  14. Complex wavefront sensing with a plenoptic sensor

    Science.gov (United States)

    Wu, Chensheng; Ko, Jonathan; Davis, Christopher C.

    2016-09-01

    There are many techniques to achieve basic wavefront sensing tasks in the weak atmospheric turbulence regime. However, in strong and deep turbulence situations, the complexity of a propagating wavefront increases significantly. Typically, beam breakup will happen and various portions of the beam will randomly interfere with each other. Consequently, some conventional techniques for wavefront sensing turn out to be inaccurate and misleading. For example, a Shack-Hartmann sensor will be confused by multi-spot/zero-spot result in some cells. The curvature sensor will be affected by random interference patterns for both the image acquired before the focal plane and the image acquired after the focal plane. We propose the use of a plenoptic sensor to solve complex wavefront sensing problems. In fact, our results show that even for multiple beams (their wavelengths can be the same) passing through the same turbulent channel, the plenoptic sensor can reconstruct the turbulence-induced distortion accurately. In this paper, we will demonstrate the plenoptic mapping principle to analyze and reconstruct the complex wavefront of a distorted laser beam.

  15. An iterative wavefront sensing algorithm for high-contrast imaging systems *

    Institute of Scientific and Technical Information of China (English)

    Jiang-Pei Dou; De-Qing Ren; Yong-Tian Zhu

    2011-01-01

    Wavefront sensing from multiple focal plane images is a promising technique for high-contrast imaging systems. However, the wavefront error of an optics system can be properly reconstructed only when it is very small. This paper presents an iterative optimization algorithm for the direct measurement of large static wavefront errors from only one focal plane image. We first measure the intensity of the pupil image to get the pupil function of the system and acquire the aberrated image on the focal plane with a phase error that will be measured. Then we induce a dynamic phase on the tested pupil function and calculate the associated intensity of the reconstructed image on the focal plane. The algorithm will then try to minimize the intensity difference between the reconstructed image and the aberrated test image in the focal plane, where the induced phase is a variable of the optimization algorithm.The simulation shows that the wavefront of an optical system can theoretically be reconstructed with high precision, which indicates that such an iterative algorithm may be an effective way to perform wavefront sensing for high-contrast imaging systems.

  16. Asymmetric cryptography based on wavefront sensing.

    Science.gov (United States)

    Peng, Xiang; Wei, Hengzheng; Zhang, Peng

    2006-12-15

    A system of asymmetric cryptography based on wavefront sensing (ACWS) is proposed for the first time to our knowledge. One of the most significant features of the asymmetric cryptography is that a trapdoor one-way function is required and constructed by analogy to wavefront sensing, in which the public key may be derived from optical parameters, such as the wavelength or the focal length, while the private key may be obtained from a kind of regular point array. The ciphertext is generated by the encoded wavefront and represented with an irregular array. In such an ACWS system, the encryption key is not identical to the decryption key, which is another important feature of an asymmetric cryptographic system. The processes of asymmetric encryption and decryption are formulized mathematically and demonstrated with a set of numerical experiments.

  17. Modeling of high-precision wavefront sensing with new generation of CMT avalanche photodiode infrared detectors.

    Science.gov (United States)

    Gousset, Silvère; Petit, Cyril; Michau, Vincent; Fusco, Thierry; Robert, Clelia

    2015-12-01

    Near-infrared wavefront sensing allows for the enhancement of sky coverage with adaptive optics. The recently developed HgCdTe avalanche photodiode arrays are promising due to their very low detector noise, but still present an imperfect cosmetic that may directly impact real-time wavefront measurements for adaptive optics and thus degrade performance in astronomical applications. We propose here a model of a Shack-Hartmann wavefront measurement in the presence of residual fixed pattern noise and defective pixels. To adjust our models, a fine characterization of such an HgCdTe array, the RAPID sensor, is proposed. The impact of the cosmetic defects on the Shack-Hartmann measurement is assessed through numerical simulations. This study provides both a new insight on the applicability of cadmium mercury telluride (CMT) avalanche photodiodes detectors for astronomical applications and criteria to specify the cosmetic qualities of future arrays.

  18. Phase error correction in wavefront curvature sensing via phase retrieval

    DEFF Research Database (Denmark)

    Almoro, Percival; Hanson, Steen Grüner

    2008-01-01

    Wavefront curvature sensing with phase error correction system is carried out using phase retrieval based on a partially-developed volume speckle field. Various wavefronts are reconstructed: planar, spherical, cylindrical, and a wavefront passing through the side of a bare optical fiber. Spurious...

  19. Optimization of scanning strategy of digital Shack-Hartmann wavefront sensing.

    Science.gov (United States)

    Guo, Wenjiang; Zhao, Liping; Li, Xiang; Chen, I-Ming

    2012-01-01

    In the traditional Shack-Hartmann wavefront sensing (SHWS) system, a lenslet array with a bigger configuration is desired to achieve a higher lateral resolution. However, practical implementation limits the configuration and this parameter is contradicted with the measurement range. We have proposed a digital scanning technique by making use of the high flexibility of a spatial light modulator to sample the reflected wavefront [X. Li, L. P. Zhao, Z. P. Fang, and C. S. Tan, "Improve lateral resolution in wavefront sensing with digital scanning technique," in Asia-Pacific Conference of Transducers and Micro-Nano Technology (2006)]. The lenslet array pattern is programmed to laterally scan the whole aperture. In this paper, the methodology to optimize the scanning step for the purpose of form measurement is proposed. The correctness and effectiveness are demonstrated in numerical simulation and experimental investigation.

  20. Transmitted wavefront error of a volume phase holographic grating at cryogenic temperature.

    Science.gov (United States)

    Lee, David; Taylor, Gordon D; Baillie, Thomas E C; Montgomery, David

    2012-06-01

    This paper describes the results of transmitted wavefront error (WFE) measurements on a volume phase holographic (VPH) grating operating at a temperature of 120 K. The VPH grating was mounted in a cryogenically compatible optical mount and tested in situ in a cryostat. The nominal root mean square (RMS) wavefront error at room temperature was 19 nm measured over a 50 mm diameter test aperture. The WFE remained at 18 nm RMS when the grating was cooled. This important result demonstrates that excellent WFE performance can be obtained with cooled VPH gratings, as required for use in future cryogenic infrared astronomical spectrometers planned for the European Extremely Large Telescope.

  1. High-speed SPGD wavefront controller for an adaptive optics system without wavefront sensor

    Science.gov (United States)

    Wang, Caixia; Li, Xinyang; Li, Mei; Ye, Jongwei; Chen, Bo

    2010-10-01

    A non-conventional adaptive optics system based on direct system performance metric optimization is illustrated. The system does not require wave-front sensor which is difficult to work under the poor condition such as beam cleanup for the anomalous light beam. The system comprises a high speed wavefront controller based on Stochastic Parallel Gradient Descent (SPGD) Algorithm, a deformable mirror, a tip/tilt mirror and a far-field system performance metric sensor. The architecture of the wave-front controller is based on a combination of Field Programmable Gate Array (FPGA) and floating-point Digital Signal Processor (DSP). The Zernike coefficient information is applied to improve the iteration speed. The experimental results show that the beam cleanup system based on SPGD keep a high iteration speed. The controller can compensate the wavefront aberration and tilt excursion effectively.

  2. Liquid crystal wavefront corrector on silicon

    NARCIS (Netherlands)

    Loktev, M.; Vdovin, G.; Nanver, L.

    2005-01-01

    A reflective-type liquid crystal (LC) wavefront corrector with modal addressing is described. The corrector’s backplane has an array of pixel electrodes interconnected by a network of discrete resistors. The resistive network serves to form the local voltage profile that controls the phase distribut

  3. First laboratory results with the LINC-NIRVANA high layer wavefront sensor

    Science.gov (United States)

    Zhang, Xianyu; Gaessler, Wolfgang; Conrad, Albert R.; Bertram, Thomas; Arcidiacono, Carmelo; Herbst, Thomas M.; Kuerster, Martin; Bizenberger, Peter; Meschke, Daniel; Rix, Hans-Walter; Rao, Changhui; Mohr, Lars; Briegel, Florian; Kittmann, Frank; Berwein, Juergen; Trowitzsch, Jan; Schreiber, Laura; Ragazzoni, Roberto; Diolaiti, Emiliano

    2011-08-01

    In the field of adaptive optics, multi-conjugate adaptive optics (MCAO) can greatly increase the size of the corrected field of view (FoV) and also extend sky coverage. By applying layer oriented MCAO (LO-MCAO) [4], together with multiple guide stars (up to 20) and pyramid wavefront sensors [7], LINC-NIRVANA (L-N for short) [1] will provide two AO-corrected beams to a Fizeau interferometer to achieve 10 milliarcsecond angular resolution on the Large Binocular Telescope. This paper presents first laboratory results of the AO performance achieved with the high layer wavefront sensor (HWS). This sensor, together with its associated deformable mirror (a Xinetics-349), is being operated in one of the L-N laboratories. AO reference stars, spread across a 2 arc-minute FoV and with aberrations resulting from turbulence introduced at specific layers in the atmosphere, are simulated in this lab environment. This is achieved with the Multi-Atmosphere Phase screen and Stars (MAPS) [2] unit. From the wavefront data, the approximate residual wavefront error after correction has been calculated for different turbulent layer altitudes and wind speeds. Using a somewhat undersampled CCD, the FWHM of stars in the nearly 2 arc-minute FoV has also been measured. These test results demonstrate that the high layer wavefront sensor of LINC-NIRVANA will be able to achieve uniform AO correction across a large FoV.

  4. Wavefront alignment research of segmented mirror synthetic aperture optical (SAO) system

    Science.gov (United States)

    Deng, Jian; An, Xiaoqiang; Tian, Hao

    2010-05-01

    Wavefront control technology and imaging experiment are introduced for a segmented mirror SAO system with deformable sub-mirrors. This system is a RC style with 300mm aperture, 4.5 F#, +/-0.4°FOV, 0.45~0.75μm wave band, and diffraction-limit design MTF. The primary mirror is composed by three sub-mirrors, with parabolic shape, and each deformable sub-mirror has 19 actuators to control and keep the surface shape, and 5 actuators to align sub-mirrors location in 5 degree of freedom. Interferometer is used to feed back and control exit wavefront error, and base on measurement and finite element analysis, location and quanitity of actuators are optimized, making the surface shape and misadjustment errors interact and compensate each other, and the synthetic system exit pupil wavefront error is controlled. The integrated exit pupil wavefront errors are gotten by ZYGO interferometer, and central FOV is 0.077λRMS, and edge FOV is 0.093λRMS. At the end, an imaging experiment is executed, and good results are obtained, which proves, the deformable sub-mirrors have the ability to meliorate alignment and the latter can retroact the former, and this relationship iterate make system exit pupil wavefront error convergence and improve segmented mirror SAO system imaging ability.

  5. Nondestructive Measurements for Diagnostics of Advanced Reactor Passive Components

    Energy Technology Data Exchange (ETDEWEB)

    Prowant, Matthew S.; Dib, Gerges; Roy, Surajit; Luzi, Lorenzo; Ramuhalli, Pradeep

    2016-09-20

    Information on advanced reactor (AdvRx) component condition and failure probability is necessary to maintaining adequate safety margins and avoiding unplanned shutdowns, both of which have regulatory and economic consequences. Prognostic health management (PHM) technologies provide one approach to addressing these needs by providing the technical means for lifetime management of significant passive components and reactor internals. However, such systems require measurement data that are sensitive to degradation of the component. This paper describes results to date of ongoing research on nondestructive measurements of component condition for degradation mechanisms of relevance to AdvRx concepts. The focus of this paper is on in-situ ultrasonic measurements during high-temperature creep degradation. The data were analyzed to assess the sensitivity of the measurements to creep degradation, with the specific objective of assessing the suitability of the resulting correlations for remaining life prediction. The details of the measurements, results of data analysis, and ongoing research in this area are discussed.

  6. Wavefront-sensor-induced beam size error: physical mechanism, sensitivity-analysis and correction method

    NARCIS (Netherlands)

    Koek, W.D.; Zwet, E.J. van

    2015-01-01

    When using a commonly-used quadri-wave lateral shearing interferometer wavefront sensor (QWLSI WFS) for beam size measurements on a high power CO2 laser, artefacts have been observed in the measured irradiance distribution. The grating in the QWLSI WFS not only generates the diffracted first orders

  7. Wavefront-sensor-induced beam size error: physical mechanism, sensitivity-analysis and correction method

    NARCIS (Netherlands)

    Koek, W.D.; Zwet, E.J. van

    2015-01-01

    When using a commonly-used quadri-wave lateral shearing interferometer wavefront sensor (QWLSI WFS) for beam size measurements on a high power CO2 laser, artefacts have been observed in the measured irradiance distribution. The grating in the QWLSI WFS not only generates the diffracted first orders

  8. Hybrid iterative wavefront shaping for high-speed focusing through scattering media

    Science.gov (United States)

    Hemphill, Ashton S.; Wang, Lihong V.

    2016-03-01

    A major limiting factor of optical imaging in biological applications is the diffusion of light by tissue, preventing focusing at depths greater than ~1 mm in the body. To overcome this issue, phase-based wavefront shaping alters the phase of sections of the incident wavefront to counteract aberrations in phase caused by scattering. This enables focusing through scattering media beyond the optical diffusion limit and increases signal compared to amplitude-based compensation. However, in previous studies, speed of optimization has typically been limited by the use of a liquid crystal spatial light modulator (SLM) for measurement and display. SLMs usually have refresh rates of less than 100 Hz and require much longer than the speckle correlation time of tissue in vivo, usually on the order of milliseconds, to determine the optimal wavefront. Here, we present a phase-based iterative wavefront shaping method based on an onaxis digital micromirror device (DMD) in conjunction with an electro-optic modulator (EOM) for measurement and a fast SLM for display. By combining phase modulation from an EOM with the modal selection of the DMD, we take advantage of DMDs higher refresh rate, approximately 23 kHz, for iterative phase measurement. The slower SLM requires one update for display following the rapid determination of the optimal wavefront via the DMD, allowing for high-speed wavefront shaping. Using this system, we are able to focus through scattering media using 64 modes in under 8 milliseconds, on the order of the speckle correlation time for tissue in vivo.

  9. Amplitude and phase beam characterization using a two-dimensional wavefront sensor

    Energy Technology Data Exchange (ETDEWEB)

    Neal, D.R.; Alford, W.J.; Gruetzner, J.K.; Warren, M.E.

    1996-09-01

    We have developed a two-dimensional Shack-Hartman wavefront sensor that uses binary optic lenslet arrays to directly measure the wavefront slope (phase gradient) and amplitude of the laser beam. This sensor uses an array of lenslets that dissects the beam into a number of samples. The focal spot location of each of these lenslets (measured by a CCD camera) is related to the incoming wavefront slope over the lenslet. By integrating these measurements over the laser aperture, the wavefront or phase distribution can be determined. Since the power focused by each lenslet is also easily determined, this allows a complete measurement of the intensity and phase distribution of the laser beam. Furthermore, all the information is obtained in a single measurement. Knowing the complete scalar field of the beam allows the detailed prediction of the actual beam`s characteristics along its propagation path. In particular, the space- beamwidth product M{sup 2}, can be obtained in a single measurement. The intensity and phase information can be used in concert with information about other elements in the optical train to predict the beam size, shape, phase and other characteristics anywhere in the optical train. We present preliminary measurements of an Ar{sup +} laser beam and associated M{sup 2} calculations.

  10. High-precision system identification method for a deformable mirror in wavefront control.

    Science.gov (United States)

    Huang, Lei; Ma, Xingkun; Bian, Qi; Li, Tenghao; Zhou, Chenlu; Gong, Mali

    2015-05-10

    Based on a mathematic model, the relation between the accuracy of the influence matrix and the performance of the wavefront correction is established. Based on the least squares method, a two-step system identification is proposed to improve the accuracy of the influence matrix, where the measurement noise can be suppressed and the nonlinearity of the deformable mirror can be compensated. The validity of the two-step system identification method is tested in the experiment, where improvements in wavefront correction precision as well as closed-loop control efficiency were observed.

  11. Calibration of wavefront distortion in light modulator setup by Fourier analysis of multi-beam interference

    CERN Document Server

    Leszczyński, Adam

    2015-01-01

    We present a method to calibrate wavefront distortion of the spatial light modulator setup by registering far field images of several gaussian beams diffracted off the modulator. The Fourier transform of resulting interference images reveals phase differences between typically 5 movable points on the modulator. Repeating this measurement yields wavefront surface. Next, the amplitude efficiency is calibrated be registering near field image. As a verification we produced a superposition of 7th and 8th Bessel beams with different phase velocities and observed their interference.

  12. Calibration of wavefront distortion in light modulator setup by Fourier analysis of multibeam interference.

    Science.gov (United States)

    Leszczyński, Adam; Wasilewski, Wojciech

    2016-04-01

    We present a method to calibrate wavefront distortion of the spatial light modulator setup by registering far-field images of several Gaussian beams diffracted off the modulator. The Fourier transform of resulting interference images reveals phase differences among typically five movable points on the modulator. Repeating this measurement yields a wavefront surface. Next, the amplitude efficiency is calibrated for registering the near-field image. For verification, we produced a superposition of seventh and eighth Bessel beams with different phase velocities and observed their interference.

  13. Advanced Measurement Devices for the Microgravity Electromagnetic Levitation Facility EML

    Science.gov (United States)

    Brillo, Jurgen; Fritze, Holger; Lohofer, Georg; Schulz, Michal; Stenzel, Christian

    2012-01-01

    This paper reports on two advanced measurement devices for the microgravity electromagnetic levitation facility (EML), which is currently under construction for the use onboard the "International Space Station (ISS)": the "Sample Coupling Electronics (SCE)" and the "Oxygen Sensing and Control Unit (OSC)". The SCE measures by a contactless, inductive method the electrical resistivity and the diameter of a spherical levitated metallic droplet by evaluating the voltage and electrical current applied to the levitation coil. The necessity of the OSC comes from the insight that properties like surface tension or, eventually, viscosity cannot seriously be determined by the oscillating drop method in the EML facility without knowing the conditions of the surrounding atmosphere. In the following both measurement devices are explained and laboratory test results are presented.

  14. Military target task performance after wavefront-guided (WFG) and wavefront-optimized (WFO) photorefractive keratectomy (PRK)

    Science.gov (United States)

    Maurer, Tana; Deaver, Dawne; Howell, Christopher; Moyer, Steve; Nguyen, Oanh; Mueller, Greg; Ryan, Denise; Sia, Rose K.; Stutzman, Richard; Pasternak, Joseph; Bower, Kraig

    2014-06-01

    Major decisions regarding life and death are routinely made on the modern battlefield, where visual function of the individual soldier can be of critical importance in the decision-making process. Glasses in the combat environment have considerable disadvantages: degradation of short term visual performance can occur as dust and sweat accumulate on lenses during a mission or patrol; long term visual performance can diminish as lenses become increasingly scratched and pitted; during periods of intense physical trauma, glasses can be knocked off the soldier's face and lost or broken. Although refractive surgery offers certain benefits on the battlefield when compared to wearing glasses, it is not without potential disadvantages. As a byproduct of refractive surgery, elevated optical aberrations can be induced, causing decreases in contrast sensitivity and increases in the symptoms of glare, halos, and starbursts. Typically, these symptoms occur under low light level conditions, the same conditions under which most military operations are initiated. With the advent of wavefront aberrometry, we are now seeing correction not only of myopia and astigmatism but of other, smaller optical aberrations that can cause the above symptoms. In collaboration with the Warfighter Refractive Eye Surgery Program and Research Center (WRESP-RC) at Fort Belvoir and Walter Reed National Military Medical Center (WRNMMC), the overall objective of this study is to determine the impact of wavefront guided (WFG) versus wavefront-optimized (WFO) photorefractive keratectomy (PRK) on military task visual performance. Psychophysical perception testing was conducted before and after surgery to measure each participant's performance regarding target detection and identification using thermal imagery. The results are presented here.

  15. A Survey of Advanced Microwave Frequency Measurement Techniques

    Directory of Open Access Journals (Sweden)

    Anand Swaroop Khare

    2012-06-01

    Full Text Available Microwaves are radio waves with wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. The science of photonics includes the generation, emission, modulation, signal processing, switching, transmission, amplification, detection and sensing of light. Microwave photonics has been introduced for achieving ultra broadband signal processing. Instantaneous Frequency Measurement (IFM receivers play an important role in electronic warfare. Technologies used for signal processing, include conventional direct Radio Frequency (RF techniques, digital techniques, intermediate frequency (IF techniques and photonic techniques. Direct RF techniques suffer an increased loss, high dispersion, and unwanted radiation problems in high frequencies. The systems that use traditional RF techniques can be bulky and often lack the agility required to perform advanced signal processing in rapidly changing environments. In this paper we discussed a survey of Microwave Frequency Measurement Techniques. The microwaves techniques are categorized based upon different approaches. This paper provides the major advancement in the Microwave Frequency MeasurementTechniques research; using these approaches the features and categories in the surveyed existing work.

  16. Advanced Aerodynamic Measurement Technology (Technologies avancees de mesure aerodynamique)

    Science.gov (United States)

    1998-05-01

    19th AIAA Advanced Measurement and Ground Testing Technology Conference, New Orleans, LA, June 17- 20, 1996. 17 Hart , R.C., Balla, R.J. and Herring...Deutsche Forschungsanstalt für Luft- und Raumfahrt Linder Höhe, D-51147 Köln, Germany and F. Grisch, P. Bouchardy Office National d’Etudees et de...trpy) in Du Pont Chroma Clear, (5) Ru(trpy)/Zeolite in GP-197, (6) EuTTA in dope, (7) Ru(bpy) in Du Pont Chroma Clear, (8) Perylenedicarboximide in

  17. Advances in non-invasive measures of vocal acoustics.

    Science.gov (United States)

    LaBlance, G R; Steckol, K F; Cooper, M H

    1991-10-01

    Objective assessment of vocal pitch, loudness, and quality is a crucial adjunct to endoscopy in the diagnosis and treatment of vocal pathology. Historically, this assessment was made through subjective, perceptual measures that were questionable in terms of validity and reliability. Recent advances in electronic technology now permit objective analysis of the acoustic characteristics of voice. Kay Elemetric's Visi-Pitch, DSP 5500 Digital Spectrograph, and Nasometer are representative of these new instruments and are used as illustrations in the discussion of the assessment of speech acoustics.

  18. Cryogenic wavefront correction using membrane deformable mirrors.

    Science.gov (United States)

    Dyson, H; Sharples, R; Dipper, N; Vdovin, G

    2001-01-01

    Micro-machined membrane deformable mirrors (MMDMs) are being evaluated for their suitability as wavefront correctors at cryogenic temperatures. Presented here are experimental results for the change in the initial mirror figure of 37-channel MMDMs from OKO Technologies upon cooling to T=78K. The changes in the influence functions are also explored. Of the sample of 3 mirrors tested, one was found to have sufficiently small initial static aberrations to be useful as a wavefront corrector at this temperature. The influence functions at T=78K were found to be similar in shape to both those at room temperature and theoretical predictions of the MMDMs surface shape. The magnitude of the surface deflection at T=78K was reduced by around 20% compared with room temperature values.

  19. Wavefront-sensing-based autofocusing in microscopy

    Science.gov (United States)

    Xu, Jing; Tian, Xiaolin; Meng, Xin; Kong, Yan; Gao, Shumei; Cui, Haoyang; Liu, Fei; Xue, Liang; Liu, Cheng; Wang, Shouyu

    2017-08-01

    Massive image acquisition is required along the optical axis in the classical image-analysis-based autofocus method, which significantly decreases autofocus efficiency. A wavefront-sensing-based autofocus technique is proposed to increase the speed of autofocusing and obtain high localization accuracy. Intensities at different planes along the optical axis can be computed numerically after extracting the wavefront at defocus position with the help of the transport-of-intensity equation method. According to the focus criterion, the focal plane can then be determined, and after sample shifting to this plane, the in-focus image can be recorded. The proposed approach allows for fast, precise focus detection with fewer image acquisitions compared to classical image-analysis-based autofocus techniques, and it can be applied in commercial microscopes only with an extra illumination filter.

  20. Microgenetic optimization algorithm for optimal wavefront shaping

    CERN Document Server

    Anderson, Benjamin R; Gunawidjaja, Ray; Eilers, Hergen

    2015-01-01

    One of the main limitations of utilizing optimal wavefront shaping in imaging and authentication applications is the slow speed of the optimization algorithms currently being used. To address this problem we develop a micro-genetic optimization algorithm ($\\mu$GA) for optimal wavefront shaping. We test the abilities of the $\\mu$GA and make comparisons to previous algorithms (iterative and simple-genetic) by using each algorithm to optimize transmission through an opaque medium. From our experiments we find that the $\\mu$GA is faster than both the iterative and simple-genetic algorithms and that both genetic algorithms are more resistant to noise and sample decoherence than the iterative algorithm.

  1. Advanced Measurements of Silicon Carbide Ceramic Matrix Composites

    Energy Technology Data Exchange (ETDEWEB)

    Farhad Farzbod; Stephen J. Reese; Zilong Hua; Marat Khafizov; David H. Hurley

    2012-08-01

    Silicon carbide (SiC) is being considered as a fuel cladding material for accident tolerant fuel under the Light Water Reactor Sustainability (LWRS) Program sponsored by the Nuclear Energy Division of the Department of Energy. Silicon carbide has many potential advantages over traditional zirconium based cladding systems. These include high melting point, low susceptibility to corrosion, and low degradation of mechanical properties under neutron irradiation. In addition, ceramic matrix composites (CMCs) made from SiC have high mechanical toughness enabling these materials to withstand thermal and mechanical shock loading. However, many of the fundamental mechanical and thermal properties of SiC CMCs depend strongly on the fabrication process. As a result, extrapolating current materials science databases for these materials to nuclear applications is not possible. The “Advanced Measurements” work package under the LWRS fuels pathway is tasked with the development of measurement techniques that can characterize fundamental thermal and mechanical properties of SiC CMCs. An emphasis is being placed on development of characterization tools that can used for examination of fresh as well as irradiated samples. The work discuss in this report can be divided into two broad categories. The first involves the development of laser ultrasonic techniques to measure the elastic and yield properties and the second involves the development of laser-based techniques to measurement thermal transport properties. Emphasis has been placed on understanding the anisotropic and heterogeneous nature of SiC CMCs in regards to thermal and mechanical properties. The material properties characterized within this work package will be used as validation of advanced materials physics models of SiC CMCs developed under the LWRS fuels pathway. In addition, it is envisioned that similar measurement techniques can be used to provide process control and quality assurance as well as measurement of

  2. Wavefront analysis of nonlinear self-amplified spontaneous-emission free-electron laser harmonics in the single-shot regime.

    Science.gov (United States)

    Bachelard, R; Mercère, P; Idir, M; Couprie, M-E; Labat, M; Chubar, O; Lambert, G; Zeitoun, Ph; Kimura, H; Ohashi, H; Higashiya, A; Yabashi, M; Nagasono, M; Hara, T; Ishikawa, T

    2011-06-10

    The single-shot spatial characteristics of the vacuum ultraviolet self-amplified spontaneous emission of a free electron laser (FEL) is measured at different stages of amplification up to saturation with a Hartmann wavefront sensor. We show that the fundamental radiation at 61.5 nm tends towards a single-mode behavior as getting closer to saturation. The measurements are found in good agreement with simulations and theory. A near diffraction limited wavefront was measured. The analysis of Fresnel diffraction through the Hartmann wavefront sensor hole array also provides some further insight for the evaluation of the FEL transverse coherence, of high importance for various applications.

  3. Wavefront Analysis of Nonlinear Self-Amplified Spontaneous-Emission Free-Electron Laser Harmonics in the Single-Shot Regime

    Energy Technology Data Exchange (ETDEWEB)

    Bachelard, R.; Chubar, O.; Mercere, P.; Idir, M.; Couprie, M.E.; Lambert, G.; Zeitoun, Ph.; Kimura, H.; Ohashi, H.; Higashiya, A.; Yabashi, M.; Nagasono, M.; Hara, T. and Ishikawa, T.

    2011-06-08

    The single-shot spatial characteristics of the vacuum ultraviolet self-amplified spontaneous emission of a free electron laser (FEL) is measured at different stages of amplification up to saturation with a Hartmann wavefront sensor. We show that the fundamental radiation at 61.5 nm tends towards a single-mode behavior as getting closer to saturation. The measurements are found in good agreement with simulations and theory. A near diffraction limited wavefront was measured. The analysis of Fresnel diffraction through the Hartmann wavefront sensor hole array also provides some further insight for the evaluation of the FEL transverse coherence, of high importance for various applications.

  4. High order dark wavefront sensing simulations

    CERN Document Server

    Ragazzoni, Roberto; Farinato, Jacopo; Viotto, Valentina; Bergomi, Maria; Dima, Marco; Magrin, Demetrio; Marafatto, Luca; Greggio, Davide; Carolo, Elena; Vassallo, Daniele

    2016-01-01

    Dark wavefront sensing takes shape following quantum mechanics concepts in which one is able to "see" an object in one path of a two-arm interferometer using an as low as desired amount of light actually "hitting" the occulting object. A theoretical way to achieve such a goal, but in the realm of wavefront sensing, is represented by a combination of two unequal beams interferometer sharing the same incoming light, and whose difference in path length is continuously adjusted in order to show different signals for different signs of the incoming perturbation. Furthermore, in order to obtain this in white light, the path difference should be properly adjusted vs the wavelength used. While we incidentally describe how this could be achieved in a true optomechanical setup, we focus our attention to the simulation of a hypothetical "perfect" dark wavefront sensor of this kind in which white light compensation is accomplished in a perfect manner and the gain is selectable in a numerical fashion. Although this would ...

  5. Characterisation of advanced windows. Determination of thermal properties by measurements

    Energy Technology Data Exchange (ETDEWEB)

    Duer, K.

    2001-04-01

    This report describes work carried out with the aim of facilitating a full energy performance characterisation of advanced windows and glazings by means of measurements. The energy performance of windows and glazings are characterised by two parameters: The thermal transmittance (U-value) and the total solar energy transmittance (g-value) and methods to determine these two parameters by measurements have been investigated. This process has included the improvement of existing equipment and existing measuring methods as well as the development of new measuring equipment and new methods of measuring and data treatment. Measurements of the thermal transmittance of windows and glazings in a guarded hot box have been investigated. The calibration and measuring procedures for determining the U-values of facade windows were analysed and a suggestion for a new calibration and measuring procedure for determining the U-values of roof windows in a guarded hot box was elaborated. The accuracy of the guarded hot box measurements was examined by comparisons to measurements in a hot-plate device and excellent agreement between the results was obtained. Analysis showed that the expected uncertainty in the U-value measurement is about 5% for a specimen with a U-value of 1.75 W/m{sup 2}K. The U-values of three different windows were measured in two separate round robin tests applying two different calibration procedures. The windows U-values where ranging from 1.1 to 2.5 W/m{sup 2}K and all measured results were within the expected uncertainties of the measurements. On the basis of the investigations on hot box measurements a high degree of confidence in the measurement accuracy and the measuring procedure of the guarded hot box at the Department of Buildings and Energy has been obtained. Indoor g-value measurements in a calorimetric test facility (the METSET) mounted in a solar simulator have been investigated and a number of problems regarding these measurements have been

  6. Wavefront shaping with an electrowetting liquid lens using surface harmonics (Conference Presentation)

    Science.gov (United States)

    Strauch, Matthias; Konijnenberg, Sander; Shao, Yifeng; Urbach, H. Paul

    2017-02-01

    Liquid lenses are used to correct for low order wavefront aberrations. Electrowetting liquid lenses can nowadays control defocus and astigmatism effectively, so they start being used for ophthalmology applications. To increase the performance and applicability, we introduce a new driving mechanism to create, detect and correct higher order aberrations using standing waves on the liquid interface. The speed of a liquid lens is in general limited, because the liquid surface cannot follow fast voltage changes, while providing a spherical surface. Surface waves are created instead and with them undesired aberrations. We try to control those surface waves to turn them into an effective wavefront shaping tool. We introduce a model, which treats the liquid lens as a circular vibrating membrane with adjusted boundary conditions. Similar to tunable acoustic gradient (TAG) lenses, the nature of the surface modes are predicted to be Bessel functions. Since Bessel functions are a full set of orthogonal basis functions any surface can be created as a linear combination of different Bessel functions. The model was investigated experimentally in two setups. First the point spread functions were studied and compared to a simulation of the intensity distribution created by Fresnel propagated Bessel surfaces. Second the wavefronts were measured directly using a spatial light modulator. The surface resonance frequencies confirm the predictions made by the model as well as the wavefront measurements. By superposition of known surface modes, it is possible to create new surface shapes, which can be used to simulate and measure the human eye.

  7. Laboratory simulation of atmospheric turbulence-induced optical wavefront distortion

    Science.gov (United States)

    Taylor, Travis S.; Gregory, Don A.

    2002-11-01

    Real-time liquid crystal television-based technique for simulating optical wavefront distortion due to atmospheric turbulence is presented and demonstrated. A liquid crystal television (LCTV) operating in the "phase mostly" mode was used as an array of spatially correlated phase delays. A movie of the arrays in motion was then generated and displayed on the LCTV. The turbulence simulation system was verified by passing a collimated and doubled diode pumped Nd:YVO 4 laser beam (532 nm) through the transparent LCTV screen. The beam was then passed through a lens and the power spectra of the turbulence information carrying beam was detected as a measure of the far-field distribution. The same collimated laser beam, without the LCTV, was also transmitted down an open-air range and the power spectra detected as a measure of a real far-field distribution. Accepted turbulence parameters were measured for both arrangements and then compared.

  8. System and Method for Null-Lens Wavefront Sensing

    Science.gov (United States)

    Hill, Peter C. (Inventor); Thompson, Patrick L. (Inventor); Aronstein, David L. (Inventor); Bolcar, Matthew R. (Inventor); Smith, Jeffrey S. (Inventor)

    2015-01-01

    A method of measuring aberrations in a null-lens including assembly and alignment aberrations. The null-lens may be used for measuring aberrations in an aspheric optic with the null-lens. Light propagates from the aspheric optic location through the null-lens, while sweeping a detector through the null-lens focal plane. Image data being is collected at locations about said focal plane. Light is simulated propagating to the collection locations for each collected image. Null-lens aberrations may extracted, e.g., applying image-based wavefront-sensing to collected images and simulation results. The null-lens aberrations improve accuracy in measuring aspheric optic aberrations.

  9. Measurement and modeling of advanced coal conversion processes

    Energy Technology Data Exchange (ETDEWEB)

    Solomon, P.R.; Serio, M.A.; Hamblen, D.G. (Advanced Fuel Research, Inc., East Hartford, CT (USA)); Smoot, L.D.; Brewster, B.S. (Brigham Young Univ., Provo, UT (USA))

    1990-01-01

    The overall objective of this program is the development of predictive capability for the design, scale up, simulation, control and feedstock evaluation in advanced coal conversion devices. This technology is important to reduce the technical and economic risks inherent in utilizing coal, a feedstock whose variable and often unexpected behavior presents a significant challenge. This program will merge significant advances made at Advanced Fuel Research, Inc. (AFR) in measuring and quantitatively describing the mechanisms in coal conversion behavior, with technology being developed at Brigham Young University (BYU) in comprehensive computer codes for mechanistic modeling of entrained-bed gasification. Additional capabilities in predicting pollutant formation will be implemented and the technology will be expanded to fixed-bed reactors. The foundation to describe coal-specific conversion behavior is AFR's Functional Group (FG) and Devolatilization, Vaporization, and Crosslinking (DVC) models, developed under previous and on-going METC sponsored programs. These models have demonstrated the capability to describe the time dependent evolution of individual gas species, and the amount and characteristics of tar and char. The combined FG-DVC model will be integrated with BYU's comprehensive two-dimensional reactor model, PCGC-2, which is currently the most widely used reactor simulation for combustion or gasification. Success in this program will be a major step in improving in predictive capabilities for coal conversion processes including: demonstrated accuracy and reliability and a generalized first principles'' treatment of coals based on readily obtained composition data. The progress during the fifteenth quarterly of the program is presented. 56 refs., 41 figs., 5 tabs.

  10. Advanced Active-Magnetic-Bearing Thrust-Measurement System

    Science.gov (United States)

    Imlach, Joseph; Kasarda, Mary; Blumber, Eric

    2008-01-01

    An advanced thrust-measurement system utilizes active magnetic bearings to both (1) levitate a floating frame in all six degrees of freedom and (2) measure the levitation forces between the floating frame and a grounded frame. This system was developed for original use in measuring the thrust exerted by a rocket engine mounted on the floating frame, but can just as well be used in other force-measurement applications. This system offers several advantages over prior thrust-measurement systems based on mechanical support by flexures and/or load cells: The system includes multiple active magnetic bearings for each degree of freedom, so that by selective use of one, some, or all of these bearings, it is possible to test a given article over a wide force range in the same fixture, eliminating the need to transfer the article to different test fixtures to obtain the benefit of full-scale accuracy of different force-measurement devices for different force ranges. Like other active magnetic bearings, the active magnetic bearings of this system include closed-loop control subsystems, through which the stiffness and damping characteristics of the magnetic bearings can be modified electronically. The design of the system minimizes or eliminates cross-axis force-measurement errors. The active magnetic bearings are configured to provide support against movement along all three orthogonal Cartesian axes, and such that the support along a given axis does not produce force along any other axis. Moreover, by eliminating the need for such mechanical connections as flexures used in prior thrust-measurement systems, magnetic levitation of the floating frame eliminates what would otherwise be major sources of cross-axis forces and the associated measurement errors. Overall, relative to prior mechanical-support thrust-measurement systems, this system offers greater versatility for adaptation to a variety of test conditions and requirements. The basic idea of most prior active

  11. Back-scatter analysis based algorithms for increasing transmission through highly-scattering random media using phase-only modulated wavefronts

    CERN Document Server

    Jin, Curtis; Michielssen, Eric; Rand, Stephen

    2014-01-01

    Recent theoretical and experimental advances have shed light on the existence of so-called `perfectly transmitting' wavefronts with transmission coefficients close to 1 in strongly backscattering random media. These perfectly transmitting eigen-wavefronts can be synthesized by spatial amplitude and phase modulation. Here, we consider the problem of transmission enhancement using phase-only modulated wavefronts. We develop physically realizable iterative and non-iterative algorithms for increasing the transmission through such random media using backscatter analysis. We theoretically show that, despite the phase-only modulation constraint, the non-iterative algorithms will achieve at least about 25$\\pi$% or about 78.5% transmission assuming there is at least one perfectly transmitting eigen-wavefront and that the singular vectors of the transmission matrix obey a maximum entropy principle so that they are isotropically random. We numerically analyze the limits of phase-only modulated transmission in 2-D with f...

  12. Recent advances in automation, robotics and measuring techniques

    CERN Document Server

    Zieliński, Cezary; Kaliczyńska, Małgorzata

    2014-01-01

    This book presents the recent advances and developments in control, automation, robotics, and measuring techniques. It presents contributions of top experts in the fields, focused on both theory and industrial practice. The particular chapters present a deep analysis of a specific technical problem which is in general followed by a numerical analysis and simulation, and results of an implementation for the solution of a real world problem. The book presents the results of the International Conference AUTOMATION 2014 held 26 - 28 March, 2014 in Warsaw, Poland on Automation – Innovations and Future Prospectives The presented theoretical results, practical solutions and guidelines will be useful for both researchers working in the area of engineering sciences and for practitioners solving industrial problems.

  13. Advanced multipoles for accelerator magnets theoretical analysis and their measurement

    CERN Document Server

    Schnizer, Pierre

    2017-01-01

    This monograph presents research on the transversal beam dynamics of accelerators and evaluates and describes the respective magnetic field homogeneity.  The widely used cylindrical circular multipoles have disadvantages for elliptical apertures or curved trajectories, and the book also introduces new types of advanced multipole magnets, detailing their application, as well as the numerical data and measurements obtained. The research presented here provides more precise descriptions of the field and better estimates of the beam dynamics. Moreover, the effects of field inhomogeneity can be estimated with higher precision than before. These findings are further elaborated to demonstrate their usefulness for real magnets and accelerator set ups, showing their advantages over cylindrical circular multipoles. The research findings are complemented with data obtained from the new superconducting beam guiding magnet models (SIS100) for the FAIR (Facility for Antiproton and Ion Research) project.  Lastly, the book...

  14. Advanced quantitative measurement methodology in physics education research

    Science.gov (United States)

    Wang, Jing

    The ultimate goal of physics education research (PER) is to develop a theoretical framework to understand and improve the learning process. In this journey of discovery, assessment serves as our headlamp and alpenstock. It sometimes detects signals in student mental structures, and sometimes presents the difference between expert understanding and novice understanding. Quantitative assessment is an important area in PER. Developing research-based effective assessment instruments and making meaningful inferences based on these instruments have always been important goals of the PER community. Quantitative studies are often conducted to provide bases for test development and result interpretation. Statistics are frequently used in quantitative studies. The selection of statistical methods and interpretation of the results obtained by these methods shall be connected to the education background. In this connecting process, the issues of educational models are often raised. Many widely used statistical methods do not make assumptions on the mental structure of subjects, nor do they provide explanations tailored to the educational audience. There are also other methods that consider the mental structure and are tailored to provide strong connections between statistics and education. These methods often involve model assumption and parameter estimation, and are complicated mathematically. The dissertation provides a practical view of some advanced quantitative assessment methods. The common feature of these methods is that they all make educational/psychological model assumptions beyond the minimum mathematical model. The purpose of the study is to provide a comparison between these advanced methods and the pure mathematical methods. The comparison is based on the performance of the two types of methods under physics education settings. In particular, the comparison uses both physics content assessments and scientific ability assessments. The dissertation includes three

  15. UA wavefront control lab: design overview and implementation of new wavefront sensing techniques

    Science.gov (United States)

    Miller, Kelsey; Guyon, Olivier; Codona, Johanan; Knight, Justin; Rodack, Alexander

    2015-09-01

    We present an overview of the design of a new testbed for studying coronagraphic imaging and wavefront control using a variety of pupil and coronagraph architectures. The testbed is designed to explore optimal use of starlight (including starlight rejected by the coronagraph) for wavefront control, system self-calibration, and point spread function (PSF) calibration. It is also compatible with coronagraph designs for centrally obscured and segmented apertures, and includes shaped or apodized pupils, a range of focal plane masks and Lyot stops of multiple sizes, and an optional PIAA apodizing stage. Starlight is reflected and imaged from the focal plane mask and Lyot stop for low-order wavefront sensing. Both a segmented and a continuous sheet MEMS DM are included to simulate segmented telescope pupils, apply known test phase patterns, and implement a controllable phase apodization coronagraph. The testbed is adaptable and is currently being used to investigate three different techniques: (1) the differential optical transfer function (dOTF), (2) low-order wavefront sensing (LOWFS) with a hybrid-Lyot coronagraph, and (3) linear dark field control (LDFC).

  16. Wavefront-error performance characterization for the James Webb Space Telescope (JWST) Integrated Science Instrument Module (ISIM) science instruments

    Science.gov (United States)

    Aronstein, David L.; Smith, J. S.; Zielinski, Thomas P.; Telfer, Randal; Tournois, Severine C.; Moore, Dustin B.; Fienup, James R.

    2016-07-01

    The science instruments (SIs) comprising the James Webb Space Telescope (JWST) Integrated Science Instrument Module (ISIM) were tested in three cryogenic-vacuum test campaigns in the NASA Goddard Space Flight Center (GSFC)'s Space Environment Simulator (SES) test chamber. In this paper, we describe the results of optical wavefront-error performance characterization of the SIs. The wavefront error is determined using image-based wavefront sensing, and the primary data used by this process are focus sweeps, a series of images recorded by the instrument under test in its as-used configuration, in which the focal plane is systematically changed from one image to the next. High-precision determination of the wavefront error also requires several sources of secondary data, including 1) spectrum, apodization, and wavefront-error characterization of the optical ground-support equipment (OGSE) illumination module, called the OTE Simulator (OSIM), 2) f/# and pupil-distortion measurements made using a pseudo-nonredundant mask (PNRM), and 3) pupil-geometry predictions for each SI field point tested, which are complicated because of a tricontagon-shaped outer perimeter and small holes that appear in the exit pupil due to the way that different light sources are injected into the optical path by the OGSE. One set of wavefront-error tests, for the coronagraphic channel of the Near-Infrared Camera (NIRCam) Longwave instruments, was performed using data from transverse-translation diversity (TTD) sweeps instead of focus sweeps, in which a subaperture is translated and/or rotated across the exit pupil of the system from one image to the next. Several optical-performance requirements that were verified during this ISIM Element-level testing are levied on the uncertainties of various wavefront-error-related quantities rather than on the wavefront errors themselves. This paper also gives an overview of the methodology, based on Monte Carlo simulations of the wavefront-sensing analysis

  17. Wavefront sensors for optical diagnostics in fluid mechanics: Application to heated flow, turbulence and droplet evaporation

    Energy Technology Data Exchange (ETDEWEB)

    Neal, D.R.; O`Hern, T.J.; Torczynski, J.R.; Warren, M.E.; Shul, R. [Sandia National Labs., Albuquerque, NM (United States); McKechnie, T.S. [POD Associates, Inc., Albuquerque, NM (United States)

    1993-09-01

    Optical measurement techniques are extremely useful in fluid mechanics because of their non-invasive nature. However, it is often difficult to separate measurement effects due to pressure, temperature and density in real flows. Using a variation of a Shack-Hartmann wavefront sensor, we have made density measurements that have extremely large dynamic range coupled with excellent sensitivity at high temporal and spatial resolution. We have examined several classes of flow including volumetrically heated gas, turbulence and droplet evaporation.

  18. Carbon Dioxide Measurements from Space: Scientific Advance and Societal Benefit

    Science.gov (United States)

    Boland, S. W.; Duren, R. M.; Miller, C. E.

    2009-04-01

    The dawn of the 21st Century finds spaceborne sensors poised to revolutionize the atmospheric CO2 record by providing high-quality measurements with unprecedented spatio-temporal coverage and density. Space-based CO2 observations will augment local and regional measurements from ground and airborne sensors, providing global context for existing measurements and covering regions not readily accessible or instrumented by other means. Hyperspectral data from the Atmospheric Infrared Sounder (AIRS), launched in 2002, have been used to produce global maps of CO2 concentrations in the mid-troposphere. These data provide important new constraints on the global distribution and transport of CO2. Future satellite missions dedicated to CO2 observations will collect precise global measurements, enabling more detailed process studies and contributing to further improvements in coupled carbon-climate model development, initialization, and validation. Japan's GOSAT mission, scheduled for launch in January 2009 will measure CO2 and CH4 spectral radiances via thermal and near infrared spectrometry to study the transport mechanisms of greenhouse gases with an emphasis on identification of CO2 sources and sinks on sub-continental scales in support of the Kyoto protocol. NASA's Orbiting Carbon Observatory (OCO), scheduled to launch in February 2009, will deliver measurements of column-averaged CO2 dry air mole fraction, XCO2, with the precision, temporal and spatial resolution, and coverage needed to characterize the variability of CO2 sources and sinks on regional spatial scales and seasonal to interannual time scales. Satellite CO2 observations, combined with continued ground and airborne measurements, will improve our understanding of the natural processes and human activities that regulate the atmospheric abundance and distribution of this important greenhouse gas, generating both scientific advance and societal benefit. Deriving actionable information from these observation

  19. Improved quantitative visualization of hypervelocity flow through wavefront estimation based on shadow casting of sinusoidal gratings.

    Science.gov (United States)

    Medhi, Biswajit; Hegde, Gopalakrishna M; Gorthi, Sai Siva; Reddy, Kalidevapura Jagannath; Roy, Debasish; Vasu, Ram Mohan

    2016-08-01

    A simple noninterferometric optical probe is developed to estimate wavefront distortion suffered by a plane wave in its passage through density variations in a hypersonic flow obstructed by a test model in a typical shock tunnel. The probe has a plane light wave trans-illuminating the flow and casting a shadow of a continuous-tone sinusoidal grating. Through a geometrical optics, eikonal approximation to the distorted wavefront, a bilinear approximation to it is related to the location-dependent shift (distortion) suffered by the grating, which can be read out space-continuously from the projected grating image. The processing of the grating shadow is done through an efficient Fourier fringe analysis scheme, either with a windowed or global Fourier transform (WFT and FT). For comparison, wavefront slopes are also estimated from shadows of random-dot patterns, processed through cross correlation. The measured slopes are suitably unwrapped by using a discrete cosine transform (DCT)-based phase unwrapping procedure, and also through iterative procedures. The unwrapped phase information is used in an iterative scheme, for a full quantitative recovery of density distribution in the shock around the model, through refraction tomographic inversion. Hypersonic flow field parameters around a missile-shaped body at a free-stream Mach number of ∼8 measured using this technique are compared with the numerically estimated values. It is shown that, while processing a wavefront with small space-bandwidth product (SBP) the FT inversion gave accurate results with computational efficiency; computation-intensive WFT was needed for similar results when dealing with larger SBP wavefronts.

  20. Optimization-based wavefront sensorless adaptive optics for multiphoton microscopy

    NARCIS (Netherlands)

    Antonello, J.; Werkhoven, T. van; Verhaegen, M.; Truong, H.H.; Keller, C.U.; Gerritsen, H.C.

    2014-01-01

    Optical aberrations have detrimental effects in multiphoton microscopy. These effects can be curtailed by implementing model-based wavefront sensorless adaptive optics, which only requires the addition of a wavefront shaping device, such as a deformable mirror (DM) to an existing microscope. The abe

  1. The National Ignition Facility (NIF) wavefront control system

    Energy Technology Data Exchange (ETDEWEB)

    Van Atta, L; Bliss, E; Bruns, D; Feldman, M; Grey, A; Henesian, M; J; Koch, J; LaFiandra, C; Lawson; Sacks, R; Salmon, T; Toeppen, J; Winters, S; Woods, B; Zacharias, R

    1998-08-17

    A wavefront control system will be employed on NIF to correct beam aberrations that otherwise would limit the minimum target focal spot size. For most applications, NIF requires a focal spot that is a few times the diffraction limit. Sources of aberrations that must be corrected include prompt pump-induced distortions in the laser slabs, thermal distortions in the laser slabs from previous shots, manufacturing figure errors in the optics, beam off-axis effects, gas density variations, and gravity, mounting, and coating- induced optic distortions. The NIF Wavefront Control System consists of five subsystems: 1) a deformable mirror, 2) a wavefront sensor, 3) a computer controller, 4) a wavefront reference system, and 5) a system of fast actuators to allow the wavefront control system to operate to within one second of the laser shot. The system includes the capability for in situ calibrations and operates in closed loop prior to the shot. Shot wavefront data is recorded. This paper describes the function, realization, and performance of each wavefront control subsystem. Subsystem performance will be characterized by computer models and by test results. The focal spot improvement in the NIF laser system effected by the wavefront control system will be characterized through computer models.

  2. Geometry of fast magnetosonic rays, wavefronts and shock waves

    Science.gov (United States)

    Núñez, Manuel

    2016-11-01

    Fast magnetosonic waves in a two-dimensional plasma are studied in the geometrical optics approximation. The geometry of rays and wavefronts influences decisively the formation and ulterior evolution of shock waves. It is shown that the curvature of the curve where rays start and the angle between rays and wavefronts are the main parameters governing a wide variety of possible outcomes.

  3. Experimental study of an optimised Pyramid wave-front sensor for Extremely Large Telescopes

    Science.gov (United States)

    Bond, Charlotte Z.; El Hadi, Kacem; Sauvage, Jean-François; Correia, Carlos; Fauvarque, Olivier; Rabaud, Didier; Lamb, Masen; Neichel, Benoit; Fusco, Thierry

    2016-07-01

    Over the last few years the Laboratoire d'Astrophysique de Marseille (LAM) has been heavily involved in R&D for adaptive optics systems dedicated to future large telescopes, particularly in preparation for the European Extremely Large Telescope (E-ELT). Within this framework an investigation into a Pyramid wave-front sensor is underway. The Pyramid sensor is at the cutting edge of high order, high precision wave-front sensing for ground based telescopes. Investigations have demonstrated the ability to achieve a greater sensitivity than the standard Shack-Hartmann wave-front sensor whilst the implementation of a Pyramid sensor on the Large Binocular Telescope (LBT) has provided compelling operational results.1, 2 The Pyramid now forms part of the baseline for several next generation Extremely Large Telescopes (ELTs). As such its behaviour under realistic operating conditions must be further understood in order to optimise performance. At LAM a detailed investigation into the performance of the Pyramid aims to fully characterise the behaviour of this wave-front sensor in terms of linearity, sensitivity and operation. We have implemented a Pyramid sensor using a high speed OCAM2 camera (with close to 0 readout noise and a frame rate of 1.5kHz) in order to study the performance of the Pyramid within a full closed loop adaptive optics system. This investigation involves tests on all fronts, from theoretical models and numerical simulations to experimental tests under controlled laboratory conditions, with an aim to fully understand the Pyramid sensor in both modulated and non-modulated configurations. We include results demonstrating the linearity of the Pyramid signals, compare measured interaction matrices with those derived in simulation and evaluate the performance in closed loop operation. The final goal is to provide an on sky comparison between the Pyramid and a Shack-Hartmann wave-front sensor, at Observatoire de la Côte d'Azur (ONERA-ODISSEE bench). Here we

  4. Construction and testing of wavefront reference sources for interferometry of ultra-precise imaging systems

    Energy Technology Data Exchange (ETDEWEB)

    Johnson, M A; Phillion, D W; Sommargren, G E; Decker, T A; Taylor, J S; Gomei, Y; Kakuchi, O; Takeuchi, S

    2005-07-01

    We have built and calibrated a set of 532-nm wavelength wavefront reference sources that fill a numerical aperture of 0.3. Early data show that they have a measured departure from sphericity of less than 0.2 nm RMS (0.4 milliwaves) and a reproducibility of better than 0.05 nm rms. These devices are compact, portable, fiber-fed, and are intended as sources of measurement and reference waves in wavefront measuring interferometers used for metrology of EUVL optical elements and systems. Keys to wave front accuracy include fabrication of an 800-nm pinhole in a smooth reflecting surface as well as a calibration procedure capable of measuring axisymmetric and non-axisymmetric errors.

  5. Advanced Techniques for Power System Identification from Measured Data

    Energy Technology Data Exchange (ETDEWEB)

    Pierre, John W.; Wies, Richard; Trudnowski, Daniel

    2008-11-25

    Time-synchronized measurements provide rich information for estimating a power-system's electromechanical modal properties via advanced signal processing. This information is becoming critical for the improved operational reliability of interconnected grids. A given mode's properties are described by its frequency, damping, and shape. Modal frequencies and damping are useful indicators of power-system stress, usually declining with increased load or reduced grid capacity. Mode shape provides critical information for operational control actions. This project investigated many advanced techniques for power system identification from measured data focusing on mode frequency and damping ratio estimation. Investigators from the three universities coordinated their effort with Pacific Northwest National Laboratory (PNNL). Significant progress was made on developing appropriate techniques for system identification with confidence intervals and testing those techniques on field measured data and through simulation. Experimental data from the western area power system was provided by PNNL and Bonneville Power Administration (BPA) for both ambient conditions and for signal injection tests. Three large-scale tests were conducted for the western area in 2005 and 2006. Measured field PMU (Phasor Measurement Unit) data was provided to the three universities. A 19-machine simulation model was enhanced for testing the system identification algorithms. Extensive simulations were run with this model to test the performance of the algorithms. University of Wyoming researchers participated in four primary activities: (1) Block and adaptive processing techniques for mode estimation from ambient signals and probing signals, (2) confidence interval estimation, (3) probing signal design and injection method analysis, and (4) performance assessment and validation from simulated and field measured data. Subspace based methods have been use to improve previous results from block

  6. Advanced metrology of surface defects measurement for aluminum die casting

    Directory of Open Access Journals (Sweden)

    D. Myszka

    2011-07-01

    Full Text Available The scientific objective of the research is to develop a strategy to build computer based vision systems for inspection of surface defects inproducts, especially discontinuities which appear in castings after machining. In addition to the proposed vision inspection method theauthors demonstrates the development of the advanced computer techniques based on the methods of scanning to measure topography ofsurface defect in offline process control. This method allow to identify a mechanism responsible for the formation of casting defects. Also,the method allow investigating if the, developed vision inspection system for identification of surface defects have been correctlyimplemented for an online inspection. Finally, in order to make casting samples with gas and shrinkage porosity defects type, the LGT gas meter was used . For this task a special camera for a semi-quantitative assessment of the gas content in aluminum alloy melts, using a Straube-Pfeiffer method was used. The results demonstrate that applied solution is excellent tool in preparing for various aluminum alloysthe reference porosity samples, identified next by the computer inspection system.

  7. Making a measurable difference in advanced Huntington disease care.

    Science.gov (United States)

    Moskowitz, Carol Brown; Rao, Ashwini K

    2017-01-01

    Neurologists' role in the care of people with advanced Huntington disease (HD) (total functional capacity <7), often limited by a lack of clinical research to support good practice, includes the following: (1) provide comprehensive health records to an interdisciplinary care staff before admission to a more intense care setting (home health services, day program, assisted living, group home, long-term skilled nursing facility, palliative care); (2) consult with and refer to rehabilitation (occupational therapy, physical therapy, speech and language pathology), behavioral and psychiatric professionals for problem-solving strategies, which must be reviewed with direct care staff before implementation; (3) encourage and support qualitative and quantitative interdisciplinary research studies, and randomized controlled studies of nonpharmacologic interventions; and (4) assist in the development of meaningful measures to further document what works to provide a good quality of life for the patient and family and a comfortable thoughtful approach to a good death. Collaborative models of care depend on: (1) clear communication; (2) ongoing education and support programs; with (3) pharmacologic and rehabilitation interventions, always in the context of respect for the person with HD, a preservation of the individuals' dignity, autonomy, and individual preferences. Copyright © 2017 Elsevier B.V. All rights reserved.

  8. Spline based least squares integration for two-dimensional shape or wavefront reconstruction

    Science.gov (United States)

    Huang, Lei; Xue, Junpeng; Gao, Bo; Zuo, Chao; Idir, Mourad

    2017-04-01

    In this work, we present a novel method to handle two-dimensional shape or wavefront reconstruction from its slopes. The proposed integration method employs splines to fit the measured slope data with piecewise polynomials and uses the analytical polynomial functions to represent the height changes in a lateral spacing with the pre-determined spline coefficients. The linear least squares method is applied to estimate the height or wavefront as a final result. Numerical simulations verify that the proposed method has less algorithm errors than two other existing methods used for comparison. Especially at the boundaries, the proposed method has better performance. The noise influence is studied by adding white Gaussian noise to the slope data. Experimental data from phase measuring deflectometry are tested to demonstrate the feasibility of the new method in a practical measurement.

  9. Visible and Infrared Wavefront Sensing detectors review in Europe - part I

    Science.gov (United States)

    Feautrier, Philippe; Gach, Jean-luc

    2013-12-01

    The purpose of this review is to give an overview of the state of the art wavefront sensor detectors developments held in Europe for the last decade. A major breakthrough has been achieved with the development by e2v technologies of the CCD220 between 2004 and 2012. Another major breakthrough is currently achieved with the very successful development of fast low noise infrared arrays called RAPID. The astonishing results of this device will be showed for the first time in an international conference at AO4ELT3.The CCD220, a 240x240 pixels 8 outputs EMCCD (CCD with internal multiplication), offers less than 0.2 e readout noise at a frame rate of 1500 Hz with negligible dark current. The OCAM2 camera is the commercial product that drives this advanced device. This system, commercialized by First Light Imaging, is quickly described in this paper. An upgrade of OCAM2 is currently developed to boost its frame rate to 2 kHz, opening the window of XAO wavefront sensing for the ELT using 4 synchronized cameras and pyramid wavefront sensing. This upgrade and the results obtained are described extensively elsewhere in this conference (Gach et al).Since this major success, new detector developments started in Europe. The NGSD CMOS device is fully dedicated to Natural and Laser Guide Star AO for the E-ELT with ESO involvement. The spot elongation from a LGS Shack Hartman wavefront sensor necessitates an increase of the pixel format. The NGSD will be a 880x840 pixels CMOS detector with a readout noise of 3 e (goal 1e) at 700 Hz frame rate. New technologies will be developed for that purpose: advanced CMOS pixel architecture, CMOS back thinned and back illuminated device for very high QE, full digital outputs with signal digital conversion on chip. This innovative device will be used on the European ELT but also interests potentially all giant telescopes.Additional developments also started in 2009 for wavefront sensing in the infrared based on a new technological breakthrough

  10. Nephrology Nurse Perceptions Toward Advance Care Planning: Validation of a Measure.

    Science.gov (United States)

    Haras, Mary S; Astroth, Kim S; Hesson-McInnis, Matthew; Woith, Wendy M; Kossman, Susan P

    2015-01-01

    Advance care planning is critical for persons with chronic kidney disease because they face a shortened lifespan. There is a paucity of reliable and valid measures exploring nephrology nurse perceptions toward advance care planning. This article reports the results of testing the factor structure, reliability, and validity of a newly developed measure of nephrology nurse perceptions toward advance care planning as well as information on nephrology nurses'perceptions on advance care planning. Measuring nephrology nurse perceptions toward advance care planning may facilitate planning of interventions to assist nurses to become more active in the process.

  11. A review of hemorheology: Measuring techniques and recent advances

    Science.gov (United States)

    Sousa, Patrícia C.; Pinho, Fernando T.; Alves, Manuel A.; Oliveira, Mónica S. N.

    2016-02-01

    Significant progress has been made over the years on the topic of hemorheology, not only in terms of the development of more accurate and sophisticated techniques, but also in terms of understanding the phenomena associated with blood components, their interactions and impact upon blood properties. The rheological properties of blood are strongly dependent on the interactions and mechanical properties of red blood cells, and a variation of these properties can bring further insight into the human health state and can be an important parameter in clinical diagnosis. In this article, we provide both a reference for hemorheological research and a resource regarding the fundamental concepts in hemorheology. This review is aimed at those starting in the field of hemodynamics, where blood rheology plays a significant role, but also at those in search of the most up-to-date findings (both qualitative and quantitative) in hemorheological measurements and novel techniques used in this context, including technical advances under more extreme conditions such as in large amplitude oscillatory shear flow or under extensional flow, which impose large deformations comparable to those found in the microcirculatory system and in diseased vessels. Given the impressive rate of increase in the available knowledge on blood flow, this review is also intended to identify areas where current knowledge is still incomplete, and which have the potential for new, exciting and useful research. We also discuss the most important parameters that can lead to an alteration of blood rheology, and which as a consequence can have a significant impact on the normal physiological behavior of blood.

  12. Prototype pipeline for LSST wavefront sensing and reconstruction

    Science.gov (United States)

    Claver, Charles F.; Chandrasekharan, Srinivasan; Liang, Ming; Xin, Bo; Alagoz, Enver; Arndt, Kirk; Shipsey, Ian P.

    2012-09-01

    The Large Synoptic Survey Telescope (LSST) uses an Active Optics System (AOS) to maintain system alignment and surface figure on its three large mirrors. Corrective actions fed to the LSST AOS are determined from 4 curvature based wavefront sensors located on the corners of the inscribed square within the 3.5 degree field of view. Each wavefront sensor is a split detector such that the halves are 1mm on either side of focus. In this paper we describe the development of the Active Optics Pipeline prototype that simulates processing the raw image data from the wavefront sensors through to wavefront estimation on to the active optics corrective actions. We also describe various wavefront estimation algorithms under development for the LSST active optics system. The algorithms proposed are comprised of the Zernike compensation routine which improve the accuracy of the wavefront estimate. Algorithm development has been aided by a bench top optical simulator which we also describe. The current software prototype combines MATLAB modules for image processing, tomographic reconstruction, atmospheric turbulence and Zemax for optical ray-tracing to simulate the closed loop behavior of the LSST AOS. We describe the overall simulation model and results for image processing using simulated images and initial results of the wavefront estimation algorithms.

  13. Ocular wavefront aberrations in the common marmoset Callithrix jacchus: effects of age and refractive error.

    Science.gov (United States)

    Coletta, Nancy J; Marcos, Susana; Troilo, David

    2010-11-23

    The common marmoset, Callithrix jacchus, is a primate model for emmetropization studies. The refractive development of the marmoset eye depends on visual experience, so knowledge of the optical quality of the eye is valuable. We report on the wavefront aberrations of the marmoset eye, measured with a clinical Hartmann-Shack aberrometer (COAS, AMO Wavefront Sciences). Aberrations were measured on both eyes of 23 marmosets whose ages ranged from 18 to 452 days. Twenty-one of the subjects were members of studies of emmetropization and accommodation, and two were untreated normal subjects. Eleven of the 21 experimental subjects had worn monocular diffusers and 10 had worn binocular spectacle lenses of equal power. Monocular deprivation or lens rearing began at about 45 days of age and ended at about 108 days of age. All refractions and aberration measures were performed while the eyes were cyclopleged; most aberration measures were made while subjects were awake, but some control measurements were performed under anesthesia. Wavefront error was expressed as a seventh-order Zernike polynomial expansion, using the Optical Society of America's naming convention. Aberrations in young marmosets decreased up to about 100 days of age, after which the higher-order RMS aberration leveled off to about 0.10 μm over a 3 mm diameter pupil. Higher-order aberrations were 1.8 times greater when the subjects were under general anesthesia than when they were awake. Young marmoset eyes were characterized by negative spherical aberration. Form-deprived eyes of the monocular deprivation animals had greater wavefront aberrations than their fellow untreated eyes, particularly for asymmetric aberrations in the odd-numbered Zernike orders. Both lens-treated and form-deprived eyes showed similar significant increases in Z3(-3) trefoil aberration, suggesting the increase in trefoil may be related to factors that do not involve visual feedback.

  14. Wavefront shaping for opaque cylindrical lenses

    CERN Document Server

    Di Battista, Diego; Ancora, Daniele; Lemonaki, Krystalia; Liapis, Evangelos; Tzortzakis, Stelios; Zacharakis, Giannis

    2016-01-01

    Wavefront shaping has revolutionized the concepts of optical imaging and focusing. Contrary to what was believed, strong scattering in the optical paths can be exploited in favor of light focusing through turbid media and ultimately improve optical imaging and light manipulation capabilities. The use of light shapers and appropriately engineered scattering structures, i.e. opaque lenses enables the production of nano-scale confined foci and of extended fields of view. Exploiting this concept we fabricate configurable scattering structures by direct femtosecond laser writing. The properly shaped light trespassing the customized structure, a photonic lattice of parallel rods, forms a light-sheet at user defined positions. We demonstrate that our technique enables light-sheets with sub-micron resolution and extended depth of focus, a significant advantage when compared to the existing free space systems. Moreover, our approach permits to focus light of different wavelengths onto the same defined position without...

  15. Manipulation of wavefront using helical metamaterials.

    Science.gov (United States)

    Yang, Zhenyu; Wang, Zhaokun; Tao, Huan; Zhao, Ming

    2016-08-01

    Helical metamaterials, a kind of 3-dimensional structure, has relatively strong coupling effect among the helical nano-wires. Therefore, it is expected to be a good candidate for generating phase shift and controlling wavefront with high efficiency. In this paper, using the finite-difference time-domain (FDTD) method, we studied the phase shift properties in the helical metamaterials. It is found that the phase shift occurs for both transmitted and reflected light waves. And the maximum of reflection coefficients can reach over 60%. In addition, the phase shift (φ) is dispersionless in the range of 600 nm to 860 nm, that is, it is only dominated by the initial angle (θ) of the helix. The relationship between them is φ = ± 2θ. Using Jones calculus we give a further explanation for these properties. Finally, by arranging the helixes in an array with a constant phase gradient, the phenomenon of anomalous refraction was also observed in a broad wavelength range.

  16. The NGS Pyramid wavefront sensor for ERIS

    Science.gov (United States)

    Riccardi, A.; Antichi, J.; Quirós-Pacheco, F.; Esposito, S.; Carbonaro, L.; Agapito, G.; Biliotti, V.; Briguglio, R.; Di Rico, G.; Dolci, M.; Ferruzzi, D.; Pinna, E.; Puglisi, A.; Xompero, M.; Marchetti, E.; Fedrigo, E.; Le Louarn, M.; Conzelmann, R.; Delabre, B.; Amico, P.; Hubin, N.

    2014-07-01

    ERIS is the new Single Conjugate Adaptive Optics (AO) instrument for VLT in construction at ESO with the collaboration of Max-Planck Institut fuer Extraterrestrische Physik, ETH-Institute for Astronomy and INAF - Osservatorio Astrofisico di Arcetri. The ERIS AO system relies on a 40×40 sub-aperture Pyramid Wavefront Sensor (PWFS) for two operating modes: a pure Natural Guide Star high-order sensing for high Strehl and contrast correction and a low-order visible sensing in support of the Laser Guide Star AO mode. In this paper we present in detail the preliminary design of the ERIS PWFS that is developed under the responsibility of INAF-Osservatorio Astrofisico di Arcetri in collaboration with ESO.

  17. Hamilton's Optics: The Power of Wavefronts

    Indian Academy of Sciences (India)

    2016-06-01

    Building on work by Fermat and Huygens, Hamiltontransformed the study of geometrical opticsin his very first paper, presented when still inhis teens. His ‘characteristic function’ was ananalytical way to describe wavefronts, and in hishands a powerful tool to look at families of raysrather than isolated ones. His prediction of internaland external conical refraction in somecrystals and its spectacular verification in a fewmonths established his reputation among his contemporaries.This formulation of optics uncoveredmany general properties, not easy to seein the conventional method of tracing individualrays. The deepest outcome of his early opticalwork was a parallel view of the mechanics ofparticles, which played a fundamental role in thebirth of quantum mechanics and continues to bethe standard framework for classical mechanicsup to the present time.

  18. Wavefront Propagation and Fuzzy Based Autonomous Navigation

    Directory of Open Access Journals (Sweden)

    Adel Al-Jumaily

    2005-06-01

    Full Text Available Path planning and obstacle avoidance are the two major issues in any navigation system. Wavefront propagation algorithm, as a good path planner, can be used to determine an optimal path. Obstacle avoidance can be achieved using possibility theory. Combining these two functions enable a robot to autonomously navigate to its destination. This paper presents the approach and results in implementing an autonomous navigation system for an indoor mobile robot. The system developed is based on a laser sensor used to retrieve data to update a two dimensional world model of therobot environment. Waypoints in the path are incorporated into the obstacle avoidance. Features such as ageing of objects and smooth motion planning are implemented to enhance efficiency and also to cater for dynamic environments.

  19. Propagation of aberrated wavefronts using a ray transfer matrix.

    Science.gov (United States)

    Raasch, Thomas W

    2014-05-01

    A ray transfer matrix is used to calculate the propagation of aberrated wavefronts across a homogeneous refractive index. The wavefront is represented by local surface normals, i.e., by a ray bundle, and the propagation is accomplished by transferring those rays across the space. Wavefront shape is generated from the slopes and positions of the collection of rays. Calculation methods are developed for the paraxial case, for higher-order expansions, and for the exact tangent case. A numerical example is used to compare results between an analytical method and the methods developed here.

  20. Initial Performance of the Keck AO Wavefront Controller System

    Energy Technology Data Exchange (ETDEWEB)

    Johansson, E M; Acton, D S; An, J R; Avicola, K; Beeman, B V; Brase, J M; Carrano, C J; Gathright, J; Gavel, D T; Hurd, R L; Lai, O; Lupton, W; Macintosh, B A; Max, C E; Olivier, S S; Shelton, J C; Stomski, P J; Tsubota, K; Waltjen, K E; Watson, J A; Wizinowich, P L

    2001-03-01

    The wavefront controller for the Keck Observatory AO system consists of two separate real-time control loops: a tip-tilt control loop to remove tilt from the incoming wavefront, and a deformable mirror control loop to remove higher-order aberrations. In this paper, we describe these control loops and analyze their performance using diagnostic data acquired during the integration and testing of the AO system on the telescope. Disturbance rejection curves for the controllers are calculated from the experimental data and compared to theory. The residual wavefront errors due to control loop bandwidth are also calculated from the data, and possible improvements to the controller performance are discussed.

  1. Advanced radiation measurement techniques in diagnostic radiology and molecular imaging.

    Science.gov (United States)

    Del Guerra, Alberto; Belcari, Nicola; Llacer, Gabriela Llosa; Marcatili, Sara; Moehrs, Sascha; Panetta, Daniele

    2008-01-01

    This paper reports some technological advances recently achieved in the fields of micro-CT and small animal PET instrumentation. It highlights a balance between image-quality improvement and dose reduction. Most of the recent accomplishments in these fields are due to the use of novel imaging sensors such as CMOS-based X-ray detectors and silicon photomultipliers (SiPM). Some of the research projects carried out at the University of Pisa for the development of such advanced radiation imaging technology are also described.

  2. Defining Neighborhood Boundaries for Social Measurement: Advancing Social Work Research

    Science.gov (United States)

    Foster, Kirk A.; Hipp, J. Aaron

    2011-01-01

    Much of the current neighborhood-based research uses variables aggregated on administrative boundaries such as zip codes, census tracts, and block groups. However, other methods using current technological advances in geographic sciences may broaden our ability to explore the spatial concentration of neighborhood factors affecting individuals and…

  3. Holographic Wavefront Correction for ShADOE LIDAR Receivers Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Current shared aperture diffractive optical elements (ShADOE) have intrinsic residual wavefront errors on the order of 50 waves which limits the angular resolution...

  4. Manipulating acoustic wavefront by inhomogeneous impedance and steerable extraordinary reflection.

    Science.gov (United States)

    Zhao, Jiajun; Li, Baowen; Chen, Zhining; Qiu, Cheng-Wei

    2013-01-01

    We unveil the connection between the acoustic impedance along a flat surface and the reflected acoustic wavefront, in order to empower a wide wariety of novel applications in acoustic community. Our designed flat surface can generate double reflections: the ordinary reflection and the extraordinary one whose wavefront is manipulated by the proposed impedance-governed generalized Snell's law of reflection (IGSL). IGSL is based on Green's function and integral equation, instead of Fermat's principle for optical wavefront manipulation. Remarkably, via the adjustment of the designed specific acoustic impedance, extraordinary reflection can be steered for unprecedented acoustic wavefront while that ordinary reflection can be surprisingly switched on or off. The realization of the complex discontinuity of the impedance surface has been proposed using Helmholtz resonators.

  5. A Method for Wavefront Curvature Ranging of Speech Sources ...

    African Journals Online (AJOL)

    A Method for Wavefront Curvature Ranging of Speech Sources. ... A new approach for estimating the location of a speech source in a reverberant environment is presented. The approach ... EMAIL FREE FULL TEXT EMAIL FREE FULL TEXT

  6. Holographic Wavefront Correction for SHADOE LIDAR Receivers Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Current shared aperture diffractive optical elements (SHADOE) have intrinsic residual wavefront errors on the order of 20 waves which limits the angular resolution...

  7. Wavefront error correction and Earth-like planet detection by Self-Coherent Camera in space

    CERN Document Server

    Galicher, R; Rousset, G

    2008-01-01

    In the context of exoplanet detection, the performance of coronagraphs is limited by wavefront errors. To efficiently correct for these aberrations with a deformable mirror, it is mandatory to measure them using the science detector with a very high accuracy. The Self-Coherent Camera which is based on light incoherence between star and its environment enables an estimation of these wavefront errors. That estimation is directly derived from the encoded speckles in the science image. This avoids differential errors due to beam separation and non common optics. Earth-like planet detection is demonstrated by numerical simulations under realistic assumptions for a space telescope. The Self-Coherent Camera is an attractive technique for future space telescopes. It is also one of the techniques under investigation for the E-ELT planet finder so-called EPICS.

  8. Relationship between corneal and ocular higher order wavefront aberrations and age in children

    Science.gov (United States)

    Saito, Aya; Ito, Misae; Kawamorita, Takushi; Shimizu, Kimiya

    2017-05-01

    Abstract Purpose To evaluate the relationship between corneal and ocular higher order wavefront aberrations (HOAs) and age in young subjects aged 20 years or less. Methods Corneal and ocular HOAs of the right eyes of 87 normal subjects were measured using videokeratography and the Hartmann-Shack wavefront aberrometer (KR-9000PW; Topcon Corp., Tokyo, Japan). The HOAs were calculated using Zernike polynomials up to the sixth order. From the Zernike coefficients, the root mean squares (RMS) of coma and spherical aberration were calculated. Results Corneal spherical-like aberrations significantly correlated with age (r = 0.420, p Conclusion In children, the corneal and ocular total HOAs did not vary with age. Compared to the previous reports in adults, we found fewer corneal and ocular HOAs in children.

  9. Wavefront sensorless adaptive optics fluorescence biomicroscope for in vivo retinal imaging in mice.

    Science.gov (United States)

    Wahl, Daniel J; Jian, Yifan; Bonora, Stefano; Zawadzki, Robert J; Sarunic, Marinko V

    2016-01-01

    Cellular-resolution in vivo fluorescence imaging is a valuable tool for longitudinal studies of retinal function in vision research. Wavefront sensorless adaptive optics (WSAO) is a developing technology that enables high-resolution imaging of the mouse retina. In place of the conventional method of using a Shack-Hartmann wavefront sensor to measure the aberrations directly, WSAO uses an image quality metric and a search algorithm to drive the shape of the adaptive element (i.e. deformable mirror). WSAO is a robust approach to AO and it is compatible with a compact, low-cost lens-based system. In this report, we demonstrated a hill-climbing algorithm for WSAO with a variable focus lens and deformable mirror for non-invasive in vivo imaging of EGFP (enhanced green fluorescent protein) labelled ganglion cells and microglia cells in the mouse retina.

  10. Angle-sensitive pixel design for wavefront sensing

    CERN Document Server

    Zheng, Guoan

    2013-01-01

    Conventional image sensors are only responsive to the intensity variation of the incoming light wave. By encoding the wavefront information into the balanced detection scheme, we demonstrate an image sensor pixel design that is capable to detect both the local intensity and wavefront information simultaneously. With the full compatibility to the CMOS fabrication process, the proposed pixel design can benefit a variety of applications, including phase microscopy, lensless imaging and machine vision.

  11. Pyramid wavefront sensors for astronomy and for the human eye

    OpenAIRE

    Bergomi, Maria

    2013-01-01

    WaveFront Sensors (WFSs) may be defined as the heart of an adaptive optics system since they analyze the radiation coming from reference sources and allow to quantify the distortion of a wavefront. Among the varieties of existing WFSs, my PhD research thesis focuses especially on innovative optical systems taking advantage of the peculiarities of the Pyramid WFS. In my PhD project I have designed, implemented, characterized or studied three different applications characterized by the f...

  12. Wavefront sensing in a partially illuminated, rotating pupil

    Science.gov (United States)

    Bertram, Thomas; Kumar Radhakrishnan Santhakumari, Kalyan; Marafatto, Luca; Arcidiacono, Carmelo; Berwein, Jürgen; Ragazzoni, Roberto; Herbst, Thomas M.

    2014-08-01

    LINC-NIRVANA is the near-infrared interferometric imaging camera for the Large Binocular Telescope. Once operational, it will provide an unprecedented combination of angular resolution, sensitivity, and field of view. Its pyramid-based layer-oriented MCAO systems are conjugated to the ground layer and to an additional layer in the upper atmosphere. The Groundlayer Wavefront Sensor optically coadds the light of up to 12 reference stars in the pupil, the Highlayer Wavefront Sensor optically combines the light of up to 8 reference stars in its metapupil. Each Wavefront Sensor has its own associated field derotator. It introduces a dependency of the sensor-actuator relation on the angle of the field derotator, which requires regular updates of the reconstructor in closed loop. In addition, the Highlayer Wavefront Sensor has to be able to reconstruct the incoming wavefronts by analyzing an only partially illuminated metapupil. The distribution of illuminated subapertures depends on the distribution of reference stars. For each pointing, a specific reconstruction matrix has to be generated, which only considers the illuminated subapertures. In this contribution we will present the concept of LINC-NIRVANA's wavefront reconstruction mechanism and report on laboratory and on-sky tests.

  13. Hybridized wavefront shaping for high-speed, high-efficiency focusing through dynamic diffusive media

    Science.gov (United States)

    Hemphill, Ashton S.; Tay, Jian Wei; Wang, Lihong V.

    2016-12-01

    One of the prime limiting factors of optical imaging in biological applications is the diffusion of light by tissue, which prevents focusing at depths greater than the optical diffusion limit (typically ˜1 mm). To overcome this challenge, wavefront shaping techniques that use a spatial light modulator (SLM) to correct the phase of the incident wavefront have recently been developed. These techniques are able to focus light through scattering media beyond the optical diffusion limit. However, the low speeds of typically used liquid crystal SLMs limit the focusing speed. Here, we present a method using a digital micromirror device (DMD) and an electro-optic modulator (EOM) to measure the scattering-induced aberrations, and using a liquid crystal SLM to apply the correction to the illuminating wavefront. By combining phase modulation from an EOM with the DMD's ability to provide selective illumination, we exploit the DMD's higher refresh rate for phase measurement. We achieved focusing through scattering media in less than 8 ms, which is sufficiently short for certain in vivo applications, as it is comparable to the speckle correlation time of living tissue.

  14. Advanced Tethersonde for High-Speed Flux Measurements Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Flux measurements of trace gases and other quantities, such as latent heat, are of great importance in scientific field research. One typical flux measurement setup...

  15. Handbook of microwave component measurements with advanced VNA techniques

    CERN Document Server

    Dunsmore, Joel P

    2012-01-01

    This book provides state-of-the-art coverage for making measurements on RF and Microwave Components, both active and passive. A perfect reference for R&D and Test Engineers, with topics ranging from the best practices for basic measurements, to an in-depth analysis of errors, correction methods, and uncertainty analysis, this book provides everything you need to understand microwave measurements. With primary focus on active and passive measurements using a Vector Network Analyzer, these techniques and analysis are equally applicable to measurements made with Spectrum Analyzers or Noise Figure

  16. Photon counting arrays for AO wavefront sensors

    CERN Document Server

    Vallerga, J; McPhate, J; Mikulec, Bettina; Clark, Allan G; Siegmund, O; CERN. Geneva

    2005-01-01

    Future wavefront sensors for AO on large telescopes will require a large number of pixels and must operate at high frame rates. Unfortunately for CCDs, there is a readout noise penalty for operating faster, and this noise can add up rather quickly when considering the number of pixels required for the extended shape of a sodium laser guide star observed with a large telescope. Imaging photon counting detectors have zero readout noise and many pixels, but have suffered in the past with low QE at the longer wavelengths (>500 nm). Recent developments in GaAs photocathode technology, CMOS ASIC readouts and FPGA processing electronics have resulted in noiseless WFS detector designs that are competitive with silicon array detectors, though at ~40% the QE of CCDs. We review noiseless array detectors and compare their centroiding performance with CCDs using the best available characteristics of each. We show that for sub-aperture binning of 6x6 and greater that noiseless detectors have a smaller centroid error at flu...

  17. On-Orbit Multi-Field Wavefront Control with a Kalman Filter

    Science.gov (United States)

    Lou, John; Sigrist, Norbert; Basinger, Scott; Redding, David

    2008-01-01

    A document describes a multi-field wavefront control (WFC) procedure for the James Webb Space Telescope (JWST) on-orbit optical telescope element (OTE) fine-phasing using wavefront measurements at the NIRCam pupil. The control is applied to JWST primary mirror (PM) segments and secondary mirror (SM) simultaneously with a carefully selected ordering. Through computer simulations, the multi-field WFC procedure shows that it can reduce the initial system wavefront error (WFE), as caused by random initial system misalignments within the JWST fine-phasing error budget, from a few dozen micrometers to below 50 nm across the entire NIRCam Field of View, and the WFC procedure is also computationally stable as the Monte-Carlo simulations indicate. With the incorporation of a Kalman Filter (KF) as an optical state estimator into the WFC process, the robustness of the JWST OTE alignment process can be further improved. In the presence of some large optical misalignments, the Kalman state estimator can provide a reasonable estimate of the optical state, especially for those degrees of freedom that have a significant impact on the system WFE. The state estimate allows for a few corrections to the optical state to push the system towards its nominal state, and the result is that a large part of the WFE can be eliminated in this step. When the multi-field WFC procedure is applied after Kalman state estimate and correction, the stability of fine-phasing control is much more certain. Kalman Filter has been successfully applied to diverse applications as a robust and optimal state estimator. In the context of space-based optical system alignment based on wavefront measurements, a KF state estimator can combine all available wavefront measurements, past and present, as well as measurement and actuation error statistics to generate a Maximum-Likelihood optimal state estimator. The strength and flexibility of the KF algorithm make it attractive for use in real-time optical system

  18. Wavefront sensor based diagnostic of FERMI FEL photon beam (Conference Presentation)

    Science.gov (United States)

    Raimondi, Lorenzo; Mahne, Nicola; Manfredda, Michele; Svetina, Cristian; Cocco, Daniele; Capotondi, Flavio; Pedersoli, Emanuele; Kiskinova, Maya; Zangrando, Marco

    2016-09-01

    FERMI is the first seeded EUV-SXR free electron laser (FEL) user facility, and it is operated at Elettra Sincrotrone Trieste. Two of the four already operating beamlines, namely LDM (Low Density Matter) and DiProI (Diffraction and Projection Imaging), use a Kirkpatrick-Baez (K-B) active X-ray optics system for focusing the FEL pulses onto the target under investigation. A wafefront sensor is used as diagnostic for the characterization of the focused spot and for the optimization of the parameters of these active optical systems as well. The aim of this work is, first, to describe in detail the optimization procedure using the wavefront sensor through the minimization of the Zernike coefficients, and second, report on the final results obtained on the K-B optical system at the DiProI endstation. The wavefront sensor, mounted out of focus behind the DiProI chamber, allows to compute the intensity distribution of the FEL beam, typically a mix between several modes resulting in a "noisy hyper-Gaussian" intensity profile, and the wavefront residual from ideal propagation shape and after tilt correction. Combining these two measures we can obtain the electric field of the wave out of focus. Propagating back the electric field we reconstruct the focal spot in far field approximation. In this way the sensor works as a diagnostic reconstructing the focal spot. On the other hand, after modelling the electric field with a Zernike polynomial it is easy and fast to optimize the mirror bending and the optical system angles by minimizing the aberrations, quantified in terms of Zernike coefficients. Since each coefficient corresponds to a single parameter, they can be minimized one at the time. Online wavefront measurements have made possible the optimization of the bending acting on the mirror curvature, and of the (pitch and roll) angle positions of the K-B system. From the wavefront measurements we have inferred a focal spot for DiProI of 5.5 μm x 6.2 μm at 32 nm wavelength

  19. Combining Placido and Corneal Wavefront Data for the Detection of Forme Fruste Keratoconus.

    Science.gov (United States)

    Saad, Alain; Gatinel, Damien

    2016-08-01

    To evaluate the accuracy of a new objective method based on Placido disk-derived data for the detection of eyes at risk of ectasia. One hundred nineteen eyes of 176 patients were included and separated into two groups, normal and forme fruste keratoconus (FFKC), using automated corneal classification software. Normal eyes (n = 114) were classified as negative for keratoconus and keratoconus suspect and had undergone LASIK with unremarkable follow-up for 4 years. The FFKC group was composed of 62 topographically normal eyes of patients with keratoconus in the fellow eye. Anterior topographic parameters, obtained from specular topography using Placido-based indices and corneal wavefront Zernike coefficients, were compared between groups. Receiver operating characteristic (ROC) curves were used to identify cut-off points in discriminating between keratoconic and normal eyes. Validation was performed on an external group of eyes. A discriminant function was built combining four corneal wavefront variables and four Placido variables. The area under the receiver operating characteristic was 0.970 with this eight-variable model. The validation of this function had 63% sensitivity for detecting FFKC and 100% sensitivity for detecting keratoconus, with a specificity of 82%. Indices generated from corneal wavefront and Placido measurements can assist in identifying early or mild forms of keratoconus undetected by a Placido-based neural network program. [J Refract Surg. 2016;32(8):510-516.]. Copyright 2016, SLACK Incorporated.

  20. An Efficient Pipeline Wavefront Phase Recovery for the CAFADIS Camera for Extremely Large Telescopes

    Directory of Open Access Journals (Sweden)

    Eduardo Magdaleno

    2009-12-01

    Full Text Available In this paper we show a fast, specialized hardware implementation of the wavefront phase recovery algorithm using the CAFADIS camera. The CAFADIS camera is a new plenoptic sensor patented by the Universidad de La Laguna (Canary Islands, Spain: international patent PCT/ES2007/000046 (WIPO publication number WO/2007/082975. It can simultaneously measure the wavefront phase and the distance to the light source in a real-time process. The pipeline algorithm is implemented using Field Programmable Gate Arrays (FPGA. These devices present architecture capable of handling the sensor output stream using a massively parallel approach and they are efficient enough to resolve several Adaptive Optics (AO problems in Extremely Large Telescopes (ELTs in terms of processing time requirements. The FPGA implementation of the wavefront phase recovery algorithm using the CAFADIS camera is based on the very fast computation of two dimensional fast Fourier Transforms (FFTs. Thus we have carried out a comparison between our very novel FPGA 2D-FFTa and other implementations.

  1. Measuring up advances in how we assess reading ability

    CERN Document Server

    Sabatini, John; O'Reilly, Tenaha

    2012-01-01

    Sabatini, Albro and O'Reilly believe that in light of federal legislation towards common core standards and assessments, as well as significant national investments in reading and literacy education, it is a critical and opportune time to bring together the research and measurement community to address fundamental issues of measuring reading comprehension, in theory and in practice.

  2. Safety Assessment of Advanced Imaging Sequences I: Measurements

    DEFF Research Database (Denmark)

    Jensen, Jørgen Arendt; Rasmussen, Morten Fischer; Pihl, Michael Johannes;

    2016-01-01

    intensity measurement program. The approach can measure and store data for a full imaging sequence in 3.8 to 8.2 s per spatial position. Based on Ispta, MI, and probe surface temperature, the method gives the ability to determine whether a sequence is within US FDA limits, or alternatively indicate how...

  3. Theory and application of differential OTF (dOTF) wavefront sensing

    Science.gov (United States)

    Codona, Johanan L.

    2012-07-01

    A new image-based technique for measuring the complex field in the pupil of a telescope is presented. The simplest form of the method uses two point source images, one with a small modification introduced in the pupil. The processing of the images is very simple and non-iterative. The method is based on a specially-defined complex functional derivative of the OTF. This derivative is approximated empirically by the difference between the Fourier transforms of the two PSFs: the differential OTF or "dOTF." Due to the complex conjugate in the OTF, the dOTF includes two complex images of the complex pupil field overlapping at the point of pupil modification. By placing the modification near the edge of the pupil, the overlap region can be minimized. The overlap region is typically small, but can be eliminated altogether by using a second modification and a third image. The technique can use broadband light, but the result incurs a radial blurring proportional to the fractional bandwidth. This is also easily dealt with using another modification and image. Although the dOTF a poor match for high frame rate astronomical AO applications, it has many potential uses. Optical shop testing, non-common-path wavefront error estimation, alignment and vignetting, telescope segment phasing, general imaging system diagnostics and testing applications are considered. More advanced applications are possible with extensions to the theory, such as extended incoherence background scenes as sources instead of stars, and 3-D tomographic aberration and transmission mapping open up many new applications.

  4. The advance and development of damage measurement technique of rock

    Institute of Scientific and Technical Information of China (English)

    YANG Geng-she(杨更社)

    2003-01-01

    The key problem of rock damage mechanics is that determination of the variable of rock damage and the establishment of damage constitutive relation of rock, which is inevitable involved in the measurement problem of rock. In this paper, the measurement technology and method of rock damage are comprehensively narrated, analyzed and studied. On the basis of the narrating the former study, a new method (Computerized Tomography,CT for short) is introduced, which is applied to rock damage measurement. On the other hand, some newest study results and laws in the field are also introduced, which are from some scholars, the author of this paper.

  5. The new magnetic measurement system at the Advanced Photon Source.

    Energy Technology Data Exchange (ETDEWEB)

    Eidelman, Y.; Deriy, B.; Makarov, O.; Vasserman, I.

    2002-03-15

    A new system for precise measurements of the field integrals and multipole components of the APS magnetic insertion devices is described. A stretched coil is used to measure magnetic field characteristics. The hardware includes a number of servomotors to move (translate or rotate) the coil and a fast data acquisition board to measure the coil signal. A PC under Linux is used as a control workstation. The user interface is written as a Tcl/tk script; the hardware is accessed from the script through a shared C-library. A description of the hardware system and the control program is given.

  6. The new Magnetic Measurement System at the Advanced Photon Source

    CERN Document Server

    Eidelman, Y; Makarov, O P; Vasserman, I B; Eidelman, Yu.

    2001-01-01

    A new system for precise measurements of the field integrals and multipole components of the APS magnetic insertion devices is described. A stretched coil is used to measure magnetic field characteristics. The hardware includes a number of servomotors to move (translate or rotate) the coil and a fast data acquisition board to measure the coil signal. A PC under Linux is used as a control workstation. The user interface is written as a Tcl/tk script. The hardware is accessed from the script through a shared C-library. A description of the hardware system and the control program is given.

  7. Advances in bioanalytical techniques to measure steroid hormones in serum.

    Science.gov (United States)

    French, Deborah

    2016-06-01

    Steroid hormones are measured clinically to determine if a patient has a pathological process occurring in the adrenal gland, or other hormone responsive organs. They are very similar in structure making them analytically challenging to measure. Additionally, these hormones have vast concentration differences in human serum adding to the measurement complexity. GC-MS was the gold standard methodology used to measure steroid hormones clinically, followed by radioimmunoassay, but that was replaced by immunoassay due to ease of use. LC-MS/MS has now become a popular alternative owing to simplified sample preparation than for GC-MS and increased specificity and sensitivity over immunoassay. This review will discuss these methodologies and some new developments that could simplify and improve steroid hormone analysis in serum.

  8. Concepts and recent advances in generalized information measures and statistics

    CERN Document Server

    Kowalski, Andres M

    2013-01-01

    Since the introduction of the information measure widely known as Shannon entropy, quantifiers based on information theory and concepts such as entropic forms and statistical complexities have proven to be useful in diverse scientific research fields. This book contains introductory tutorials suitable for the general reader, together with chapters dedicated to the basic concepts of the most frequently employed information measures or quantifiers and their recent applications to different areas, including physics, biology, medicine, economics, communication and social sciences. As these quantif

  9. [The research advance of measuring techniques on corneoscleral constitutive parameters].

    Science.gov (United States)

    Bao, Fangjun; Deng, Manli; Wang, Qinmei

    2015-11-01

    The occurrence and development of myopia and keratoconus is closely related to the changes of scleral and corneal biomechanical properties. The accurate measurement of biomechanical properties for corneoscleral tissure is very important on diagnosis of eye diseases, improvement of ocular operation, ocular biological parameter measurement and invention of ophthalmic instrument. Corneoscleral tissue, composed of bundles of compact and staggered collagen fiber and extracellular matrix, constitute the outer surface of the eyeball. The inhomogeneous distribution of the diameter, gap and amount of collagen fiber, makes its biomechanical characteristics really complex, characterized by nonlinear, viscoelastic, anisotropic, regional variation and age-related variation and etc. With the development of medical diagnostic technology, the importance of the ocular biomechanical property measurement is increasingly recognized. Nevertheless, measuring technology on ocular biomechanics properties are still not well understood by the majority of ophthalmologists. In order to facilitate the researchers to select a suitable measuring platform and method, the development of international corneoscleral biomechanical propertiy measuring technology was reviewed in this article.

  10. Wavefront sensing with the differential optical transfer function

    Science.gov (United States)

    Hart, Michael; Codona, Johanan L.

    2012-10-01

    Recently a new technique for estimating the complex field in the pupil of a telescope from image-plane intensity measurements has been introduced by Codona.1, 2 The simplest form of the method uses two images of a point source, one with a small modification introduced in the pupil. The algorithm to recover the pupil field uses a functional derivative of the optical transfer function (OTF), and is simple and non-iterative. The derivative is approximated empirically by the difference between the Fourier transforms of the two PSFs: the differential OTF or dOTF. In keeping with the Hermitian symmetry of the OTF, the dOTF includes two conjugate copies of the pupil field overlapping at the point of modification. By placing the modification near the edge of the pupil, the overlap region can be kept small. It can be eliminated altogether by using a second modification and a third image. The technique can be used in broadband light, at the cost of blurring in the recovered phase that is proportional to the fractional bandwidth. Although the dOTF is unlikely to find application in high frame rate astronomical adaptive optics, it has many potential uses such as optical shop testing, non-common-path wavefront error estimation, segmented telescope phasing and general imaging system diagnostics. In this paper, we review the dOTF concept, theory, and initial experiments to demonstrate the technique.

  11. Harmonic source wavefront aberration correction for ultrasound imaging

    Science.gov (United States)

    Dianis, Scott W.; von Ramm, Olaf T.

    2011-01-01

    A method is proposed which uses a lower-frequency transmit to create a known harmonic acoustical source in tissue suitable for wavefront correction without a priori assumptions of the target or requiring a transponder. The measurement and imaging steps of this method were implemented on the Duke phased array system with a two-dimensional (2-D) array. The method was tested with multiple electronic aberrators [0.39π to 1.16π radians root-mean-square (rms) at 4.17 MHz] and with a physical aberrator 0.17π radians rms at 4.17 MHz) in a variety of imaging situations. Corrections were quantified in terms of peak beam amplitude compared to the unaberrated case, with restoration between 0.6 and 36.6 dB of peak amplitude with a single correction. Standard phantom images before and after correction were obtained and showed both visible improvement and 14 dB contrast improvement after correction. This method, when combined with previous phase correction methods, may be an important step that leads to improved clinical images. PMID:21303031

  12. Psychometric properties of three measures assessing advanced theory of mind: Evidence from people with schizophrenia.

    Science.gov (United States)

    Chen, Kuan-Wei; Lee, Shih-Chieh; Chiang, Hsin-Yu; Syu, Ya-Cing; Yu, Xiao-Xuan; Hsieh, Ching-Lin

    2017-08-17

    Patients with schizophrenia tend to have deficits in advanced Theory of Mind (ToM). The "Reading the mind in the eyes" test (RMET), the Faux Pas Task, and the Strange Stories are commonly used for assessing advanced ToM. However, most of the psychometric properties of these 3 measures in patients with schizophrenia are unknown. The aims of this study were to validate the psychometric properties of the 3 advanced ToM measures in patients with schizophrenia, including: (1) test-retest reliability; (2) random measurement error; (3) practice effect; (4) concurrent validity; and (5) ecological validity. We recruited 53 patients with schizophrenia, who completed the 3 measures twice, 4 weeks apart. The Revised Social Functioning Scale-Taiwan short version (R-SFST) was completed within 3 days of first session of assessments. We found that the intraclass correlation coefficients of the RMET, Strange Stories, and Faux Pas Task were 0.24, 0.5, and 0.76. All 3 advanced ToM measures had large random measurement error, trivial to small practice effects, poor concurrent validity, and low ecological validity. We recommend that the scores of the 3 advanced ToM measures be interpreted with caution because these measures may not provide reliable and valid results on patients' advanced ToM abilities. Copyright © 2017 Elsevier B.V. All rights reserved.

  13. Wave-front propagation of rinsing flows on rotating semiconductor wafers

    Science.gov (United States)

    Frostad, John M.; Ylitalo, Andy; Walls, Daniel J.; Mui, David S. L.; Fuller, Gerald G.

    2016-11-01

    The semiconductor manufacturing industry is migrating to a cleaning technology that involves dispersing cleaning solutions onto a rotating wafer, similar to spin-coating. Advantages include a more continuous overall fabrication process, lower particle level, no cross contamination from the back side of a wafer, and less usage of harsh chemicals for a lower environmental impact. Rapid rotation of the wafer during rinsing can be more effective, but centrifugal forces can pull spiral-like ribbons of liquid radially outward from the advancing wave-front where particles can build up, causing higher instances of device failure at these locations. A better understanding of the rinsing flow is essential for reducing yield losses while taking advantage of the benefits of rotation. In the present work, high-speed video and image processing are used to study the dynamics of the advancing wave-front from an impinging jet on a rotating substrate. The flow-rate and rotation-speed are varied for substrates coated with a thin layer of a second liquid that has a different surface tension than the jet liquid. The difference in surface tension of the two fluids gives rise to Marangoni stresses at the interface that have a significant impact on the rinsing process, despite the extremely short time-scales involved.

  14. Genesis of return stroke current evolution at the wavefront

    Science.gov (United States)

    Kumar, Udaya; Raysaha, Rosy Balaram

    2013-07-01

    The channel dynamics at the wavefront is complex and is primarily responsible for the evolution of return stroke current. The enhancement of channel conductance at the wavefront is necessary for the evolution of current and hence, return stroke. In this regard several questions arise like: (i) what causes the enhancement of conductance, (ii) as the channel core temperature and electrical conductance are closely related, does one support the other and (iii) is the increase in core temperature on the nascent section of the channel the result of free burning arc of the wavefront just below. The present work investigates on these issues with appropriate transient thermal analysis and a macroscopic physical model for the lightning return stroke. Results clearly indicate that the contribution from the thermal field of the wavefront region to the adjacent nascent channel section is negligible as compared to the field enhancement brought in by the same. In other words, the whole process of return stroke evolution is dependent on the local heat generation at the nascent section caused by the enhancement of electric field due to the arrival of the wavefront.

  15. Evaluation of repeatability of higher-order aberrations measurement, in pseudophakic eyes by I-Trace wavefront analyzer%i-Trace像差分析仪在人工晶体眼高阶像差测量的可重复性研究

    Institute of Scientific and Technical Information of China (English)

    徐力; 刘奕志; 何明光; 柳夏玲; 曾明兵

    2008-01-01

    Objective To assess the repeatability in measuring higher-order aberrations (HOAs) in intraocular lens (IOL)eyes by a ray trace wavefront analyzer. Methods HOAs were consecutively examined 3 times across a 5.0 ram aperture diameter in 47 intraoeular lens (IOL) eyes using a ray trace wavefront analyzer. Root-mean-square (RMS) values of total higher-order aberrations (THOA), total coma-like aberrations (TC), total spherical-like aberrations (TSA) and total trefoil-like aberrations (TT) were recorded. The repeatability of measurements was assessed by Pearson correlation analysis between each pair of measures and the intra-class correlation coefficient (ICC) among the 3 measurements. The mirror symmetry of HOAs between each pair of the eyes was studied using Pearson correlation analysis. Results In IOL eyes HOAs measurements, all ICC>.73 (P .57 (P 0.05). But the mean RMS values of THOA,TT had low correlation between right and left eyes. Conclusions The repeatability of i-Trace wavefi'ont analyzer in measuring HOAs in IOL eyes is better. There have good symmetry in the TSA mean RMS values between fight and left eyes, while the mean RMS values of THOA, TC and TT have bad symmetry between right and left eyes.%目的 评价i-Trace波前像差分析仪测量人工晶体眼高阶像差的可重复性.方法 随机选取47只人工晶体眼,连续3次测量5.0mm扫描直径下高阶像差,包括总高阶像差(THOA),总慧差(TC),总球差(TSA),总三叶草(TT),以均方根(RMS)表示.3次测量的可重复性用组间相关系数(ICC)评价,两次测量间的重复性以Pearson相关系数评价.用Pearson相关系数分析左右眼高阶像差的对称性.结果 高阶像差测量3次测量ICC均大于0.73(P<0.01),两次测量间Pearson相关系数r均大于0.57(P<0.01).双眼RMS值对称性分析,左右眼TSA有相关性,而THOA、TC、TT无相关性.结论 i-Trace像差分析仪在人工晶体眼高阶像差测量的可重复性较强.TSA的RMS值双眼对称性显著,而THOA、TC、TT双眼对称性较差.

  16. Advances in the Conceptualization and Measurement of Critical Consciousness

    Science.gov (United States)

    Diemer, Matthew A.; McWhirter, Ellen Hawley; Ozer, Emily J.; Rapa, Luke J.

    2015-01-01

    This article reviews three emergent measures of critical consciousness (CC), which refers to marginalized or oppressed people's critical reflection on oppressive social, economic, or political conditions, the motivation to address perceived injustice, and action taken to counter such injustice in a liberatory manner (Freire in "Education for…

  17. Advanced spherical near-field antenna measurement techniques

    DEFF Research Database (Denmark)

    Nielsen, Jeppe Majlund; Pivnenko, Sergey; Breinbjerg, Olav

    2011-01-01

    The DTU-ESA facility has since the 1980es provided highly accurate antenna radiation pattern measurements and gain calibration by use of the probe corrected spherical nearfield technique, both for ESA (the European Space Agency) and other customers and continues to do so. Recent years activities ...

  18. Safety Assessment of Advanced Imaging Sequences I: Measurements

    DEFF Research Database (Denmark)

    Jensen, Jørgen Arendt; Rasmussen, Morten Fischer; Pihl, Michael Johannes

    2016-01-01

    distributions. The method is several orders of magnitude faster than approaches using an oscilloscope, and it also facilitates validating the emitted pressure field and the scanner’s emission sequence software. It has been implemented using the experimental SARUS scanner and the Onda AIMS III intensity...... measurement system (Onda Corporation, Sunnyvale, CA, USA). Four different sequences have been measured: a fixed focus emission, a duplex sequence containing B-mode and flow emissions, a vector flow sequence with B-mode and flow emissions in 17 directions, and finally a synthetic aperture (SA) duplex flow...... sequence. A BK8820e (BK Medical, Herlev, Denmark) convex array probe is used for the first three sequences and a BK8670 linear array probe for the SA sequence. The method is shown to give the same intensity values within 0.24% of the AIMS III Soniq 5.0 (Onda Corporation, Sunnyvale, CA, USA) commercial...

  19. Advances in Fast Response Acoustically Derived Air Temperature Measurements

    Science.gov (United States)

    Bogoev, Ivan; Jacobsen, Larry; Horst, Thomas; Conrad, Benjamin

    2016-04-01

    Fast-response accurate air-temperature measurements are required when estimating turbulent fluxes of heat, water and carbon dioxide by open-path eddy-covariance technique. In comparison with contact thermometers like thermocouples, ultra-sonic thermometers do not suffer from solar radiation loading, water vapor condensation and evaporative cooling effects. Consequently they have the potential to provide more accurate true air temperature measurements. The absolute accuracy of the ultrasonic thermometer is limited by the following parameters: the distance between the transducer pairs, transducer delays associated with the electrical-acoustic signal conversion that vary with temperature, components of the wind vector that are normal to the ultrasonic paths, and humidity. The distance between the transducer pairs is commonly obtained by coordinate measuring machine. Improved accuracy demonstrated in this study results from increased stiffness in the anemometer head to better maintain the ultrasonic path-length distances. To further improve accuracy and account for changes in transducer delays and distance as a function of temperature, these parameters are characterized in a zero-wind chamber over the entire operating temperature range. When the sonic anemometer is combined with a co-located fast-response water vapor analyzer, like in the IRGASON instrument, speed of sound can be compensated for humidity effects on a point-by-point basis resulting in a true fast-response air temperature measurement. Laboratory test results show that when the above steps are implemented in the calibration of the ultrasonic thermometer air-temperature accuracy better than ±0.5 degrees Celsius can be achieved over the entire operating range. The approach is also validated in a field inter-comparison with an aspirated thermistor probe mounted in a radiation shield.

  20. A Survey of Advanced Microwave Frequency Measurement Techniques

    OpenAIRE

    Anand Swaroop Khare,

    2012-01-01

    Microwaves are radio waves with wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. The science of photonics includes the generation, emission, modulation, signal processing, switching, transmission, amplification, detection and sensing of light. Microwave photonics has been introduced for achieving ultra broadband signal processing. Instantaneous Frequency Measurement (IFM) receivers play an important ro...

  1. Advanced structural analysis of nanoporous materials by thermal response measurements.

    Science.gov (United States)

    Oschatz, Martin; Leistner, Matthias; Nickel, Winfried; Kaskel, Stefan

    2015-04-07

    Thermal response measurements based on optical adsorption calorimetry are presented as a versatile tool for the time-saving and profound characterization of the pore structure of porous carbon-based materials. This technique measures the time-resolved temperature change of an adsorbent during adsorption of a test gas. Six carbide and carbon materials with well-defined nanopore architecture including micro- and/or mesopores are characterized by thermal response measurements based on n-butane and carbon dioxide as the test gases. With this tool, the pore systems of the model materials can be clearly distinguished and accurately analyzed. The obtained calorimetric data are correlated with the adsorption/desorption isotherms of the materials. The pore structures can be estimated from a single experiment due to different adsorption enthalpies/temperature increases in micro- and mesopores. Adsorption/desorption cycling of n-butane at 298 K/1 bar with increasing desorption time allows to determine the pore structure of the materials in more detail due to different equilibration times. Adsorption of the organic test gas at selected relative pressures reveals specific contributions of particular pore systems to the increase of the temperature of the samples and different adsorption mechanisms. The use of carbon dioxide as the test gas at 298 K/1 bar provides detailed insights into the ultramicropore structure of the materials because under these conditions the adsorption of this test gas is very sensitive to the presence of pores smaller than 0.7 nm.

  2. A summary period measure of immigrant advancement in the U.S.

    Directory of Open Access Journals (Sweden)

    John Pitkin

    2011-02-01

    Full Text Available This paper proposes a method for summarizing the pace of advancement of the foreign-born population in a given period. The method standardizes for variations in the duration of residence or age composition of immigrant groups, attainments possessed by different groups when first observed after entry, and other temporal effects on measured advances, forming an index of Expected Lifetime Advance based on the pace of change in a period. The measure is applied to Mexican and Asian immigrants. Between the 1980s and the 1990s, the rates of advancement for Mexicans accelerated in six out of seven social, economic, and civic outcomes. Rates of advancement for Asians were similar in both decades.

  3. Comparative study of infrared wavefront sensing solutions for adaptive optics

    Science.gov (United States)

    Plantet, C.; Fusco, T.; Guerineau, N.; Derelle, S.; Robert, C.

    2016-07-01

    The development of new low-noise infrared detectors, such as RAPID (CEA LETI/Sofradir) or SAPHIRA (Selex), has given the possibility to consider infrared wavefront sensing at low ux. We propose here a comparative study of near infrared (J and H bands) wavefront sensing concepts for mid and high orders estimation on a 8m- class telescope, relying on three existing wavefront sensors: the Shack-Hartmann sensor, the pyramid sensor and the quadri-wave lateral shearing interferometer. We consider several conceptual designs using the RAPID camera, making a trade-off between background flux, optical thickness and compatibility with a compact cryostat integration. We then study their sensitivity to noise in order to compare them in different practical scenarios. The pyramid provides the best performance, with a gain up to 0.5 magnitude, and has an advantageous setup.

  4. Miniaturized Shack-Hartmann Wavefront-Sensors for Starbugs

    CERN Document Server

    Goodwin, Michael; Richards, Samuel; Zheng, Jessica; Lawrence, Jon; Leon-Saval, Sergio; Argyros, Alexander

    2014-01-01

    The ability to position multiple miniaturized wavefront sensors precisely over large focal surfaces are advantageous to multi-object adaptive optics. The Australian Astronomical Observatory (AAO) has prototyped a compact and lightweight Shack-Hartmann wavefront-sensor that fits into a standard Starbug parallel fibre positioning robot. Each device makes use of a polymer coherent fibre imaging bundle to relay an image produced by a microlens array placed at the telescope focal plane to a re-imaging camera mounted elsewhere. The advantages of the polymer fibre bundle are its high-fill factor, high-throughput, low weight, and relatively low cost. Multiple devices can also be multiplexed to a single low-noise camera for cost efficiencies per wavefront sensor. The use of fibre bundles also opens the possibility of applications such as telescope field acquisition, guiding, and seeing monitors to be positioned by Starbugs. We present the design aspects, simulations and laboratory test results.

  5. Polarization-resolved microscopy through scattering media via wavefront shaping

    CERN Document Server

    de Aguiar, Hilton B; Brasselet, Sophie

    2015-01-01

    Wavefront shaping has revolutionized imaging deep in scattering media, being able to spatially and temporally refocus light through or inside the medium. However, wavefront shaping is not compatible yet with polarization-resolved microscopy given the need of polarizing optics to refocus light with a controlled polarization state. Here, we show that wavefront shaping is not only able to restore a focus, but it can also recover the injected polarization state without using any polarizing optics at the detection. This counter-intuitive effect occurs up to several transport mean free path thick samples, which exhibit a speckle with a completely scrambled state. Remarkably, an arbitrary rotation of the input polarization does not degrade the quality of the focus. This unsupervised re-polarization - out of the originally scrambled polarization state - paves the way for polarization-resolved structural microscopy at unprecedented depths. We exploit this phenomenon and demonstrate second harmonic generation (SHG) str...

  6. Traveling wavefront solutions to nonlinear reaction-diffusion-convection equations

    Science.gov (United States)

    Indekeu, Joseph O.; Smets, Ruben

    2017-08-01

    Physically motivated modified Fisher equations are studied in which nonlinear convection and nonlinear diffusion is allowed for besides the usual growth and spread of a population. It is pointed out that in a large variety of cases separable functions in the form of exponentially decaying sharp wavefronts solve the differential equation exactly provided a co-moving point source or sink is active at the wavefront. The velocity dispersion and front steepness may differ from those of some previously studied exact smooth traveling wave solutions. For an extension of the reaction-diffusion-convection equation, featuring a memory effect in the form of a maturity delay for growth and spread, also smooth exact wavefront solutions are obtained. The stability of the solutions is verified analytically and numerically.

  7. Wavefront manipulation with a dipolar metasurface under coherent control

    Science.gov (United States)

    Kang, Ming; Wang, Hui-Tian; Zhu, Weiren

    2017-07-01

    Full phase manipulation with equal amplitude is critical for optical wavefront engineering in various systems. Here we theoretically explore a general approach for optical wavefront manipulation using dipolar metasurfaces under the coherent control. From the microscopic perspective, we theoretically show that the dispersion of a dipolar metasurface under the coherent control can provide the phase manipulation within a full range of [0, 2π] and retain an equal amplitude simultaneously. As an example, such a dipolar metasurface can be constructed by compensatory H-shaped unit resonators to avoid polarization conversion. Specifically, we confirm the feasibility of designed metasurfaces for achieving the beam bending and the vortex-phase beam by the full-wave simulation. The proposed approach enriches the well-established wavefront engineering for extending the functionality of metasurface under the coherent control.

  8. Acoustic Wavefront Manipulation: Impedance Inhomogeneity and Extraordinary Reflection

    CERN Document Server

    Zhao, Jiajun; Chen, Zhining; Li, Baowen

    2013-01-01

    Optical wavefront can be manipulated by interfering elementary beams with phase inhomogeneity. Therefore a surface allowing huge, abrupt and position-variant phase change would enable all possibilities of wavefront engineering. However, one may not have the luxury of efficient abrupt-phase-changing materials in acoustics. This motivates us to establish a counterpart mechanism for acoustics, in order to empower the wide spectrum of novel acoustic applications. Remarkably, the proposed impedance-governed generalized Snell's law (IGSL) of reflection is distinguished from that in optics. Via the manipulation of inhomogeneous acoustic impedance, extraordinary reflection can be tailored for unprecedented wavefront manipulation while ordinary reflection can be surprisingly switched on or off. Our results may power the acoustic-wave manipulation and engineering. We demonstrate novel acoustic applications by planar surfaces designed with IGSL.

  9. Imaging spheres with general incident wavefronts using a dipole decomposition

    Science.gov (United States)

    Izen, Steven H.; Ovryn, Ben

    1998-06-01

    Although scattering for spheres with plane wave illumination was solved precisely by Mie in 1909, often it is of interest to image spheres with non-planar illumination. An extension of Mie theory which incorporates non-planar illumination requires knowledge of the coefficients for a spherical harmonic expansion of the incident wavefront about the center of the sphere. These coefficients have been determined for a few special cases, such as Gaussian beams, which have a relatively simple model. Using a vectorized Huygen's principle, a general vector wavefront can be represented as a superposition of dipole sources. We have computed the spherical wave function expansion coefficients of an arbitrarily placed dipole and hence the scattering from a sphere illuminated by a general wavefront can be computed. As a special case, Mie's solution of plane wave scattering was recovered. POtential applications include scattering with partially coherent illumination. Experimental results from the scattering from polystyrene spheres using Koehler illumination show agreement with numerical tests.

  10. Spatio-temporal wavefront shaping in a microwave cavity

    CERN Document Server

    del Hougne, Philipp; Fink, Mathias; Lerosey, Geoffroy

    2016-01-01

    Controlling waves in complex media has become a major topic of interest, notably through the concepts of time reversal and wavefront shaping. Recently, it was shown that spatial light modulators can counter-intuitively focus waves both in space and time through multiple scattering media when illuminated with optical pulses. In this letter we transpose the concept to a microwave cavity using flat arrays of electronically tunable resonators. We prove that maximizing the Green's function between two antennas at a chosen time yields diffraction limited spatio-temporal focusing. Then, changing the photons' dwell time inside the cavity, we modify the relative distribution of the spatial and temporal degrees of freedom (DoF), and we demonstrate that it has no impact on the field enhancement: wavefront shaping makes use of all available DoF, irrespective of their spatial or temporal nature. Our results prove that wavefront shaping using simple electronically reconfigurable arrays of reflectors is a viable approach to...

  11. Advanced spherical near-field antenna measurement techniques

    DEFF Research Database (Denmark)

    Nielsen, Jeppe Majlund; Pivnenko, Sergey; Breinbjerg, Olav

    2011-01-01

    The DTU-ESA facility has since the 1980es provided highly accurate antenna radiation pattern measurements and gain calibration by use of the probe corrected spherical nearfield technique, both for ESA (the European Space Agency) and other customers and continues to do so. Recent years activities...... and showing the capabilities of each participating facility. A special campaign was carried out with the aim of establishing a reference radiation pattern for the DTU-ESA VAST-12 antenna. The on-ground calibration of the MIRAS space radiometer for ESA's SMOS mission was carried out at the DTU-ESA facility...

  12. Advances in traceability of Freeform Measurements on CMMs

    DEFF Research Database (Denmark)

    Savio, Enrico; Hansen, Hans Nørgaard; Larsen, Erik;

    2001-01-01

    the need for complex calibrated items to be used in the substitution method for uncertainty assessment. The procedure is beeing investigated as one of the possible approaches for the new ISO 15530 series on uncertainty assessment for CMMs. The calibration of freeform surfaces is here presented...... as an example. A turbine blade has been calibrated using a CAD-based measuring system and a software tool to perform data collection, analysis, calculation and display of uncertainty. The measurands are represented by the local deviations from nominal points, with spacing of 0.2 mm in 9 different sections...

  13. Asphericity analysis using corneal wavefront and topographic meridional fits

    Science.gov (United States)

    Arba-Mosquera, Samuel; Merayo-Lloves, Jesús; de Ortueta, Diego

    2010-03-01

    The calculation of corneal asphericity as a 3-D fit renders more accurate results when it is based on the corneal wavefront aberrations rather than on the corneal topography of the principal meridians. A more accurate prediction could be obtained for hyperopic treatments compared to myopic treatments. We evaluate a method to calculate corneal asphericity and asphericity changes after refractive surgery. Sixty eyes of 15 consecutive myopic patients and 15 consecutive hyperopic patients (n=30 each) are retrospectively evaluated. Preoperative and 3-month-postoperative topographic and corneal wavefront analyses are performed using corneal topography. Ablations are performed using a laser with an aberration-free profile. Topographic changes in asphericity and corneal aberrations are evaluated for a 6-mm corneal diameter. The induction of corneal spherical aberrations and asphericity changes correlates with the achieved defocus correction. Preoperatively as well as postoperatively, asphericity calculated from the topography meridians correlates with asphericity calculated from the corneal wavefront in myopic and hyperopic treatments. A stronger correlation between postoperative asphericity and the ideally expected/predicted asphericity is obtained based on aberration-free assumptions calculated from corneal wavefront values rather than from the meridians. In hyperopic treatments, a better correlation can be obtained compared to the correlation in myopic treatments. Corneal asphericity calculated from corneal wavefront aberrations represents a 3-D fit of the corneal surface; asphericity calculated from the main topographic meridians represents a 2-D fit of the principal corneal meridians. Postoperative corneal asphericity can be calculated from corneal wavefront aberrations with higher fidelity than from corneal topography of the principal meridians. Hyperopic treatments show a greater accuracy than myopic treatments.

  14. Wavefront Sensing for WFIRST with a Linear Optical Model

    Science.gov (United States)

    Jurling, Alden S.; Content, David A.

    2012-01-01

    In this paper we develop methods to use a linear optical model to capture the field dependence of wavefront aberrations in a nonlinear optimization-based phase retrieval algorithm for image-based wavefront sensing. The linear optical model is generated from a ray trace model of the system and allows the system state to be described in terms of mechanical alignment parameters rather than wavefront coefficients. This approach allows joint optimization over images taken at different field points and does not require separate convergence of phase retrieval at individual field points. Because the algorithm exploits field diversity, multiple defocused images per field point are not required for robustness. Furthermore, because it is possible to simultaneously fit images of many stars over the field, it is not necessary to use a fixed defocus to achieve adequate signal-to-noise ratio despite having images with high dynamic range. This allows high performance wavefront sensing using in-focus science data. We applied this technique in a simulation model based on the Wide Field Infrared Survey Telescope (WFIRST) Intermediate Design Reference Mission (IDRM) imager using a linear optical model with 25 field points. We demonstrate sub-thousandth-wave wavefront sensing accuracy in the presence of noise and moderate undersampling for both monochromatic and polychromatic images using 25 high-SNR target stars. Using these high-quality wavefront sensing results, we are able to generate upsampled point-spread functions (PSFs) and use them to determine PSF ellipticity to high accuracy in order to reduce the systematic impact of aberrations on the accuracy of galactic ellipticity determination for weak-lensing science.

  15. Wavefront sensing for WFIRST with a linear optical model

    Science.gov (United States)

    Jurling, Alden S.; Content, David A.

    2012-09-01

    In this paper we develop methods to use a linear optical model to capture the field dependence of wavefront aberrations in a nonlinear optimization-based phase retrieval algorithm for image-based wavefront sensing. The linear optical model is generated from a ray trace model of the system and allows the system state to be described in terms of mechanical alignment parameters rather than wavefront coefficients. This approach allows joint optimization over images taken at different field points and does not require separate convergence of phase retrieval at individual field points. Because the algorithm exploits field diversity, multiple defocused images per field point are not required for robustness. Furthermore, because it is possible to simultaneously fit images of many stars over the field, it is not necessary to use a fixed defocus to achieve adequate signal-to-noise ratio despite having images with high dynamic range. This allows high performance wavefront sensing using in-focus science data. We applied this technique in a simulation model based on the Wide Field Infrared Survey Telescope (WFIRST) Intermediate Design Reference Mission (IDRM) imager using a linear optical model with 25 field points. We demonstrate sub-thousandth-wave wavefront sensing accuracy in the presence of noise and moderate undersampling for both monochromatic and polychromatic images using 25 high-SNR target stars. Using these high-quality wavefront sensing results, we are able to generate upsampled point-spread functions (PSFs) and use them to determine PSF ellipticity to high accuracy in order to reduce the systematic impact of aberrations on the accuracy of galactic ellipticity determination for weak-lensing science.

  16. Wavefront sensors and algorithms for adaptive optical systems

    Science.gov (United States)

    Lukin, V. P.; Botygina, N. N.; Emaleev, O. N.; Konyaev, P. A.

    2010-07-01

    The results of recent works related to techniques and algorithms for wave-front (WF) measurement using Shack-Hartmann sensors show their high efficiency in solution of very different problems of applied optics. The goal of this paper was to develop a sensitive Shack-Hartmann sensor with high precision WF measurement capability on the base of modern technology of optical elements making and new efficient methods and computational algorithms of WF reconstruction. The Shack-Hartmann sensors sensitive to small WF aberrations are used for adaptive optical systems, compensating the wave distortions caused by atmospheric turbulence. A high precision Shack-Hartmann WF sensor has been developed on the basis of a low-aperture off-axis diffraction lens array. The device is capable of measuring WF slopes at array sub-apertures of size 640×640 μm with an error not exceeding 4.80 arcsec (0.15 pixel), which corresponds to the standard deviation equal to 0.017λ at the reconstructed WF with wavelength λ . Also the modification of this sensor for adaptive system of solar telescope using extended scenes as tracking objects, such as sunspot, pores, solar granulation and limb, is presented. The software package developed for the proposed WF sensors includes three algorithms of local WF slopes estimation (modified centroids, normalized cross-correlation and fast Fourierdemodulation), as well as three methods of WF reconstruction (modal Zernike polynomials expansion, deformable mirror response functions expansion and phase unwrapping), that can be selected during operation with accordance to the application.

  17. Broadband manipulation of acoustic wavefronts by pentamode metasurface

    Energy Technology Data Exchange (ETDEWEB)

    Tian, Ye; Wei, Qi, E-mail: weiqi@nju.edu.cn; Cheng, Ying [Key Laboratory of Modern Acoustics, Department of Physics, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093 (China); Xu, Zheng [School of Physics Science and Engineering, Tongji University, Shanghai 200092 (China); Liu, Xiaojun, E-mail: liuxiaojun@nju.edu.cn [Key Laboratory of Modern Acoustics, Department of Physics, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093 (China); State Key Laboratory of Acoustics, Institute of Acoustics, Chinese Academy of Sciences, Beijing 100190 (China)

    2015-11-30

    An acoustic metasurface with a sub-wavelength thickness can manipulate acoustic wavefronts freely by the introduction of abrupt phase variation. However, the existence of a narrow bandwidth and a low transmittance limits further applications. Here, we present a broadband and highly transparent acoustic metasurface based on a frequency-independent generalized acoustic Snell's law and pentamode metamaterials. The proposal employs a gradient velocity to redirect refracted waves and pentamode metamaterials to improve impedance matching between the metasurface and the background medium. Excellent wavefront manipulation based on the metasurface is further demonstrated by anomalous refraction, generation of non-diffracting Bessel beam, and sub-wavelength flat focusing.

  18. Advances in corneal topography measurements with conical null-screens

    Science.gov (United States)

    Campos-García, Manuel; Cossio-Guerrero, Cesar; Huerta-Carranza, Oliver; Moreno-Oliva, Víctor I.

    2015-09-01

    In this work we report the design of a null-screen for corneal topography. To avoid the difficulties in the alignment of the test system due to the face contour (eyebrows, nose, or eyelids), we design a conical null-screen with a novel radial points distribution drawn on it in such a way that its image, which is formed by reflection on the test surface, becomes an exact array of circular spots if the surface is perfect. Additionally, an algorithm to compute the sagittal and meridional radii of curvature for the corneal surface is presented. The sagittal radius is obtained from the surface normal, and the meridional radius is calculated from a function fitted to the derivative of the sagittal curvature by using the surfacenormals raw data. Experimental results for the testing a calibration spherical surface are shown. Also, we perform some corneal topography measurements.

  19. The coronagraphic Modal Wavefront Sensor: a hybrid focal-plane sensor for the high-contrast imaging of circumstellar environments

    Science.gov (United States)

    Wilby, M. J.; Keller, C. U.; Snik, F.; Korkiakoski, V.; Pietrow, A. G. M.

    2017-01-01

    The raw coronagraphic performance of current high-contrast imaging instruments is limited by the presence of a quasi-static speckle (QSS) background, resulting from instrumental Non-Common Path Errors (NCPEs). Rapid development of efficient speckle subtraction techniques in data reduction has enabled final contrasts of up to 10-6 to be obtained, however it remains preferable to eliminate the underlying NCPEs at the source. In this work we introduce the coronagraphic Modal Wavefront Sensor (cMWS), a new wavefront sensor suitable for real-time NCPE correction. This combines the Apodizing Phase Plate (APP) coronagraph with a holographic modal wavefront sensor to provide simultaneous coronagraphic imaging and focal-plane wavefront sensing with the science point-spread function. We first characterise the baseline performance of the cMWS via idealised closed-loop simulations, showing that the sensor is able to successfully recover diffraction-limited coronagraph performance over an effective dynamic range of ±2.5 radians root-mean-square (rms) wavefront error within 2-10 iterations, with performance independent of the specific choice of mode basis. We then present the results of initial on-sky testing at the William Herschel Telescope, which demonstrate that the sensor is capable of NCPE sensing under realistic seeing conditions via the recovery of known static aberrations to an accuracy of 10 nm (0.1 radians) rms error in the presence of a dominant atmospheric speckle foreground. We also find that the sensor is capable of real-time measurement of broadband atmospheric wavefront variance (50% bandwidth, 158 nm rms wavefront error) at a cadence of 50 Hz over an uncorrected telescope sub-aperture. When combined with a suitable closed-loop adaptive optics system, the cMWS holds the potential to deliver an improvement of up to two orders of magnitude over the uncorrected QSS floor. Such a sensor would be eminently suitable for the direct imaging and spectroscopy of

  20. Assessment of wavefront aberration and contrast sensitivity test as evaluation of postoperative visual quality

    OpenAIRE

    Min Gong; Yi Liu; Bi Yang

    2013-01-01

    Effective methods of evaluating postoperative visual quality include wavefront aberration and contrast sensitivity test. This article provides a review of the concepts and clinical applications as well as their interactions of wavefront aberration and contrast sensitivity test.This article also provides a comprehensive assessment of the effectiveness of wavefront aberration and contrast sensitivity test as evaluation tools of postoperative visual quality.

  1. The AOLI low-order non-linear curvature wavefront sensor: a method for high sensitivity wavefront reconstruction

    CERN Document Server

    Crass, Jonathan; Femenia, Bruno; King, David L; Mackay, Craig D; Rebolo-López, Rafael; Labadie, Lucas; Garrido, Antonio Pérez; Balcells, Marc; Sánchez, Anastasio Díaz; Fuensalida, Jesús Jimenez; Lopez, Roberto L; Oscoz, Alejandro; Prieto, Jorge A Pérez; Rodríguez-Ramos, Luis F; Villó, Isidro

    2012-01-01

    The Adaptive Optics Lucky Imager (AOLI) is a new instrument under development to demonstrate near diffraction limited imaging in the visible on large ground-based telescopes. We present the adaptive optics system being designed for the instrument comprising a large stroke deformable mirror, fixed component non-linear curvature wavefront sensor and photon-counting EMCCD detectors. We describe the optical design of the wavefront sensor where two photoncounting CCDs provide a total of four reference images. Simulations of the optical characteristics of the system are discussed, with their relevance to low and high order AO systems. The development and optimisation of high-speed wavefront reconstruction algorithms are presented. Finally we discuss the results of simulations to demonstrate the sensitivity of the system.

  2. Chromatic aberration measurement for transmission interferometric testing.

    Science.gov (United States)

    Seong, Kibyung; Greivenkamp, John E

    2008-12-10

    A method of chromatic aberration measurement is described based on the transmitted wavefront of an optical element obtained from a Mach-Zehnder interferometer. The chromatic aberration is derived from transmitted wavefronts measured at five different wavelengths. Reverse ray tracing is used to remove induced aberrations associated with the interferometer from the measurement. In the interferometer, the wavefront transmitted through the sample is tested against a plano reference, allowing for the absolute determination of the wavefront radius of curvature. The chromatic aberrations of a singlet and a doublet have been measured.

  3. Measurement-Based Performance Evaluation of Advanced MIMO Transceiver Designs

    Science.gov (United States)

    Trautwein, Uwe; Schneider, Christian; Thomä, Reiner

    2005-12-01

    This paper describes the methodology and the results of performance investigations on a multiple-input multiple-output (MIMO) transceiver scheme for frequency-selective radio channels. The method relies on offline simulations and employs real-time MIMO channel sounder measurement data to ensure a realistic channel modeling. Thus it can be classified in between the performance evaluation using some predefined channel models and the evaluation of a prototype hardware in field experiments. New aspects for the simulation setup are discussed, which are frequently ignored when using simpler model-based evaluations. Example simulations are provided for an iterative ("turbo") MIMO equalizer concept. The dependency of the achievable bit error rate performance on the propagation characteristics and on the variation in some system design parameters is shown, whereas the antenna constellation is of particular concern for MIMO systems. Although in many of the considered constellations turbo MIMO equalization appears feasible in real field scenarios, there exist cases with poor performance as well, indicating that in practical applications link adaptation of the transmitter and receiver processing to the environment is necessary.

  4. Measurement-Based Performance Evaluation of Advanced MIMO Transceiver Designs

    Directory of Open Access Journals (Sweden)

    Schneider Christian

    2005-01-01

    Full Text Available This paper describes the methodology and the results of performance investigations on a multiple-input multiple-output (MIMO transceiver scheme for frequency-selective radio channels. The method relies on offline simulations and employs real-time MIMO channel sounder measurement data to ensure a realistic channel modeling. Thus it can be classified in between the performance evaluation using some predefined channel models and the evaluation of a prototype hardware in field experiments. New aspects for the simulation setup are discussed, which are frequently ignored when using simpler model-based evaluations. Example simulations are provided for an iterative ("turbo" MIMO equalizer concept. The dependency of the achievable bit error rate performance on the propagation characteristics and on the variation in some system design parameters is shown, whereas the antenna constellation is of particular concern for MIMO systems. Although in many of the considered constellations turbo MIMO equalization appears feasible in real field scenarios, there exist cases with poor performance as well, indicating that in practical applications link adaptation of the transmitter and receiver processing to the environment is necessary.

  5. Advanced Measurement and Modeling Techniques for Improved SOFC Cathodes

    Energy Technology Data Exchange (ETDEWEB)

    Stuart Adler; L. Dunyushkina; S. Huff; Y. Lu; J. Wilson

    2006-12-31

    The goal of this project was to develop an improved understanding of factors governing performance and degradation of mixed-conducting SOFC cathodes. Two new diagnostic tools were developed to help achieve this goal: (1) microelectrode half-cells for improved isolation of cathode impedance on thin electrolytes, and (2) nonlinear electrochemical impedance spectroscopy (NLEIS), a variant of traditional impedance that allows workers to probe nonlinear rates as a function of frequency. After reporting on the development and efficacy of these tools, this document reports on the use of these and other tools to better understand performance and degradation of cathodes based on the mixed conductor La{sub 1-x}Sr{sub x}CoO{sub 3-{delta}} (LSC) on gadolinia or samaria-doped ceria (GDC or SDC). We describe the use of NLEIS to measure O{sub 2} exchange on thin-film LSC electrodes, and show that O{sub 2} exchange is most likely governed by dissociative adsorption. We also describe parametric studies of porous LSC electrodes using impedance and NLEIS. Our results suggest that O{sub 2} exchange and ion transport co-limit performance under most relevant conditions, but it is O{sub 2} exchange that is most sensitive to processing, and subject to the greatest degradation and sample-to-sample variation. We recommend further work that focuses on electrodes of well-defined or characterized geometry, and probes the details of surface structure, composition, and impurities. Parallel work on primarily electronic conductors (LSM) would also be of benefit to developers, and to improved understanding of surface vs. bulk diffusion.

  6. A New Method for Finding Optical Aberrations on the Basis of Analysis of the Object Hologram Without Additional Measurements

    Science.gov (United States)

    Matkivsky, V. A.; Moiseev, A. A.; Shilyagin, P. A.; Shabanov, D. V.; Gelikonov, G. V.; Gelikonov, V. M.

    2016-11-01

    We propose a new method of compensating for the wavefront aberrations during the image processing. The method employs the digital-holography potential. The developed algorithms allow one to find the wavefront distortions caused by the optical-path nonuniformities during the interference recording of images without additional measurements (i.e., without using the reference point source and measuring the wavefront distortions). The possibility of decreasing the wavefront aberrations from tens to several radians using digital methods is demonstrated.

  7. Residual stress measurement with high energy x-rays at the Advanced Photon Source.

    Energy Technology Data Exchange (ETDEWEB)

    Winholtz, R. A.; Haeffner, D. R.; Green, R.E.L.; Varma, R.; Hammond, D.

    2000-03-02

    Preliminary measurements with high energy x-rays from the SRI CAT 1-ID beam line at the Advanced Photon show great promise for the measurement of stress and strain using diffraction. Comparisons are made with neutron measurements. Measurements of strains in a 2 mm thick 304 stainless steel weld show that excellent strain and spatial resolutions are possible. With 200 {micro}m slits, strain resolutions of 1 x 10{sup {minus}5} were achieved.

  8. Simplex-based wavefront control for the mitigation of dynamic distortions caused by atmospheric turbulence

    Science.gov (United States)

    Nikulin, Vladimir V.; Zhang, Dave

    2005-04-01

    Laser communication systems operating in the atmosphere require certain power and beam quality to establish and maintain a reliable communication link. Although such systems utilize the most advanced materials and technologies, their performance is adversely affected by optical turbulence, often posing a serious problem, even for short-range links. Atmospheric effects change optical properties of the propagation channel, causing signal fades, beam wander and scintillations. A common method of mitigating turbulence effects suggests dynamic wavefront control. In this paper the proposed technique is based on correction of the distorted beam using an electrically addressed programmable spatial light modulator (SLM). The phase profile that we impose on the distorted laser beam is described using Zernike formalism to calculate the wavefront OPD function. The Nelder-Mead simplex optimization algorithm is used as a correction procedure that provides fast results, required for real-time operation. In general, calculation of the required phase profile for an SLM with large number of pixels could be highly computationally intensive. Coupling modulator inputs to the first several Zernike coefficients allows significant reduction of the dimension of the optimization problem. The algorithm is tested in the simulation environment and its ability to compensate dynamic distortions is assessed. The results show that both dimension of the input space and the initial conditions affect the speed and convergence to a particular minimum. Recommendations for improving the system performance are also presented.

  9. Control of two-photon quantum walk in a complex multimode system by wavefront shaping

    CERN Document Server

    Defienne, Hugo; Walmsley, Ian A; Smith, Brian J; Gigan, Sylvain

    2015-01-01

    Multi-photon interferences in complex multimode structures - quantum walks - are of both funda- mental and technological interest. They rely on the ability to design the complex network where the walk occurs. Here, we demonstrate the control of quantum walks of two indistinguishable photons in a complex linear system - a highly multimode fiber - by means of wavefront shaping techniques. Using the measured transmission matrix of the fiber, we demonstrate the ability to address arbitrary output modes of the two-photon speckle pattern, and simultaneous control of the quantum inter- ferences. This work provides a reconfigurable platform for multi-photon, multimode interference experiments and a route to high-dimensional quantum systems.

  10. Light-efficient, quantum-limited interferometric wavefront estimation by virtual mode sensing.

    Science.gov (United States)

    Lauterbach, Marcel A; Ruckel, Markus; Denk, Winfried

    2006-05-01

    We describe and analyze an interferometer-based virtual modal wavefront sensor (VMWS) that can be configured to measure, for example, Zernike coefficients directly. This sensor is particularly light efficient because the determination of each modal coefficient benefits from all the available photons. Numerical simulations show that the VMWS outperforms state-of-the-art phase unwrapping at low light levels. Including up to Zernike mode 21, aberrations can be determined with a precision of about 0.17 rad (lambda/37) using low resolution (65 x 65 pixels) images and only about 400 photons total.

  11. Estimation of phase wave-front aberration distribution function using wavelet transform profilometry.

    Science.gov (United States)

    Rahbar, Kambiz; Faez, Karim; Attaran-Kakhki, Ebrahim

    2012-06-01

    Reduction of image quality under the effects of wavefront aberration of the optical system has a direct impact on the vision system's performance. This paper tries to estimate the amount of aberration with the use of wavelet transform profilometry. The basic idea is based on the principle that under aberration effects, the position of the fringes' image on the image plane will change, and this change correlates with the amount of aberration. So the distribution of aberration function can directly be extracted through measuring the amount of changes in the fringes' image on the image plane. Experimental results and the empirical validity of this idea are evaluated.

  12. Receding-horizon adaptive contyrol of aero-optical wavefronts

    NARCIS (Netherlands)

    Tesch, J.; Gibson, S.; Verhaegen, M.

    2013-01-01

    A new method for adaptive prediction and correction of wavefront errors in adaptive optics (AO) is introduced. The new method is based on receding-horizon control design and an adaptive lattice filter. Experimental results presented illustrate the capability of the new adaptive controller to predict

  13. Bending light on demand by holographic sculpturing its wavefront

    CERN Document Server

    Latychevskaia, Tatiana

    2015-01-01

    A classical light beam propagates along a straight line and does not bend unless in a medium of variable refractive index. It is well known that by modifying the wavefront in a certain manner, the light intensity can be turned into a certain shape. Examples are optical lenses or Fresnel Zone Plates for focusing an incident wave to a point at the focal plane. Another example are Airy beams created by modifying the phase distribution of the wavefront into an Airy function resulting in a bending of the light intensity while propagating. A further example is holography, where the phase of the wavefront passing through a hologram is changed to mimic the object wavefront, thus providing the illusion that the original object is present in space. However, all these known techniques allow for limited light modifications: either focusing within a limited region in space2 or shaping a certain class of parametric curves along the optical axis or creating a bend in a quadratic-dependent declination as in the case of Airy ...

  14. Liquid deformable mirror for high-order wavefront correction

    NARCIS (Netherlands)

    Vuelban, E.M.; Bhattacharya, N.; Braat, J.J.M.

    2006-01-01

    We propose and demonstrate a novel liquid deformable mirror, based on electrocapillary actuation, for highorder wavefront correction. The device consists of a two-dimensional array of vertically oriented microchannels filled with two immiscible liquids, an aqueous electrolyte, and a viscous dielectr

  15. Describing the Corneal Shape after Wavefront-Optimized Photorefractive Keratectomy

    NARCIS (Netherlands)

    de Jong, Tim; Wijdh, Robert H. J.; Koopmans, Steven A.; Jansonius, Nomdo M.

    2014-01-01

    PURPOSE: To develop a procedure for describing wavefront-optimized photorefractive keratectomy (PRK) corneas and to characterize PRK-induced changes in shape. METHODS: We analyzed preoperative and postoperative corneal elevation data of 41 eyes of 41 patients (mean [±SD] age, 38 [±11] years) who und

  16. Note on wavefront dislocation in surface water waves

    NARCIS (Netherlands)

    Karjanto, Natanael; Groesen, van E.

    2007-01-01

    At singular points of a wave field, where the amplitude vanishes, the phase may become singular and wavefront dislocation may occur. In this Letter we investigate for wave fields in one spatial dimension the appearance of these essentially linear phenomena. We introduce the Chu–Mei quotient as it is

  17. Linear-constraint wavefront control for exoplanet coronagraphic imaging systems

    Science.gov (United States)

    Sun, He; Eldorado Riggs, A. J.; Kasdin, N. Jeremy; Vanderbei, Robert J.; Groff, Tyler Dean

    2017-01-01

    A coronagraph is a leading technology for achieving high-contrast imaging of exoplanets in a space telescope. It uses a system of several masks to modify the diffraction and achieve extremely high contrast in the image plane around target stars. However, coronagraphic imaging systems are very sensitive to optical aberrations, so wavefront correction using deformable mirrors (DMs) is necessary to avoid contrast degradation in the image plane. Electric field conjugation (EFC) and Stroke minimization (SM) are two primary high-contrast wavefront controllers explored in the past decade. EFC minimizes the average contrast in the search areas while regularizing the strength of the control inputs. Stroke minimization calculates the minimum DM commands under the constraint that a target average contrast is achieved. Recently in the High Contrast Imaging Lab at Princeton University (HCIL), a new linear-constraint wavefront controller based on stroke minimization was developed and demonstrated using numerical simulation. Instead of only constraining the average contrast over the entire search area, the new controller constrains the electric field of each single pixel using linear programming, which could led to significant increases in speed of the wavefront correction and also create more uniform dark holes. As a follow-up of this work, another linear-constraint controller modified from EFC is demonstrated theoretically and numerically and the lab verification of the linear-constraint controllers is reported. Based on the simulation and lab results, the pros and cons of linear-constraint controllers are carefully compared with EFC and stroke minimization.

  18. Wavefronts and caustic associated with Durnin’s beams

    Science.gov (United States)

    de Jesús Cabrera-Rosas, Omar; Espíndola-Ramos, Ernesto; Alejandro Juárez-Reyes, Salvador; Julián-Macías, Israel; Ortega-Vidals, Paula; Silva-Ortigoza, Gilberto; Silva-Ortigoza, Ramón; Sosa-Sánchez, Citlalli Teresa

    2017-01-01

    The aim of the present work is to give a geometrical characterization of Durnin’s beams. That is, we compute the wavefronts and caustic associated with the nondiffracting solutions to the scalar wave equation introduced by Durnin. To this end, first we show that in an isotropic optical medium \\psi ({r},t)={{{e}}}{{i}[{k}0S({r})-ω t]} is an exact solution of the wave equation, if and only if, S is a solution of both the eikonal and Laplace equations, then from one and two-parameter families of this type of solution and the superposition principle we define new solutions of the wave equation, in particular we show that the ideal nondiffracting beams are one example of this type of construction in free space. Using this fact, the wavefronts and caustic associated with those beams are computed. We find that their caustic has only one branch, which is invariant under translations along the direction of evolution of the beam. Finally, the Bessel beam of order m is worked out explicitly and we find that it is characterized by wavefronts that are deformations of conical ones and the caustic is an infinite cylinder of radius proportional to m. In the case m = 0, the wavefronts are cones and the caustic degenerates into an infinite line.

  19. Model-based aberration correction in a closed-loop wavefront-sensor-less adaptive optics system.

    Science.gov (United States)

    Song, H; Fraanje, R; Schitter, G; Kroese, H; Vdovin, G; Verhaegen, M

    2010-11-08

    In many scientific and medical applications, such as laser systems and microscopes, wavefront-sensor-less (WFSless) adaptive optics (AO) systems are used to improve the laser beam quality or the image resolution by correcting the wavefront aberration in the optical path. The lack of direct wavefront measurement in WFSless AO systems imposes a challenge to achieve efficient aberration correction. This paper presents an aberration correction approach for WFSlss AO systems based on the model of the WFSless AO system and a small number of intensity measurements, where the model is identified from the input-output data of the WFSless AO system by black-box identification. This approach is validated in an experimental setup with 20 static aberrations having Kolmogorov spatial distributions. By correcting N=9 Zernike modes (N is the number of aberration modes), an intensity improvement from 49% of the maximum value to 89% has been achieved in average based on N+5=14 intensity measurements. With the worst initial intensity, an improvement from 17% of the maximum value to 86% has been achieved based on N+4=13 intensity measurements.

  20. Analysis of a digital phase retrieval method for wave-front reconstruction

    Institute of Scientific and Technical Information of China (English)

    Wei Huang; Dean Liu; Xuejie Zhang; Yan Zhang; Jianqiang Zhu

    2011-01-01

    A phase retrieval algorithm which only needs to measure the intensity distribution at two positions to be effective is used to reconstruct the laser wave-front. Results are obtained from the phase retrieval algorithm in the visible band and the effects of the measurement error on the phase retrieval process are simulated. The algorithm is not sensitive to absolute amplitude measurement error, but is sensitive to the relative distribution of light intensity.%@@ A phase retrieval algorithm which only needs to measure the intensity distribution at two positions to be effective is used to reconstruct the laser wave-front.Results are obtained from the phase retrieval algorithm in the visible band and the effects of the measurement error on the phase retrieval process are simulated.The algorithm is not sensitive to absolute amplitude measurement error, but is sensitive to the relative distribution of light intensity.

  1. ADVANCING THE FUNDAMENTAL UNDERSTANDING AND SCALE-UP OF TRISO FUEL COATERS VIA ADVANCED MEASUREMENT AND COMPUTATIONAL TECHNIQUES

    Energy Technology Data Exchange (ETDEWEB)

    Biswas, Pratim; Al-Dahhan, Muthanna

    2012-11-01

    to advance the fundamental understanding of the hydrodynamics by systematically investigating the effect of design and operating variables, to evaluate the reported dimensionless groups as scaling factors, and to establish a reliable scale-up methodology for the TRISO fuel particle spouted bed coaters based on hydrodynamic similarity via advanced measurement and computational techniques. An additional objective is to develop an on-line non-invasive measurement technique based on gamma ray densitometry (i.e. Nuclear Gauge Densitometry) that can be installed and used for coater process monitoring to ensure proper performance and operation and to facilitate the developed scale-up methodology. To achieve the objectives set for the project, the work will use optical probes and gamma ray computed tomography (CT) (for the measurements of solids/voidage holdup cross-sectional distribution and radial profiles along the bed height, spouted diameter, and fountain height) and radioactive particle tracking (RPT) (for the measurements of the 3D solids flow field, velocity, turbulent parameters, circulation time, solids lagrangian trajectories, and many other of spouted bed related hydrodynamic parameters). In addition, gas dynamic measurement techniques and pressure transducers will be utilized to complement the obtained information. The measurements obtained by these techniques will be used as benchmark data to evaluate and validate the computational fluid dynamic (CFD) models (two fluid model or discrete particle model) and their closures. The validated CFD models and closures will be used to facilitate the developed methodology for scale-up, design and hydrodynamic similarity. Successful execution of this work and the proposed tasks will advance the fundamental understanding of the coater flow field and quantify it for proper and safe design, scale-up, and performance. Such achievements will overcome the barriers to AGR applications and will help assure that the US maintains

  2. ADVANCING THE FUNDAMENTAL UNDERSTANDING AND SCALE-UP OF TRISO FUEL COATERS VIA ADVANCED MEASUREMENT AND COMPUTATIONAL TECHNIQUES

    Energy Technology Data Exchange (ETDEWEB)

    Biswas, Pratim; Al-Dahhan, Muthanna

    2012-11-01

    to advance the fundamental understanding of the hydrodynamics by systematically investigating the effect of design and operating variables, to evaluate the reported dimensionless groups as scaling factors, and to establish a reliable scale-up methodology for the TRISO fuel particle spouted bed coaters based on hydrodynamic similarity via advanced measurement and computational techniques. An additional objective is to develop an on-line non-invasive measurement technique based on gamma ray densitometry (i.e. Nuclear Gauge Densitometry) that can be installed and used for coater process monitoring to ensure proper performance and operation and to facilitate the developed scale-up methodology. To achieve the objectives set for the project, the work will use optical probes and gamma ray computed tomography (CT) (for the measurements of solids/voidage holdup cross-sectional distribution and radial profiles along the bed height, spouted diameter, and fountain height) and radioactive particle tracking (RPT) (for the measurements of the 3D solids flow field, velocity, turbulent parameters, circulation time, solids lagrangian trajectories, and many other of spouted bed related hydrodynamic parameters). In addition, gas dynamic measurement techniques and pressure transducers will be utilized to complement the obtained information. The measurements obtained by these techniques will be used as benchmark data to evaluate and validate the computational fluid dynamic (CFD) models (two fluid model or discrete particle model) and their closures. The validated CFD models and closures will be used to facilitate the developed methodology for scale-up, design and hydrodynamic similarity. Successful execution of this work and the proposed tasks will advance the fundamental understanding of the coater flow field and quantify it for proper and safe design, scale-up, and performance. Such achievements will overcome the barriers to AGR applications and will help assure that the US maintains

  3. Comparison of visual performance between conventional LASIK and wavefront-guided LASIK with iris-registration

    Institute of Scientific and Technical Information of China (English)

    ZHANG Jing; ZHOU Yue-hua; WANG Ning-li; LI Rui

    2008-01-01

    Background Laser in situ keratomileusis(LASIK)has become an efficient and commonly performed procedure to reduce refractive errors.In order to further increase the postoperative visual quality,the wavefront-guided refractive surgery has been a research hotspot in customized surgery. This study was conducted to compare the visual acuity,higher-order aberration,and contrast sensitivity of wavefront-guided LAStK with iris-registration and conventional LASIK.Methods Two hundred and eleven myopic eyes of 109 patients were enrolled in this prospective study and randomly divided into two groups:the wavefront-guided LASIK(wg LASIK)group(94 eyes)and conventional LASIK group(117 eyes).A Wavescan Wavefront aberrometer was used to analyze Zernike coefficients and the root-mean-square(RMS)of higher order aberrations with 6.0 mm pupil size,and Optec 6500 visual function instrument was used to measure contrast sensitivity(CS)under 5 spatiaI frequencies before and after surgery in both groups.Results The uncorrected visual acuity(UCVA)and the mean spherical equivalent(SE)in wg LASIK group were significantly better than those in conventional LASIK(UCVA,z=2.339,P=0.019;SE,t=2.838,P=0.005)at 3 months after surgery.Moreover,the increase in Z3-3,Z3 1,Z3 3,Z4 0,Z5 -1,Z5 1,Z5 5 and Z6 -6 in wg LASIK group was statistically smaller than that in conventional LASIK group(P<0.05).In wg LASIK group,eyes with a higher amount of the preoperative RMS of the higher order aberrations(RMSh≥0.30 μm)showed a statistically lower increase(13.5%)than those in conventional LASIK group at 3 months after surgery(33.3%)(P=0.004).And the values of 4th order spherical aberration(4thSA)and the root mean square of 6th order aberration(RMS6)in wg LASIK group were significantly lower than those in conventional group in eyes which had higher preoperative astigmatism(≥1.0D)(4thSA,P=0.03;RMS6,P=0.02).Wg LASIK group showed better CS values than the correspondingly preoperative values at all spatial frequencies

  4. Experience with wavefront sensor and deformable mirror interfaces for wide-field adaptive optics systems

    CERN Document Server

    Basden, A G; Bharmal, N A; Bitenc, U; Brangier, M; Buey, T; Butterley, T; Cano, D; Chemla, F; Clark, P; Cohen, M; Conan, J -M; de Cos, F J; Dickson, C; Dipper, N A; Dunlop, C N; Feautrier, P; Fusco, T; Gach, J L; Gendron, E; Geng, D; Goodsell, S J; Gratadour, D; Greenaway, A H; Guesalaga, A; Guzman, C D; Henry, D; Holck, D; Hubert, Z; Huet, J M; Kellerer, A; Kulcsar, C; Laporte, P; Roux, B Le; Looker, N; Longmore, A J; Marteaud, M; Martin, O; Meimon, S; Morel, C; Morris, T J; Myers, R M; Osborn, J; Perret, D; Petit, C; Raynaud, H; Reeves, A P; Rousset, G; Lasheras, F Sanchez; Rodriguez, M Sanchez; Santos, J D; Sevin, A; Sivo, G; Stadler, E; Stobie, B; Talbot, G; Todd, S; Vidal, F; Younger, E J

    2016-01-01

    Recent advances in adaptive optics (AO) have led to the implementation of wide field-of-view AO systems. A number of wide-field AO systems are also planned for the forthcoming Extremely Large Telescopes. Such systems have multiple wavefront sensors of different types, and usually multiple deformable mirrors (DMs). Here, we report on our experience integrating cameras and DMs with the real-time control systems of two wide-field AO systems. These are CANARY, which has been operating on-sky since 2010, and DRAGON, which is a laboratory adaptive optics real-time demonstrator instrument. We detail the issues and difficulties that arose, along with the solutions we developed. We also provide recommendations for consideration when developing future wide-field AO systems.

  5. Experience with wavefront sensor and deformable mirror interfaces for wide-field adaptive optics systems

    Science.gov (United States)

    Basden, A. G.; Atkinson, D.; Bharmal, N. A.; Bitenc, U.; Brangier, M.; Buey, T.; Butterley, T.; Cano, D.; Chemla, F.; Clark, P.; Cohen, M.; Conan, J.-M.; de Cos, F. J.; Dickson, C.; Dipper, N. A.; Dunlop, C. N.; Feautrier, P.; Fusco, T.; Gach, J. L.; Gendron, E.; Geng, D.; Goodsell, S. J.; Gratadour, D.; Greenaway, A. H.; Guesalaga, A.; Guzman, C. D.; Henry, D.; Holck, D.; Hubert, Z.; Huet, J. M.; Kellerer, A.; Kulcsar, C.; Laporte, P.; Le Roux, B.; Looker, N.; Longmore, A. J.; Marteaud, M.; Martin, O.; Meimon, S.; Morel, C.; Morris, T. J.; Myers, R. M.; Osborn, J.; Perret, D.; Petit, C.; Raynaud, H.; Reeves, A. P.; Rousset, G.; Sanchez Lasheras, F.; Sanchez Rodriguez, M.; Santos, J. D.; Sevin, A.; Sivo, G.; Stadler, E.; Stobie, B.; Talbot, G.; Todd, S.; Vidal, F.; Younger, E. J.

    2016-06-01

    Recent advances in adaptive optics (AO) have led to the implementation of wide field-of-view AO systems. A number of wide-field AO systems are also planned for the forthcoming Extremely Large Telescopes. Such systems have multiple wavefront sensors of different types, and usually multiple deformable mirrors (DMs). Here, we report on our experience integrating cameras and DMs with the real-time control systems of two wide-field AO systems. These are CANARY, which has been operating on-sky since 2010, and DRAGON, which is a laboratory AO real-time demonstrator instrument. We detail the issues and difficulties that arose, along with the solutions we developed. We also provide recommendations for consideration when developing future wide-field AO systems.

  6. Computer Generated Hologram System for Wavefront Measurement System Calibration

    Science.gov (United States)

    Olczak, Gene

    2011-01-01

    Computer Generated Holograms (CGHs) have been used for some time to calibrate interferometers that require nulling optics. A typical scenario is the testing of aspheric surfaces with an interferometer placed near the paraxial center of curvature. Existing CGH technology suffers from a reduced capacity to calibrate middle and high spatial frequencies. The root cause of this shortcoming is as follows: the CGH is not placed at an image conjugate of the asphere due to limitations imposed by the geometry of the test and the allowable size of the CGH. This innovation provides a calibration system where the imaging properties in calibration can be made comparable to the test configuration. Thus, if the test is designed to have good imaging properties, then middle and high spatial frequency errors in the test system can be well calibrated. The improved imaging properties are provided by a rudimentary auxiliary optic as part of the calibration system. The auxiliary optic is simple to characterize and align to the CGH. Use of the auxiliary optic also reduces the size of the CGH required for calibration and the density of the lines required for the CGH. The resulting CGH is less expensive than the existing technology and has reduced write error and alignment error sensitivities. This CGH system is suitable for any kind of calibration using an interferometer when high spatial resolution is required. It is especially well suited for tests that include segmented optical components or large apertures.

  7. A New Computerised Advanced Theory of Mind Measure for Children with Asperger Syndrome: The ATOMIC

    Science.gov (United States)

    Beaumont, Renae B.; Sofronoff, Kate

    2008-01-01

    This study examined the ability of children with Asperger Syndrome (AS) to attribute mental states to characters in a new computerised, advanced theory of mind measure: The Animated Theory of Mind Inventory for Children (ATOMIC). Results showed that children with AS matched on IQ, verbal comprehension, age and gender performed equivalently on…

  8. Advances in Treatment Integrity Research: Multidisciplinary Perspectives on the Conceptualization, Measurement, and Enhancement of Treatment Integrity

    Science.gov (United States)

    Schulte, Ann C.; Easton, Julia E.; Parker, Justin

    2009-01-01

    Documenting treatment integrity is an important issue in research and practice in any discipline concerned with prevention and intervention. However, consensus concerning the dimensions of treatment integrity and how they should be measured has yet to emerge. Advances from three areas in which significant treatment integrity work has taken…

  9. Advances in Children's Rights and Children's Well-Being Measurement: Implications for School Psychologists

    Science.gov (United States)

    Kosher, Hanita; Jiang, Xu; Ben-Arieh, Asher; Huebner, E. Scott

    2014-01-01

    Recent years have brought important changes to the profession of school psychology, influenced by larger social, scientific, and political trends. These trends include the emergence of children's rights agenda and advances in children's well-being measurement. During these years, a growing public attention and commitment to the notion of…

  10. A New Computerised Advanced Theory of Mind Measure for Children with Asperger Syndrome: The ATOMIC

    Science.gov (United States)

    Beaumont, Renae B.; Sofronoff, Kate

    2008-01-01

    This study examined the ability of children with Asperger Syndrome (AS) to attribute mental states to characters in a new computerised, advanced theory of mind measure: The Animated Theory of Mind Inventory for Children (ATOMIC). Results showed that children with AS matched on IQ, verbal comprehension, age and gender performed equivalently on…

  11. MEASURING BETA FUNCTION AND PHASE ADVANCE IN RHIC WITH AN AC DIPOLE.

    Energy Technology Data Exchange (ETDEWEB)

    BAI,M.PEGGS,S.ROSER,T.SATOGATA,T.

    2003-05-12

    High energy hadron collider operation requires accurate measurements of the beta functions and phase advances, to check the linear optics and to locate gradient errors. During the RHIC 2003 run, two AC dipoles with vertical and horizontal magnetic field [1] were used to measure the linear optics at storage and at injection energies. The two AC dipoles are set up to adiabatically induce sizable coherent oscillations at a frequency close to the betatron frequencies. The beta functions and phase advances are then calculated from the 1024 turn-by-turn measurements available from all the RHIC BPMs (Beam Position Monitors). Because the coherent excitation is adiabatic, the beam emittance is preserved after the measurement. The algorithm is discussed in this paper, and experimental results are presented.

  12. Gemini Planet Imager Observational Calibrations III: Empirical Measurement Methods and Applications of High-Resolution Microlens PSFs

    OpenAIRE

    Ingraham, Patrick; Ruffio, Jean-Baptiste; Perrin, Marshall D.; Wolff, Schuyler G.; Draper, Zachary H.; Maire, Jerome; Marchis, Franck; Fesquet, Vincent

    2014-01-01

    The newly commissioned Gemini Planet Imager (GPI) combines extreme adaptive optics, an advanced coronagraph, precision wavefront control and a lenslet-based integral field spectrograph (IFS) to measure the spectra of young extrasolar giant planets between 0.9-2.5 um. Each GPI detector image, when in spectral model, consists of ~37,000 microspectra which are under or critically sampled in the spatial direction. This paper demonstrates how to obtain high-resolution microlens PSFs and discusses ...

  13. Common-Path Interferometric Wavefront Sensing for Space Telescopes

    Science.gov (United States)

    Wallace, James Kent

    2011-01-01

    This paper presents an optical configuration for a common-path phase-shifting interferometric wavefront sensor.1 2 This sensor has a host of attractive features which make it well suited for space-based adaptive optics. First, it is strictly reflective and therefore operates broadband, second it is common mode and therefore does not suffer from systematic errors (like vibration) that are typical in other interferometers, third it is a phase-shifting interferometer and therefore benefits from both the sensitivity of interferometric sensors as well as the noise rejection afforded by synchronous detection. Unlike the Shack-Hartman wavefront sensor, it has nearly uniform sensitivity to all pupil modes. Optical configuration, theory and simulations for such a system will be discussed along with predicted performance.

  14. Terahertz wavefront control by tunable metasurface made of graphene ribbons

    Energy Technology Data Exchange (ETDEWEB)

    Yatooshi, Takumi; Ishikawa, Atsushi, E-mail: a-ishikawa@okayama-u.ac.jp; Tsuruta, Kenji [Department of Electrical and Electronic Engineering, Okayama University, 3-1-1 Tsushimanaka, Kitaku, Okayama 700-8530 (Japan)

    2015-08-03

    We propose a tunable metasurface consisting of an array of graphene ribbons on a silver mirror with a SiO{sub 2} gap layer to control reflected wavefront at terahertz frequencies. The graphene ribbons exhibit localized plasmon resonances depending on their Fermi levels to introduce abrupt phase shifts along the metasurface. With interference of the Fabry-Perot resonances in the SiO{sub 2} layer, phase shift through the system is largely accumulated, covering the 0-to-2π range for full control of the wavefront. Numerical simulations prove that wide-angle beam steering up to 53° with a high reflection efficiency of 60% is achieved at 5 THz within a switching time shorter than 0.6 ps.

  15. Discontinuous Electromagnetic Fields Using Huygens Sources For Wavefront Manipulation

    CERN Document Server

    Selvanayagam, Michael

    2013-01-01

    We introduce the idea of discontinuous electric and magnetic fields at a boundary to design and shape wavefronts in an arbitrary manner. To create this discontinuity in the field we use electric and magnetic currents which act like a Huygens source to radiate the desired wavefront. These currents can be synthesized either by an array of electric and magnetic dipoles or by a combined impedance and admittance surface. A dipole array is an active implementation to impose discontinuous fields while the impedance/admittance surface acts as a passive one. We then expand on our previous work showing how electric and magnetic dipole arrays can be used to cloak an object demonstrating two novel cloaking schemes. We also show how to arbitrarily refract a beam using a set of impedance and admittance surfaces. Refraction using the idea of discontinuous fields is shown to be a more general case of refraction using phase discontinuities.

  16. Wavefront modulation of water surface wave by a metasurface

    Institute of Scientific and Technical Information of China (English)

    孙海涛; 程营; 王敬时; 刘晓峻

    2015-01-01

    We design a planar metasurface to modulate the wavefront of a water surface wave (WSW) on a deep sub-wavelength scale. The metasurface is composed of an array of coiling-up-space units with specially designed parameters, and can take on the work of steering the wavefront when it is pierced into water. Like their acoustic counterparts, the modulation of WSW is ascribed to the gradient phase shift of the coiling-up-space units, which can be perfectly tuned by changing the coiling plate length and channel number inside the units. According to the generalized Snell’s law, negative refraction and‘driven’ surface mode of WSW are also demonstrated at certain incidences. Specially, the transmitted WSW could be efficiently guided out by linking a symmetrically-corrugated channel in‘driven’ surface mode. This work may have potential applications in water wave energy extraction and coastal protection.

  17. Performance of current measurement system in poloidal field power supply for Experimental Advanced Superconducting Tokamak

    Science.gov (United States)

    Liu, D. M.; Li, J.; Wan, B. N.; Lu, Z.; Wang, L. S.; Jiang, L.; Lu, C. H.; Huang, J.

    2016-11-01

    As one of the core subsystems of the Experimental Advanced Superconducting Tokamak (EAST), the poloidal field power system supplies energy to EAST's superconducting coils. To measure the converter current in the poloidal field power system, a current measurement system has been designed. The proposed measurement system is composed of a Rogowski coil and a newly designed integrator. The results of the resistor-inductor-capacitor discharge test and the converter equal current test show that the current measurement system provides good reliability and stability, and the maximum error of the proposed system is less than 1%.

  18. Spherical aberration and other higher-order aberrations in the human eye : from summary wave-front analysis data to optical variables relevant to visual perception

    NARCIS (Netherlands)

    Jansonius, Nomdo M.

    2010-01-01

    Wave-front analysis data from the human eye are commonly presented using the aberration coefficient c(4)(0) (primary spherical aberration) together with an overall measure of all higher-order aberrations. If groups of subjects are compared, however, the relevance of an observed difference cannot eas

  19. Hybrid architecture active wavefront sensing and control system, and method

    Science.gov (United States)

    Feinberg, Lee D. (Inventor); Dean, Bruce H. (Inventor); Hyde, Tristram T. (Inventor)

    2011-01-01

    According to various embodiments, provided herein is an optical system and method that can be configured to perform image analysis. The optical system can comprise a telescope assembly and one or more hybrid instruments. The one or more hybrid instruments can be configured to receive image data from the telescope assembly and perform a fine guidance operation and a wavefront sensing operation, simultaneously, on the image data received from the telescope assembly.

  20. Wavefront Reconstruction and Mirror Surface Optimizationfor Adaptive Optics

    Science.gov (United States)

    2014-06-01

    correction. A DM has a reflective surface with actuators along the back struc- ture that apply forces causing the mirror surface to adapt to a desired shape...actuators. The actuators cause forces along the back of the mirror structure and the mirror surface deflects to form the conjugate shape of the wavefront...optical axis of the primary mirror. The interferometer and null corrector are mounted to remove the 81 Interferometer Null corrector Hexapod ❋✐❣✉r

  1. Novel technology for reducing wavefront image processing latency

    Science.gov (United States)

    Barr, David; Schwartz, Noah; Vick, Andy; Coughlan, John; Halsall, Rob; Basden, Alastair; Dipper, Nigel

    2016-07-01

    Adaptive optics is essential for the successful operation of the future Extremely Large Telescopes (ELTs). At the heart of these AO system lies the real-time control which has become computationally challenging. A majority of the previous efforts has been aimed at reducing the wavefront reconstruction latency by using many-core hardware accelerators such as Xeon Phis and GPUs. These modern hardware solutions offer a large numbers of cores combined with high memory bandwidths but have restrictive input/output (I/O). The lack of efficient I/O capability makes the data handling very inefficient and adds both to the overall latency and jitter. For example a single wavefront sensor for an ELT scale adaptive optics system can produce hundreds of millions of pixels per second that need to be processed. Passing all this data through a CPU and into GPUs or Xeon Phis, even by reducing memory copies by using systems such as GPUDirect, is highly inefficient. The Mellanox TILE series is a novel technology offering a high number of cores and multiple 10 Gbps Ethernet ports. We present results of the TILE-Gx36 as a front-end wavefront sensor processing unit. In doing so we are able to greatly reduce the amount of data needed to be transferred to the wavefront reconstruction hardware. We show that the performance of the Mellanox TILE-GX36 is in-line with typical requirements, in terms of mean calculation time and acceptable jitter, for E-ELT first-light instruments and that the Mellanox TILE series is a serious contender for all E-ELT instruments.

  2. The speed of reaction-diffusion wavefronts in nonsteady media

    Energy Technology Data Exchange (ETDEWEB)

    Mendez, Vicenc [Departament de Medicina, Facultat de Ciencies de la Salut, Universitat Internacional de Catalunya. c/Gomera s/n, 08190-Sant Cugat del Valles (Barcelona) (Spain); Fort, Joaquim [Departament de Fisica, Universitat de Girona, Campus Montilivi, 17071 Girona, Catalonia (Spain); Pujol, Toni [Departament de Fisica, Universitat de Girona, Campus Montilivi, 17071 Girona, Catalonia (Spain)

    2003-04-11

    The evolution of the speed of wavefronts for reaction-diffusion equations with time-varying parameters is analysed. We make use of singular perturbative analysis to study the temporal evolution of the speed for pushed fronts. The analogy with Hamilton-Jacobi dynamics allows us to consider the problem for pulled fronts, which is described by Kolmogorov-Petrovskii-Piskunov (KPP) reaction kinetics. Both analytical studies are in good agreement with the results of numerical solutions.

  3. The speed of reaction-diffusion wavefronts in nonsteady media

    CERN Document Server

    Méndez, V; Pujol, T

    2003-01-01

    The evolution of the speed of wavefronts for reaction-diffusion equations with time-varying parameters is analysed. We make use of singular perturbative analysis to study the temporal evolution of the speed for pushed fronts. The analogy with Hamilton-Jacobi dynamics allows us to consider the problem for pulled fronts, which is described by Kolmogorov-Petrovskii-Piskunov (KPP) reaction kinetics. Both analytical studies are in good agreement with the results of numerical solutions.

  4. Preparing for JWST wavefront sensing and control operations

    Science.gov (United States)

    Perrin, Marshall D.; Acton, D. Scott; Lajoie, Charles-Philippe; Knight, J. Scott; Lallo, Matthew D.; Allen, Marsha; Baggett, Wayne; Barker, Elizabeth; Comeau, Thomas; Coppock, Eric; Dean, Bruce H.; Hartig, George; Hayden, William L.; Jordan, Margaret; Jurling, Alden; Kulp, Trey; Long, Joseph; McElwain, Michael W.; Meza, Luis; Nelan, Edmund P.; Soummer, Remi; Stansberry, John; Stark, Christopher; Telfer, Randal; Welsh, Andria L.; Zielinski, Thomas P.; Zimmerman, Neil T.

    2016-07-01

    The James Webb Space Telescopes segmented primary and deployable secondary mirrors will be actively con- trolled to achieve optical alignment through a complex series of steps that will extend across several months during the observatory's commissioning. This process will require an intricate interplay between individual wavefront sensing and control tasks, instrument-level checkout and commissioning, and observatory-level calibrations, which involves many subsystems across both the observatory and the ground system. Furthermore, commissioning will often exercise observatory capabilities under atypical circumstances, such as fine guiding with unstacked or defocused images, or planning targeted observations in the presence of substantial time-variable offsets to the telescope line of sight. Coordination for this process across the JWST partnership has been conducted through the Wavefront Sensing and Control Operations Working Group. We describe at a high level the activities of this group and the resulting detailed commissioning operations plans, supporting software tools development, and ongoing preparations activities at the Science and Operations Center. For each major step in JWST's wavefront sensing and control, we also explain the changes and additions that were needed to turn an initial operations concept into a flight-ready plan with proven tools. These efforts are leading to a robust and well-tested process and preparing the team for an efficient and successful commissioning of JWSTs active telescope.

  5. Research on technique of wavefront retrieval based on Foucault test

    Science.gov (United States)

    Yuan, Lvjun; Wu, Zhonghua

    2010-05-01

    During finely grinding the best fit sphere and initial stage of polishing, surface error of large aperture aspheric mirrors is too big to test using common interferometer. Foucault test is widely used in fabricating large aperture mirrors. However, the optical path is disturbed seriously by air turbulence, and changes of light and dark zones can not be identified, which often lowers people's judging ability and results in making mistake to diagnose surface error of the whole mirror. To solve the problem, the research presents wavefront retrieval based on Foucault test through digital image processing and quantitative calculation. Firstly, real Foucault image can be gained through collecting a variety of images by CCD, and then average these image to eliminate air turbulence. Secondly, gray values are converted into surface error values through principle derivation, mathematical modeling, and software programming. Thirdly, linear deviation brought by defocus should be removed by least-square method to get real surface error. At last, according to real surface error, plot wavefront map, gray contour map and corresponding pseudo color contour map. The experimental results indicates that the three-dimensional wavefront map and two-dimensional contour map are able to accurately and intuitively show surface error on the whole mirrors under test, and they are beneficial to grasp surface error as a whole. The technique can be used to guide the fabrication of large aperture and long focal mirrors during grinding and initial stage of polishing the aspheric surface, which improves fabricating efficiency and precision greatly.

  6. Curvature Wavefront Sensing for the Large Synoptic Survey Telescope

    CERN Document Server

    Xin, Bo; Liang, Ming; Chandrasekharan, Srinivasan; Angeli, George; Shipsey, Ian

    2015-01-01

    The Large Synoptic Survey Telescope (LSST) will use an active optics system (AOS) to maintain alignment and surface figure on its three large mirrors. Corrective actions fed to the LSST AOS are determined from information derived from 4 curvature wavefront sensors located at the corners of the focal plane. Each wavefront sensor is a split detector such that the halves are 1mm on either side of focus. In this paper we describe the extensions to published curvature wavefront sensing algorithms needed to address challenges presented by the LSST, namely the large central obscuration, the fast f/1.23 beam, off-axis pupil distortions, and vignetting at the sensor locations. We also describe corrections needed for the split sensors and the effects from the angular separation of different stars providing the intra- and extra-focal images. Lastly, we present simulations that demonstrate convergence, linearity, and negligible noise when compared to atmospheric effects when the algorithm extensions are applied to the LS...

  7. Photorefractive keratectomy combined with corneal wavefront-guided and hyperaspheric ablation profiles to correct myopia.

    Science.gov (United States)

    Lee, Hun; Park, Si Yoon; Yong Kang, David Sung; Ha, Byoung Jin; Choi, Jin Young; Kim, Eung Kweon; Seo, Kyoung Yul; Kim, Tae-Im

    2016-06-01

    To evaluate the effects of photorefractive keratectomy (PRK) combined with corneal wavefront-guided ablation profiles and hyperaspheric ablation profiles on changes in higher-order aberrations (HOAs). Yonsei University College of Medicine and Eyereum Clinic, Seoul, South Korea. Comparative observational case series. Medical records of patients who had corneal wavefront-guided hyperaspheric PRK, corneal wavefront-guided mild-aspheric PRK, or non-corneal wavefront-guided mild-aspheric PRK were analyzed. The logMAR uncorrected distance visual acuity (UDVA), manifest refraction spherical equivalent (MRSE), and changes in corneal aberrations (root-mean-square [RMS] HOAs, spherical aberration, coma) were evaluated 1, 3, and 6 months postoperatively. The records of 61 patients (96 eyes) were reviewed. There was no statistically significant difference in logMAR UDVA or MRSE between the 3 groups at any timepoint. Corneal RMS HOAs were significantly smaller in the corneal wavefront-guided hyperaspheric group and the corneal wavefront-guided mild-aspheric group than in the noncorneal wavefront-guided mild-aspheric group at each timepoint. Corneal spherical aberration was significantly smaller for corneal wavefront-guided hyperaspheric PRK than for noncorneal wavefront-guided mild-aspheric PRK 6 months postoperatively. Changes in corneal spherical aberration (preoperatively and 6 months postoperatively) in corneal wavefront-guided hyperaspheric PRK were significantly smaller than in corneal wavefront-guided mild-aspheric PRK (P = .046). Corneal coma was significantly smaller with corneal wavefront-guided hyperaspheric PRK and corneal wavefront-guided mild-aspheric PRK than with noncorneal wavefront-guided mild-aspheric PRK 3 months and 6 months postoperatively. Corneal wavefront-guided hyperaspheric PRK induced less corneal spherical aberration 6 months postoperatively than corneal wavefront-guided mild-aspheric PRK and noncorneal wavefront-guided mild-aspheric PRK

  8. Reliability and validity of advanced theory-of-mind measures in middle childhood and adolescence.

    Science.gov (United States)

    Hayward, Elizabeth O; Homer, Bruce D

    2017-09-01

    Although theory-of-mind (ToM) development is well documented for early childhood, there is increasing research investigating changes in ToM reasoning in middle childhood and adolescence. However, the psychometric properties of most advanced ToM measures for use with older children and adolescents have not been firmly established. We report on the reliability and validity of widely used, conventional measures of advanced ToM with this age group. Notable issues with both reliability and validity of several of the measures were evident in the findings. With regard to construct validity, results do not reveal a clear empirical commonality between tasks, and, after accounting for comprehension, developmental trends were evident in only one of the tasks investigated. Statement of contribution What is already known on this subject? Second-order false belief tasks have acceptable internal consistency. The Eyes Test has poor internal consistency. Validity of advanced theory-of-mind tasks is often based on the ability to distinguish clinical from typical groups. What does this study add? This study examines internal consistency across six widely used advanced theory-of-mind tasks. It investigates validity of tasks based on comprehension of items by typically developing individuals. It further assesses construct validity, or commonality between tasks. © 2017 The British Psychological Society.

  9. Enhancing the performance of the light field microscope using wavefront coding.

    Science.gov (United States)

    Cohen, Noy; Yang, Samuel; Andalman, Aaron; Broxton, Michael; Grosenick, Logan; Deisseroth, Karl; Horowitz, Mark; Levoy, Marc

    2014-10-06

    Light field microscopy has been proposed as a new high-speed volumetric computational imaging method that enables reconstruction of 3-D volumes from captured projections of the 4-D light field. Recently, a detailed physical optics model of the light field microscope has been derived, which led to the development of a deconvolution algorithm that reconstructs 3-D volumes with high spatial resolution. However, the spatial resolution of the reconstructions has been shown to be non-uniform across depth, with some z planes showing high resolution and others, particularly at the center of the imaged volume, showing very low resolution. In this paper, we enhance the performance of the light field microscope using wavefront coding techniques. By including phase masks in the optical path of the microscope we are able to address this non-uniform resolution limitation. We have also found that superior control over the performance of the light field microscope can be achieved by using two phase masks rather than one, placed at the objective's back focal plane and at the microscope's native image plane. We present an extended optical model for our wavefront coded light field microscope and develop a performance metric based on Fisher information, which we use to choose adequate phase masks parameters. We validate our approach using both simulated data and experimental resolution measurements of a USAF 1951 resolution target; and demonstrate the utility for biological applications with in vivo volumetric calcium imaging of larval zebrafish brain.

  10. An effective trace-guided wavefront navigation and map-building approach for autonomous mobile robots

    Science.gov (United States)

    Luo, Chaomin; Krishnan, Mohan; Paulik, Mark; Jan, Gene Eu

    2013-12-01

    This paper aims to address a trace-guided real-time navigation and map building approach of an autonomous mobile robot. Wave-front based global path planner is developed to generate a global trajectory for an autonomous mobile robot. Modified Vector Field Histogram (M-VFH) is employed based on the LIDAR sensor information to guide the robot locally to be autonomously traversed with obstacle avoidance by following traces provided by the global path planner. A local map composed of square grids is created through the local navigator while the robot traverses with limited LIDAR sensory information. From the measured sensory information, a map of the robot's immediate limited surroundings is dynamically built for the robot navigation. The real-time wave-front based navigation and map building methodology has been successfully demonstrated in a Player/Stage simulation environment. With the wave-front-based global path planner and M-VFH local navigator, a safe, short, and reasonable trajectory is successfully planned in a majority of situations without any templates, without explicitly optimizing any global cost functions, and without any learning procedures. Its effectiveness, feasibility, efficiency and simplicity of the proposed real-time navigation and map building of an autonomous mobile robot have been successfully validated by simulation and comparison studies. Comparison studies of the proposed approach with the other path planning approaches demonstrate that the proposed method is capable of planning more reasonable and shorter collision-free trajectories autonomously.

  11. Stress activated contractile wavefronts in the mechanically-excitable embryonic heart

    Science.gov (United States)

    Chiou, Kevin; Majkut, Stephanie; Discher, Dennis; Lubensky, Tom; Liu, Andrea

    2014-03-01

    The heart is a prime example of a robust, active system with behavior-the heart beat-that is extraordinarily well timed and coordinated. For more than half a century, electrical activity induced by ion release and diffusion has been argued to be the mechanism driving cardiac action. But recent work indicates that this phenomenon is also regulated by mechanical activity. In the embryonic avian heart tube, the speed of the contractile wavefront traversing the heart tube with each beat is measured to be a monotonic, linear function of tissue stiffness. Traditional electrical conduction models of excitation-contraction cannot explain this dependence; such a result indicates that the myocardium is mechanically excitable. Here, we extend this work by using experimental observations of stiffness-dependent behavior in isolated cardiomyocytes as an input to study contractile wavefronts in the tissue as a whole. We model the heart tube as an active, overdamped elastic network where the primary stress mediator is the extracellular matrix. Using this simple model, we explain experimental observations of the systolic wave and predict qualitatively new behavior.

  12. Spatial-temporal-covariance-based modeling, analysis, and simulation of aero-optics wavefront aberrations.

    Science.gov (United States)

    Vogel, Curtis R; Tyler, Glenn A; Wittich, Donald J

    2014-07-01

    We introduce a framework for modeling, analysis, and simulation of aero-optics wavefront aberrations that is based on spatial-temporal covariance matrices extracted from wavefront sensor measurements. Within this framework, we present a quasi-homogeneous structure function to analyze nonhomogeneous, mildly anisotropic spatial random processes, and we use this structure function to show that phase aberrations arising in aero-optics are, for an important range of operating parameters, locally Kolmogorov. This strongly suggests that the d5/3 power law for adaptive optics (AO) deformable mirror fitting error, where d denotes actuator separation, holds for certain important aero-optics scenarios. This framework also allows us to compute bounds on AO servo lag error and predictive control error. In addition, it provides us with the means to accurately simulate AO systems for the mitigation of aero-effects, and it may provide insight into underlying physical processes associated with turbulent flow. The techniques introduced here are demonstrated using data obtained from the Airborne Aero-Optics Laboratory.

  13. Multi time-step wave-front reconstruction for tomographic Adaptive-Optics systems

    CERN Document Server

    Ono, Yoshito H; Oya, Shin; Lardiere, Olivier; Andersen, David R; Correia, Carlos; Jackson, Kate; Bradley, Colin

    2016-01-01

    In tomographic adaptive-optics (AO) systems, errors due to tomographic wave-front reconstruction limit the performance and angular size of the scientific field of view (FoV), where AO correction is effective. We propose a multi time-step tomographic wave-front reconstruction method to reduce the tomographic error by using the measurements from both the current and the previous time-steps simultaneously. We further outline the method to feed the reconstructor with both wind speed and direction of each turbulence layer. An end-to-end numerical simulation, assuming a multi-object AO (MOAO) system on a 30 m aperture telescope, shows that the multi time-step reconstruction increases the Strehl ratio (SR) over a scientific FoV of 10 arcminutes in diameter by a factor of 1.5--1.8 when compared to the classical tomographic reconstructor, depending on the guide star asterism and with perfect knowledge of wind speeds and directions. We also evaluate the multi time-step reconstruction method and the wind estimation meth...

  14. Active compensation of wavefront aberrations by controllable heating of lens with electric film heater matrix.

    Science.gov (United States)

    Chen, Hua; Hou, Lv; Zhou, Xinglin

    2016-08-20

    We present a new apparatus for active compensation of wavefront aberrations by controllable heating of a lens using a film heater matrix. The annular electric film heater matrix, comprising 24 individual heaters, is attached to the periphery of a lens. Utilizing the linear superposition, and wavefront change proportional to the heating energy properties induced by heating, a controllable wavefront can be defined by solving a linear function. The two properties of wavefront change of a lens have been confirmed through a specially designed experiment. The feasibility of the compensation method is validated by compensating the wavefront of a plate lens. The results show that the wavefront of the lens changes from 12.52 to 2.95 nm rms after compensation. With a more precise electric controlling board, better results could be achieved.

  15. Asymptotic stability of monostable wavefronts in discrete-time integral recursions

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    The aim of this work is to study the traveling wavefronts in a discrete-time integral recursion with a Gauss kernel in R2.We first establish the existence of traveling wavefronts as well as their precise asymptotic behavior.Then,by employing the comparison principle and upper and lower solutions technique,we prove the asymptotic stability and uniqueness of such monostable wavefronts in the sense of phase shift and circumnutation.We also obtain some similar results in R.

  16. Optical study on the vision correction and supernormal vision based on the wave-front aberrations of human eye

    Institute of Scientific and Technical Information of China (English)

    MU GuoGuang; WANG ZhaoQi; LIU YongJi; QUAN Wei; WANG Yang; WANG Wei

    2007-01-01

    In this paper we present the recent research results in the field of vision correction and supernormal vision according to the actual measurements of the wave-front aberrations and the corneal surface topography, the clinical detection of the visual function and the laser corneal refractive surgery, and the optimization of the optical system. These include the features of the aberrations of human eye with different pupil sizes, different fields of view and temporal accommodation, the influence of the polychromatic illumination of the visible wavelength on the supernormal vision,and the effect of the existing laser corneal refractive surgery on the wave-front aberrations of the eye. It is shown that the wave-front aberration of human eye is of temporal variation and of synthesis with multi impact factors. To achieve supernormal vision, an optimum engineering data for the customized laser corneal surgery should be firstly acquired, which may involve the dynamic free-form optical surface. Although the myopia can be corrected by the laser in situ keratomileusis (LASlK) in a certain degree, it brings about negative effects under scotopic conditions.

  17. Optical study on the vision correction and supernormal vision based on the wave-front aberrations of human eye

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    In this paper we present the recent research results in the field of vision correction and supernormal vision according to the actual measurements of the wave-front aberrations and the corneal surface topography,the clinical detection of the visual function and the laser corneal refractive surgery,and the optimization of the optical system. These include the features of the aberrations of human eye with different pupil sizes,different fields of view and temporal accommodation,the influence of the polychromatic illumination of the visible wavelength on the supernormal vision,and the effect of the existing laser corneal refractive surgery on the wave-front ab-errations of the eye. It is shown that the wave-front aberration of human eye is of temporal variation and of synthesis with multi impact factors. To achieve super-normal vision,an optimum engineering data for the customized laser corneal sur-gery should be firstly acquired,which may involve the dynamic free-form optical surface. Although the myopia can be corrected by the laser in situ keratomileusis(LASIK) in a certain degree,it brings about negative effects under scotopic condi-tions.

  18. A Novel Microcharacterization Technique in the Measurement of Strain and Orientation Gradient in Advanced Materials

    Science.gov (United States)

    Garmestai, H.; Harris, K.; Lourenco, L.

    1997-01-01

    Representation of morphology and evolution of the microstructure during processing and their relation to properties requires proper experimental techniques. Residual strains, lattice distortion, and texture (micro-texture) at the interface and the matrix of a layered structure or a functionally gradient material and their variation are among parameters important in materials characterization but hard to measure with present experimental techniques. Current techniques available to measure changes in interred material parameters (residual stress, micro-texture, microplasticity) produce results which are either qualitative or unreliable. This problem becomes even more complicated in the case of a temperature variation. These parameters affect many of the mechanical properties of advanced materials including stress-strain relation, ductility, creep, and fatigue. A review of some novel experimental techniques using recent advances in electron microscopy is presented here to measure internal stress, (micro)texture, interracial strength and (sub)grain formation and realignment. Two of these techniques are combined in the chamber of an Environmental Scanning Electron Microscope to measure strain and orientation gradients in advanced materials. These techniques which include Backscattered Kikuchi Diffractometry (BKD) and Microscopic Strain Field Analysis are used to characterize metallic and intermetallic matrix composites and superplastic materials. These techniques are compared with the more conventional x-ray diffraction and indentation techniques.

  19. Numerical estimation of the curvature of a light wavefront in a weak gravitational field

    CERN Document Server

    Miguel, A San; Pascual-Sanchez, J -F

    2009-01-01

    The geometry of a light wavefront evolving in the 3--space associated with a post-Newtonian relativistic spacetime from a flat wavefront is studied numerically by means of the ray tracing method. For a discretization of the bidimensional wavefront the surface fitting technique is used to determine the curvature of this surface at each vertex of the mesh. The relationship between the curvature of a wavefront and the change of the arrival time at different points on the Earth is also numerically discussed.

  20. Advanced digital speckle correlation method for strain measurement and nondestructive testing

    Science.gov (United States)

    Jin, Guan-chang; Bao, Nai-Keng; Chung, Po Sheun

    1997-03-01

    An advanced digital speckle correlation method (DSCM) is presented in this paper. The advantages of this method will not only improve the processing speed but also increase the measuring accuracy. Some mathematics tools are derived and a powerful computing program is developed for further applications. A new feature of the measuring sensitivity of DSCM that can be varied by different amplification of the optical arrangement is first presented. This advantage may be superior to those available in other optical metrology methods like Electronic Speckle Pattern Interferometry (ESPI) in micro-deformation measurements. The applications of strain measurement and nondestructive testing are described and the advantages of DSCM are obvious. Some examples of material behavior measurement and plastic strain measurement are presented. Due to the high sensitivity of DSCM, another potential application in nondestructive testing (NDT) is also described in this paper. From the application examples given, this advanced DSCM proves to be a new and effective optical strain sensing technique especially for small objects or micro-deformation measurements.

  1. Final Technical Report: Advanced Measurement and Analysis of PV Derate Factors.

    Energy Technology Data Exchange (ETDEWEB)

    King, Bruce Hardison [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Burton, Patrick D. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Hansen, Clifford [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Jones, Christian Birk [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

    2015-12-01

    The Advanced Measurement and Analysis of PV Derate Factors project focuses on improving the accuracy and reducing the uncertainty of PV performance model predictions by addressing a common element of all PV performance models referred to as “derates”. Widespread use of “rules of thumb”, combined with significant uncertainty regarding appropriate values for these factors contribute to uncertainty in projected energy production.

  2. Scenarios and performance measures for advanced ISDN satellite design and experiments

    Science.gov (United States)

    Pepin, Gerard R.

    1991-01-01

    Described here are the contemplated input and expected output for the Interim Service Integrated Services Digital Network (ISDN) Satellite (ISIS) and Full Service ISDN Satellite (FSIS) Models. The discrete event simulations of these models are presented with specific scenarios that stress ISDN satellite parameters. Performance measure criteria are presented for evaluating the advanced ISDN communication satellite designs of the NASA Satellite Communications Research (SCAR) Program.

  3. An Assessment of Wind Plant Complex Flows Using Advanced Doppler Radar Measurements

    Science.gov (United States)

    Gunter, W. S.; Schroeder, J.; Hirth, B.; Duncan, J.; Guynes, J.

    2015-12-01

    As installed wind energy capacity continues to steadily increase, the need for comprehensive measurements of wind plant complex flows to further reduce the cost of wind energy has been well advertised by the industry as a whole. Such measurements serve diverse perspectives including resource assessment, turbine inflow and power curve validation, wake and wind plant layout model verification, operations and maintenance, and the development of future advanced wind plant control schemes. While various measurement devices have been matured for wind energy applications (e.g. meteorological towers, LIDAR, SODAR), this presentation will focus on the use of advanced Doppler radar systems to observe the complex wind flows within and surrounding wind plants. Advanced Doppler radars can provide the combined advantage of a large analysis footprint (tens of square kilometers) with rapid data analysis updates (a few seconds to one minute) using both single- and dual-Doppler data collection methods. This presentation demonstrates the utility of measurements collected by the Texas Tech University Ka-band (TTUKa) radars to identify complex wind flows occurring within and nearby operational wind plants, and provide reliable forecasts of wind speeds and directions at given locations (i.e. turbine or instrumented tower sites) 45+ seconds in advance. Radar-derived wind maps reveal commonly observed features such as turbine wakes and turbine-to-turbine interaction, high momentum wind speed channels between turbine wakes, turbine array edge effects, transient boundary layer flow structures (such as wind streaks, frontal boundaries, etc.), and the impact of local terrain. Operational turbine or instrumented tower data are merged with the radar analysis to link the observed complex flow features to turbine and wind plant performance.

  4. Advanced glycation end products measured by skin autofluorescence in a population with central obesity

    OpenAIRE

    den Engelsen, Corine; van den Donk, Maureen; Gorter, Kees J; Salomé, Philippe L; Rutten, Guy E

    2012-01-01

    Accumulation of advanced glycation end products (AGEs) is enhanced by chronic hyperglycemia and oxidative stress and this process may contribute to the pathogenesis of vascular disease. Skin autofluorescence (AF), a measure of accumulation of AGEs in skin collagen, is associated with vascular disease in patients with diabetes.   Because central obesity enhances oxidative stress people with central obesity might already have increased accumulation of AGEs before diabetes or cardiovascular dise...

  5. 12 CFR Appendix D to Part 325 - Capital Adequacy Guidelines for Banks: Internal-Ratings-Based and Advanced Measurement Approaches

    Science.gov (United States)

    2010-01-01

    ... transactions. Current exposure is also called replacement cost. Default—(1) Retail. (i) A retail exposure of a...-Ratings-Based and Advanced Measurement Approaches D Appendix D to Part 325 Banks and Banking FEDERAL... Advanced Measurement Approaches Part IGeneral Provisions Section 1Purpose, Applicability, Reservation...

  6. NASA programs in advanced sensors and measurement technology for aeronautical applications

    Science.gov (United States)

    Conway, Bruce A.

    1990-01-01

    NASA involvement in the development, implementation, and experimental use of advanced aeronautical sensors and measurement technologies is presently discussed within the framework of specific NASA research centers' activities. The technology thrusts are in the fields of high temperature strain gages and microphones, laser light-sheet flow visualization, LTA, LDV, and LDA, tunable laser-based aviation meteorology, and fiber-optic CARS measurements. IR thermography and close-range photogrammetry are undergoing substantial updating and application. It is expected that 'smart' sensors will be increasingly widely used, especially in conjunction with smart structures in aircraft and spacecraft.

  7. Recent advances in measuring chromospheric magnetic fields in the He I 10830 Å line

    Science.gov (United States)

    Lagg, A.

    During the last decade advances in instrumentation, atomic physics and modeling have greatly improved the access to the chromospheric magnetic field vector. High sensitivity polarimeters like the Tenerife Infrared Polarimeter (TIP2, VTT) or the Spectro-Polarimeter for Infrared and Optical Regions (SPINOR, HAO) lead to reliable Zeeman measurements using the He I 10830 Å triplet. The simultaneously measured Si I 10827 Å line provides additional information on the structure of the underlying photosphere. Theoretical modeling of the Hanle and the Paschen-Back effect helped to significantly improve the analysis of polarization measurements in the He I triplet, allowing to directly visualize the magnetic structure of spicules, polar prominences and active regions. Here, I will summarize the results of chromospheric magnetic field measurements using this interesting triplet obtained in the last couple of years and discuss the great potential it has to further uncover the complex structure of the chromosphere and its coupling to the photosphere.

  8. Advances in children's rights and children's well-being measurement: implications for school psychologists.

    Science.gov (United States)

    Kosher, Hanita; Jiang, Xu; Ben-Arieh, Asher; Huebner, E Scott

    2014-03-01

    Recent years have brought important changes to the profession of school psychology, influenced by larger social, scientific, and political trends. These trends include the emergence of children's rights agenda and advances in children's well-being measurement. During these years, a growing public attention and commitment to the notion of children's rights has developed, which is best expressed in the United Nations Convention on the Rights of the Child. The Convention outlines the conditions necessary to ensure and promote children's well-being and calls for the ongoing monitoring of children's well-being for accountability purposes. We articulate advances in children's rights and children's well-being measurement in the context of children's schooling experiences in general and for school psychology in particular. We highlight implications for the assessment roles of school psychologists, who occupy a unique position at the intersection of multiple subsystems of children's overall ecosystems. We argue that the synergy between a rights-based agenda and advances in children's well-being assessment methodology can provide valuable opportunities for school psychology. This synergy can help school communities establish perspective and goals for children's well-being in rights respecting ways, using the most promising well-being assessment strategies. PsycINFO Database Record (c) 2014 APA, all rights reserved.

  9. Arbitrary optical wavefront shaping via spin-to-orbit coupling

    CERN Document Server

    Larocque, Hugo; Bouchard, Frédéric; Fickler, Robert; Upham, Jeremy; Boyd, Robert W; Karimi, Ebrahim

    2016-01-01

    Converting spin angular momentum to orbital angular momentum has been shown to be a practical and efficient method for generating optical beams carrying orbital angular momentum and possessing a space-varying polarized field. Here, we present novel liquid crystal devices for tailoring the wavefront of optical beams through the Pancharatnam-Berry phase concept. We demonstrate the versatility of these devices by generating an extensive range of optical beams such as beams carrying $\\pm200$ units of orbital angular momentum along with Bessel, Airy and Ince-Gauss beams. We characterize both the phase and the polarization properties of the generated beams, confirming our devices' performance.

  10. Towards feasible and effective predictive wavefront control for adaptive optics

    Energy Technology Data Exchange (ETDEWEB)

    Poyneer, L A; Veran, J

    2008-06-04

    We have recently proposed Predictive Fourier Control, a computationally efficient and adaptive algorithm for predictive wavefront control that assumes frozen flow turbulence. We summarize refinements to the state-space model that allow operation with arbitrary computational delays and reduce the computational cost of solving for new control. We present initial atmospheric characterization using observations with Gemini North's Altair AO system. These observations, taken over 1 year, indicate that frozen flow is exists, contains substantial power, and is strongly detected 94% of the time.

  11. Towards feasible and effective predictive wavefront control for adaptive optics

    Energy Technology Data Exchange (ETDEWEB)

    Poyneer, L A; Veran, J

    2008-06-04

    We have recently proposed Predictive Fourier Control, a computationally efficient and adaptive algorithm for predictive wavefront control that assumes frozen flow turbulence. We summarize refinements to the state-space model that allow operation with arbitrary computational delays and reduce the computational cost of solving for new control. We present initial atmospheric characterization using observations with Gemini North's Altair AO system. These observations, taken over 1 year, indicate that frozen flow is exists, contains substantial power, and is strongly detected 94% of the time.

  12. Deformable Membrane Mirror for Wavefront Correction (Short Communication

    Directory of Open Access Journals (Sweden)

    Amita Gupta

    2009-11-01

    Full Text Available Deformable or adaptive mirrors are used in modern adaptive optics systems for direct correction of the aberrations in the light wavefront. Conventional deformable mirrors used for this purpose are expensive electromechanical devices. Deformable membrane mirror fabricated using microelectromechanical systems (MEMS technology is a low cost, compact adaptive optical element for correction of the lower-order optical aberrations such as defocus and astigmatism. In this paper, important aspects of device design and simulation, fabrication techniques, and test results are discussed.Defence Science Journal, 2009, 59(6, pp.590-594, DOI:http://dx.doi.org/10.14429/dsj.59.1563

  13. Advanced NSCLC First Pass Perfusion at 64-slice CT: Reproducibility of Volume-based Quantitative Measurement

    Directory of Open Access Journals (Sweden)

    Jie HU

    2010-05-01

    Full Text Available Background and objective The aim of this study is to explore the reproducibility of volume-based quantitative measurement of non-small cell lung cancer (NSCLC perfusion at 64-slice CT. Methods Fourteen patients with proved advanced NSCLC were enrolled in this dynamic first pass volume-based CT perfusion (CTP study (8×5 mm collimation, and they underwent the second scan within 24 h. According to the longest diameters, those patients were classified to ≤3 cm and >3 cm groups, and each group had 7 patients. Intraclass correlation coefficient (ICC and Bland-Altman statistics were used to evaluate the reproducibility of CTP imaging. Results In both groups of advanced NSCLC, the reproducibility with BF, BV, and PS values were good (ICC >0.75 for all, but mean transit time (MTT values. For advanced NSCLC (≤3 cm, repeatability coefficient (RC values with blood flow (BF, blood volume (BV, MTT and permeability surface area product (PS values were 56%, 45%, 114%, and 78%, respectively, and the 95% change intervals of RC were -39%-53%, -29%-62%, -83%-145%, and -57%-98%, respectively. For advanced NSCLC (>3 cm, those values were 46%, 30%, 59%, and 33%, respectively, and the 95% change intervals of RC were -48%-45%, -33%-26%, -54%-64%, and -18%-48%. Conclusion There is greater reproducibility of tumor size >3 cm than that of ≤3 cm. BF and BV could be addressed for reliable clinical application in antiangiogenesis therapeutic monitoring with advanced NSCLC patients.

  14. Error analysis of compensation cutting technique for wavefront error of KH2PO4 crystal.

    Science.gov (United States)

    Tie, Guipeng; Dai, Yifan; Guan, Chaoliang; Zhu, Dengchao; Song, Bing

    2013-09-20

    Considering the wavefront error of KH(2)PO(4) (KDP) crystal is difficult to control through face fly cutting process because of surface shape deformation during vacuum suction, an error compensation technique based on a spiral turning method is put forward. An in situ measurement device is applied to measure the deformed surface shape after vacuum suction, and the initial surface figure error, which is obtained off-line, is added to the in situ surface shape to obtain the final surface figure to be compensated. Then a three-axis servo technique is utilized to cut the final surface shape. In traditional cutting processes, in addition to common error sources such as the error in the straightness of guide ways, spindle rotation error, and error caused by ambient environment variance, three other errors, the in situ measurement error, position deviation error, and servo-following error, are the main sources affecting compensation accuracy. This paper discusses the effect of these three errors on compensation accuracy and provides strategies to improve the final surface quality. Experimental verification was carried out on one piece of KDP crystal with the size of Φ270 mm×11 mm. After one compensation process, the peak-to-valley value of the transmitted wavefront error dropped from 1.9λ (λ=632.8 nm) to approximately 1/3λ, and the mid-spatial-frequency error does not become worse when the frequency of the cutting tool trajectory is controlled by use of a low-pass filter.

  15. Measures to minimize cross-contamination risks in Advanced Therapy Medicinal Product manufacturing

    Directory of Open Access Journals (Sweden)

    Livia Roseti

    2014-12-01

    Full Text Available Current European regulations define in vitro expanded cells for clinical purposes as substantially manipulated and include them in the class of Advanced Therapy Medicinal Products to be manufactured in compliance with current Good Manufacturing Practice. These quality requirements are generally thought to be elaborate and costly. However, they ensure three main product characteristics: safety, consistency, and absence of cross-contamination. The term crosscontamination is used to indicate misidentification of one cell line or culture by another. The Good Manufacturing Practice Guidelines suggest some recommendations in order to prevent cross-contaminations and require a demonstration that the implemented actions are effective. Here we report some practical examples useful both to minimize crosscontamination risks in an Advanced Therapy Medicinal Products production process and to evaluate the efficacy of the adopted measures.

  16. Advanced distillation curve measurements for corrosive fluids: Application to two crude oils

    Energy Technology Data Exchange (ETDEWEB)

    Lisa Starkey Ott; Beverly L. Smith; Thomas J. Bruno [National Institute of Standards and Technology, Boulder, CO (United States). Physical and Chemical Properties Division

    2008-10-15

    We have recently introduced several important improvements in the measurement of distillation curves for complex fluids. The modifications include a composition-explicit data channel for each distillate fraction (for both qualitative and quantitative analysis) and corrosivity assessment of each distillate fraction. The composition-explicit information is achieved with a new sampling approach that allows precise qualitative as well as quantitative analyses of each fraction, on the fly. We have applied the new method to a variety of fluids, including simple n-alkanes, rocket propellant, gasoline, jet fuels, and a hydrocarbon fluid made corrosive with dissolved hydrogen sulfide. In the current contribution, we present the application of the advanced distillation curve method to two samples of crude oil. A primary motivation behind the work is to precisely measure the distillation curves of these oils using our advanced distillation apparatus; these low uncertainty measurements of true thermodynamic state points can be used for equation of state development and differentiation of crude oil samples. Then, the information content of each distillation was extended much further by use of the composition-explicit data channel: gas chromatography-mass spectrometry (GC-MS), infrared spectrophotometry (IR), gas chromatography with sulfur chemiluminescence detection (GC-SCD), and the copper strip corrosion test (CSCT) were used for each distillate volume fraction sampled. Consequently, for each volume fraction of crude oil distillate sampled, we can address the composition, quantitate the total sulfur content, and measure the corrosivity. 39 refs., 6 figs., 2 tabs.

  17. Expected gain in the pyramid wavefront sensor with limited Strehl ratio

    Science.gov (United States)

    Viotto, V.; Ragazzoni, R.; Bergomi, M.; Magrin, D.; Farinato, J.

    2016-09-01

    Context. One of the main properties of the pyramid wavefront sensor is that, once the loop is closed, and as the reference star image shrinks on the pyramid pin, the wavefront estimation signal-to-noise ratio can considerably improve. This has been shown to translate into a gain in limiting magnitude when compared with the Shack-Hartmann wavefront sensor, in which the sampling on the wavefront is performed before the light is split into four quadrants, which does not allow the quality of the focused spot to increase. Since this property is strictly related to the size of the re-imaged spot on the pyramid pin, the better the wavefront correction, the higher the gain. Aims: The goal of this paper is to extend the descriptive and analytical computation of this gain that was given in a previous paper, to partial wavefront correction conditions, which are representative for most of the wide field correction adaptive optics systems. Methods: After focusing on the low Strehl ratio regime, we analyze the minimum spatial sampling required for the wavefront sensor correction to still experience a considerable gain in sensitivity between the pyramid and the Shack-Hartmann wavefront sensors. Results: We find that the gain can be described as a function of the sampling in terms of the Fried parameter.

  18. Sensitivity adjustable contouring by digital holography and a virtual reference wavefront

    Science.gov (United States)

    Cai, L. Z.; Liu, Q.; Yang, X. L.; Wang, Y. R.

    2003-06-01

    A new method of contouring using digital holography and a virtual reference wavefront is reported. In this method, an object wave is first recorded and then digitally reconstructed. At the same time, a reference wave is digitally introduced to interfere with the reconstructed object wave to form a contour pattern. Since the form or curvature of the reference wave can be arbitrarily designed and artificially generated by a computer, the contouring sensitivity (the depth interval) can be easily adjusted for different purpose. The effectiveness of this method has been verified by computer simulations with both the conventional off-axis hologram and the phase-shifting hologram. The simplicity of optical setup and the unique ability of changing contouring sensitivity in this technique make it attractive potential in practical measurements.

  19. In-focus wavefront sensing using non-redundant mask-induced pupil diversity

    CERN Document Server

    Greenbaum, Alexandra

    2016-01-01

    Wavefront estimation using in-focus image data is critical to many applications. This data is invariant to a sign flip with complex conjugation of the complex amplitude in the pupil, making for a non-unique solution. Information from an in-focus image taken through a non-redundant pupil mask (NRM) can break this ambiguity, enabling the true aberration to be determined. We demonstrate this by priming a full pupil Gerchberg-Saxton phase retrieval with NRM fringe phase information. We apply our method to measure simulated aberrations on the segmented James Webb Space Telescope (JWST) mirror using full pupil and NRM data from its Near Infrared Imager and Slitless Spectrograph (NIRISS).

  20. Correlation between Post-LASIK Starburst Symptom and Ocular Wavefront Aberrations

    Institute of Scientific and Technical Information of China (English)

    LIU Yong-Ji; MU Guo-Guang; WANG Zhao-Qi; WANG Yan

    2006-01-01

    Monochromatic aberrations in post laser in-situ keratomileusis (LASIK) eyes are measured. The data are categorized into reference group and starburst group according to the visual symptoms. Statistic analysis has been made to find the correJation between the ocular wavefront aberrations and the starburst symptom. The rms aberrations of the 3rd and 4th orders for the starburst group are significantly larger than those for the reference group. The starburst symptom shows a strong correlation with vertical coma, total coma, spherical aberrations. For 3-mm pupil size and 5.8-mm pupil size, the modulation transfer function (MTF) of the starburst group are lower than those of the reference group, but their visual acuities are close. MTF and PSF analyses are made for two groups, and the results are consistent with the statistical analysis, which means the difference between the two groups is mainly due to the third- and fourth-order Zernike aberrations.

  1. A Demonstration of Wavefront Sensing and Mirror Phasing from the Image Domain

    CERN Document Server

    Pope, Benjamin; Cheetham, Anthony; Martinache, Frantz; Norris, Barnaby; Tuthill, Peter

    2014-01-01

    In astronomy and microscopy, distortions in the wavefront affect the dynamic range of a high contrast imaging system. These aberrations are either imposed by a turbulent medium such as the atmosphere, by static or thermal aberrations in the optical path, or by imperfectly phased subapertures in a segmented mirror. Active and adaptive optics (AO), consisting of a wavefront sensor and a deformable mirror, are employed to address this problem. Nevertheless, the non-common-path between the wavefront sensor and the science camera leads to persistent quasi-static speckles that are difficult to calibrate and which impose a floor on the image contrast. In this paper we present the first experimental demonstration of a novel wavefront sensor requiring only a minor asymmetric obscuration of the pupil, using the science camera itself to detect high order wavefront errors from the speckle pattern produced. We apply this to correct errors imposed on a deformable microelectromechanical (MEMS) segmented mirror in a closed l...

  2. Analytical Model for Ring Heater Thermal Compensation in Advanced LIGO

    CERN Document Server

    Ramette, Joshua; Brooks, Aidan; Blair, Carl; Wang, Haoyu; Heintze, Matthew

    2015-01-01

    Advanced laser interferometer gravitational-wave detectors use high laser power to achieve design sensitivity. A small part of this power is absorbed in the interferometer cavity mirrors where it creates thermal lenses, causing aberrations in the main laser beam that must be minimized by the actuation of "ring heaters," additional heater elements that are aimed to reduce the temperature gradients in the mirrors. In this article we derive the first analytical model of the temperature field generated by an ideal ring heater. We express the resulting optical aberration contribution to the main laser beam in this axisymmetric case. Used in conjunction with wavefront measurements, our model provides a more complete understanding of the thermal state of the cavity mirrors and will allow a more efficient use of the ring heaters in Advanced LIGO.

  3. Advanced flow measurement and active flow control of aircraft with MEMS

    Institute of Scientific and Technical Information of China (English)

    Jiang Chengyu; Deng Jinjun; Ma Binghe; Yuan Weizheng

    2012-01-01

    Advanced flow measurement and active flow control need the development of new type devices and systems. Micro-electro-mechanical systems (MEMS) technologies become the important and feasible approach for micro transducers fabrication. This paper introduces research works of MEMS/NEMS Lab in flow measurement sensors and active flow control actuators. Micro sensors include the flexible thermal sensor array, capacitive shear stress sensor and high sensitivity pressure sensor. Micro actuators are the balloon actuator and synthetic jet actuator respectively. Through wind tunnel test, these micro transducers achieve the goals of shear stress and pressure distribution measurement, boundary layer separation control, lift enhancement, etc. And unmanned aerial vehicle (UAV) flight test verifies the ability of maneuver control of micro actuator. In the future work, micro sensor and actuator can be combined into a closed-loop control system to construct aerodynamic smart skin system for aircraft.

  4. Virtual charge state separator as an advanced tool coupling measurements and simulations

    Science.gov (United States)

    Yaramyshev, S.; Vormann, H.; Adonin, A.; Barth, W.; Dahl, L.; Gerhard, P.; Groening, L.; Hollinger, R.; Maier, M.; Mickat, S.; Orzhekhovskaya, A.

    2015-05-01

    A new low energy beam transport for a multicharge uranium beam will be built at the GSI High Current Injector (HSI). All uranium charge states coming from the new ion source will be injected into GSI heavy ion high current HSI Radio Frequency Quadrupole (RFQ), but only the design ions U4 + will be accelerated to the final RFQ energy. A detailed knowledge about injected beam current and emittance for pure design U4 + ions is necessary for a proper beam line design commissioning and operation, while measurements are possible only for a full beam including all charge states. Detailed measurements of the beam current and emittance are performed behind the first quadrupole triplet of the beam line. A dedicated algorithm, based on a combination of measurements and the results of advanced beam dynamics simulations, provides for an extraction of beam current and emittance values for only the U4 + component of the beam. The proposed methods and obtained results are presented.

  5. Applications of Advanced Nondestructive Measurement Techniques to Address Safety of Flight Issues on NASA Spacecraft

    Science.gov (United States)

    Prosser, Bill

    2016-01-01

    Advanced nondestructive measurement techniques are critical for ensuring the reliability and safety of NASA spacecraft. Techniques such as infrared thermography, THz imaging, X-ray computed tomography and backscatter X-ray are used to detect indications of damage in spacecraft components and structures. Additionally, sensor and measurement systems are integrated into spacecraft to provide structural health monitoring to detect damaging events that occur during flight such as debris impacts during launch and assent or from micrometeoroid and orbital debris, or excessive loading due to anomalous flight conditions. A number of examples will be provided of how these nondestructive measurement techniques have been applied to resolve safety critical inspection concerns for the Space Shuttle, International Space Station (ISS), and a variety of launch vehicles and unmanned spacecraft.

  6. Model-based aberration correction in a closed-loop wavefront-sensor-less adaptive optics system

    NARCIS (Netherlands)

    Song, H.; Fraanje, R.; Schitter, G.; Kroese, H.; Vdovin, G.; Verhaegen, M.

    2010-01-01

    In many scientific and medical applications, such as laser systems and microscopes, wavefront-sensor-less (WFSless) adaptive optics (AO) systems are used to improve the laser beam quality or the image resolution by correcting the wavefront aberration in the optical path. The lack of direct wavefront

  7. Wavefront modulation of water surface wave by a metasurface

    Science.gov (United States)

    Sun, Hai-Tao; Cheng, Ying; Wang, Jing-Shi; Liu, Xiao-Jun

    2015-10-01

    We design a planar metasurface to modulate the wavefront of a water surface wave (WSW) on a deep sub-wavelength scale. The metasurface is composed of an array of coiling-up-space units with specially designed parameters, and can take on the work of steering the wavefront when it is pierced into water. Like their acoustic counterparts, the modulation of WSW is ascribed to the gradient phase shift of the coiling-up-space units, which can be perfectly tuned by changing the coiling plate length and channel number inside the units. According to the generalized Snell’s law, negative refraction and ‘driven’ surface mode of WSW are also demonstrated at certain incidences. Specially, the transmitted WSW could be efficiently guided out by linking a symmetrically-corrugated channel in ‘driven’ surface mode. This work may have potential applications in water wave energy extraction and coastal protection. Project supported by the National Basic Research Program of China (Grant No. 2012CB921504), the National Natural Science Foundation of China (Grant Nos. 11474162, 11274171, 11274099, and 11204145), and the Specialized Research Fund for the Doctoral Program of Higher Education, China (Grant Nos. 20110091120040 and 20120091110001).

  8. Wavefront shaping based on three-dimensional optoacoustic feedback

    Science.gov (United States)

    Deán-Ben, X. L.; Estrada, Héctor; Ozbek, Ali; Razansky, Daniel

    2015-07-01

    Wavefront shaping techniques have recently evolved as a promising tool to control the light distribution in optically-scattering media. These techniques are based on spatially-modulating the phase of an incident light beam to create positive interference (focusing) at specific locations in the speckle pattern of the scattered wavefield. The optimum phase distribution (mask) of the spatial light modulator that allows focusing at the target location(s) is determined iteratively by monitoring the light intensity at such target. In this regard, optoacoustic (photoacoustic) imaging may provide the convenient advantage of simultaneous feedback information on light distribution in an entire region of interest. Herein, we showcase that volumetric optoacoustic images can effectively be used as a feedback mechanism in an iterative optimization algorithm allowing controlling the light distribution after propagation through a scattering sample. Experiments performed with absorbing microparticles distributed in a three-dimensional region showcase the feasibility of enhancing the light intensity at specific points. The advantages provided by optoacoustic imaging in terms of spatial and temporal resolution anticipate new capabilities of wavefront shaping techniques in biomedical optics.

  9. Fast modulation and dithering on a pyramid wavefront sensor bench

    Science.gov (United States)

    van Kooten, Maaike; Bradley, Colin; Veran, Jean-Pierre; Herriot, Glen; Lardiere, Olivier

    2016-07-01

    A pyramid wavefront sensor (PWFS) bench has been setup at NRC-Herzberg (Victoria, Canada) to investigate, first, the feasibility of a double roof prism PWFS, and second, test the proposed pyramid wavefront sensing methodology to be used in NFIRAOS for the Thirty Meter Telescope. Traditional PWFS require shallow angles and strict apex tolerances, making them difficult to manufacture. Roof prisms, on the other hand, are common optical components and can easily be made to the desired specifications. Understanding the differences between a double roof prism PWFS and traditional PWFS will allow for the double roof prism PWFS to become more widely used as an alternative to the standard pyramid, especially in a laboratory setting. In this work, the response of the double roof prism PWFS as the amount of modulation is changed, is compared to an ideal PWFS modelled using the adaptive optics toolbox, OOMAO in MATLAB. The object oriented toolbox uses physical optics to model complete AO systems. Fast modulation and dithering using a PI mirror has been implemented using a micro-controller to drive the mirror and trigger the camera. The various trade offs of this scheme, in a controlled laboratory environment, are studied and reported.

  10. Wavefront construction Kirchhoff migration with ray-amplitude corrections

    Energy Technology Data Exchange (ETDEWEB)

    Fehler, Michael C.; Hildebrand, S. T. (Steve T.); Huang, L. (Lian-Jie); Alde, D. M. (Douglas M.)

    2002-01-01

    Kirchhoff migration using ray tracing travel times has been a popular imaging method for many years. There are significant limitations in the ability of Kirchhoff migration using only first arrivals to reliably image regions of complex structure. Thus, new methods for imaging have been sought. One approach for improving imaging capability is to use ray tracing methods that allow the calculation of multiple-valued travel time tables to be used in migration. Additional improvements in ray-based imaging methods may be obtained by including amplitudes and phases of rays calculated using some ray tracing approach. One approach for calculating multiple-valued travel time tables along with estimates of amplitudes and phases is the use of wavefront construction ray tracing. We introduce our wavefront construction-based migration algorithm and present some example images obtained using the method. We compare the images obtained with those obtained using a dual-domain wave-equation migration method that we call Extended Local Rytov Fourier migration method.

  11. Optically sensitive Medipix2 detector for adaptive optics wavefront sensing

    CERN Document Server

    Vallerga, John; Tremsina, Anton; Siegmund, Oswald; Mikulec, Bettina; Clark, Allan G; CERN. Geneva

    2005-01-01

    A new hybrid optical detector is described that has many of the attributes desired for the next generation adaptive optics (AO) wavefront sensors. The detector consists of a proximity focused microchannel plate (MCP) read out by multi-pixel application specific integrated circuit (ASIC) chips developed at CERN ("Medipix2") with individual pixels that amplify, discriminate and count input events. The detector has 256 x 256 pixels, zero readout noise (photon counting), can be read out at 1 kHz frame rates and is abutable on 3 sides. The Medipix2 readout chips can be electronically shuttered down to a temporal window of a few microseconds with an accuracy of 10 ns. When used in a Shack-Hartmann style wavefront sensor, a detector with 4 Medipix chips should be able to centroid approximately 5000 spots using 7 x 7 pixel sub-apertures resulting in very linear, off-null error correction terms. The quantum efficiency depends on the optical photocathode chosen for the bandpass of interest.

  12. X-ray wavefront modeling of Bragg diffraction from crystals

    Science.gov (United States)

    Sutter, John P.

    2011-09-01

    The diffraction of an X-ray wavefront from a slightly distorted crystal can be modeled by the Takagi-Taupin theory, an extension of the well-known dynamical diffraction theory for perfect crystals. Maxwell's equations applied to a perturbed periodic medium yield two coupled differential equations in the incident and diffracted amplitude. These equations are discretized for numerical calculation into the determination of the two amplitudes on the points of an integration mesh, beginning with the incident amplitudes at the crystal's top surface. The result is a set of diffracted amplitudes on the top surface (in the Bragg geometry) or the bottom surface (in the Laue geometry), forming a wavefront that in turn can be propagated through free space using the Fresnel- Huygens equations. The performance of the Diamond Light Source I20 dispersive spectrometer has here been simulated using this method. Methods are shown for transforming displacements calculated by finite element analysis into local lattice distortions, and for efficiently performing 3-D linear interpolations from these onto the Takagi-Taupin integration mesh, allowing this method to be extended to crystals under thermal load or novel mechanical bender designs.

  13. PYRAMIR: Exploring the On-Sky Performance of the World’s First Near-Infrared Pyramid Wavefront Sensor

    Science.gov (United States)

    Peter, D.; Feldt, M.; Henning, T.; Hippler, S.; Aceituno, J.; Montoya, L.; Costa, J.; Dorner, B.

    2010-01-01

    This paper presents the on-sky performance of the unmodulated infrared pyramid wavefront sensor PYRAMIR mounted on the ALFA adaptive optics system at the 3.5 m telescope of the Calar Alto Observatory. The performance of the system is compared with the performance of the Shack-Hartmann wavefront sensor of the ALFA system. We carried out a series of measurements to characterize the performance of PYRAMIR under open-loop tip-tilt compensation, and high-order closed-loop conditions, using stars of different magnitudes. We measured the tip-tilt jitter by following the centroid position of a stellar image on a fast series of frames. Additionally from the pyramid wavefront sensor data we could estimate the tip-tilt jitter in closed-loop. Under closed-loop conditions we also measured the long-exposure Strehl ratio. We compared the results of the wavefront sensor measurements with those of the Shack-Hartmann sensor on the same telescope, especially regarding the distribution of the error budged over the Karhunen-Loève modes, and the power spectral density. Our first finding is that we can indeed start up this nonmodulated pyramid system, even under bad seeing conditions. Under good conditions the Strehl ratio reaches ≥60% in K‧ band. We found that the minimum signal-to-noise ratio (S/N) in each subaperture required to close the high-order loop is only 0.4. This is a surprisingly low number. To compare the performance to existing systems, we introduce the S/N per subaperture per loop cycle as a device-independent measure. Using this scheme, we find that the ratio between the low-order residuals and the high-order residuals in the case of PYRAMIR is lower than that of the Shack-Hartmann system, especially in the faint flux regime. This is an important finding because it means that the pyramid-based system removes the halo, i.e., light scattered by the atmosphere, around the target star better than a Shack-Hartmann sensor-based system. A comparison of the power spectral

  14. Measuring and Advancing Experimental Design Ability in an Introductory Course without Altering Existing Lab Curriculum†

    Science.gov (United States)

    Shanks, Ryan A.; Robertson, Chuck L.; Haygood, Christian S.; Herdliksa, Anna M.; Herdliska, Heather R.; Lloyd, Steven A.

    2017-01-01

    Introductory biology courses provide an important opportunity to prepare students for future courses, yet existing cookbook labs, although important in their own way, fail to provide many of the advantages of semester-long research experiences. Engaging, authentic research experiences aid biology students in meeting many learning goals. Therefore, overlaying a research experience onto the existing lab structure allows faculty to overcome barriers involving curricular change. Here we propose a working model for this overlay design in an introductory biology course and detail a means to conduct this lab with minimal increases in student and faculty workloads. Furthermore, we conducted exploratory factor analysis of the Experimental Design Ability Test (EDAT) and uncovered two latent factors which provide valid means to assess this overlay model’s ability to increase advanced experimental design abilities. In a pre-test/post-test design, we demonstrate significant increases in both basic and advanced experimental design abilities in an experimental and comparison group. We measured significantly higher gains in advanced experimental design understanding in students in the experimental group. We believe this overlay model and EDAT factor analysis contribute a novel means to conduct and assess the effectiveness of authentic research experiences in an introductory course without major changes to the course curriculum and with minimal increases in faculty and student workloads. PMID:28904647

  15. The measurement of response shift in patients with advanced prostate cancer and their partners

    Directory of Open Access Journals (Sweden)

    O'Boyle Ciaran

    2005-03-01

    Full Text Available Abstract Background There is increasing evidence to support the phenomenon of response shift (RS in quality of life (QoL studies, with many current QoL measures failing to allow for this. If significant response shift occurs amongst prostate cancer patients, it will be necessary to allow for this in the design of future clinical research and to reassess the conclusions of previous studies that have not allowed for this source of bias. This study therefore aimed to assess the presence of RS and psychosocial morbidity in patients with advanced prostate cancer and their partners. Methods 55 consecutive advanced prostate cancer patients and their partners completed the Prostate Cancer Patient & Partner questionnaire (PPP, shortly after diagnosis and again at 3 months and 6 months. At the follow-up visits, both patients and partners also completed a then-test in order to assess RS. Results Partners consistently showed greater psychological morbidity than patients in relation to the prostate cancer. This was most marked on the General Cancer Distress (GCD subscale (p Conclusion These results suggest the presence of RS in patients with advanced prostate cancer and their partners, with higher levels of psychosocial morbidity noted amongst partners. This is the first study to identify RS in partners and calls into question the interpretation of all studies assessing changes in QoL that fail to allow for this phenomenon.

  16. Measuring and Advancing Experimental Design Ability in an Introductory Course without Altering Existing Lab Curriculum

    Directory of Open Access Journals (Sweden)

    Ryan A. Shanks

    2017-05-01

    Full Text Available Introductory biology courses provide an important opportunity to prepare students for future courses, yet existing cookbook labs, although important in their own way, fail to provide many of the advantages of semester-long research experiences. Engaging, authentic research experiences aid biology students in meeting many learning goals. Therefore, overlaying a research experience onto the existing lab structure allows faculty to overcome barriers involving curricular change. Here we propose a working model for this overlay design in an introductory biology course and detail a means to conduct this lab with minimal increases in student and faculty workloads. Furthermore, we conducted exploratory factor analysis of the Experimental Design Ability Test (EDAT and uncovered two latent factors which provide valid means to assess this overlay model’s ability to increase advanced experimental design abilities. In a pre-test/post-test design, we demonstrate significant increases in both basic and advanced experimental design abilities in an experimental and comparison group. We measured significantly higher gains in advanced experimental design understanding in students in the experimental group. We believe this overlay model and EDAT factor analysis contribute a novel means to conduct and assess the effectiveness of authentic research experiences in an introductory course without major changes to the course curriculum and with minimal increases in faculty and student workloads.

  17. Measured performance of 12 demonstation projects - IEA Task 13 "advanced solar low energy buildings"

    DEFF Research Database (Denmark)

    Thomsen, Kirsten Engelund; Schultz, Jørgen Munthe; Poel, Bart

    2005-01-01

    This paper presents the results obtained from measurements and experiences gained from interviews on 12 advanced solar low energy houses designed and built as part of the IEA Solar Heating and Cooling Programme – Task 13. Three years after the IEA Task 13 formally ended, the results were collected...... % compared with typical houses was achieved. Prevention of overheating requires special attention also at northern lati-tudes. Interviews with occupants revealed the need to explain the building's behaviour thoroughly to its users and elaboration of user manuals....

  18. Measurements of neutron cross sections for advanced nuclear energy systems at n_TOF (CERN

    Directory of Open Access Journals (Sweden)

    Barbagallo M.

    2014-03-01

    Full Text Available The n_TOF facility operates at CERN with the aim of addressing the request of high accuracy nuclear data for advanced nuclear energy systems as well as for nuclear astrophysics. Thanks to the features of the neutron beam, important results have been obtained on neutron induced fission and capture cross sections of U, Pu and minor actinides. Recently the construction of another beam line has started; the new line will be complementary to the first one, allowing to further extend the experimental program foreseen for next measurement campaigns.

  19. Advancements in remote physiological measurement and applications in human-computer interaction

    Science.gov (United States)

    McDuff, Daniel

    2017-04-01

    Physiological signals are important for tracking health and emotional states. Imaging photoplethysmography (iPPG) is a set of techniques for remotely recovering cardio-pulmonary signals from video of the human body. Advances in iPPG methods over the past decade combined with the ubiquity of digital cameras presents the possibility for many new, lowcost applications of physiological monitoring. This talk will highlight methods for recovering physiological signals, work characterizing the impact of video parameters and hardware on these measurements, and applications of this technology in human-computer interfaces.

  20. Reconstructing the Poynting vector skew angle and wave-front of optical vortex beams via two-channel moir\\'e deflectometery

    CERN Document Server

    Yeganeh, Mohammad; Dashti, Mohsen; Slussarenko, Sergei; Santamato, Enrico; Karimi, Ebrahim

    2013-01-01

    A novel approach based on the two-channel moir\\'e deflectometry has been used to measure both wave-front and transverse component of the Poynting vector of an optical vortex beam. Generated vortex beam by the q-plate, an inhomogeneous liquid crystal cell, has been analyzed with such technique. The measured topological charge of generated beams are in an excellent agreement with theoretical prediction.

  1. Two immunochemical assays to measure advanced glycation end-products in serum from dialysis patients.

    Science.gov (United States)

    Zhang, Xiaohong; Frischmann, Matthias; Kientsch-Engel, Rose; Steinmann, Katharina; Stopper, Helga; Niwa, Toshimitsu; Pischetsrieder, Monika

    2005-01-01

    Advanced glycation end-products are uremic toxins that accumulate in the serum and tissues of patients with chronic renal failure. Here, we established two enzyme-linked immunosorbent assays (ELISAs) for N(epsilon)-carboxymethyllysine and imidazolone to analyze advanced glycation end-products in human serum. Both ELISAs detected advanced glycation end-products bound to human serum albumin in a dose-dependent way. Whereas the formation of imida-zolone was independent of the presence of oxygen, concentrations of N(epsilon)-carboxymethyllysine epitopes increased 20-fold under oxidative conditions. The N(epsilon)-carboxymethyllysine ELISA showed a similar response to free, peptide-bound and protein-bound N(epsilon)-carboxymethyllysine, whereas the imidazolone antibody showed slightly higher affinity toward peptide-bound compared to protein-bound imidazolone. In human serum, linear dilution ranges from 1:10 to 1:40 (N(epsilon)-carboxymethyllysine ELISA) and from 1:2 to 1:8 (imidazolone ELISA) were found. The recovery of N(epsilon)-carboxymethyllysine from serum was 101 +/- 10% and 94 +/- 12%, respectively, and 93 +/- 15% and 97 +/- 12% for imidazolone. The coefficients of variation for intra-assay variability were 0.26-2.7% (N(epsilon)-carboxymethyllysine) and 0.1-2.4% (imidazolone), and 8.3-13.4% (N(epsilon)-carboxymethyllysine) and 7.8-12.5% (imidazolone) for inter-assay variability. In serum samples from hemodialysis patients (n = 20) and controls (n =20), an approximately two-fold increase was detected in the patient group (p < 0.001). The combination of the N(epsilon)-carboxymethyllysine and imidazolone ELISAs is a valuable tool to measure serum concentrations of advanced glycation end-products for clinical studies.

  2. 12 CFR Appendix C to Part 3 - Capital Adequacy Guidelines for Banks: Internal-Ratings-Based and Advanced Measurement Approaches

    Science.gov (United States)

    2010-01-01

    ... loss must reflect the net present value of cash flows as of the default date using a discount rate...-Ratings-Based and Advanced Measurement Approaches C Appendix C to Part 3 Banks and Banking COMPTROLLER OF... Appendix C to Part 3—Capital Adequacy Guidelines for Banks: Internal-Ratings-Based and Advanced...

  3. Measurements of Bauschinger effect and transient behavior of a quenched and partitioned advanced high strength steel

    Energy Technology Data Exchange (ETDEWEB)

    Zang, Shun-lai, E-mail: shawn@mail.xjtu.edu.cn [School of Mechanical Engineering, Xi' an Jiaotong University, No. 28, Xianning Road, Xi' an, Shaanxi (China); Sun, Li [Manufacturing Process Research, General Motors China Science Lab, No. 56, Jinwan Road, Shanghai (China); Niu, Chao [School of Mechanical Engineering, Xi' an Jiaotong University, No. 28, Xianning Road, Xi' an, Shaanxi (China)

    2013-12-01

    In recent decades, the needs for new advanced high strength steels (AHSS) with high ductility and strength have rapidly increased to achieve the targets of more fuel-efficient and safer vehicles in automotive industry. However, several undesirable phenomena are experimentally observed during the forming of such materials, particularly with complex loading and large plastic deformation. Springback is one of the most important problems that should be compensated in sheet metal forming process. In this paper, we investigated the hardening behavior of a Q and P (quench and partitioning) steel designated by QP980CR, which is a new third generation advance high strength steel, from the Baosteel Group Corp. in Shanghai, China. The uni-axial tensile and cyclic simple shear tests were conducted. The uni-axial tensile tests were performed on the specimens at 0°, 45° and 90° to rolling direction (RD). The flow stress and transverse strain evolution were obtained in view of the digital image correlation (DIC) measurement. The plastic anisotropy was optimized from the uni-axial tensile tests and thereafter incorporated into the simulations of cyclic simple shear tests. The cyclic simple shear tests were conducted with three prestrains to measure the Bauschinger effect, transient behavior and permanent softening, and to determine the material parameters of the combined isotropic-kinematic hardening model.

  4. Advances in quantitative hepcidin measurements by time-of-flight mass spectrometry.

    Directory of Open Access Journals (Sweden)

    Dorine W Swinkels

    Full Text Available Assays for the detection of the iron regulatory hormone hepcidin in plasma or urine have not yet been widely available, whereas quantitative comparisons between hepcidin levels in these different matrices were thus far even impossible due to technical restrictions. To circumvent these limitations, we here describe several advances in time-of flight mass spectrometry (TOF MS, the most important of which concerned spiking of a synthetic hepcidin analogue as internal standard into serum and urine samples. This serves both as a control for experimental variation, such as recovery and matrix-dependent ionization and ion suppression, and at the same time allows value assignment to the measured hepcidin peak intensities. The assay improvements were clinically evaluated using samples from various patients groups and its relevance was further underscored by the significant correlation of serum hepcidin levels with serum iron indices in healthy individuals. Most importantly, this approach allowed kinetic studies as illustrated by the paired analyses of serum and urine samples, showing that more than 97% of the freely filtered serum hepcidin can be reabsorbed in the kidney. Thus, the here reported advances in TOF MS-based hepcidin measurements represent critical steps in the accurate quantification of hepcidin in various body fluids and pave the way for clinical studies on the kinetic behavior of hepcidin in both healthy and diseased states.

  5. Spectral and Wavefront Error Performance of WFIRST/AFTA Prototype Filters

    Science.gov (United States)

    Quijada, Manuel; Seide, Laurie; Marx, Cathy; Pasquale, Bert; McMann, Joseph; Hagopian, John; Dominguez, Margaret; Gong, Qian; Morey, Peter

    2016-01-01

    The Cycle 5 design baseline for the Wide-Field Infrared Survey Telescope Astrophysics Focused Telescope Assets (WFIRSTAFTA) instrument includes a single wide-field channel (WFC) instrument for both imaging and slit-less spectroscopy. The only routinely moving part during scientific observations for this wide-field channel is the element wheel (EW) assembly. This filter-wheel assembly will have 8 positions that will be populated with 6 bandpass filters, a blank position, and a Grism that will consist of a three-element assembly to disperse the full field with an undeviated central wavelength for galaxy redshift surveys. All filter elements in the EW assembly will be made out of fused silica substrates (110 mm diameter) that will have the appropriate bandpass coatings according to the filter designations (Z087, Y106, J129, H158, F184, W149 and Grism). This paper presents and discusses the performance (including spectral transmission and reflectedtransmitted wavefront error measurements) of a subset of bandpass filter coating prototypes that are based on the WFC instrument filter compliment. The bandpass coating prototypes that are tested in this effort correspond to the Z087, W149, and Grism filter elements. These filter coatings have been procured from three different vendors to assess the most challenging aspects in terms of the in-band throughput, out of band rejection (including the cut-on and cutoff slopes), and the impact the wavefront error distortions of these filter coatings will have on the imaging performance of the de-field channel in the WFIRSTAFTA observatory.

  6. Spectral and Wavefront Error Performance of WFIRST-AFTA Bandpass Filter Coating Prototypes

    Science.gov (United States)

    Quijada, Manuel A.; Seide, Laurie; Pasquale, Bert A.; McMann, Joseph C.; Hagopian, John G.; Dominguez, Margaret Z.; Gong, Quian; Marx, Catherine T.

    2016-01-01

    The Cycle 5 design baseline for the Wide-Field Infrared Survey Telescope Astrophysics Focused Telescope Assets (WFIRST/AFTA) instrument includes a single wide-field channel (WFC) instrument for both imaging and slit-less spectroscopy. The only routinely moving part during scientific observations for this wide-field channel is the element wheel (EW) assembly. This filter-wheel assembly will have 8 positions that will be populated with 6 bandpass filters, a blank position, and a Grism that will consist of a three-element assembly to disperse the full field with an undeviated central wavelength for galaxy redshift surveys. All filter elements in the EW assembly will be made out of fused silica substrates (110 mm diameter) that will have the appropriate bandpass coatings according to the filter designations (Z087, Y106, J129, H158, F184, W149 and Grism). This paper presents and discusses the performance (including spectral transmission and reflected/transmitted wavefront error measurements) of a subset of bandpass filter coating prototypes that are based on the WFC instrument filter compliment. The bandpass coating prototypes that are tested in this effort correspond to the Z087, W149, and Grism filter elements. These filter coatings have been procured from three different vendors to assess the most challenging aspects in terms of the in-band throughput, out of band rejection (including the cut-on and cutoff slopes), and the impact the wavefront error distortions of these filter coatings will have on the imaging performance of the wide-field channel in the WFIRST/AFTA observatory.

  7. Advancing the extended parallel process model through the inclusion of response cost measures.

    Science.gov (United States)

    Rintamaki, Lance S; Yang, Z Janet

    2014-01-01

    This study advances the Extended Parallel Process Model through the inclusion of response cost measures, which are drawbacks associated with a proposed response to a health threat. A sample of 502 college students completed a questionnaire on perceptions regarding sexually transmitted infections and condom use after reading information from the Centers for Disease Control and Prevention on the health risks of sexually transmitted infections and the utility of latex condoms in preventing sexually transmitted infection transmission. The questionnaire included standard Extended Parallel Process Model assessments of perceived threat and efficacy, as well as questions pertaining to response costs associated with condom use. Results from hierarchical ordinary least squares regression demonstrated how the addition of response cost measures improved the predictive power of the Extended Parallel Process Model, supporting the inclusion of this variable in the model.

  8. Audio-band coating thermal noise measurement for Advanced LIGO with a multimode optical resonator

    Science.gov (United States)

    Gras, S.; Yu, H.; Yam, W.; Martynov, D.; Evans, M.

    2017-01-01

    In modern high precision optical instruments, such as in gravitational wave detectors or frequency references, thermally induced fluctuations in the reflective coatings can be a limiting noise source. This noise, known as coating thermal noise, can be reduced by choosing materials with low mechanical loss. Examination of new materials becomes a necessity in order to further minimize the coating thermal noise and thus improve sensitivity of next generation instruments. We present a novel approach to directly measure coating thermal noise using a high finesse folded cavity in which multiple Hermite-Gaussian modes coresonate. This method is used to probe surface fluctuations on the order 10-17 m /√{Hz } in the frequency range 30-400 Hz. We applied this technique to measure thermal noise and loss angle of the coating used in Advanced LIGO.

  9. Measuring neutron star tidal deformability with Advanced LIGO: black hole - neutron star binaries

    Science.gov (United States)

    Kumar, Prayush; Pürrer, Michael; Pfeiffer, Harald

    2017-01-01

    The pioneering observations of gravitational waves (GW) by Advanced LIGO have ushered us into an era of observational GW astrophysics. Compact binaries remain the primary target sources for GW observations, of which black hole - neutron star (BHNS) binaries form an important subset. GWs from coalescing BHNS systems carry signatures of the tidal distortion of the neutron star by its companion black hole during inspiral, as well as of its disruption close to merger. In this talk, I will discuss how well we can measure tidal effects from individual and populations of LIGO observations of disruptive BHNS mergers. I will also talk about how our measurements of non-tidal parameters can get affected by ignoring tidal effects in BHNS parameter estimation.

  10. Comparing three different approaches to the measurement of needs concerning fatigue in patients with advanced cancer

    DEFF Research Database (Denmark)

    Madsen, Ulla Riis; Groenvold, Mogens; Petersen, Morten Aagaard

    2015-01-01

    PURPOSE: To identify patients having fatigue, it is necessary to assess the patients fatigue systematically. This study investigates three different approaches to the assessment of needs concerning fatigue in patients with advanced cancer and addresses the following questions. METHODS: In a cross......-sectional nationwide survey, patients were asked about their needs concerning fatigue in three different ways: Fatigue intensity was measured with the European Organisation for Research and Treatment of Cancer quality of life questionnaire, fatigue burden (the extent fatigue was a problem) and fatigue felt need...... (whether the patient experienced an unmet need regarding their fatigue) was measured with the Three-Levels-of-Needs Questionnaire. The relations between these three approaches were investigated using cross-tabulations, polychromic correlations, receiver operating curves, and area under the curve. RESULTS...

  11. Measurements of the subcriticality using advanced technique of shooting source during operation of NPP reactors

    Science.gov (United States)

    Lebedev, G. V.; Petrov, V. V.; Bobylyov, V. T.; Butov, R. I.; Zhukov, A. M.; Sladkov, A. A.

    2014-12-01

    According to the rules of nuclear safety, the measurements of the subcriticality of reactors should be carried out in the process of performing nuclear hazardous operations. An advanced technique of shooting source of neutrons is proposed to meet this requirement. As such a source, a pulsed neutron source (PNS) is used. In order to realize this technique, it is recommended to enable a PNS with a frequency of 1-20 Hz. The PNS is stopped after achieving a steady-state (on average) number of neutrons in the reactor volume. The change in the number of neutrons in the reactor volume is measured in time with an interval of discreteness of ˜0.1 s. The results of these measurements with the application of a system of point-kinetics equations are used in order to calculate the sought subcriticality. The basic idea of the proposed technique used to measure the subcriticality is elaborated in a series of experiments on the Kvant assembly. The conditions which should be implemented in order to obtain a positive result of measurements are formulated. A block diagram of the basic version of the experimental setup is presented, whose main element is a pulsed neutron generator.

  12. Wave-front error breakdown in laser guide star multi-object adaptive optics validated on-sky by Canary

    Science.gov (United States)

    Martin, O. A.; Gendron, É.; Rousset, G.; Gratadour, D.; Vidal, F.; Morris, T. J.; Basden, A. G.; Myers, R. M.; Correia, C. M.; Henry, D.

    2017-01-01

    Context. Canary is the multi-object adaptive optics (MOAO) on-sky pathfinder developed in the perspective of multi-object spectrograph on extremely large telescopes (ELTs). In 2013, Canary was operated on-sky at the William Herschel telescope (WHT), using three off-axis natural guide stars (NGS) and four off-axis Rayleigh laser guide stars (LGS), in open-loop, with the on-axis compensated turbulence observed with a H-band imaging camera and a Truth wave-front sensor (TS) for diagnostic purposes. Aims: Our purpose is to establish a reliable and accurate wave-front error breakdown for LGS MOAO. This will enable a comprehensive analysis of Canary on-sky results and provide tools for validating simulations of MOAO systems for ELTs. Methods: To evaluate the MOAO performance, we compared the Canary on-sky results running in MOAO, in single conjugated adaptive optics (SCAO) and in ground layer adaptive optics (GLAO) modes, over a large set of data acquired in 2013. We provide a statistical study of the seeing. We also evaluated the wave-front error breakdown from both analytic computations, one based on a MOAO system modelling and the other on the measurements from the Canary TS. We have focussed especially on the tomographic error and we detail its vertical error decomposition. Results: We show that Canary obtained 30.1%, 21.4% and 17.1% H-band Strehl ratios in SCAO, MOAO and GLAO respectively, for median seeing conditions with 0.66'' of total seeing including 0.59'' at the ground. Moreover, we get 99% of correlation over 4500 samples, for any AO modes, between two analytic computations of residual phase variance. Based on these variances, we obtain a reasonable Strehl-ratio (SR) estimation when compared to the measured IR image SR. We evaluate the gain in compensation for the altitude turbulence brought by MOAO when compared to GLAO.

  13. Fine cophasing of segmented aperture telescopes with ZELDA, a Zernike wavefront sensor in the diffraction-limited regime

    Science.gov (United States)

    Janin-Potiron, P.; N'Diaye, M.; Martinez, P.; Vigan, A.; Dohlen, K.; Carbillet, M.

    2017-07-01

    Context. Segmented aperture telescopes require an alignment procedure with successive steps from coarse alignment to monitoring process in order to provide very high optical quality images for stringent science operations such as exoplanet imaging. The final step, referred to as fine phasing, calls for a high sensitivity wavefront sensing and control system in a diffraction-limited regime to achieve segment alignment with nanometric accuracy. In this context, Zernike wavefront sensors represent promising options for such a calibration. A concept called the Zernike unit for segment phasing (ZEUS) was previously developed for ground-based applications to operate under seeing-limited images. Such a concept is, however, not suitable for fine cophasing with diffraction-limited images. Aims: We revisit ZELDA, a Zernike sensor that was developed for the measurement of residual aberrations in exoplanet direct imagers, to measure segment piston, tip, and tilt in the diffraction-limited regime. Methods: We introduce a novel analysis scheme of the sensor signal that relies on piston, tip, and tilt estimators for each segment, and provide probabilistic insights to predict the success of a closed-loop correction as a function of the initial wavefront error. Results: The sensor unambiguously and simultaneously retrieves segment piston and tip-tilt misalignment. Our scheme allows for correction of these errors in closed-loop operation down to nearly zero residuals in a few iterations. This sensor also shows low sensitivity to misalignment of its parts and high ability for operation with a relatively bright natural guide star. Conclusions: Our cophasing sensor relies on existing mask technologies that make the concept already available for segmented apertures in future space missions.

  14. MPACT FY2011 Advanced Time-Correlated Measurement Research at INL

    Energy Technology Data Exchange (ETDEWEB)

    D. L. Chichester; S. A. Pozzi; J. L. Dolan; M. Flaska; S. M. Watson

    2011-09-01

    Simulations and experiments have been carried out to investigate advanced time-correlated measurement methods for characterizing and assaying nuclear material for safeguarding the nuclear fuel cycle. These activities are part of a project studying advanced instrumentation techniques in support of the U.S. Department of Energy's Fuel Cycle Research and Development program and its Materials Protection, Accounting, and Control Technologies (MPACT) program. For fiscal year 2011 work focused on examining the practical experimental aspects of using a time-tagged, associated-particle electronic neutron generator for interrogating low-enrichment uranium in combination with steady-state interrogation using a moderated 241Am-Li neutron source. Simulation work for the project involved the use of the MCNP-PoliMi Monte Carlo simulation tool to determine the relative strength and the time-of-flight energy spectra of different sample materials under irradiation. Work also took place to develop a post-processor parser code to extract comparable data from the MCNP5&6 codes. Experiments took place using a commercial deuterium-tritium associated-particle electronic neutron generator to irradiate a number of uranium-bearing material samples. Time-correlated measurements of neutron and photon signatures of these measurements were made using five liquid scintillator detectors in a novel array, using high-speed waveform digitizers for data collection. This report summarizes the experiments that took place in FY2011, presents preliminary analyses that have been carried out to date for a subpart of these experiments, and describes future activities planned in this area. The report also describes support Idaho National Laboratory gave to Oak Ridge National Laboratory in 2011 to facilitate 2-dimensional imagery of mixed-oxide fuel pins for safeguards applications as a part of the MPACT program.

  15. Broadband reflected wavefronts manipulation using structured phase gradient metasurfaces

    Science.gov (United States)

    Wang, Xiao-Peng; Wan, Le-Le; Chen, Tian-Ning; Song, Ai-Ling; Du, Xiao-Wen

    2016-06-01

    Acoustic metasurface (AMS) is a good candidate to manipulate acoustic waves due to special acoustic performs that cannot be realized by traditional materials. In this paper, we design the AMS by using circular-holed cubic arrays. The advantages of our AMS are easy assemble, subwavelength thickness, and low energy loss for manipulating acoustic waves. According to the generalized Snell's law, acoustic waves can be manipulated arbitrarily by using AMS with different phase gradients. By selecting suitable hole diameter of circular-holed cube (CHC), some interesting phenomena are demonstrated by our simulations based on finite element method, such as the conversion of incoming waves into surface waves, anomalous reflections (including negative reflection), acoustic focusing lens, and acoustic carpet cloak. Our results can provide a simple approach to design AMSes and use them in wavefront manipulation and manufacturing of acoustic devices.

  16. Multicore-Optimized Wavefront Diamond Blocking for Optimizing Stencil Updates

    KAUST Repository

    Malas, T.

    2015-07-02

    The importance of stencil-based algorithms in computational science has focused attention on optimized parallel implementations for multilevel cache-based processors. Temporal blocking schemes leverage the large bandwidth and low latency of caches to accelerate stencil updates and approach theoretical peak performance. A key ingredient is the reduction of data traffic across slow data paths, especially the main memory interface. In this work we combine the ideas of multicore wavefront temporal blocking and diamond tiling to arrive at stencil update schemes that show large reductions in memory pressure compared to existing approaches. The resulting schemes show performance advantages in bandwidth-starved situations, which are exacerbated by the high bytes per lattice update case of variable coefficients. Our thread groups concept provides a controllable trade-off between concurrency and memory usage, shifting the pressure between the memory interface and the CPU. We present performance results on a contemporary Intel processor.

  17. Monotone traveling wavefronts of the KPP-Fisher delayed equation

    CERN Document Server

    Gomez, Adrian

    2010-01-01

    In the early 2000's, Gourley (2000), Wu et al. (2001), Ashwin et al. (2002) initiated the study of the positive wavefronts in the delayed Kolmogorov-Petrovskii-Piskunov-Fisher equation. Since then, this model has become one of the most popular objects in the studies of traveling waves for the monostable delayed reaction-diffusion equations. In this paper, we give a complete solution to the problem of existence and uniqueness of monotone waves in the KPP-Fisher equation. We show that each monotone traveling wave can be found via an iteration procedure. The proposed approach is based on the use of special monotone integral operators (which are different from the usual Wu-Zou operator) and appropriate upper and lower solutions associated to them. The analysis of the asymptotic expansions of the eventual traveling fronts at infinity is another key ingredient of our approach.

  18. A comparison report of three advanced methods for drug-cyclodextrin interaction measurements.

    Science.gov (United States)

    Singh, Vikramjeet; He, Yaping; Wang, Caifen; Xu, Jianghui; Xu, Xiaonan; Li, Haiyan; Singh, Parbeen; York, Peter; Sun, Lixin; Zhang, Jiwen

    2017-02-05

    Three advanced methods, high performance affinity chromatography (HPAC), surface plasmon resonance (SPR) and surface plasmon resonance imaging (SPRi) were compared and evaluated for determining the drug-cyclodextrin (CD) interactions herein. In total, 18 sparingly soluble drugs were selected for this comparative study. The three methods share a unique connection in the working principles and strategies. The same strategies of CD fixation onto solid phase were used in HPAC and SPR for the measurements, whereas, the SPR and SPRi share identical working principles. However, whilst these relationships are evident, no strong correlation was found between kinetic constants obtained from the three methods: Four drugs, namely, prednisolone, pseudolaric acid B, diazepam and gramisetron failed to show any response on SPR, whereas, the kinetics parameters from SPRi and HPAC were successfully measured. From a comparative review of all the kinetic data, random results without any trends were observed (ka, kd and KA) regardless of the relationships between the three methods: It is apparent that the measurement conditions (volume, flow rate, buffers), non-specific adsorption and experimental procedures had a strong impact on the generated data. The relative advantages and limitations of each method are critically presented on the basis of generated data. This comparative study provides a basis to further upgrade these techniques for confident measurement of drug-CDs interactions. Copyright © 2016 Elsevier B.V. All rights reserved.

  19. Advancements in Root Growth Measurement Technologies and Observation Capabilities for Container-Grown Plants

    Directory of Open Access Journals (Sweden)

    Lesley A. Judd

    2015-07-01

    Full Text Available The study, characterization, observation, and quantification of plant root growth and root systems (Rhizometrics has been and remains an important area of research in all disciplines of plant science. In the horticultural industry, a large portion of the crops grown annually are grown in pot culture. Root growth is a critical component in overall plant performance during production in containers, and therefore it is important to understand the factors that influence and/or possible enhance it. Quantifying root growth has varied over the last several decades with each method of quantification changing in its reliability of measurement and variation among the results. Methods such as root drawings, pin boards, rhizotrons, and minirhizotrons initiated the aptitude to measure roots with field crops, and have been expanded to container-grown plants. However, many of the published research methods are monotonous and time-consuming. More recently, computer programs have increased in use as technology advances and measuring characteristics of root growth becomes easier. These programs are instrumental in analyzing various root growth characteristics, from root diameter and length of individual roots to branching angle and topological depth of the root architecture. This review delves into the expanding technologies involved with expertly measuring root growth of plants in containers, and the advantages and disadvantages that remain.

  20. Fast wavefront optimization for focusing through biological tissue (Conference Presentation)

    Science.gov (United States)

    Blochet, Baptiste; Bourdieu, Laurent; Gigan, Sylvain

    2017-02-01

    The propagation of light in biological tissues is rapidly dominated by multiple scattering: ballistic light is exponentially attenuated, which limits the penetration depth of conventional microscopy techniques. For coherent light, the recombination of the different scattered paths creates a complex interference: speckle. Recently, different wavefront shaping techniques have been developed to coherently manipulate the speckle. It opens the possibility to focus light through complex media and ultimately to image in them, provided however that the medium can be considered as stationary. We have studied the possibility to focus in and through time-varying biological tissues. Their intrinsic temporal dynamics creates a fast decorrelation of the speckle pattern. Therefore, focusing through biological tissues requires fast wavefront shaping devices, sensors and algorithms. We have investigated the use of a MEMS-based spatial light modulator (SLM) and a fast photodetector, combined with FPGA electronics to implement a closed-loop optimization. Our optimization process is just limited by the temporal dynamics of the SLM (200µs) and the computation time (45µs), thus corresponding to a rate of 4 kHz. To our knowledge, it's the fastest closed loop optimization using phase modulators. We have studied the focusing through colloidal solutions of TiO2 particles in glycerol, allowing tunable temporal stability, and scattering properties similar to biological tissues. We have shown that our set-up fulfills the required characteristics (speed, enhancement) to focus through biological tissues. We are currently investigating the focusing through acute rat brain slices and the memory effect in dynamic scattering media.

  1. Operation modes of a liquid-crystal modal wave-front corrector.

    Science.gov (United States)

    Loktev, Mikhail; Vdovin, Gleb; Guralnik, Igor

    2004-04-10

    Liquid-crystal modal wave-front correctors provide much better wave-front correction than do piston correctors with the same number of actuators; moreover, use of additional degrees of freedom of the driving ac voltage signals may further improve device performance. Some practical aspects of the operation of liquid-crystal modal wave-front correctors are discussed. Special attention is paid to the interference of various contact responses and to the formation of required phase shapes through wider control of signal frequencies and electric phase shifts. The study is based on an analytic approach and numerical investigation; major theoretical conclusions are verified experimentally.

  2. The DeMi CubeSat: Wavefront Control with a MEMS Deformable Mirror in Space

    Science.gov (United States)

    Douglas, Ewan S.; Bendek, Eduardo; Marinan, Anne; Belikov, Ruslan; Merck, John; Cahoy, Kerri Lynn

    2017-01-01

    High-contrast imaging instruments on future space telescopes will require precise wavefront correction to detect small exoplanets near their host stars. High-actuator count microelectromechanical system (MEMS) deformable mirrors provide a compact form of wavefront control. The 6U DeMi CubeSat will demonstrate wavefront control with a MEMS deformable mirror over a yearlong mission. The payload includes both an internal laser source and a small telescope, with both focal plane and pupil plane sensing, for deformable mirror characterization. We detail the DeMi payload design, and describe future astrophysics enabled by high-actuator count deformable mirrors and small satellites.

  3. Collaborative effects of wavefront shaping and optical clearing agent in optical coherence tomography

    CERN Document Server

    Yu, Hyeonseung; Jo, YoungJu; Lee, KyeoReh; Tuchin, Valery V; Jeong, Yong; Park, YongKeun

    2016-01-01

    We demonstrate that simultaneous application of optical clearing agents (OCAs) and complex wavefront shaping in optical coherence tomography (OCT) can provide significant enhancement of the penetration depth and imaging quality. OCA reduces optical inhomogeneity of a highly scattering sample, and the wavefront shaping of illumination light controls multiple scattering, resulting in an enhancement of the penetration depth and signal-to-noise ratio. A tissue phantom study shows that concurrent applications of OCA and wavefront shaping successfully operate in OCT imaging. The penetration depth enhancement is further demonstrated for ex vivo mouse ears, revealing hidden structures inaccessible with conventional OCT imaging.

  4. Wavefront sensing for deformable space-based optics exploiting natural and synthetic guide stars

    Science.gov (United States)

    McComas, Brian K.; Friedman, Edward J.

    2002-08-01

    Natural and synthetic guide stars can serve as beacons for Shack-Hartmann wavefront sensors in space-based applications. In this paper, the authors determine the key equations that govern the optimization of the wavefront sensor employed on a space- based imaging system. There are two major products of this analysis. First, the number of subapertures can be optimized. Second, the number of modes used in the wavefront recovery can be optimized. Finally, the process for optimizing these values is explained. For the examples shown, the optimal number of retrieved modes and the optimal number of subapertures are determined.

  5. Advanced intensity-modulation continuous-wave lidar techniques for ASCENDS CO2 column measurements

    Science.gov (United States)

    Campbell, Joel F.; Lin, Bing; Nehrir, Amin R.; Harrison, F. W.; Obland, Michael D.; Meadows, Byron

    2015-10-01

    Global atmospheric carbon dioxide (CO2) measurements for the NASA Active Sensing of CO2 Emissions over Nights, Days, and Seasons (ASCENDS) space mission are critical for improving our understanding of global CO2 sources and sinks. Advanced Intensity- Modulated Continuous-Wave (IM-CW) lidar techniques are investigated as a means of facilitating CO2 measurements from space to meet the ASCENDS measurement requirements. In recent numerical, laboratory and flight experiments we have successfully used the Binary Phase Shift Keying (BPSK) modulation technique to uniquely discriminate surface lidar returns from intermediate aerosol and cloud contamination. We demonstrate the utility of BPSK to eliminate sidelobes in the range profile as a means of making Integrated Path Differential Absorption (IPDA) column CO2 measurements in the presence of optically thin clouds, thereby eliminating the need to correct for sidelobe bias errors caused by the clouds. Furthermore, high accuracy and precision ranging to the surface as well as to the top of intermediate cloud layers, which is a requirement for the inversion of column CO2 number density measurements to column CO2 mixing ratios, has been demonstrated using new hyperfine interpolation techniques that takes advantage of the periodicity of the modulation waveforms. This approach works well for both BPSK and linear swept-frequency modulation techniques. The BPSK technique under investigation has excellent auto-correlation properties while possessing a finite bandwidth. A comparison of BPSK and linear swept-frequency is also discussed in this paper. These results are extended to include Richardson-Lucy deconvolution techniques to extend the resolution of the lidar beyond that implied by limit of the bandwidth of the modulation, where it is shown useful for making tree canopy measurements.

  6. Advanced Intensity-Modulation Continuous-Wave Lidar Techniques for ASCENDS O2 Column Measurements

    Science.gov (United States)

    Campbell, Joel F.; Lin, Bing; Nehrir, Amin R.; Harrison, F. Wallace; Obland, Michael D.; Meadows, Byron

    2015-01-01

    Global atmospheric carbon dioxide (CO2) measurements for the NASA Active Sensing of CO2 Emissions over Nights, Days, and Seasons (ASCENDS) space mission are critical for improving our understanding of global CO2 sources and sinks. Advanced Intensity- Modulated Continuous-Wave (IM-CW) lidar techniques are investigated as a means of facilitating CO2 measurements from space to meet the ASCENDS measurement requirements. In recent numerical, laboratory and flight experiments we have successfully used the Binary Phase Shift Keying (BPSK) modulation technique to uniquely discriminate surface lidar returns from intermediate aerosol and cloud contamination. We demonstrate the utility of BPSK to eliminate sidelobes in the range profile as a means of making Integrated Path Differential Absorption (IPDA) column CO2 measurements in the presence of optically thin clouds, thereby eliminating the need to correct for sidelobe bias errors caused by the clouds. Furthermore, high accuracy and precision ranging to the surface as well as to the top of intermediate cloud layers, which is a requirement for the inversion of column CO2 number density measurements to column CO2 mixing ratios, has been demonstrated using new hyperfine interpolation techniques that takes advantage of the periodicity of the modulation waveforms. This approach works well for both BPSK and linear swept-frequency modulation techniques. The BPSK technique under investigation has excellent auto-correlation properties while possessing a finite bandwidth. A comparison of BPSK and linear swept-frequency is also discussed in this paper. These results are extended to include Richardson-Lucy deconvolution techniques to extend the resolution of the lidar beyond that implied by limit of the bandwidth of the modulation, where it is shown useful for making tree canopy measurements.

  7. Investigation of the isoplanatic patch and wavefront aberration along the pupillary axis compared to the line of sight in the eye

    OpenAIRE

    Nowakowski, Maciej; Sheehan, Matthew; Neal, Daniel; Goncharov, Alexander V.

    2012-01-01

    Conventional optical systems usually provide best image quality on axis, while showing unavoidable gradual decrease in image quality towards the periphery of the field. The optical system of the human eye is not an exception. Within a limiting boundary the image quality can be considered invariant with field angle, and this region is known as the isoplanatic patch. We investigate the isoplanatic patch of eight healthy eyes and measure the wavefront aberration along the pupillary axis compared...

  8. Wavefront sensorless adaptive optics versus sensor-based adaptive optics for in vivo fluorescence retinal imaging (Conference Presentation)

    Science.gov (United States)

    Wahl, Daniel J.; Zhang, Pengfei; Jian, Yifan; Bonora, Stefano; Sarunic, Marinko V.; Zawadzki, Robert J.

    2017-02-01

    Adaptive optics (AO) is essential for achieving diffraction limited resolution in large numerical aperture (NA) in-vivo retinal imaging in small animals. Cellular-resolution in-vivo imaging of fluorescently labeled cells is highly desirable for studying pathophysiology in animal models of retina diseases in pre-clinical vision research. Currently, wavefront sensor-based (WFS-based) AO is widely used for retinal imaging and has demonstrated great success. However, the performance can be limited by several factors including common path errors, wavefront reconstruction errors and an ill-defined reference plane on the retina. Wavefront sensorless (WFS-less) AO has the advantage of avoiding these issues at the cost of algorithmic execution time. We have investigated WFS-less AO on a fluorescence scanning laser ophthalmoscopy (fSLO) system that was originally designed for WFS-based AO. The WFS-based AO uses a Shack-Hartmann WFS and a continuous surface deformable mirror in a closed-loop control system to measure and correct for aberrations induced by the mouse eye. The WFS-less AO performs an open-loop modal optimization with an image quality metric. After WFS-less AO aberration correction, the WFS was used as a control of the closed-loop WFS-less AO operation. We can easily switch between WFS-based and WFS-less control of the deformable mirror multiple times within an imaging session for the same mouse. This allows for a direct comparison between these two types of AO correction for fSLO. Our results demonstrate volumetric AO-fSLO imaging of mouse retinal cells labeled with GFP. Most significantly, we have analyzed and compared the aberration correction results for WFS-based and WFS-less AO imaging.

  9. Using saliva to measure endogenous cortisol in nursing home residents with advanced dementia.

    Science.gov (United States)

    Woods, Diana Lynn; Kovach, Christine R; Raff, Hershel; Joosse, Laura; Basmadjian, Alicia; Hegadoren, Kathleen M

    2008-06-01

    Two research teams determined the feasibility of saliva collection for cortisol measurement in nursing home residents with advanced dementia. Study aims were to: (a) determine if sufficient saliva could be obtained for assay and (b) examine whether cortisol values exhibited range and variability for meaningful interpretation. Useable samples were consistent across sites, suggesting that saliva collection for cortisol assay is a viable method in this setting. Cortisol values showed range and variability. More than half of the residents showed the normal adult pattern of high morning levels decreasing throughout the day. A third of the participants demonstrated an increase in the evening cortisol levels, while the remaining profiles were flat, suggesting hypothalamic-pituitary-adrenal (HPA) dysregulation in this population.

  10. Recent Beam Measurements and New Instrumentation at the Advanced Light Source

    Energy Technology Data Exchange (ETDEWEB)

    Sannibale, F.; Baptiste, K.; Barry, W.; Chin, M.; /LBL, Berkeley; Filippetto, D.; /Frascati; Jaegerhofer, L.; /Vienna, Tech. U.; Julian, J.; Kwiatkowski, S.; Low, R.; Plate, D.; Portmann, G.; Robin, D.; Scarvie, T.; /LBL, Berkeley; Stupakov, G.; /SLAC; Weber, J.; Zolotorev, M.; /LBL, Berkeley

    2012-04-11

    The Advanced Light Source (ALS) in Berkeley was the first of the soft x-ray third generation light source ever built, and since 1993 has been in continuous and successful operation serving a large community of users in the VUV and soft x-ray community. During these years the storage ring underwent through several important upgrades that allowed maintaining the performance of this veteran facility at the forefront. The ALS beam diagnostics and instrumentation have followed a similar path of innovation and upgrade and nowadays include most of the modem and last generation devices and technologies that are commercially available and used in the recently constructed third generation light sources. In this paper we will not focus on such already widely known systems, but we will concentrate our effort in the description of some measurements techniques, instrumentation and diagnostic systems specifically developed at the ALS and used during the last few years.

  11. Measuring Antioxidant Activity in Bioorganic Samples by the Differential Oxygen Uptake Apparatus: Recent Advances

    Directory of Open Access Journals (Sweden)

    Riccardo Amorati

    2017-01-01

    Full Text Available The measure of O2 consumption during the inhibited autoxidation of an easily oxidizable substrate is one of the most reliable and predictive methods to assess antioxidant activity, especially for structure-activity relationship studies, for food and industrial applications. The differential oxygen uptake apparatus described herein represents a powerful and cost-effective way to obtain antioxidant activity from inhibited autoxidation studies. These experiments provide the rate constant and the stoichiometry of the reaction between antioxidants and peroxyl radicals (ROO∙, which are involved in the propagation of radical damage. We show the operation principles and the utility of this instrumentation in the bioorganic laboratory, with regard to the recent advances in this field, ranging from the study of natural antioxidants in biomimetic system, to the use of substrates generating hydroperoxyl radicals, and to the evaluation of novel nanoantioxidants.

  12. Measurements of nonlinear harmonic generation at the Advanced Photon Source's SASE FEL

    CERN Document Server

    Biedron, S G; Borland, M; Dejus, Roger J; Den Hartog, P K; Erdmann, M; Fawley, W M; Freund, H P; Gluskin, E; Huang, Z; Kim, K J; Lewellen, J W; Li, Y; Lumpkin, Alex H; Milton, S V; Moog, E; Nassiri, A; Sajaev, Vadim; Wiemerslage, G; Yang, B X

    2002-01-01

    SASE saturation was recently achieved at the Advanced Photon Source's SASE FEL in the low-energy undulator test line at 530 nm and 385 nm. The electron beam microbunching becomes more and more prominent until saturation is achieved. This bunching causes nonlinear harmonic emission that extends the usefulness of a SASE system in achieving shorter FEL wavelengths for the same electron beam energy. We have investigated the intensity of the fundamental and second harmonic undulator radiation as a function of distance along the undulator line and present the experimental results and compare them to numerical simulations. In addition, we have measured the single-shot second harmonic spectra as well as the simultaneous fundamental and second harmonic spectra and present the experimental results.

  13. Efficacy and toxicity in brain tumor treatment - quantitative Measurements using advanced MRI

    DEFF Research Database (Denmark)

    Ravn, Søren

    2016-01-01

    and are now being used for presurgical and radiation therapy (RT) planning. More advanced MRI sequences have gained attention. Sequences such as diffusion-weighted imaging (DWI), perfusion-weighted imaging (PWI) and functional magnetic resonance imaging (fMRI) have entered the clinical world concurrently......From the clinical introduction in the 1980s, MRI has grown to become an indispensable brain imaging modality, mainly due to its excellent ability to visualize soft tissues. Morphologically, T1- and T2-weighted brain tumor MRI have been part of routine diagnostic radiology for more than two decades...... with the introduction of magnets with higher field strength. Ongoing technical development has enabled a change from semiquantitative measurements to a true quantitative approach. This step is expected to have a great impact on the treatment of brain tumor patients in the future. The aim of this Ph.D. dissertation...

  14. Cruise noise of an advanced single-rotation propeller measured from an adjacent aircraft

    Science.gov (United States)

    Woodward, Richard P.; Loeffler, Irvin J.; Ranaudo, Richard J.

    1989-01-01

    Results are reported from flight measurements of the noise from a full-scale SR-7L advanced single-rotation turbofan model mounted on the wing of the NASA Lewis Propfan Test Assessment (PTA) aircraft (a modified Gulfstream II). Data obtained on the PTA with an outboard microphone boom and by the NASA Lewis acoustically instrumented Learjet flying along several sidelines relative to the PTA are presented in tables and graphs and briefly discussed. It is found that the PTA-boom and Learjet sound levels are in good agreement at Mach 0.69 and altitude 20,000 ft, but the Learjet values are significantly lower than the boom levels at Mach 0.79 and altitude 36,000 ft.

  15. Differential precision of corneal Pentacam HR measurements in early and advanced keratoconus.

    Science.gov (United States)

    Flynn, Tom H; Sharma, Daya P; Bunce, Catey; Wilkins, Mark R

    2016-09-01

    Serial Scheimpflug corneal tomography to monitor the progression of keratoconus has become standard practice in most countries where corneal cross-linking is available. The tomographic definitions of progression are, however, poorly defined. The aims of this study were: (a) to estimate the 95% limits of intraobserver and interobserver agreement of corneal shape parameters on Pentacam in patients with keratoconus and (b) to investigate whether these limits of agreement varied according to disease severity. 96 adult patients with keratoconus and no corneal scarring or history of previous surgery were recruited from a corneal clinic in a tertiary ophthalmology hospital. One eye of each subject was scanned twice by each of the two observers with the Pentacam HR. 95% limits of intraobserver and interobserver agreement for K1, K2, Kmax and corneal thickness at the thinnest corneal location (TCT) were calculated. Reproducibility of keratometry measures was better for early keratoconus than advanced keratoconus. In patients of Pentacam-derived Krumeich stage 1 or 2, the 95% limits of interobserver agreement for Kmax were from -0.90 to 1.01. In patients of Pentacam-derived Krumeich stage >2, the 95% limits of interobserver agreement for Kmax were from -3.71 to 3.86. Keratometric measurements on Pentacam HR are less reproducible in advanced keratoconus than in early keratoconus. In patients of Pentacam-derived Krumeich stage 1 or 2, an increase in K1, K2 or Kmax of more than 1 dioptre is likely to represent the real change in the corneal shape. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/

  16. High resolution retinal image restoration with wavefront sensing and self-extracted filtering

    Science.gov (United States)

    Yang, Shuyu; Erry, Gavin; Nemeth, Sheila; Mitra, Sunanda; Soliz, Peter

    2005-04-01

    Diagnosis and treatment of retinal diseases such as diabetic retinopathy commonly rely on a clear view of the retina. The challenge in obtaining high quality retinal image lies in the design of the imaging system that can reduce the strong aberrations of the human eye. Since the amplitudes of human eye aberrations decrease rapidly as the aberration order goes up, it is more cost-effective to correct low order aberrations with adaptive optical devices while process high order aberrations through image processing. A cost effective fundus imaging device that can capture high quality retinal images with 2-5 times higher resolution than conventional retinal images has been designed [1]. This imager improves image quality by attaching complementary adaptive optical components to a conventional fundus camera. However, images obtained with the high resolution camera are still blurred due to some uncorrected aberrations as well as defocusing resulting from non-isoplanatic effect. Therefore, advanced image restoration algorithms have been employed for further improvement in image quality. In this paper, we use wavefront-based and self-extracted blind deconvolution techniques to restore images captured by the high resolution fundus camera. We demonstrate that through such techniques, pathologies that are critical to retinal disease diagnosis but not clear or not observable in the original image can be observed clearly in the restored images. Image quality evaluation is also used to finalize the development of a cost-effective, fast, and automated diagnostic system that can be used clinically.

  17. Advancement of an Infra-Red Technique for Whole-Field Concentration Measurements in Fluidized Beds

    Science.gov (United States)

    Medrano, Jose A.; de Nooijer, Niek C. A.; Gallucci, Fausto; van Sint Annaland, Martin

    2016-01-01

    For a better understanding and description of the mass transport phenomena in dense multiphase gas-solids systems such as fluidized bed reactors, detailed and quantitative experimental data on the concentration profiles is required, which demands advanced non-invasive concentration monitoring techniques with a high spatial and temporal resolution. A novel technique based on the selective detection of a gas component in a gas mixture using infra-red properties has been further developed. The first stage development was carried out using a very small sapphire reactor and CO2 as tracer gas. Although the measuring principle was demonstrated, the real application was hindered by the small reactor dimensions related to the high costs and difficult handling of large sapphire plates. In this study, a new system has been developed, that allows working at much larger scales and yet with higher resolution. In the new system, propane is used as tracer gas and quartz as reactor material. In this study, a thorough optimization and calibration of the technique is presented which is subsequently applied for whole-field measurements with high temporal resolution. The developed technique allows the use of a relatively inexpensive configuration for the measurement of detailed concentration fields and can be applied to a large variety of important chemical engineering topics. PMID:26927127

  18. Advancement of an Infra-Red Technique for Whole-Field Concentration Measurements in Fluidized Beds

    Directory of Open Access Journals (Sweden)

    Jose A. Medrano

    2016-02-01

    Full Text Available For a better understanding and description of the mass transport phenomena in dense multiphase gas-solids systems such as fluidized bed reactors, detailed and quantitative experimental data on the concentration profiles is required, which demands advanced non-invasive concentration monitoring techniques with a high spatial and temporal resolution. A novel technique based on the selective detection of a gas component in a gas mixture using infra-red properties has been further developed. The first stage development was carried out using a very small sapphire reactor and CO2 as tracer gas. Although the measuring principle was demonstrated, the real application was hindered by the small reactor dimensions related to the high costs and difficult handling of large sapphire plates. In this study, a new system has been developed, that allows working at much larger scales and yet with higher resolution. In the new system, propane is used as tracer gas and quartz as reactor material. In this study, a thorough optimization and calibration of the technique is presented which is subsequently applied for whole-field measurements with high temporal resolution. The developed technique allows the use of a relatively inexpensive configuration for the measurement of detailed concentration fields and can be applied to a large variety of important chemical engineering topics.

  19. Measurements of Intra-Beam Scattering at Low Emittance in the Advanced Light Source

    Energy Technology Data Exchange (ETDEWEB)

    Byrd, J.; Corlett, J.; Nishimura, H.; Robin, D.; De Santis, S.; Steier, C.; Wolski, A.; Wu, Y.; /LBL, Berkeley; Bane, K.; Raubenheimer, T.; Ross, M.; Sheppard, J.; Smith,; /SLAC

    2006-03-13

    The beam emittance at the interaction point of linear colliders is expected to be strongly influenced by the emittance of the beams extracted from the damping rings. Intra-beam scattering (IBS) potentially limits the minimum emittance of low-energy storage rings, and this effect strongly influences the choice of energy of damping rings [1]. Theoretical analysis suggests that the NLC damping rings will experience modest emittance growth at 1.98 GeV, however there is little experimental data of IBS effects for very low-emittance machines in the energy regime of interest. The Advanced Light Source (ALS) at Lawrence Berkeley National Laboratory is a third-generation synchrotron light source operating with high-intensity, low-emittance beams at energies of approximately 1-2 GeV, and with emittance coupling capability of 1% or less. We present measurements of the beam growth in three dimensions as a function of current, for normalized natural horizontal emittance of approximately 1-10 mm-mrad at energies of 0.7-1.5 GeV, values comparable to the parameters in an NLC damping ring. Using a dedicated diagnostic beamline with an x-ray scintillator imaging system, measurements of the transverse beamsize are made, and bunch length measurements are made using an optical streak camera. Emittance growth as a function of bunch current is determined, and compared with preliminary calculation estimates.

  20. Test Mass Temperature Field and Laser Aberration Modeling in Advanced LIGO

    Science.gov (United States)

    Ramette, Joshua; Kasprzack, Marie; Gonzalez, Gabriela; Brooks, Aidan; Blair, Carl; Kandhasamy, Shivaraj; Wang, Haoyu; LIGO Collaboration

    2017-01-01

    Advanced LIGO uses high laser power in the main interferometer arm cavities to achieve design sensitivity. A small part of this power is absorbed in the interferometer cavity mirrors where it creates thermal lenses. Actuation by ``ring heaters,'' additional heater elements aimed to reduce the temperature gradients in the mirrors, minimizes aberrations in the main laser beam due to thermal lensing. We derive the first analytical model of the temperature field contribution in the mirrors generated by an ideal ring heater. In addition, we simulate the test mass temperature field using finite element analysis software and find agreement with the prediction of our ring heater analytical model and existing models for self-heating of the test mass by the main laser beam. From our ring heater temperature field models, we then express the resulting optical aberration contribution in the main laser and compare to Hartmann wavefront sensor measurements of the aberration. Used in conjunction with wavefront measurements, our model provides a more complete understanding of the thermal state of the cavity mirrors and will allow a more efficient use of the ring heaters in Advanced LIGO. We thank the National Science Foundation for supporting this work (NSF grant #1262890 and #1205882).

  1. Advanced-warning system risk-reduction experiments: the Multispectral Measurements Program (MSMP) and the Balloon Altitude Mosaic Measurements (BAMM)

    Science.gov (United States)

    Hasegawa, Ken R.

    2000-12-01

    MSMP and BAMM were commissioned by the Air Force Space Division (AFSD) in the late seventies to generate data in support of the Advanced Warning System (AWS), a development activity to replace the space-based surveillance satellites of the Defense Support Program (DSP). These programs were carried out by the Air Force Geophysics Laboratory with planning and mentoring by Irving Spiro of The Aerospace Corporation, acting on behalf of the program managers, 1st Lt. Todd Frantz, 1st Lt. Gordon Frantom, and 1st Lt. Ken Hasegawa of the technology program office at AFSD. The motivation of MSMP was the need for characterizing the exhaust plumes of the thrusters aboard post-boost vehicles, a primary target for the infrared sensors of the proposed AWS system. To that end, the experiments consisted of a series of Aries rocket launches from White Sands Missile Range in which dual payloads were carried aloft and separately deployed at altitudes above 100 km. One module contained an ensemble of sensors spanning the spectrum from the vacuum ultraviolet to the long wave infrared, all slaved to an rf tracker locked onto a beacon on the target module. The target was a small pressure-fed liquid-propellant rocket engine, a modified Atlas vernier, programmed for a series of maneuvers in the vicinity of the instrument module. As part of this program, diagnostic measurements of the target engine exhaust were made at Rocketdyne, and shock tube experiments on excitation processes were carried out by staff members of Calspan.

  2. Joseph F. Keithley Award For Advances in Measurement Science: Resonant Ultrasound Spectroscopy: An Odyssey in Measurement Science

    Science.gov (United States)

    Migliori, Albert

    Perhaps the speeds of sound, or, equivalently, the elastic moduli are some of the most fundamental attributes of a solid, connecting to fundamental physics, metallurgy, non-destructive testing, and more. Unlike most of the quantities used to characterize condensed matter, the elastic moduli are fourth-rank tensors containing a wealth of detail, directional information, and consistency constraints that provide some of the most revealing probes of solids. We describe here the current state of the art in one method, Resonant Ultrasound Spectroscopy, where the mechanical resonances of a specimen of regular shape (easy to measure) are analyzed (difficult computational problem) to obtain the full elastic tensor. With modern advances in electronics and analysis, fractions of a part per million changes in elastic moduli are detectable providing new and important insight into grand challenges in condensed matter physics. This work was supported as part of the Materials Science of Actinides, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0001089.

  3. Advanced Intensity-Modulation Continuous-Wave Lidar Techniques for Column CO2 Measurements

    Science.gov (United States)

    Campbell, J. F.; Lin, B.; Nehrir, A. R.; Obland, M. D.; Liu, Z.; Browell, E. V.; Chen, S.; Kooi, S. A.; Fan, T. F.

    2015-12-01

    Global and regional atmospheric carbon dioxide (CO2) measurements for the NASA Active Sensing of CO2 Emissions over Nights, Days, and Seasons (ASCENDS) space mission and Atmospheric Carbon and Transport (ACT) - America airborne investigation are critical for improving our understanding of global CO2 sources and sinks. Advanced Intensity-Modulated Continuous-Wave (IM-CW) lidar techniques are being investigated as a means of facilitating CO2 measurements from space and airborne platforms to meet the mission science measurement requirements. In recent numerical, laboratory and flight experiments we have successfully used the Binary Phase Shift Keying (BPSK) modulation technique to uniquely discriminate surface lidar returns from intermediate aerosol and cloud returns. We demonstrate the utility of BPSK to eliminate sidelobes in the range profile as a means of making Integrated Path Differential Absorption (IPDA) column CO2 measurements in the presence of intervening optically thin clouds, thereby minimizing bias errors caused by the clouds. Furthermore, high accuracy and precision ranging to the Earth's surface as well as to the top of intermediate cloud layers, which is a requirement for the inversion of column CO2 number density measurements to column CO2 mixing ratios, has been demonstrated using new hyperfine interpolation techniques that takes advantage of the periodicity of the modulation waveforms. This approach works well for both BPSK and linear swept-frequency modulation techniques and provides very high (at sub-meter level) range resolution. The BPSK technique under investigation has excellent auto-correlation properties while possessing a finite bandwidth. A comparison of BPSK and linear swept-frequency is also discussed in this paper. These techniques are used in a new data processing architecture to support the ASCENDS CarbonHawk Experiment Simulator (ACES) and ACT-America programs.

  4. Efficient polarization insensitive complex wavefront control using Huygens' metasurfaces based on dielectric resonant meta-atoms

    CERN Document Server

    Chong, Katie E; Staude, Isabelle; James, Anthony; Dominguez, Jason; Liu, Sheng; Subramania, Ganapathi S; Decker, Manuel; Neshev, Dragomir N; Brener, Igal; Kivshar, Yuri S

    2016-01-01

    Subwavelength-thin metasurfaces have shown great promises for the control of optical wavefronts, thus opening new pathways for the development of efficient flat optics. In particular, Huygens' metasurfaces based on all-dielectric resonant meta-atoms have already shown a huge potential for practical applications with their polarization insensitivity and high transmittance efficiency. Here, we experimentally demonstrate a polarization insensitive holographic Huygens' metasurface based on dielectric resonant meta-atoms capable of complex wavefront control at telecom wavelengths. Our metasurface produces a hologram image in the far-field with 82% transmittance efficiency and 40% imaging efficiency. Such efficient complex wavefront control shows that Huygens' metasurfaces based on resonant dielectric meta-atoms are a big step towards practical applications of metasurfaces in wavefront design related technologies, including computer-generated holograms, ultra-thin optics, security and data storage devices.

  5. Modeling the Effect of Wave-front Aberrations in Fiber-based Scanning Optical Microscopy

    NARCIS (Netherlands)

    Verstraete, H.R.G.W.; Verhaegen, M.H.G.; Kalkman, J.

    2013-01-01

    In scanning microscopy and optical coherence tomography, aberrations of the wave-front cause a loss in intensity and resolution. Intensity and resolution are quantified using Fresnel propagation, Fraunhofer diffraction, and the calculation of overlap integrals.

  6. Wavefront correction with a ferrofluid deformable mirror: experimental results and recent developments

    CERN Document Server

    Brousseau, Denis; Thibaul, Simon; Ritcey, Anna M; Parent, Jocelyn; Seddiki, Omar; Dery, Jean-Philippe; Faucher, Luc; Vassallo, Julien; Naderian, Azadeh

    2008-01-01

    We present the research status of a deformable mirror made of a magnetic liquid whose surface is actuated by a triangular array of small current carrying coils. We demonstrate that the mirror can correct a 11 microns low order aberrated wavefront to a residual RMS wavefront error 0.05 microns. Recent developments show that these deformable mirrors can reach a frequency response of several hundred hertz. A new method for linearizing the response of these mirrors is also presented.

  7. Optogenetic signaling-pathway regulation through scattering skull using wavefront shaping

    CERN Document Server

    Yoon, Jonghee; Lee, KyeoReh; Kim, Nury; Kim, Jin Man; Park, Jongchan; Choi, Chulhee; Heo, Won Do; Park, YongKeun

    2015-01-01

    We introduce a non-invasive approach for optogenetic regulation in biological cells through highly scattering skull tissue using wavefront shaping. The wavefront of the incident light was systematically controlled using a spatial light modulator in order to overcome multiple light-scattering in a mouse skull layer and to focus light on the target cells. We demonstrate that illumination with shaped waves enables spatiotemporal regulation of intracellular Ca2+ level at the individual-cell level.

  8. FGF4 and FGF8 comprise the wavefront activity that controls somitogenesis

    OpenAIRE

    L A Naiche; Holder, Nakisha; Lewandoski, Mark

    2011-01-01

    Somites form along the embryonic axis by sequential segmentation from the presomitic mesoderm (PSM) and differentiate into the segmented vertebral column as well as other unsegmented tissues. Somites are thought to form via the intersection of two activities known as the clock and the wavefront. Previous work has suggested that fibroblast growth factor (FGF) activity may be the wavefront signal, which maintains the PSM in an undifferentiated state. However, it is unclear which (if any) of the...

  9. A structured review of health utility measures and elicitation in advanced/metastatic breast cancer

    Directory of Open Access Journals (Sweden)

    Hao Y

    2016-06-01

    Full Text Available Yanni Hao,1 Verena Wolfram,2 Jennifer Cook2 1Novartis Pharmaceuticals, East Hanover, NJ, USA; 2Adelphi Values, Bollington, UK Background: Health utilities are increasingly incorporated in health economic evaluations. Different elicitation methods, direct and indirect, have been established in the past. This study examined the evidence on health utility elicitation previously reported in advanced/metastatic breast cancer and aimed to link these results to requirements of reimbursement bodies. Methods: Searches were conducted using a detailed search strategy across several electronic databases (MEDLINE, EMBASE, Cochrane Library, and EconLit databases, online sources (Cost-effectiveness Analysis Registry and the Health Economics Research Center, and web sites of health technology assessment (HTA bodies. Publications were selected based on the search strategy and the overall study objectives. Results: A total of 768 publications were identified in the searches, and 26 publications, comprising 18 journal articles and eight submissions to HTA bodies, were included in the evidence review. Most journal articles derived utilities from the European Quality of Life Five-Dimensions questionnaire (EQ-5D. Other utility measures, such as the direct methods standard gamble (SG, time trade-off (TTO, and visual analog scale (VAS, were less frequently used. Several studies described mapping algorithms to generate utilities from disease-specific health-related quality of life (HRQOL instruments such as European Organization for Research and Treatment of Cancer Quality of Life Questionnaire – Core 30 (EORTC QLQ-C30, European Organization for Research and Treatment of Cancer Quality of Life Questionnaire – Breast Cancer 23 (EORTC QLQ-BR23, Functional Assessment of Cancer Therapy – General questionnaire (FACT-G, and Utility-Based Questionnaire-Cancer (UBQ-C; most used EQ-5D as the reference. Sociodemographic factors that affect health utilities, such as age, sex

  10. Optical modeling and polarization calibration for CMB measurements with ACTPol and Advanced ACTPol

    Science.gov (United States)

    Koopman, Brian; Austermann, Jason; Cho, Hsiao-Mei; Coughlin, Kevin P.; Duff, Shannon M.; Gallardo, Patricio A.; Hasselfield, Matthew; Henderson, Shawn W.; Ho, Shuay-Pwu Patty; Hubmayr, Johannes; Irwin, Kent D.; Li, Dale; McMahon, Jeff; Nati, Federico; Niemack, Michael D.; Newburgh, Laura; Page, Lyman A.; Salatino, Maria; Schillaci, Alessandro; Schmitt, Benjamin L.; Simon, Sara M.; Vavagiakis, Eve M.; Ward, Jonathan T.; Wollack, Edward J.

    2016-07-01

    array of detectors for Advanced ACTPol, the next generation upgrade to ACTPol, will be deployed in 2016. We plan to continue using both techniques and compare them to astrophysical source measurements for the Advanced ACTPol polarization calibration.

  11. Measurement of non-axisymmetry in centres of advanced mergers of galaxies

    CERN Document Server

    Jog, C J; Jog, Chanda J.; Maybhate, Aparna

    2006-01-01

    We measure the non-axisymmetry in the luminosity distribution in the inner few kpc of the remnants of advanced mergers of galaxies with a view to understand the relaxation in the central regions. For this, we analyze the images from the 2MASS archival data for a selected sample of 12 merging galaxies, which show signs of interaction but have a single nucleus. The central regions are fitted by elliptical isophotes whose centres are allowed to vary to get the best fit. The centres of isophotes show a striking sloshing pattern with a spatial variation of up to 20-30 % within the central 1 kpc. This indicates mass asymmetry and a dynamically unrelaxed behaviour. Next, we Fourier-analyze the galaxy images while keeping the centre constant and measure the deviation from axisymmetry in terms of the fractional Fourier amplitudes (A_1, A_2 etc) as a function of radius. All mergers show a high value of lopsidedness (upto A_1 ~ 0.2) in the central 5 kpc. The m=2 asymmetry is even stronger, with values of A_2 upto ~ 0.3,...

  12. EDITORIAL: Advances in Measurement Technology and Intelligent Instruments for Production Engineering

    Science.gov (United States)

    Gao, Wei; Takaya, Yasuhiro; Gao, Yongsheng; Krystek, Michael

    2008-08-01

    . Neuschaefer-Rube et al, also from PTB, present procedures and standards to test tactile and optical microsensors and micro-computed tomography systems, which are similar to the established tests for classical coordinate measuring machines and assess local and global sensor characteristics. The last three papers are related to micro/nano-metrology and intelligent instrumentation. Jiang et al from Tohoku University describe the fabrication of piezoresistive nanocantilevers for ultra-sensitive force detection by using spin-out diffusion, EB lithography and FAB etching, respectively. Y-C Liu et al from National Taiwan University develop an economical and highly sensitive optical accelerometer using a commercial optical pickup head. Michihata et al from Osaka University experimentally investigate the positioning sensing property and accuracy of a laser trapping probe for a nano-coordinate measuring machine. As guest editors, we believe that this special feature presents the newest information on advances in measurement technology and intelligent instruments from basic research to applied systems for Production Engineering. We would like to thank all the authors for their great contributions to this special feature and the referees for their careful reviews of the papers. We would also like to express our thanks and appreciation to Professor P Hauptmann, Editor-in-Chief of MST, for his kind offer to publish selected ISMTII 2007 papers in MST, and to the publishing staff of MST for their dedicated efforts that have made this special feature possible.

  13. Epicardial wavefronts arise from widely distributed transient sources during ventricular fibrillation in the isolated swine heart

    Science.gov (United States)

    Rogers, J. M.; Walcott, G. P.; Gladden, J. D.; Melnick, S. B.; Ideker, R. E.; Kay, M. W.

    2008-01-01

    It has been proposed that ventricular fibrillation (VF) waves emanate from stable localized sources, often called 'mother rotors'. However, evidence for the existence of these rotors is conflicting. Using a new panoramic optical mapping system that can image nearly the entire ventricular epicardium, we recently excluded epicardial mother rotors as the drivers of Wiggers' stage II VF in the isolated swine heart. Furthermore, we were unable to find evidence that VF requires sustained intramural sources. The present study was designed to test the following hypotheses: (i) VF is driven by a specific region, and (ii) rotors that are long-lived, though not necessarily permanent, are the primary generators of VF wavefronts. Using panoramic optical mapping, we mapped VF wavefronts from six isolated swine hearts. Wavefronts were tracked to characterize their activation pathways and to locate their originating sources. We found that the wavefronts that participate in epicardial re-entry were not confined to a compact region; rather they activated the entire epicardial surface. New wavefronts feeding into the epicardial activation pattern were generated over the majority of the epicardium and almost all of them were associated with rotors or repetitive breakthrough patterns that lasted for less than 2 s. These findings indicate that epicardial wavefronts in this model are generated by many transitory epicardial sources distributed over the entire surface of the heart.

  14. Research on encoding multi-gray-scale phase hologram and wavefront reconstruction.

    Science.gov (United States)

    Zhang, Hongxin; Zhou, Hao; Li, Jingyao; Qiao, Yujing; Gao, Wei

    2016-04-01

    Application of computer-generated holography for wavefront generation is beneficial for optical interferometry and 3D image display. However, there is a noticeable encoding error in computer-generated holograms, which is encoded by using the object's wavefront function in a computer. The encoding error will be transmitted and amplified during fabrication of a hologram, which can cause a reconstructed error in the generated wavefront. A correction method of encoding errors based on the least-squares fitting is proposed. A validating experiment is completed by using a liquid crystal spatial light modulator to reconstruct a group of paraboloid wavefronts. The results show that encoding errors increase the reconstructed error of a wavefront less than optical system errors, and the root-mean-square value drops 0.022λ after the correction of the encoding error, but it falls 0.092λ after the correction of optical system errors. The total error has been reduced by 0.114λ. This research is helpful for prediction of encoding errors and improvement of wavefront reconstruction accuracy.

  15. Anti-aliasing Wiener filtering for wave-front reconstruction in the spatial-frequency domain for high-order astronomical adaptive-optics systems.

    Science.gov (United States)

    Correia, Carlos M; Teixeira, Joel

    2014-12-01

    Computationally efficient wave-front reconstruction techniques for astronomical adaptive-optics (AO) systems have seen great development in the past decade. Algorithms developed in the spatial-frequency (Fourier) domain have gathered much attention, especially for high-contrast imaging systems. In this paper we present the Wiener filter (resulting in the maximization of the Strehl ratio) and further develop formulae for the anti-aliasing (AA) Wiener filter that optimally takes into account high-order wave-front terms folded in-band during the sensing (i.e., discrete sampling) process. We employ a continuous spatial-frequency representation for the forward measurement operators and derive the Wiener filter when aliasing is explicitly taken into account. We further investigate and compare to classical estimates using least-squares filters the reconstructed wave-front, measurement noise, and aliasing propagation coefficients as a function of the system order. Regarding high-contrast systems, we provide achievable performance results as a function of an ensemble of forward models for the Shack-Hartmann wave-front sensor (using sparse and nonsparse representations) and compute point-spread-function raw intensities. We find that for a 32×32 single-conjugated AOs system the aliasing propagation coefficient is roughly 60% of the least-squares filters, whereas the noise propagation is around 80%. Contrast improvements of factors of up to 2 are achievable across the field in the H band. For current and next-generation high-contrast imagers, despite better aliasing mitigation, AA Wiener filtering cannot be used as a standalone method and must therefore be used in combination with optical spatial filters deployed before image formation actually takes place.

  16. Measurement of Thermo-Elastic Deformation of an Optic using a Polarization Based Shearing Interferometer

    CERN Document Server

    Beyersdorf, Peter

    2012-01-01

    A shearing interferometer is presented which uses polarization control to shear the wavefront and to modulate the interference pattern. The shear is generated by spatial walk-off in a birefringent crystal. By adjusting the orientation of the birefringent crystal, the components of the wavefront gradient can be independently measured to allow determination of the full wavefront vector gradient as well as reconstruction of the wavefront. Further, the monolithic nature of the crystal used for shearing allows the interferometer to be setup without need for precise alignment of any components. An algorithm incorporating homodyne detection is presented which analyzes the modulated interferograms to determine the components of the wavefront gradient, from which the wavefront is reconstructed. The thermal deformation of a mirror subject to heating from absorption of a Gaussian pump beam was accurately observed with a sensitivity better than \\lambda/160. We show that this sensitivity is scale invariant, and present a ...

  17. Development of an ELT XAO testbed using a Mach-Zehnder wavefront sensor: calibration of the deformable mirror

    CERN Document Server

    Delacroix, Christian; Loupias, Magali; Thiébaut, Eric; Adjali, Louisa; Leger, Jonathan; Tallon, Michel

    2015-01-01

    (abridged) Extreme adaptive optics (XAO) encounters severe difficulties to cope with the high speed (>1kHz), high accuracy and high order requirements for future extremely large telescopes. An innovative high order adaptive optics system using a self-referenced Mach-Zehnder wavefront sensor (MZWFS) allows counteracting these limitations. This sensor estimates very accurately the wavefront phase at small spatial scale by measuring intensity differences between two outputs, with a $\\lambda /4$ path length difference between its two legs, but is limited in dynamic range due to phase ambiguity. During the past few years, such an XAO system has been studied by our team in the framework of 8-meter class telescopes. In this work, we report on our latest results with the XAO testbed recently installed in our lab, and dedicated to high contrast imaging with 30m-class telescopes (such as the E-ELT or the TMT). After reminding the principle of a MZWFS and describing the optical layout of our experiment, we will show the...

  18. Wavelet-based denoising of the Fourier metric in real-time wavefront correction for single molecule localization microscopy

    Science.gov (United States)

    Tehrani, Kayvan Forouhesh; Mortensen, Luke J.; Kner, Peter

    2016-03-01

    Wavefront sensorless schemes for correction of aberrations induced by biological specimens require a time invariant property of an image as a measure of fitness. Image intensity cannot be used as a metric for Single Molecule Localization (SML) microscopy because the intensity of blinking fluorophores follows exponential statistics. Therefore a robust intensity-independent metric is required. We previously reported a Fourier Metric (FM) that is relatively intensity independent. The Fourier metric has been successfully tested on two machine learning algorithms, a Genetic Algorithm and Particle Swarm Optimization, for wavefront correction about 50 μm deep inside the Central Nervous System (CNS) of Drosophila. However, since the spatial frequencies that need to be optimized fall into regions of the Optical Transfer Function (OTF) that are more susceptible to noise, adding a level of denoising can improve performance. Here we present wavelet-based approaches to lower the noise level and produce a more consistent metric. We compare performance of different wavelets such as Daubechies, Bi-Orthogonal, and reverse Bi-orthogonal of different degrees and orders for pre-processing of images.

  19. Real-time phasing and co-phasing of a ground-based interferometer with a pyramid wavefront sensor.

    Science.gov (United States)

    Vérinaud, Christophe; Esposito, Simone

    The feasibility and remarkable performances of pyramid wavefront sensing in adaptive optics have already been demonstrated. In this paper, we investigate another potential of the pyramid wavefront sensor which is differential piston sensing in interferometry: this can be done by using a glass pyramid placed in a combined focal plane of the interferometer, and a CCD sampling the usual four diffracted images of the pupil, composed here by the interferometer apertures. From a purely geometrical point of view, no information about the differential phase between two pupils could be retrieved. However, as the sensor main component, the pyramid, is located directly in the interference pattern of the interferometer, the piston information present in the electric field of the combined focal plane modifies, after diffraction by the pyramid, the intensity distribution in the pupil plane. Thus, with only one sensor, the differential piston can be measured, in addition to the classical local tilts determination. In this paper we present the concept and give some simulation results showing the performances of a closed-loop adaptive optics correction for a ground-based two-telescope interferometer like the Large Binocular Telescope.

  20. Perceived vs. measured effects of advanced cockpit systems on pilot workload and error: are pilots' beliefs misaligned with reality?

    Science.gov (United States)

    Casner, Stephen M

    2009-05-01

    Four types of advanced cockpit systems were tested in an in-flight experiment for their effect on pilot workload and error. Twelve experienced pilots flew conventional cockpit and advanced cockpit versions of the same make and model airplane. In both airplanes, the experimenter dictated selected combinations of cockpit systems for each pilot to use while soliciting subjective workload measures and recording any errors that pilots made. The results indicate that the use of a GPS navigation computer helped reduce workload and errors during some phases of flight but raised them in others. Autopilots helped reduce some aspects of workload in the advanced cockpit airplane but did not appear to reduce workload in the conventional cockpit. Electronic flight and navigation instruments appeared to have no effect on workload or error. Despite this modest showing for advanced cockpit systems, pilots stated an overwhelming preference for using them during all phases of flight.

  1. Beamlet pulse-generation and wavefront-control system

    Energy Technology Data Exchange (ETDEWEB)

    Van Wonterghem, B.M.; Salmon, J.T.; Wilcox, R.W.

    1996-06-01

    The Beamlet pulse-generation system (or {open_quotes}front end{close_quotes}) refers to the laser hardware that generates the spatially and temporally shaped pulse that is injected into the main laser cavity. All large ICF lasers have pulse-generation systems that typically consist of a narrow-band oscillator, elector-optic modulators for temporal and bandwidth shaping, and one or more preamplifiers. Temporal shaping is used to provide the desired laser output pulse shape and also to compensate for gain saturation effects in the large-aperture amplifiers. Bandwidth is applied to fulfill specific target irradiation requirements and to avoid stimulated Brillouin scattering (SBS) in large-aperture laser components. Usually the sharp edge of the beam`s spatial intensity profile is apodized before injection in the main amplifier beam line. This prevents large-amplitude ripples on the intensity profile. Here the authors briefly review the front-end design and discuss improvements to the oscillator and modulator systems. Their main focus, however, is to describe Beamlet`s novel beam-shaping and wavefront-control systems that have recently been fully activated and tested.

  2. Suppressing Anomalous Localized Waffle Behavior in Least Squares Wavefront Reconstructors

    Energy Technology Data Exchange (ETDEWEB)

    Gavel, D

    2002-10-08

    A major difficulty with wavefront slope sensors is their insensitivity to certain phase aberration patterns, the classic example being the waffle pattern in the Fried sampling geometry. As the number of degrees of freedom in AO systems grows larger, the possibility of troublesome waffle-like behavior over localized portions of the aperture is becoming evident. Reconstructor matrices have associated with them, either explicitly or implicitly, an orthogonal mode space over which they operate, called the singular mode space. If not properly preconditioned, the reconstructor's mode set can consist almost entirely of modes that each have some localized waffle-like behavior. In this paper we analyze the behavior of least-squares reconstructors with regard to their mode spaces. We introduce a new technique that is successful in producing a mode space that segregates the waffle-like behavior into a few ''high order'' modes, which can then be projected out of the reconstructor matrix. This technique can be adapted so as to remove any specific modes that are undesirable in the final reconstructor (such as piston, tip, and tilt for example) as well as suppress (the more nebulously defined) localized waffle behavior.

  3. Continuous shearlet frames and resolution of the wavefront set

    KAUST Repository

    Grohs, Philipp

    2010-12-04

    In recent years directional multiscale transformations like the curvelet- or shearlet transformation have gained considerable attention. The reason for this is that these transforms are-unlike more traditional transforms like wavelets-able to efficiently handle data with features along edges. The main result in Kutyniok and Labate (Trans. Am. Math. Soc. 361:2719-2754, 2009) confirming this property for shearlets is due to Kutyniok and Labate where it is shown that for very special functions ψ with frequency support in a compact conical wegde the decay rate of the shearlet coefficients of a tempered distribution f with respect to the shearlet ψ can resolve the wavefront set of f. We demonstrate that the same result can be verified under much weaker assumptions on ψ, namely to possess sufficiently many anisotropic vanishing moments. We also show how to build frames for L2(ℝ2)from any such function. To prove our statements we develop a new approach based on an adaption of the Radon transform to the shearlet structure. © 2010 Springer-Verlag.

  4. Monotone traveling wavefronts of the KPP-Fisher delayed equation

    Science.gov (United States)

    Gomez, Adrian; Trofimchuk, Sergei

    In the early 2000's, Gourley (2000), Wu et al. (2001), Ashwin et al. (2002) initiated the study of the positive wavefronts in the delayed Kolmogorov-Petrovskii-Piskunov-Fisher equation u(t,x)=Δu(t,x)+u(t,x)(1-u(t-h,x)), u⩾0, x∈R. Since then, this model has become one of the most popular objects in the studies of traveling waves for the monostable delayed reaction-diffusion equations. In this paper, we give a complete solution to the problem of existence and uniqueness of monotone waves in Eq. (*). We show that each monotone traveling wave can be found via an iteration procedure. The proposed approach is based on the use of special monotone integral operators (which are different from the usual Wu-Zou operator) and appropriate upper and lower solutions associated to them. The analysis of the asymptotic expansions of the eventual traveling fronts at infinity is another key ingredient of our approach.

  5. Wavefront aberrations of x-ray dynamical diffraction beams.

    Science.gov (United States)

    Liao, Keliang; Hong, Youli; Sheng, Weifan

    2014-10-01

    The effects of dynamical diffraction in x-ray diffractive optics with large numerical aperture render the wavefront aberrations difficult to describe using the aberration polynomials, yet knowledge of them plays an important role in a vast variety of scientific problems ranging from optical testing to adaptive optics. Although the diffraction theory of optical aberrations was established decades ago, its application in the area of x-ray dynamical diffraction theory (DDT) is still lacking. Here, we conduct a theoretical study on the aberration properties of x-ray dynamical diffraction beams. By treating the modulus of the complex envelope as the amplitude weight function in the orthogonalization procedure, we generalize the nonrecursive matrix method for the determination of orthonormal aberration polynomials, wherein Zernike DDT and Legendre DDT polynomials are proposed. As an example, we investigate the aberration evolution inside a tilted multilayer Laue lens. The corresponding Legendre DDT polynomials are obtained numerically, which represent balanced aberrations yielding minimum variance of the classical aberrations of an anamorphic optical system. The balancing of classical aberrations and their standard deviations are discussed. We also present the Strehl ratio of the primary and secondary balanced aberrations.

  6. Accumulation of advanced glycation end products, measured as skin autofluorescence, in renal disease.

    Science.gov (United States)

    Hartog, Jasper W L; de Vries, Aiko P J; Lutgers, Helen L; Meerwaldt, Robbert; Huisman, Roel M; van Son, Willem J; de Jong, Paul E; Smit, Andries J

    2005-06-01

    Advanced glycation end products (AGEs) accumulate during renal failure and dialysis. Kidney transplantation is thought to reverse this accumulation by restoring renal function. Using a noninvasive and validated autofluorescence reader, we evaluated AGE levels in 285 transplant recipients (mean age, 52 years; range, 41 to 60 years), 32 dialysis patients (mean age, 56 years; range, 43 to 65 years), and 231 normal control subjects (mean age, 51 years; range, 40 to 65 years). Measurements in transplant recipients were performed for a mean of 73 months (range, 32 to 143 months) after transplantation. Dialysis patients were on dialysis therapy for a mean of 42 months (range, 17 to 107 months). Fluorescence was significantly increased in dialysis patients compared with normal control subjects (2.8 vs. 2.0 arbitrary units [a.u.], P < .0001). Although fluorescence levels were significantly decreased in transplant recipients compared with dialysis patients (2.5 vs. 2.8 a.u., P < .0001), fluorescence in transplant recipients was higher than in controls (2.5 vs. 2.0 a.u., P < .0001). In transplant recipients, fluorescence correlated positively with the duration of dialysis prior to transplantation (R = 0.21, P < .0001), and negatively with creatinine clearance (R = -0.34, P < .0001). No correlation was found between time after transplantation and fluorescence in transplant recipients (R = -0.10, P = .10). Fluorescence in dialysis patients was positively correlated with duration of dialysis (R = 0.36, P = .042). Our results, like those of others, suggest that kidney transplantation does not fully correct increased AGE levels found in dialysis patients. The increased AGE levels in kidney transplant recipients cannot be explained by the differences in renal function alone. The availability of a simple, noninvasive method (AGE-Reader) to measure AGE accumulation may be used to monitor AGE accumulation in a clinical setting as well as in a study setting.

  7. Advanced glycation end products measured by skin autofluorescence in a population with central obesity.

    Science.gov (United States)

    den Engelsen, Corine; van den Donk, Maureen; Gorter, Kees J; Salomé, Philippe L; Rutten, Guy E

    2012-01-01

    Accumulation of advanced glycation end products (AGEs) is enhanced by chronic hyperglycemia and oxidative stress and this process may contribute to the pathogenesis of vascular disease. Skin autofluorescence (AF), a measure of accumulation of AGEs in skin collagen, is associated with vascular disease in patients with diabetes.   Because central obesity enhances oxidative stress people with central obesity might already have increased accumulation of AGEs before diabetes or cardiovascular disease become manifest. To test this hypothesis, we compared the distribution of skin AF and its association with clinical and biochemical parameters in individuals with and without central obesity. Skin AF was measured by a validated AGE Reader in 816 persons with and 431 persons without central obesity, aged 20-70 y. Mean skin AF increased with age and smoking and was higher in centrally obese individuals compared with non-obese individuals (p = 0.001, after adjustment for age and smoking p = 0.13). Mean skin AF in the subgroups without central obesity and without other risk factors (n = 106), central obesity without other risk factors (n = 74) and central obesity with other risk factors (n = 742) was 1.63 ± 0.37, 1.74 ± 0.44 and 1.87 ± 0.43 AU, respectively (p for trend < 0.001, after adjustment for age and smoking p for trend = 0.12). In the group with central obesity age, current smoking, alcohol consumption, waist circumference, creatinine clearance and hs-CRP were independently associated with skin AF (R(2) = 29.4%). Waist circumference hardly contributed to the explained variance. The relationship between waist circumference and skin AF is not as obvious as we hypothesized.

  8. Multi-axial load application and DIC measurement of advanced composite beam deformation behavior

    Directory of Open Access Journals (Sweden)

    Berggreen C.

    2010-06-01

    Full Text Available For the validation of a new beam element formulation, a wide set of experimental data consisting of deformation patterns obtained for a number of specially designed composite beam elements, have been obtained. The composite materials applied in the beams consist of glass-fiber reinforced plastic with specially designed layup configurations promoting advanced coupling behavior. Furthermore, the beams are designed with different cross-section shapes. The data obtained from the experiments are also used in order to improve the general understanding related to practical implementation of mechanisms of elastic couplings due to anisotropic properties of composite materials. The knowledge gained from these experiments is therefore essential in order to facilitate an implementation of passive control in future large wind turbine blades. A test setup based on a four-column MTS servo-hydraulic testing machine with a maximum capacity of 100 kN was developed, see Figure 1. The setup allows installing and testing beams of different cross-sections applying load cases such as axial extension, shear force bending, pure bending in two principal directions as well as pure torsion, see Figure 2. In order to apply multi-axial loading, a load application system consisting of three hydraulic actuators were mounted in two planes using multi-axial servo-hydraulic control. The actuator setup consists of the main actuator on the servo-hydraulic test machine working in the vertical axis (depicted on Figure 1 placed at the testing machine crosshead and used for application of vertical forces to the specimens. Two extra actuators are placed in a horizontal plane on the T-slot table of the test machine in different positions in order to apply loading at the tip of the specimen in various configurations. In order to precisely characterize the global as well as surface deformations of the beam specimens tested, a combination of different measurement systems were used during

  9. Wavefront sensing and adaptive control in phased array of fiber collimators

    Science.gov (United States)

    Lachinova, Svetlana L.; Vorontsov, Mikhail A.

    2011-03-01

    A new wavefront control approach for mitigation of atmospheric turbulence-induced wavefront phase aberrations in coherent fiber-array-based laser beam projection systems is introduced and analyzed. This approach is based on integration of wavefront sensing capabilities directly into the fiber-array transmitter aperture. In the coherent fiber array considered, we assume that each fiber collimator (subaperture) of the array is capable of precompensation of local (onsubaperture) wavefront phase tip and tilt aberrations using controllable rapid displacement of the tip of the delivery fiber at the collimating lens focal plane. In the technique proposed, this tip and tilt phase aberration control is based on maximization of the optical power received through the same fiber collimator using the stochastic parallel gradient descent (SPGD) technique. The coordinates of the fiber tip after the local tip and tilt aberrations are mitigated correspond to the coordinates of the focal-spot centroid of the optical wave backscattered off the target. Similar to a conventional Shack-Hartmann wavefront sensor, phase function over the entire fiber-array aperture can then be retrieved using the coordinates obtained. The piston phases that are required for coherent combining (phase locking) of the outgoing beams at the target plane can be further calculated from the reconstructed wavefront phase. Results of analysis and numerical simulations are presented. Performance of adaptive precompensation of phase aberrations in this laser beam projection system type is compared for various system configurations characterized by the number of fiber collimators and atmospheric turbulence conditions. The wavefront control concept presented can be effectively applied for long-range laser beam projection scenarios for which the time delay related with the double-pass laser beam propagation to the target and back is compared or even exceeds the characteristic time of the atmospheric turbulence change

  10. Skin autofluorescence, a measure of cumulative metabolic stress and advanced glycation end products, predicts mortality in hemodialysis patients

    NARCIS (Netherlands)

    Meerwaldt, R; Hartog, JWL; Graaff, R; Huisman, RJ; Links, TP; den Hollander, NC; Thorpe, [No Value; Baynes, JW; Navis, G; Gans, ROB; Smit, AJ

    2005-01-01

    Tissue advanced glycation end products (AGE) are a measure of cumulative metabolic stress and trigger cytokines driven inflammatory reactions. AGE are thought to contribute to the chronic complications of diabetes and ESRD. Tissue autofluorescence is related to the accumulation of AGE. Therefore,

  11. Validation and downscaling of Advanced Scatterometer (ASCAT) soil moisture using ground measurements in the Western Cape, South Africa

    CSIR Research Space (South Africa)

    Moller, J

    2017-09-01

    Full Text Available of Plant and Soil: DOI: 10.1080/02571862.2017.1318962 Validation and downscaling of Advanced Scatterometer (ASCAT) soil moisture using ground measurements in the Western Cape, South Africa Moller J Jovanovic N Garcia CL Bugan RDH Mazvimavi D...

  12. Skin autofluorescence, a measure of cumulative metabolic stress and advanced glycation end products, predicts mortality in hemodialysis patients

    NARCIS (Netherlands)

    Meerwaldt, R; Hartog, JWL; Graaff, R; Huisman, RJ; Links, TP; den Hollander, NC; Thorpe, [No Value; Baynes, JW; Navis, G; Gans, ROB; Smit, AJ

    2005-01-01

    Tissue advanced glycation end products (AGE) are a measure of cumulative metabolic stress and trigger cytokines driven inflammatory reactions. AGE are thought to contribute to the chronic complications of diabetes and ESRD. Tissue autofluorescence is related to the accumulation of AGE. Therefore, sk

  13. Skin autofluorescence as a measure of advanced glycation end products deposition is elevated in peripheral artery disease

    NARCIS (Netherlands)

    De Vos, Lisanne C.; Noordzij, Marjon J.; Mulder, Douwe J.; Smit, Andries J.; Lutgers, Helen L.; Dullaart, Robin P.F.; Kamphuisen, Pieter W.; Zeebregts, Clark J.; Lefrandt, Johan

    2013-01-01

    OBJECTIVE: Evidence for an important role of advanced glycation end products (AGEs) in the development of atherosclerosis and cardiovascular disease beyond diabetes mellitus and renal disease is growing. Skin autofluorescence (SAF) is a validated noninvasive measure of tissue AGEs. We hypothesized t

  14. Longitudinal chromatic aberration of the human eye in the visible and near infrared from wavefront sensing, double-pass and psychophysics.

    Science.gov (United States)

    Vinas, Maria; Dorronsoro, Carlos; Cortes, Daniel; Pascual, Daniel; Marcos, Susana

    2015-03-01

    Longitudinal Chromatic Aberration (LCA) influences the optical quality of the eye. However, the reported LCA varies across studies, likely associated to differences in the measurement techniques. We present LCA measured in subjects using wavefront sensing, double-pass retinal images, and psychophysical methods with a custom-developed polychromatic Adaptive Optics system in a wide spectral range (450-950 nm), with control of subjects' natural aberrations. LCA measured psychophysically was significantly higher than that from reflectometric techniques (1.51 D vs 1.00 D in the 488-700 nm range). Ours results indicate that the presence of natural aberrations is not the cause for the discrepancies across techniques.

  15. Analytical model for ring heater thermal compensation in the Advanced Laser Interferometer Gravitational-wave Observatory.

    Science.gov (United States)

    Ramette, Joshua; Kasprzack, Marie; Brooks, Aidan; Blair, Carl; Wang, Haoyu; Heintze, Matthew

    2016-04-01

    Advanced laser interferometer gravitational-wave detectors use high laser power to achieve design sensitivity. A small part of this power is absorbed in the interferometer cavity mirrors where it creates thermal lenses, causing aberrations in the main laser beam that must be minimized by the actuation of "ring heaters," which are additional heater elements that are aimed to reduce the temperature gradients in the mirrors. In this article we derive the first, to the best of our knowledge, analytical model of the temperature field generated by an ideal ring heater. We express the resulting optical aberration contribution to the main laser beam in this axisymmetric case. Used in conjunction with wavefront measurements, our model provides a more complete understanding of the thermal state of the cavity mirrors and will allow a more efficient use of the ring heaters in the Advanced Laser Interferometer Gravitational-wave Observatory.

  16. Advanced beamformers for cochlear implant users: acute measurement of speech perception in challenging listening conditions.

    Directory of Open Access Journals (Sweden)

    Andreas Buechner

    Full Text Available OBJECTIVE: To investigate the performance of monaural and binaural beamforming technology with an additional noise reduction algorithm, in cochlear implant recipients. METHOD: This experimental study was conducted as a single subject repeated measures design within a large German cochlear implant centre. Twelve experienced users of an Advanced Bionics HiRes90K or CII implant with a Harmony speech processor were enrolled. The cochlear implant processor of each subject was connected to one of two bilaterally placed state-of-the-art hearing aids (Phonak Ambra providing three alternative directional processing options: an omnidirectional setting, an adaptive monaural beamformer, and a binaural beamformer. A further noise reduction algorithm (ClearVoice was applied to the signal on the cochlear implant processor itself. The speech signal was presented from 0° and speech shaped noise presented from loudspeakers placed at ±70°, ±135° and 180°. The Oldenburg sentence test was used to determine the signal-to-noise ratio at which subjects scored 50% correct. RESULTS: Both the adaptive and binaural beamformer were significantly better than the omnidirectional condition (5.3 dB±1.2 dB and 7.1 dB±1.6 dB (p<0.001 respectively. The best score was achieved with the binaural beamformer in combination with the ClearVoice noise reduction algorithm, with a significant improvement in SRT of 7.9 dB±2.4 dB (p<0.001 over the omnidirectional alone condition. CONCLUSIONS: The study showed that the binaural beamformer implemented in the Phonak Ambra hearing aid could be used in conjunction with a Harmony speech processor to produce substantial average improvements in SRT of 7.1 dB. The monaural, adaptive beamformer provided an averaged SRT improvement of 5.3 dB.

  17. Advanced multi-frequency radar: Design, preliminary measurements and particle size distribution retrieval

    Science.gov (United States)

    Majurec, Ninoslav

    In the spring of 2001 the Microwave Remote Sensing Laboratory (MIRSL) at the University of Massachusetts began the development of an advanced Multi-Frequency Radar (AMFR) system for studying clouds and precipitation. This mobile radar was designed to consist of three polarimetric Doppler subsystems operating at Ku-band (13.4 GHz), Ka-band (35.6 GHz) and W-band (94.92 GHz). This combination of frequency bands allows a measurement of a wide range of atmospheric targets ranging from weakly reflecting clouds to strong precipitation. The antenna beamwidths at each frequency were intentionally matched, ensuring consistent sampling volume. Multi-frequency radar remote sensing techniques are not widely used because few multi-frequency radars are available to the science community. One exception is the 33 GHz/95 GHz UMass Cloud Profiling Radar System (CPRS), which AMFR is intended to replace. AMFR's multi-parameter capabilities are designed for characterizing the complex microphysics of layer clouds and precipitation processes in winter storms. AMFR will also play an important role in developing algorithms and validating measurements for an upcoming generation of space-borne radars. The frequency bands selected for AMFR match those of several sensors that have been deployed or are under development. These include the Japanese Aerospace Exploration Agencies (JAXA's) Tropical Rainfall Measuring Mission (TRMM) satellite Ku-band (13 GHz) radar, the CloudSat W-band (95 GHz) radar, and the Global Precipitation Mission (GPM) satellite radars at Ku-band and Ka-band. This dissertation describes the AMFR hardware design and development. Compared to CPRS, the addition of one extra frequency band (Ku) will extend AMFR's measurement capabilities towards the larger particle sizes (precipitation). AMFR's design is based around high-power klystron amplifiers. This ensures complete coherency (CPRS uses magnetrons and coherent-on-receive technique). The partial loss in sensitivity due to

  18. Accumulation of advanced glycation end products, measured as skin autofluorescence, in renal disease

    NARCIS (Netherlands)

    Hartog, JWL; De Vries, APJ; Lutgers, HL; Meerwaldt, R; Huisman, RM; Van Son, WJ; De Jong, PE; Smit, AJ; Baynes, JW; Monnier, VM; Ames, JM; Thorpe,

    2005-01-01

    Advanced glycation end products (AGEs) accumulate during renal failure and dialysis. Kidney transplantation is thought to reverse this accumulation by restoring renal function. Using a noninvasive and validated autofluorescence reader, we evaluated AGE levels in 285 transplant recipients (mean age,

  19. Accumulation of advanced glycation end products, measured as skin autofluorescence, in renal disease

    NARCIS (Netherlands)

    Hartog, JWL; De Vries, APJ; Lutgers, HL; Meerwaldt, R; Huisman, RM; Van Son, WJ; De Jong, PE; Smit, AJ; Baynes, JW; Monnier, VM; Ames, JM; Thorpe,

    2005-01-01

    Advanced glycation end products (AGEs) accumulate during renal failure and dialysis. Kidney transplantation is thought to reverse this accumulation by restoring renal function. Using a noninvasive and validated autofluorescence reader, we evaluated AGE levels in 285 transplant recipients (mean age,

  20. Eccentric small-zone ray tracing wavefront aberrometry for refraction in keratoconus.

    Science.gov (United States)

    Fredriksson, Anneli; Behndig, Anders

    2016-11-01

    To compare objective refraction using small-zone eccentric laser ray tracing (LRT) wavefront aberrometry to standard autorefraction in keratoconus (KC), and whether the visual acuities achieved with these refractions differ from corresponding values in healthy eyes. Twenty-nine eyes of 29 patients with KC and 29 eyes of 29 healthy controls were included in this prospective unmasked case-control study. The uncorrected (UCVA) and spectacle-corrected (SCVA) Early Treatment Diabetic Retinopathy Study (ETDRS) visual acuities based on refractions derived from LRT in central and four eccentric zones were compared to those achieved with standard autorefraction. The spherical equivalent (M) and two astigmatic power vectors (C0 and C45) were calculated for all refractions. Pentacam HR(®) was used to generate keratometry readings of the corresponding zones. In KC, the refraction from the upper nasal zone rendered a higher SCVA than the standard autorefraction more often than in the controls (p refractions rendered similar SCVA:s in KC. Pentacam HR(®) showed higher keratometry readings infero-temporally, but also lower readings supero-nasally, compared to controls. In KC, eccentric LRT measurements gave better SCVA than standard autorefraction more often than in healthy eyes. Eccentric LRT may become a valuable tool in the demanding task of subjective refraction in KC. © 2016 Acta Ophthalmologica Scandinavica Foundation. Published by John Wiley & Sons Ltd.

  1. Statistics of turbulence parameters at Maunakea using the multiple wavefront sensor data of RAVEN

    Science.gov (United States)

    Ono, Yoshito H.; Correia, Carlos M.; Andersen, Dave R.; Lardière, Olivier; Oya, Shin; Akiyama, Masayuki; Jackson, Kate; Bradley, Colin

    2017-03-01

    Prior statistical knowledge of atmospheric turbulence is essential for designing, optimizing and evaluating tomographic adaptive optics systems. We present the statistics of the vertical profiles of C_N^2 and the outer scale at Maunakea estimated using a SLOpe Detection And Ranging (SLODAR) method from on-sky telemetry taken by a multi-object adaptive optics (MOAO) demonstrator, called RAVEN, on the Subaru telescope. In our SLODAR method, the profiles are estimated by fitting the theoretical autocorrelations and cross-correlations of measurements from multiple Shack-Haltmann wavefront sensors to the observed correlations via the non-linear Levenberg-Marquardt Algorithm (LMA). The analytical derivatives of the spatial phase structure function with respect to its parameters for the LMA are also developed. From a total of 12 nights in the summer season, a large ground C_N^2 fraction of 54.3 per cent is found, with median estimated seeing of 0.460 arcsec. This median seeing value is below the results for Maunakea from the literature (0.6-0.7 arcsec). The average C_N^2 profile is in good agreement with results from the literature, except for the ground layer. The median value of the outer scale is 25.5 m and the outer scale is larger at higher altitudes; these trends of the outer scale are consistent with findings in the literature.

  2. Statistics of Turbulence Parameters at Maunakea using multiple wave-front sensor data of RAVEN

    CERN Document Server

    Ono, Yoshito H; Andersen, Dave R; Lardiere, Olivier; Oya, Shin; Akiyama, Masayuki; Jackson, Kate; Bradley, Colin

    2016-01-01

    Prior statistical knowledge of the atmospheric turbulence is essential for designing, optimizing and evaluating tomographic adaptive optics systems. We present the statistics of the vertical profiles of $C_N^2$ and the outer scale at Maunakea estimated using a Slope Detection And Ranging (SLODAR) method from on-sky telemetry taken by RAVEN, which is a MOAO demonstrator in the Subaru telescope. In our SLODAR method, the profiles are estimated by a fit of the theoretical auto- and cross-correlation of measurements from multiple Shack-Haltmann wavefront sensors to the observed correlations via the non-linear Levenberg-Marquardt Algorithm (LMA), and the analytic derivatives of the spatial phase structure function with respect to its parameters for the LMA are also developed. The estimated profile has the median total seeing of 0.460$^{\\prime\\prime}$ and large $C_N^2$ fraction of the ground layer of 54.3%. The $C_N^2$ profile has a good agreement with the result from literatures, except for the ground layer. The m...

  3. High-speed imaging and wavefront sensing with an infrared avalanche photodiode array

    CERN Document Server

    Baranec, Christoph; Riddle, Reed; Hall, Donald; Jacobson, Shane; Law, Nicholas M; Chun, Mark

    2015-01-01

    Infrared avalanche photodiode arrays represent a panacea for many branches of astronomy by enabling extremely low-noise, high-speed and even photon-counting measurements at near-infrared wavelengths. We recently demonstrated the use of an early engineering-grade infrared avalanche photodiode array that achieves a correlated double sampling read noise of 0.73 e- in the lab, and a total noise of 2.52 e- on sky, and supports simultaneous high-speed imaging and tip-tilt wavefront sensing with the Robo-AO visible-light laser adaptive optics system at the Palomar Observatory 1.5-m telescope. We report here on the improved image quality achieved simultaneously at visible and infrared wavelengths by using the array as part of an image stabilization control-loop with adaptive-optics sharpened guide stars. We also discuss a newly enabled survey of nearby late M-dwarf multiplicity as well as future uses of this technology in other adaptive optics and high-contrast imaging applications.

  4. Pyramid wavefront sensing with a laser guide star for an ELT

    Science.gov (United States)

    Le Roux, Brice

    2010-07-01

    The wavefront sensor [WFS] is a key element of an Adaptive Optics [AO] system. It gives access to a direct measurement of the turbulent phase, its curvature or its slope, from which the mirror voltages are computed. The ability of the system to correct efficiently the atmospheric turbulence is strongly dependent on the performance of the WFS in estimating the turbulent phase. The Shack-Hartmann [SH] WFS has been for a long time the standard used in AO systems. In 1996, it has been proposed1 a new generation WFS, the pyramid WFS. It is a focal plane WFS, based on the principle of a Foucault knife-edge. It has been demonstrated that it provides a consistent gain with respect to the Shack-Hartmann.2,5-7 More recently, improvements were proposed to increase the pyramid performance.3, 4 On the framework of the developpement of extremely large telescopes, the interest of a pyramid wave front sensor appears clearly. But its behaviour with laser guide stars [LGS], most probably necessary in any Extremely Large Telescope [ELT], is still relatively unknown. Some WFS dedicated to LGS wave front sensing has already been proposed8,9 but a full study of the pyramid WFS behaviour is still necessary. This work's aim is to bring answers to this topic.

  5. Effect of Pupil Size on Wavefront Refraction during Orthokeratology.

    Science.gov (United States)

    Faria-Ribeiro, Miguel; Navarro, Rafael; González-Méijome, José Manuel

    2016-11-01

    It has been hypothesized that central and peripheral refraction, in eyes treated with myopic overnight orthokeratology, might vary with changes in pupil diameter. The aim of this work was to evaluate the axial and peripheral refraction and optical quality after orthokeratology, using ray tracing software for different pupil sizes. Zemax-EE was used to generate a series of 29 semi-customized model eyes based on the corneal topography changes from 29 patients who had undergone myopic orthokeratology. Wavefront refraction in the central 80 degrees of the visual field was calculated using three different quality metrics criteria: Paraxial curvature matching, minimum root mean square error (minRMS), and the Through Focus Visual Strehl of the Modulation Transfer Function (VSMTF), for 3- and 6-mm pupil diameters. The three metrics predicted significantly different values for foveal and peripheral refractions. Compared with the Paraxial criteria, the other two metrics predicted more myopic refractions on- and off-axis. Interestingly, the VSMTF predicts only a marginal myopic shift in the axial refraction as the pupil changes from 3 to 6 mm. For peripheral refraction, minRMS and VSMTF metric criteria predicted a higher exposure to peripheral defocus as the pupil increases from 3 to 6 mm. The results suggest that the supposed effect of myopic control produced by ortho-k treatments might be dependent on pupil size. Although the foveal refractive error does not seem to change appreciably with the increase in pupil diameter (VSMTF criteria), the high levels of positive spherical aberration will lead to a degradation of lower spatial frequencies, that is more significant under low illumination levels.

  6. Aligning a more than 100 degrees of freedom wavefront sensor

    Science.gov (United States)

    Marafatto, Luca; Bergomi, Maria; Brunelli, Alessandro; Dima, Marco; Farinato, Jacopo; Farisato, Giancarlo; Lessio, Luigi; Magrin, Demetrio; Ragazzoni, Roberto; Viotto, Valentina; Bertram, Thomas; Bizenberger, Peter; Brangier, Matthieu; Briegel, Florian; Conrad, Albert; De Bonis, Fulvio; Herbst, Tom; Hofferbert, Ralph; Kittmann, Frank; Kürster, Martin; Meschke, Daniel; Mohr, Lars; Rohloff, Ralf-Rainer

    2012-07-01

    LINC-NIRVANA is the Fizeau beam combiner for the LBT, with the aim to retrieve the sensitivity of a 12m telescope and the spatial resolution of a 22.8m one. Despite being only one of the four wavefront sensors of a layer-oriented MCAO system, the GWS, which is retrieving the deformation introduced by the lower atmosphere, known to be the main aberration source, reveals a noticeable internal opto-mechanical complexity. The presence of 12 small devices used to select up to the same number of NGSs, with 3 optical components each, moving in a wide annular 2'-6' arcmin Field of View and sending the light to a common pupil re-imager, and the need to obtain and keep a very good super-imposition of the pupil images on the CCD camera, led to an overall alignment procedure in which more than a hundred of degrees of freedom have to be contemporary adjusted. The rotation of the entire WFS to compensate for the sky movement, moreover, introduces a further difficulty both in the alignment and in ensuring the required pupil superposition stability. A detailed description of the alignment procedure is presented here, together with the lessons learned managing the complexity of such a WFS, which led to considerations regarding future instruments, like a possible review of numerical versus optical co-add approach, above all if close to zero read-out noise detectors will be soon available. Nevertheless, the GWS AIV has been carried out and the system will be soon mounted at LBT to perform what is called the Pathfinder experiment, which consists in ground-layer correction, taking advantage of the Adaptive Secondary deformable Mirror.

  7. An Optical Wavefront Sensor Based on a Double Layer Microlens Array

    Directory of Open Access Journals (Sweden)

    Hsiang-Chun Wei

    2011-10-01

    Full Text Available In order to determine light aberrations, Shack-Hartmann optical wavefront sensors make use of microlens arrays (MLA to divide the incident light into small parts and focus them onto image planes. In this paper, we present the design and fabrication of long focal length MLA with various shapes and arrangements based on a double layer structure for optical wavefront sensing applications. A longer focal length MLA could provide high sensitivity in determining the average slope across each microlens under a given wavefront, and spatial resolution of a wavefront sensor is increased by numbers of microlenses across a detector. In order to extend focal length, we used polydimethysiloxane (PDMS above MLA on a glass substrate. Because of small refractive index difference between PDMS and MLA interface (UV-resin, the incident light is less refracted and focused in further distance. Other specific focal lengths could also be realized by modifying the refractive index difference without changing the MLA size. Thus, the wavefront sensor could be improved with better sensitivity and higher spatial resolution.

  8. Negating effects from sodium profile variations for TMT: the MOR truth wavefront sensor of NFIRAOS

    Science.gov (United States)

    Andersen, David R.; Conan, Rodolphe; Ellerbroek, Brent; Herriot, Glen; Véran, Jean-Pierre

    2008-07-01

    The Moderate Order Radial (MOR) Truth Wavefront Sensor (TWFS) of NFIRAOS, the facility AO system for TMT, is a visible light order 12x12 subaperture Shack-Hartmann WFS. Its role is to sense radial wavefront errors arising from variations in the Sodium layer profile that are not sensed by the on-instrument near infrared tip-tilt focus wavefront sensor at a sampling frequency on the order of one Herz. It works in concert with the High Order Low bandwidth (HOL) TWFS, which will use a 120x120 subaperture Shack-Hartmann WFS that senses slow variations in telescope flexure and the rotation of the pupil. Top-level requirements for NFIRAOS leave little margin for degradation in sky coverage or additional implementation wavefront errors introduced by the operation of the MOR TWFS. In this paper, we explore MOR TWFS design trade studies on the number of subapertures, sampling rate, the width of the MOR TWFS visible bandpass, and the split in light between the MOR and HOL TWFS, and present a design for a system which meets the top level requirements by not degrading the high sky coverage of NFIRAOS (50% sky coverage at the Galactic poles) and rejecting the radial modes with a residual wavefront error of 10nm.

  9. Wavefront control of high power laser beams for the National Ignition Facility (NIF)

    Energy Technology Data Exchange (ETDEWEB)

    Bliss, E; Feldman, M; Grey, A; Koch, J; Lund, L; Sacks, R; Smith, D; Stolz, C; Van Atta, L; Winters, S; Woods, B; Zacharias, R

    1999-09-22

    The use of lasers as the driver for inertial confinement fusion and weapons physics experiments is based on their ability to produce high-energy short pulses in a beam with low divergence. Indeed, the focus ability of high quality laser beams far exceeds alternate technologies and is a major factor in the rationale for building high power lasers for such applications. The National Ignition Facility (NIF) is a large, 192-beam, high-power laser facility under construction at the Lawrence Livermore National Laboratory for fusion and weapons physics experiments. Its uncorrected minimum focal spot size is limited by laser system aberrations. The NIF includes a Wavefront Control System to correct these aberrations to yield a focal spot small enough for its applications. Sources of aberrations to be corrected include prompt pump-induced distortions in the laser amplifiers, previous-shot thermal distortions, beam off-axis effects, and gravity, mounting, and coating-induced optic distortions. Aberrations from gas density variations and optic manufacturing figure errors are also partially corrected. This paper provides an overview of the NIF Wavefront Control System and describes the target spot size performance improvement it affords. It describes provisions made to accommodate the NIF's high fluence (laser beam and flashlamp), large wavefront correction range, wavefront temporal bandwidth, temperature and humidity variations, cleanliness requirements, and exception handling requirements (e.g. wavefront out-of-limits conditions).

  10. End-To-End performance test of the LINC-NIRVANA Wavefront-Sensor system.

    Science.gov (United States)

    Berwein, Juergen; Bertram, Thomas; Conrad, Al; Briegel, Florian; Kittmann, Frank; Zhang, Xiangyu; Mohr, Lars

    2011-09-01

    LINC-NIRVANA is an imaging Fizeau interferometer, for use in near infrared wavelengths, being built for the Large Binocular Telescope. Multi-conjugate adaptive optics (MCAO) increases the sky coverage and the field of view over which diffraction limited images can be obtained. For its MCAO implementation, Linc-Nirvana utilizes four total wavefront sensors; each of the two beams is corrected by both a ground-layer wavefront sensor (GWS) and a high-layer wavefront sensor (HWS). The GWS controls the adaptive secondary deformable mirror (DM), which is based on an DSP slope computing unit. Whereas the HWS controls an internal DM via computations provided by an off-the-shelf multi-core Linux system. Using wavefront sensor data collected from a prior lab experiment, we have shown via simulation that the Linux based system is sufficient to operate at 1kHz, with jitter well below the needs of the final system. Based on that setup we tested the end-to-end performance and latency through all parts of the system which includes the camera, the wavefront controller, and the deformable mirror. We will present our loop control structure and the results of those performance tests.

  11. Representation of wavefronts in free-form transmission pupils with Complex Zernike Polynomials

    Science.gov (United States)

    Navarro, Rafael; Rivera, Ricardo; Aporta, Justiniano

    2011-01-01

    Purpose To propose and evaluate Complex Zernike polynomials (CZPs) to represent general wavefronts with non uniform intensity (amplitude) in free-from transmission pupils. Methods They consist of three stages: (1) theoretical formulation; (2) numerical implementation; and (3) two studies of the fidelity of the reconstruction obtained as a function of the number of Zernike modes used (36 or 91). In the first study, we generated complex wavefronts merging wave aberration data from a group of 11 eyes, with a generic Gaussian model of the Stiles-Crawford effective pupil transmission. In the second study we simulated the wavefront passing through different pupil stop shapes (annular, semicircular, elliptical and triangular). Results The reconstructions of the wave aberration (phase of the generalized pupil function) were always good, the reconstruction RMS error was of the order of 10−4 wave lengths, no matter the number of modes used. However, the reconstruction of the amplitude (effective transmission) was highly dependent of the number of modes used. In particular, a high number of modes is necessary to reconstruct sharp edges, due to their high frequency content. Conclusions CZPs provide a complete orthogonal basis able to represent generalized pupil functions (or complex wavefronts). This provides a unified general framework in contrast to the previous variety of ad oc solutions. Our results suggest that complex wavefronts require a higher number of CZP, but they seem especially well-suited for inhomogeneous beams, pupil apodization, etc.

  12. X-ray wavefront characterization using a rotating shearing interferometer technique.

    Science.gov (United States)

    Wang, Hongchang; Sawhney, Kawal; Berujon, Sébastien; Ziegler, Eric; Rutishauser, Simon; David, Christian

    2011-08-15

    A fast and accurate method to characterize the X-ray wavefront by rotating one of the two gratings of an X-ray shearing interferometer is described and investigated step by step. Such a shearing interferometer consists of a phase grating mounted on a rotation stage, and an absorption grating used as a transmission mask. The mathematical relations for X-ray Moiré fringe analysis when using this device are derived and discussed in the context of the previous literature assumptions. X-ray beam wavefronts without and after X-ray reflective optical elements have been characterized at beamline B16 at Diamond Light Source (DLS) using the presented X-ray rotating shearing interferometer (RSI) technique. It has been demonstrated that this improved method allows accurate calculation of the wavefront radius of curvature and the wavefront distortion, even when one has no previous information on the grating projection pattern period, magnification ratio and the initial grating orientation. As the RSI technique does not require any a priori knowledge of the beam features, it is suitable for routine characterization of wavefronts of a wide range of radii of curvature.

  13. Optimization design of an adaptive CFRC reflector for high order wave-front error control

    Science.gov (United States)

    Lan, Lan; Fang, Houfei; Wu, Ke; Jiang, Shuidong; Zhou, Yang

    2017-04-01

    The trend in future space high precision reflectors is going towards large aperture, lightweight and actively controlled deformable antennas. An adaptive shape control system for a Carbon Fiber Reinforced Composite (CFRC) reflector is conducted by Piezoelectric Ceramic Transducer (PZT) actuators. This adaptive shape control system has been shown to effectively mitigate common low order wave-front error, but it is inevitably plagued by high order wave-front error control. In order to improve the controllability of the adaptive CFRC reflector control system for high order wave-front error, the design of adaptive CFRC reflector requires optimizing further. According to numerical and experimental results, the print-through error induced by manufacturing and PZT actuators actuation is a type of predominant high order wave-front error. This paper describes a design which some secondary rib elements are embedded within the triangular cells of the primary ribs. These small secondary ribs are designed to support the reflector surface's weak region. Controllability of this new adaptive CFRC reflector control system with small secondary ribs is evaluated by generalized Zernike functions. This new design scheme can reduce high order residual error and suppress the high order wave-front error such as print-through error. Finally, design parameters of the adaptive CFRC reflector control system with small secondary ribs, such as primary rib height, secondary rib height, cut-out height of primary rib, are optimized.

  14. X-ray wavefront characterization using a rotating shearing interferometer technique

    Science.gov (United States)

    Wang, Hongchang; Sawhney, Kawal; Berujon, Sébastien; Ziegler, Eric; Rutishauser, Simon; David, Christian

    2011-08-01

    A fast and accurate method to characterize the X-ray wavefront by rotating one of the two gratings of an X-ray shearing interferometer is described and investigated step by step. Such a shearing interferometer consists of a phase grating mounted on a rotation stage, and an absorption grating used as a transmission mask. The mathematical relations for X-ray Moiré fringe analysis when using this device are derived and discussed in the context of the previous literature assumptions. X-ray beam wavefronts without and after X-ray reflective optical elements have been characterized at beamline B16 at Diamond Light Source (DLS) using the presented X-ray rotating shearing interferometer (RSI) technique. It has been demonstrated that this improved method allows accurate calculation of the wavefront radius of curvature and the wavefront distortion, even when one has no previous information on the grating projection pattern period, magnification ratio and the initial grating orientation. As the RSI technique does not require any a priori knowledge of the beam features, it is suitable for routine characterization of wavefronts of a wide range of radii of curvature.

  15. Wavefront printing technique with overlapping approach toward high definition holographic image reconstruction

    Science.gov (United States)

    Wakunami, K.; Oi, R.; Senoh, T.; Sasaki, H.; Ichihashi, Y.; Yamamoto, K.

    2016-06-01

    A hologram recording technique, generally called as "wavefront printer", has been proposed by several research groups for static three-dimensional (3D) image printing. Because the pixel number of current spatial light modulators (SLMs) is not enough to reconstruct the entire wavefront in recording process, typically, hologram data is divided into a set of subhologram data and each wavefront is recorded sequentially as a small sub-hologram cell in tiling manner by using X-Y motorized stage. However since previous works of wavefront printer do not optimize the cell size, the reconstructed images were degraded by obtrusive split line due to visible cell size caused by too large cell size for human eyesight, or by diffraction effect due to discontinuity of phase distribution caused by too small cell size. In this paper, we introduce overlapping recording approach of sub-holograms to achieve both conditions: enough smallness of apparent cell size to make cells invisible and enough largeness of recording cell size to suppress diffraction effect by keeping the phase continuity of reconstructed wavefront. By considering observing condition and optimization of the amount of overlapping and cell size, in the experiment, the proposed approach showed higher quality 3D image reconstruction while the conventional approach suffered visible split lines and cells.

  16. A sound ray tracing algorithm in three-dimensional heterogeneous media based on wavefront traveltimes interpolation

    Institute of Scientific and Technical Information of China (English)

    HUANG Yueqin; ZHANG Jianzhong

    2008-01-01

    A kind of three-dimensional(3-D) sound ray tracing algorithm in heterogeneous media is studied. This algorithm includes two steps: the first step computes the wavefront traveltimes forward; the second step traces the sound rays backward. In the first step, the computation of wavefront traveltimes at discrete grid points from the sound source, was found on Eikonal equation solutions and carried out by GMM (Group marching method) wavefront marching method based on level set. In the second step, sound ray tracing was proceeded gradually from the receiver to each cell towards the sound source, with wavefront traveltimes computed in the first step. Time values on arbitrary positions in each cuboid cell can be expressed by linear interpolation of wavefront traveltimes at the same cell's grid points. Thus,an algorithm of 3-D sound ray tracing in heterogeneous media is put forward. The simulation results indicate that this method can improve both the accuracy and the efficiency of 3-D sound ray tracing greatly.

  17. Advances in standardization of laboratory measurement procedures: implications for measuring biomarkers of folate and vitamin B-12 status in NHANES

    National Research Council Canada - National Science Library

    Bock, Jay L; Eckfeldt, John H

    2011-01-01

    Population studies such as NHANES analyze large numbers of laboratory measurements and are often performed in different laboratories using different measurement procedures and over an extended period of time...

  18. Land Surface Microwave Emissivities Derived from AMSR-E and MODIS Measurements with Advanced Quality Control

    Science.gov (United States)

    Moncet, Jean-Luc; Liang, Pan; Galantowicz, John F.; Lipton, Alan E.; Uymin, Gennady; Prigent, Catherine; Grassotti, Christopher

    2011-01-01

    A microwave emissivity database has been developed with data from the Advanced Microwave Scanning Radiometer-EOS (AMSR-E) and with ancillary land surface temperature (LST) data from the Moderate Resolution Imaging Spectroradiometer (MODIS) on the same Aqua spacecraft. The primary intended application of the database is to provide surface emissivity constraints in atmospheric and surface property retrieval or assimilation. An additional application is to serve as a dynamic indicator of land surface properties relevant to climate change monitoring. The precision of the emissivity data is estimated to be significantly better than in prior databases from other sensors due to the precise collocation with high-quality MODIS LST data and due to the quality control features of our data analysis system. The accuracy of the emissivities in deserts and semi-arid regions is enhanced by applying, in those regions, a version of the emissivity retrieval algorithm that accounts for the penetration of microwave radiation through dry soil with diurnally varying vertical temperature gradients. These results suggest that this penetration effect is more widespread and more significant to interpretation of passive microwave measurements than had been previously established. Emissivity coverage in areas where persistent cloudiness interferes with the availability of MODIS LST data is achieved using a classification-based method to spread emissivity data from less-cloudy areas that have similar microwave surface properties. Evaluations and analyses of the emissivity products over homogeneous snow-free areas are presented, including application to retrieval of soil temperature profiles. Spatial inhomogeneities are the largest in the vicinity of large water bodies due to the large water/land emissivity contrast and give rise to large apparent temporal variability in the retrieved emissivities when satellite footprint locations vary over time. This issue will be dealt with in the future by

  19. A structured review of health utility measures and elicitation in advanced/metastatic breast cancer.

    Science.gov (United States)

    Hao, Yanni; Wolfram, Verena; Cook, Jennifer

    2016-01-01

    Health utilities are increasingly incorporated in health economic evaluations. Different elicitation methods, direct and indirect, have been established in the past. This study examined the evidence on health utility elicitation previously reported in advanced/metastatic breast cancer and aimed to link these results to requirements of reimbursement bodies. Searches were conducted using a detailed search strategy across several electronic databases (MEDLINE, EMBASE, Cochrane Library, and EconLit databases), online sources (Cost-effectiveness Analysis Registry and the Health Economics Research Center), and web sites of health technology assessment (HTA) bodies. Publications were selected based on the search strategy and the overall study objectives. A total of 768 publications were identified in the searches, and 26 publications, comprising 18 journal articles and eight submissions to HTA bodies, were included in the evidence review. Most journal articles derived utilities from the European Quality of Life Five-Dimensions questionnaire (EQ-5D). Other utility measures, such as the direct methods standard gamble (SG), time trade-off (TTO), and visual analog scale (VAS), were less frequently used. Several studies described mapping algorithms to generate utilities from disease-specific health-related quality of life (HRQOL) instruments such as European Organization for Research and Treatment of Cancer Quality of Life Questionnaire - Core 30 (EORTC QLQ-C30), European Organization for Research and Treatment of Cancer Quality of Life Questionnaire - Breast Cancer 23 (EORTC QLQ-BR23), Functional Assessment of Cancer Therapy - General questionnaire (FACT-G), and Utility-Based Questionnaire-Cancer (UBQ-C); most used EQ-5D as the reference. Sociodemographic factors that affect health utilities, such as age, sex, income, and education, as well as disease progression, choice of utility elicitation method, and country settings, were identified within the journal articles. Most

  20. Land Surface Microwave Emissivities Derived from AMSR-E and MODIS Measurements with Advanced Quality Control

    Science.gov (United States)

    Moncet, Jean-Luc; Liang, Pan; Galantowicz, John F.; Lipton, Alan E.; Uymin, Gennady; Prigent, Catherine; Grassotti, Christopher

    2011-01-01

    A microwave emissivity database has been developed with data from the Advanced Microwave Scanning Radiometer-EOS (AMSR-E) and with ancillary land surface temperature (LST) data from the Moderate Resolution Imaging Spectroradiometer (MODIS) on the same Aqua spacecraft. The primary intended application of the database is to provide surface emissivity constraints in atmospheric and surface property retrieval or assimilation. An additional application is to serve as a dynamic indicator of land surface properties relevant to climate change monitoring. The precision of the emissivity data is estimated to be significantly better than in prior databases from other sensors due to the precise collocation with high-quality MODIS LST data and due to the quality control features of our data analysis system. The accuracy of the emissivities in deserts and semi-arid regions is enhanced by applying, in those regions, a version of the emissivity retrieval algorithm that accounts for the penetration of microwave radiation through dry soil with diurnally varying vertical temperature gradients. These results suggest that this penetration effect is more widespread and more significant to interpretation of passive microwave measurements than had been previously established. Emissivity coverage in areas where persistent cloudiness interferes with the availability of MODIS LST data is achieved using a classification-based method to spread emissivity data from less-cloudy areas that have similar microwave surface properties. Evaluations and analyses of the emissivity products over homogeneous snow-free areas are presented, including application to retrieval of soil temperature profiles. Spatial inhomogeneities are the largest in the vicinity of large water bodies due to the large water/land emissivity contrast and give rise to large apparent temporal variability in the retrieved emissivities when satellite footprint locations vary over time. This issue will be dealt with in the future by

  1. Wavefront depinning in semiconductor superlattices due to discrete-mapping failure

    Institute of Scientific and Technical Information of China (English)

    Wang Jun; Zheng Zhi-Gang

    2008-01-01

    We investigate the wavefronts depinning in current biased,infinitely long semiconductor superlattice systems by the method of discrete mapping and show that the wavefront depinning corresponds to the discrete mapping failure.For parameter values near the lower critical current in both discrete drift model (DD model) and discrete drift-diffusion model (DDD model),the mapping failure is determined by the important mapping step from the bottom of branch γ to branch α.For the upper critical parameters in DDD model,the key mapping step is from branch γ to the top of the corresponding branch α,and we may need several active wells to describe the wavefronts.

  2. High contrast imaging of exoplanets on ELTs using a super-Nyquist wavefront control scheme

    CERN Document Server

    Gerard, Benjamin L

    2016-01-01

    One of the key science goals for extremely large telescopes (ELTs) is the detailed characterization of already known directly imaged exoplanets. The typical adaptive optics (AO) Nyquist control region for ELTs is ~0.4 arcseconds, placing many already known directly imaged planets outside the DM control region and not allowing any standard wavefront control scheme to remove speckles that would allow higher SNR images/spectra to be acquired. This can be fixed with super-Nyquist wavefront control (SNWFC), using a sine wave phase plate to allow for wavefront control outside the central DM Nyquist region. We demonstrate that SNWFC is feasible through a simple, deterministic, non-coronagraphic, super-Nyquist speckle nulling technique in the adaptive optics laboratory at the National Research Council of Canada. We also present results in simulation of how SNWFC using the self coherent camera (SCC) can be used for high contrast imaging. This technique could be implemented on future high contrast imaging instruments t...

  3. Nonlinear photoacoustic wavefront shaping (PAWS) for single speckle-grain optical focusing in scattering media

    CERN Document Server

    Lai, Puxiang; Tay, Jian Wei; Wang, Lihong V

    2014-01-01

    Non-invasively focusing light into strongly scattering media, such as biological tissue, is highly desirable but challenging. Recently, wavefront shaping technologies guided by ultrasonic encoding or photoacoustic sensing have been developed to address this limitation. So far, these methods provide only acoustic diffraction-limited optical focusing. Here, we introduce nonlinear photoacoustic wavefront shaping (PAWS), which achieves optical diffraction-limited (i.e. single-speckle-grain) focusing in scattering media. We develop an efficient dual-pulse excitation approach to generate strong nonlinear photoacoustic (PA) signals based on the Grueneisen memory effect. These nonlinear PA signals are used as feedback to guide iterative wavefront optimization. By maximizing the amplitude of the nonlinear PA signal, light is effectively focused to a single optical speckle grain. Experimental results demonstrate a clear optical focus on the scale of 5-7 micrometers, which is ~10 times smaller than the acoustic focus in...

  4. Zonal wavefront sensing using a grating array printed on a polyester film

    Energy Technology Data Exchange (ETDEWEB)

    Pathak, Biswajit; Boruah, Bosanta R., E-mail: brboruah@iitg.ernet.in [Department of Physics, Indian Institute of Technology Guwahati, Guwahati, Assam 781039 (India); Kumar, Suraj [Department of Applied Sciences, Gauhati University, Guwahati, Assam 781014 (India)

    2015-12-15

    In this paper, we describe the development of a zonal wavefront sensor that comprises an array of binary diffraction gratings realized on a transparent sheet (i.e., polyester film) followed by a focusing lens and a camera. The sensor works in a manner similar to that of a Shack-Hartmann wavefront sensor. The fabrication of the array of gratings is immune to certain issues associated with the fabrication of the lenslet array which is commonly used in zonal wavefront sensing. Besides the sensing method offers several important advantages such as flexible dynamic range, easy configurability, and option to enhance the sensing frame rate. Here, we have demonstrated the working of the proposed sensor using a proof-of-principle experimental arrangement.

  5. On distributed wavefront reconstruction for large-scale adaptive optics systems.

    Science.gov (United States)

    de Visser, Cornelis C; Brunner, Elisabeth; Verhaegen, Michel

    2016-05-01

    The distributed-spline-based aberration reconstruction (D-SABRE) method is proposed for distributed wavefront reconstruction with applications to large-scale adaptive optics systems. D-SABRE decomposes the wavefront sensor domain into any number of partitions and solves a local wavefront reconstruction problem on each partition using multivariate splines. D-SABRE accuracy is within 1% of a global approach with a speedup that scales quadratically with the number of partitions. The D-SABRE is compared to the distributed cumulative reconstruction (CuRe-D) method in open-loop and closed-loop simulations using the YAO adaptive optics simulation tool. D-SABRE accuracy exceeds CuRe-D for low levels of decomposition, and D-SABRE proved to be more robust to variations in the loop gain.

  6. Effect of the laser wavefront in a laser-plasma accelerator

    CERN Document Server

    Beaurepaire, B; Bocoum, M; Böhle, F; Jullien, A; Rousseau, J-P; Lefrou, T; Douillet, D; Iaquaniello, G; Lopez-Martens, R; Lifschitz, A; Faure, J

    2015-01-01

    A high repetition rate electron source was generated by tightly focusing kHz, few-mJ laser pulses into an underdense plasma. This high intensity laser-plasma interaction led to stable electron beams over several hours but with strikingly complex transverse distributions even for good quality laser focal spots. Analysis of the experimental data, along with results of PIC simulations demonstrate the role of the laser wavefront on the acceleration of electrons. Distortions of the laser wavefront cause spatial inhomogeneities in the out-of-focus laser distribution and consequently, the laser pulse drives an inhomogenous transverse wakefield whose focusing/defocusing properties affect the electron distribution. These findings explain the experimental results and suggest the possibility of controlling the electron spatial distribution in laser-plasma accelerators by tailoring the laser wavefront.

  7. Bayesian inference for a wavefront model of the Neolithisation of Europe

    CERN Document Server

    Baggaley, Andrew W; Shukurov, Anvar; Boys, Richard J; Golightly, Andrew

    2012-01-01

    We consider a wavefront model for the spread of Neolithic culture across Europe, and use Bayesian inference techniques to provide estimates for the parameters within this model, as constrained by radiocarbon data from Southern and Western Europe. Our wavefront model allows for both an isotropic background spread (incorporating the effects of local geography), and a localized anisotropic spread associated with major waterways. We introduce an innovative numerical scheme to track the wavefront, allowing us to simulate the times of the first arrival at any site orders of magnitude more efficiently than traditional PDE approaches. We adopt a Bayesian approach to inference and use Gaussian process emulators to facilitate further increases in efficiency in the inference scheme, thereby making Markov chain Monte Carlo methods practical. We allow for uncertainty in the fit of our model, and also infer a parameter specifying the magnitude of this uncertainty. We obtain a magnitude for the background spread of order 1 ...

  8. Reconstruction and calibration on aero-optical wavefront ab erration based on background oriented schlieren based wavefront sensing%基于背景纹影波前传感技术的气动光学波前重构与校正∗

    Institute of Scientific and Technical Information of China (English)

    张天天; 易仕和; 朱杨柱; 何霖

    2015-01-01

    Background oriented schlieren based wavefront sensing (BOS-WS) is a new experimental technique for measuring the two-dimensional distribution of optical wavefronts and the optical path differences (OPDs) induced by the flow-field density variations. Background oriented schlieren (BOS) is traditionally used to test the flow-field density distribution, which restricts the obtaining of useful information since the obtained density information is integrated over the optical path. The OPD is very important for predicting the optical distortion when light travels through the flow field and it is tested by BOS-WS. In order to obtain the optical distortion generated by aero-optic effect, and restore the original image from the distortion known information so as to explore a new kind of supersonic imaging guidance method, theory analysis, numerical simulation and experimental methods are used based on BOS-WS. Through theoretical analysis, the wavefront measurement method based on BOS is verified and the calculation methods of using wavefront information known to predict distortion displacement field and using known displacement field to reconstruct wavefront are explored. By numerical simulation, the error sizes and the result rationalities of one stepped integral algorithm and Southwell method on the wavefront reconstruction are compared, and through the error analysis it is proved that the Southwell method is more accurate and reasonable. By a wavefront aberration experiment carried out in the flow field above the candle flame and a lens perturbation experiment, the methods of using OPD known to reconstruct distorted displacement field and correcting image distortion by the field are creatively explored. The verification experiments show the effectiveness of the correction method.%背景纹影波前传感(background oriented schlieren based wavefront sensing, BOS-WS)是利用背景纹影技术测量光学波前二维分布的新型实验手段,可定量测量光线通过

  9. Angular-divergence calculation for Experimental Advanced Superconducting Tokamak neutral beam injection ion source based on spectroscopic measurements

    Energy Technology Data Exchange (ETDEWEB)

    Chi, Yuan, E-mail: jtext@hust.edu.cn [State Key Laboratory of Advanced Electromagnetic Engineering and Technology, Huazhong University of Science and Technology, Wuhan 430074 (China); Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031 (China); Hu, Chundong [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031 (China); Zhuang, Ge [State Key Laboratory of Advanced Electromagnetic Engineering and Technology, Huazhong University of Science and Technology, Wuhan 430074 (China)

    2014-02-15

    Calorimetric method has been primarily applied for several experimental campaigns to determine the angular divergence of high-current ion source for the neutral beam injection system on the Experimental Advanced Superconducting Tokamak (EAST). A Doppler shift spectroscopy has been developed to provide the secondary measurement of the angular divergence to improve the divergence measurement accuracy and for real-time and non-perturbing measurement. The modified calculation model based on the W7AS neutral beam injectors is adopted to accommodate the slot-type accelerating grids used in the EAST's ion source. Preliminary spectroscopic experimental results are presented comparable to the calorimetrically determined value of theoretical calculation.

  10. H2-optimal control of an adaptive optics system: part I, data-driven modeling of the wavefront disturbance

    NARCIS (Netherlands)

    Hinnen, K.; Verhaegen, M.; Doelman, N.

    2005-01-01

    Even though the wavefront distortion introduced by atmospheric turbulence is a dynamic process, its temporal evolution is usually neglected in the adaptive optics (AO) control design. Most AO control systems consider only the spatial correlation in a separate wavefront reconstruction step. By accoun

  11. Wave propagation of the traffic flow dynamic model based on wavefront expansion

    Institute of Scientific and Technical Information of China (English)

    李莉; 施鹏飞

    2004-01-01

    This paper discusses propagation of perturbations along traffic flow modeled by a modified second-order macroscopic model through the wavefront expansion technique. The coefficients in this expansion satisfy a sequence of transport equations that can be solved analytically. One of these analytic solutions yields information about wavefront shock. Numerical simulations based on a Padé approximation of this expansion were done at the end of this paper and results showed that propagation of perturbations at traffic flow speed conforms to the theoretical analysis results.

  12. X-ray active mirror coupled with a Hartmann wavefront sensor

    Energy Technology Data Exchange (ETDEWEB)

    Idir, Mourad, E-mail: mourad.idir@synchrotron-soleil.f [Synchrotron SOLEIL, L' orme des Merisiers, BP 48, 91 192 Gif sur Yvette (France); Mercere, Pascal [Synchrotron SOLEIL, L' orme des Merisiers, BP 48, 91 192 Gif sur Yvette (France); Modi, Mohammed H. [X-ray Optics Section, Raja Ramanna Centre for Advanced Technology, Indore (India); Dovillaire, Guillaume; Levecq, Xavier; Bucourt, Samuel [Imagine Optic, 18 rue Charles de Gaulle, Orsay 91400 (France); Escolano, Lionel; Sauvageot, Paul [ISP System, ZI de la Herray BP 10047, Vic en Bigorre (France)

    2010-05-01

    This paper reports on the design and performances of a test prototype active X-ray mirror (AXM) which has been designed and manufactured in collaboration with the French Small and Medium Enterprise mechanical company ISP System for the national French storage ring SOLEIL. Coupled with this active X-ray mirror and also in collaboration with another French Small and Medium Enterprise (Imagine Optic) a lot of efforts have been done in order to design and fabricate a wavefront X-ray analyzer based on the Hartmann principle (Hartman wavefront sensor, HWS).

  13. 2D wave-front shaping in optical superlattices using nonlinear volume holography.

    Science.gov (United States)

    Yang, Bo; Hong, Xu-Hao; Lu, Rong-Er; Yue, Yang-Yang; Zhang, Chao; Qin, Yi-Qiang; Zhu, Yong-Yuan

    2016-07-01

    Nonlinear volume holography is employed to realize arbitrary wave-front shaping during nonlinear processes with properly designed 2D optical superlattices. The concept of a nonlinear polarization wave in nonlinear volume holography is investigated. The holographic imaging of irregular patterns was performed using 2D LiTaO3 crystals with fundamental wave propagating along the spontaneous polarization direction, and the results agree well with the theoretical predictions. This Letter not only extends the application area of optical superlattices, but also offers an efficient method for wave-front shaping technology.

  14. 110 °C range athermalization of wavefront coding infrared imaging systems

    Science.gov (United States)

    Feng, Bin; Shi, Zelin; Chang, Zheng; Liu, Haizheng; Zhao, Yaohong

    2017-09-01

    110 °C range athermalization is significant but difficult for designing infrared imaging systems. Our wavefront coding athermalized infrared imaging system adopts an optical phase mask with less manufacturing errors and a decoding method based on shrinkage function. The qualitative experiments prove that our wavefront coding athermalized infrared imaging system has three prominent merits: (1) working well over a temperature range of 110 °C; (2) extending the focal depth up to 15.2 times; (3) achieving a decoded image being approximate to its corresponding in-focus infrared image, with a mean structural similarity index (MSSIM) value greater than 0.85.

  15. Traveling wavefronts in nonlocal diffusive predator-prey system with Holling type II functional response

    Directory of Open Access Journals (Sweden)

    Shuang Li

    2015-06-01

    Full Text Available This article concerns the existence of traveling wavefronts for a nonlocal diffusive predator-prey system with functional response of Holling type II. We first establish the existence principle for the system with a general functional response by using a fixed point theorem and upper-lower solution technique. We apply this result to a predator-prey model with Holling type II functional response. We deduce the existence of traveling wavefronts that connect the zero equilibrium and the positive equilibrium.

  16. Geometry and dynamics of fast magnetosonic wavefronts near magnetic null points

    Science.gov (United States)

    Núñez, Manuel

    2017-02-01

    The behavior of two-dimensional fast magnetosonic waves in the vicinity of isolated points where the magnetic field vanishes is studied analytically. The geometry of rays and wavefronts is described, and the curvature of both is found using conformal mapping techniques. These results are applied to the formation of shock waves, obtaining that shock formation is guaranteed at a finite time for any initial condition of the perturbation when the wavefront is concave and the rays tend to focus, whereas otherwise shocks occur only for a certain range of initial conditions.

  17. Occlusion culling for computer generated hologram based on ray-wavefront conversion.

    Science.gov (United States)

    Wakunami, Koki; Yamashita, Hiroaki; Yamaguchi, Masahiro

    2013-09-23

    We propose a new method for occlusion culling in the computation of a hologram based on the mutual conversion between light-rays and wavefront. Since the occlusion culling is performed with light-ray information, conventional rendering techniques such as ray-tracing or image-based rendering can be employed. On the other hand, the wavefront is derived for the calculation of light propagation, the hologram of 3-D objects can be obtained in high accuracy. In the numerical experiment, we demonstrate that our approach can reproduce a high-resolution image for deep 3-D scene with correct occlusion effect between plural objects.

  18. In-flight Quality and Accuracy of Attitude Measurements from the CHAMP Advanced Stellar Compass

    DEFF Research Database (Denmark)

    Jørgensen, Peter Siegbjørn; Jørgensen, John Leif; Denver, Troelz;

    2005-01-01

    The German geo-observations satellite CHAMP carries highly accurate vector instruments. The orientation of these relative to the inertial reference frame is obtained using star trackers. These advanced stellar compasses (ASC) are fully autonomous units, which provide, in real time, the absolute...

  19. Understanding Fluorescence Measurements through a Guided-Inquiry and Discovery Experiment in Advanced Analytical Laboratory

    Science.gov (United States)

    Wilczek-Vera, Grazyna; Salin, Eric Dunbar

    2011-01-01

    An experiment on fluorescence spectroscopy suitable for an advanced analytical laboratory is presented. Its conceptual development used a combination of the expository and discovery styles. The "learn-as-you-go" and direct "hands-on" methodology applied ensures an active role for a student in the process of visualization and discovery of concepts.…

  20. Cognitive Load Theory: Advances in Research on Worked Examples, Animations, and Cognitive Load Measurement

    NARCIS (Netherlands)

    T.A.J.M. van Gog (Tamara); G.W.C. Paas (Fred); J. Sweller (John)

    2010-01-01

    textabstractThe contributions to this special issue document some recent advances of cognitive load theory, and are based on contributions to the Third International Cognitive Load Theory Conference (2009), Heerlen, The Netherlands. The contributions focus on developments in example-based learning,