Sample records for vls spherical gratings

  1. Spherical grating spectrometers (United States)

    O'Donoghue, Darragh; Clemens, J. Christopher


    We describe designs for spectrometers employing convex dispersers. The Offner spectrometer was the first such instrument; it has almost exclusively been employed on satellite platforms, and has had little impact on ground-based instruments. We have learned how to fabricate curved Volume Phase Holographic (VPH) gratings and, in contrast to the planar gratings of traditional spectrometers, describe how such devices can be used in optical/infrared spectrometers designed specifically for curved diffraction gratings. Volume Phase Holographic gratings are highly efficient compared to conventional surface relief gratings; they have become the disperser of choice in optical / NIR spectrometers. The advantage of spectrometers with curved VPH dispersers is the very small number of optical elements used (the simplest comprising a grating and a spherical mirror), as well as illumination of mirrors off axis, resulting in greater efficiency and reduction in size. We describe a "Half Offner" spectrometer, an even simpler version of the Offner spectrometer. We present an entirely novel design, the Spherical Transmission Grating Spectrometer (STGS), and discuss exemplary applications, including a design for a double-beam spectrometer without any requirement for a dichroic. This paradigm change in spectrometer design offers an alternative to all-refractive astronomical spectrometer designs, using expensive, fragile lens elements fabricated from CaF2 or even more exotic materials. The unobscured mirror layout avoids a major drawback of the previous generation of catadioptric spectrometer designs. We describe laboratory measurements of the efficiency and image quality of a curved VPH grating in a STGS design, demonstrating, simultaneously, efficiency comparable to planar VPH gratings along with good image quality. The stage is now set for construction of a prototype instrument with impressive performance.

  2. The LBL 55-meter spherical grating monochromator at SSRL (United States)

    McKinney, W. R.; Howells, M. R.; Lauritzen, T.; Chin, J.; DiGennaro, R.; Fong, E.; Gath, W.; Guigli, J.; Hogrefe, H.; Meneghetti, J.; Plate, D.; Heimann, P. A.; Terminello, L.; Ji, Z.; Shirley, D.; Senf, F.


    A 55 meter spherical grating monochromator has been completed at the Stanford Synchrotron Radiation Laboratory (SSRL). The monochromator includes a unique capability for water cooled gratings, and is presently operating with a fused silica grating from 180 to 820 eV. A resolution of 60 meV has been achieved at 400 eV, inferred from the linewidths of the nitrogen 1s-π∗ resonance. A photon flux of 4 × 10 10 photon/s has been observed at 440 eV and 40 mA ring current (and with 0.5 eV resolution). It is expected that this flux value will improve by a factor of approximately 10-30 when a full-performance condensing system is installed later this year. The optical and mechanical systems design of the Rowland Circle monochromator with moving entrance and exit slits is reviewed. The details of the laser interferometer encoded wavelength drive, the mounting of the water cooled gratings, and the mechanical design features which improve the stability and accuracy of the system are described. The alignment of the gratings, grating chamber, and slits is discussed.

  3. VUV-SX spherical grating monochromator beam lines at BEPC and HESYRL (United States)

    Shu, Deming; Wang, Wei; Wang, Motuo; Liu, Jing; He, Wei; Zhang, Yijuan; Liu, Wumin; Sao, Beibei; Xie, Qi; Zheng, Hongwei; Wu, Chuancou; Cong, Zhibing; Zong, Congcang; Xu, Pengsou; Cai, Yong


    Two VUV-SX spherical grating monochromator (SGM) beam lines have been designed and constructed for laboratories in China; one for the Beijing Electron-Positron Collider (BEPC) and one for the Hefei Synchrotron Radiation Laboratory (HESYRL). Each of them will cover a wide spectral range, approximately 10-1000 eV, with four or five spherical laminar gratings. Tuning of the wavelength in the monochromators is achieved by rotation of the grating and translation of a pair of stepping-motor-driven slits to follow the Rowland circle to improve the monochromator's performance. The prefocusing mirrors are different on the BEPC and HESYRL beam lines. To accept 20 mrad of the synchrotron radiation horizontally from the 800-MeV HESYRL ring, a combined Kirkpatrick-Baez-type mirror set has been developed. The 1240-mm-long horizontal prefocusing mirror consists of four 310 mm × 70 mm × 40 mm gold-coated Zerodur spherical mirrors, each of which is independently adjustable in three dimensions. In the BEPC SGM beam line, a toroidal nickel-coated aluminum prefocusing mirror intercepts up to 4.5 mrad at a distance of 12 m from the source. A heat-pipe cooling system has also been designed for this mirror to accommodate the higher power from the 2.2-2.8 GeV beam stored in BEPC in its dedicated SR mode. The optical ray tracing results, the mechanics, and control systems are described in this paper.

  4. Toroidal Variable-Line-Space Gratings: The Good, the Bad and The Ugly (United States)

    West, Edward A.; Kobayashi, Ken; Cirtain, Jonathan; Gary, Allen; Davis, John; Reader, Joseph


    Toroidal variable-line-space (VLS) gratings are an important factor in the design of an efficient VUV solar telescope that will measure the CIV (155nm) and MgII (280nm) emissions lines in the Sun's transition region. In 1983 Kita and Harada described spherical VLS gratings but the technology to commercially fabricate these devices is a recent development, especially for toroidal surfaces. This paper will describe why this technology is important in the development of the Solar Ultraviolet Magnetograph Investigation (SUMI) sounding rocket program (the good), the delays due to the conversion between the TVLS grating design and the optical fabrication (the bad), and finally the optical testing, alignment and tolerancing of the gratings (the ugly). The Solar Ultraviolet Magnetograph Investigation, SUMI, has been reported in several papers since this program began in 2000. The emphasis of this paper is to describe SUMI's Toroidal Variable-Line-Space (TVLS) gratings. These gratings help SUMI meet its scientific goals which require both high spectral resolution and high optical efficiency for magnetic field measurements in the vacuum ultraviolet wavelength band of the solar spectrum (the good). Unfortunately, the technology readiness level of these gratings has made their implementation difficult, especially for a sounding rocket payload (the bad). Therefore, this paper emphasizes the problems and solutions that were developed to use these gratings in SUMI (the ugly). Section 2 contains a short review of the scientific goals of SUMI and why this mission is important in the understanding of the 3D structure of the magnetic field on the Sun. The flight hardware that makes up the SUMI payload is described in Section 3 with emphasis on those components that affect the TVLS gratings. Section 4 emphasizes the alignment, testing and optical modeling that were developed to optimize the performance of these gratings.

  5. Central role of the Holliday junction helicase RuvAB in vlsE recombination and infectivity of Borrelia burgdorferi.

    Directory of Open Access Journals (Sweden)

    Tao Lin


    Full Text Available Antigenic variation plays a vital role in the pathogenesis of many infectious bacteria and protozoa including Borrelia burgdorferi, the causative agent of Lyme disease. VlsE, a 35 kDa surface-exposed lipoprotein, undergoes antigenic variation during B. burgdorferi infection of mammalian hosts, and is believed to be a critical mechanism by which the spirochetes evade immune clearance. Random, segmental recombination between the expressed vlsE gene and adjacent vls silent cassettes generates a large number of different VlsE variants within the infected host. Although the occurrence and importance of vlsE sequence variation is well established, little is known about the biological mechanism of vlsE recombination. To identify factors important in antigenic variation and vlsE recombination, we screened transposon mutants of genes known to be involved in DNA recombination and repair for their effects on infectivity and vlsE recombination. Several mutants, including those in BB0023 (ruvA, BB0022 (ruvB, BB0797 (mutS, and BB0098 (mutS-II, showed reduced infectivity in immunocompetent C3H/HeN mice. Mutants in ruvA and ruvB exhibited greatly reduced rates of vlsE recombination in C3H/HeN mice, as determined by restriction fragment polymorphism (RFLP screening and DNA sequence analysis. In severe combined immunodeficiency (C3H/scid mice, the ruvA mutant retained full infectivity; however, all recovered clones retained the 'parental' vlsE sequence, consistent with low rates of vlsE recombination. These results suggest that the reduced infectivity of ruvA and ruvB mutants is the result of ineffective vlsE recombination and underscores the important role that vlsE recombination plays in immune evasion. Based on functional studies in other organisms, the RuvAB complex of B. burgdorferi may promote branch migration of Holliday junctions during vlsE recombination. Our findings are consistent with those in the accompanying article by Dresser et al., and together

  6. Metrology of variable-line-spacing x-ray gratings using the APS Long Trace Profiler (United States)

    Sheung, Janet; Qian, Jun; Sullivan, Joseph; Thomasset, Muriel; Manton, Jonathan; Bean, Sunil; Takacs, Peter; Dvorak, Joseph; Assoufid, Lahsen


    As resolving power targets have increased with each generation of beamlines commissioned in synchrotron radiation facilities worldwide, diffraction gratings are quickly becoming crucial optical components for meeting performance targets. However, the metrology of variable-line-spacing (VLS) gratings for high resolution beamlines is not widespread; in particular, no metrology facility at any US DOE facility is currently equipped to fully characterize such gratings. To begin to address this issue, the Optics Group at the Advanced Photon Source at Argonne, in collaboration with SOLEIL and with support from Brookhaven National Laboratory (BNL), has developed an alternative beam path addition to the Long Trace Profiler (LTP) at Argonne's Advanced Photon Source. This significantly expands the functionality of the LTP not only to measure mirrors surface slope profile at normal incidence, but also to characterize the groove density of VLS diffraction gratings in the Littrow incidence up to 79°, which covers virtually all diffraction gratings used at synchrotrons in the first order. The LTP light source is a 20mW HeNe laser, which yields enough signal for diffraction measurements to be performed on low angle blazed gratings optimized for soft X-ray wavelengths. We will present the design of the beam path, technical requirements for the optomechanics, and our data analysis procedure. Finally, we discuss challenges still to be overcome and potential limitations with use of the LTP to perform metrology on diffraction gratings.

  7. Minimizing Grating Slope Errors in the IEX Monochromato at the Advanced Photon Source

    Energy Technology Data Exchange (ETDEWEB)

    Fisher, M. V.; Assoufid, L.; McChesney, J.; Qian, J.; Reininger, R.; Rodolakis, F


    The IEX beamline at the APS is currently in the commissioning phase. The energy resolution of the beamline was not meeting original specifications by several orders of magnitude. The monochromator, an in-focus VLS-PGM, is currently configured with a high and a medium-line-density grating. Experimental results indicated that both gratings were contributing to the poor energy resolution and this led to venting the monochromator to investigate. The initial suspicion was that a systematic error had occurred in the ruling process on the VLS gratings, but that proved to not be the case. Instead the problem was isolated to mechanical constraints used to mount the gratings into their respective side-cooled holders. Modifications were made to the holders to eliminate problematic constraints without compromising the rest of the design. Metrology performed on the gratings in the original and modified holders demonstrated a 20-fold improvement in the surface profile error which was consistent with finite element analysis performed in support of the modifications. Two gratings were successfully reinstalled and subsequent measurements with beam show a dramatic improvement in energy resolution.

  8. Voc Degradation in TF-VLS Grown InP Solar Cells

    Energy Technology Data Exchange (ETDEWEB)

    Sun, Yubo; Sun, Xingshu; Johnston, Steve; Sutter-Fella, Carolin M.; Hettick, Mark; Javey, Ali; Bermel, Peter


    Here we consider two hypotheses to explain the open-circuit voltage (VOC) degradation observed in thin-film vapor-liquid-solid (TF-VLS) grown p-type InP photovoltaic cells: bandgap narrowing and local shunting. First, a bandgap (Eg) narrowing effect is hypothesized, based on the surface inhomogeneity of VLS InP captured by the photoluminescence (PL) image. The PL data was used to estimate a spatially-resolved active VOC across surface of the InP sample. Combining this data with the effective Jsc allowed an assessment of the I-V characteristics of individual unit cells. Next, an H-SPICE diode compact model was utilized to reproduce the I-V characteristics of the whole sample. We find a good fit to the I-V performance of TF-VLS grown InP solar cell. Second, a local shunting effect was also considered as an alternative explanation of the VOC degradation effect. Again, PL image data was used, and small local shunt resistance was added in arbitrary elementary unit cells to represent certain dark spots seen in the PL image and dictate the VOC degradation occurred in the sample.

  9. Spherical models

    CERN Document Server

    Wenninger, Magnus J


    Well-illustrated, practical approach to creating star-faced spherical forms that can serve as basic structures for geodesic domes. Complete instructions for making models from circular bands of paper with just a ruler and compass. Discusses tessellation, or tiling, and how to make spherical models of the semiregular solids and concludes with a discussion of the relationship of polyhedra to geodesic domes and directions for building models of domes. "". . . very pleasant reading."" - Science. 1979 edition.

  10. Synthesis and growth mechanisms of ZrC whiskers fabricated by a VLS process

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Dongju [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of). Nuclear Materials Development Division; Song, Sung Ho [Kongju National Univ., Chungnam (Korea, Republic of). Division of Advanced Materials Engineering


    The mechanisms of nano-sized ZrC whisker formation by a vapor-liquid-solid process (VLS) are investigated, which produces a very high purity, single crystal whisker. Rectangular ZrC whiskers with a cross-sectional diameter of 100-200 nm and lengths up to tens of microns are formed under the catalytic effect of nickel. The ZrC whiskers are characterized using scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. ZrC whiskers can be used as a potential reinforcing and strengthening phase for ceramic composites.

  11. The vls antigenic variation systems of Lyme disease Borrelia: eluding host immunity through both random, segmental gene conversion and framework heterogeneity (United States)

    Norris, Steven J.


    Summary Spirochetes that cause Lyme borreliosis (also called Lyme disease) possess the vls locus, encoding an elaborate antigenic variation system. This locus contains the expression site vlsE as well as a contiguous array of vls silent cassettes, which contain variations of the central cassette region of vlsE. The locus is present on one of the many linear plasmids in the organism, e.g. plasmid lp28-1 in the strain B. burgdorferi B31. Changes in the sequence of vlsE occur continuously during mammalian infection and consist of random, segmental, unidirectional recombination events between the silent cassettes and the cassette region of vlsE. These gene conversion events do not occur during in vitro culture or the tick portion of the infection cycle of Borrelia burgdorferi or the other related Borrelia species that cause Lyme disease. The mechanism of recombination is largely unknown, but requires the RuvAB Holliday junction branch migrase. Other features of the vls locus also appear to be required, including cis locations of vlsE and the silent cassettes and high G+C content and GC skew. The vls system is required for long-term survival of Lyme Borrelia in infected mammals and represents an important mechanism of immune evasion. In addition to sequence variation, immune selection also results in significant heterogeneity in the sequence of the surface lipoprotein VlsE. Despite antigenic variation, VlsE generates a robust antibody response, and both full length VlsE and the C6 peptide (corresponding to invariant region 6) are widely used in immunodiagnostic tests for Lyme disease. PMID:26104445

  12. Epitope mapping of antibodies to VlsE protein of Borrelia burgdorferi in post-Lyme disease syndrome. (United States)

    Chandra, Abhishek; Latov, Norman; Wormser, Gary P; Marques, Adriana R; Alaedini, Armin


    The VlsE lipoprotein of Borrelia burgdorferi elicits a strong immune response during the course of Lyme disease. The present study was aimed at characterization of the epitopes of VlsE targeted by the antibody response in patients with post-Lyme disease syndrome, a condition characterized by persisting symptoms of pain, fatigue, and/or neurocognitive impairment despite antibiotic treatment of B. burgdorferi infection. Epitope mapping was carried out using microarrays that contained synthesized overlapping peptides covering the full sequence of VlsE from B. burgdorferi B31. In addition to the previously characterized IR6 region in the variable domain, specific sequences in the N- and C-terminal invariable domains of VlsE were found to be major B cell epitopes in affected patients. The crystal structure of VlsE indicated that the newly described epitopes form a contiguous region in the surface-exposed membrane-proximal part of the monomeric form of the protein. Copyright © 2011 Elsevier Inc. All rights reserved.

  13. Assessing individual radial junction solar cells over millions on VLS-grown silicon nanowires. (United States)

    Yu, Linwei; Rigutti, Lorenzo; Tchernycheva, Maria; Misra, Soumyadeep; Foldyna, Martin; Picardi, Gennaro; Roca i Cabarrocas, Pere


    Silicon nanowires (SiNWs) grown on low-cost substrates provide an ideal framework for the monolithic fabrication of radial junction photovoltaics. However, the quality of junction formation over a random matrix of SiNWs, fabricated via a vapor-liquid-solid (VLS) mechanism, has never been assessed in a realistic context. To address this, we probe the current response of individual radial junction solar cells under electron-beam and optical-beam excitations. Excellent current generation from the radial junction units, compared to their planar counterparts, has been recorded, indicating a high junction quality and effective doping in the ultra-thin SiNWs with diameters thinner than 20 nm. Interestingly, we found that the formation of radial junctions by plasma deposition can be quite robust against geometrical disorder and even the crossings of neighboring cell units. These results provide a strong support to the feasibility of building high-quality radial junction solar cells over high-throughput VLS-grown SiNWs on low-cost substrates.

  14. Evaluation of the importance of VlsE antigenic variation for the enzootic cycle of borrelia burgdorferi (United States)

    Efficient acquisition and transmission of Borrelia burgdorferi by the tick vector, and the ability to persistently infect both vector and host, are important elements for the life cycle of the Lyme disease pathogen. Previous work has provided strong evidence implicating the significance of the vls l...

  15. Spherical Camera (United States)


    Developed largely through a Small Business Innovation Research contract through Langley Research Center, Interactive Picture Corporation's IPIX technology provides spherical photography, a panoramic 360-degrees. NASA found the technology appropriate for use in guiding space robots, in the space shuttle and space station programs, as well as research in cryogenic wind tunnels and for remote docking of spacecraft. Images of any location are captured in their entirety in a 360-degree immersive digital representation. The viewer can navigate to any desired direction within the image. Several car manufacturers already use IPIX to give viewers a look at their latest line-up of automobiles. Another application is for non-invasive surgeries. By using OmniScope, surgeons can look more closely at various parts of an organ with medical viewing instruments now in use. Potential applications of IPIX technology include viewing of homes for sale, hotel accommodations, museum sites, news events, and sports stadiums.


    Directory of Open Access Journals (Sweden)

    H. Boulaassal


    Full Text Available Airborne Laser Scanning (ALS, Terrestrial Laser Scanning (TLS and Vehicle based Laser Scanning (VLS are widely used as data acquisition methods for 3D building modelling. ALS data is often used to generate, among others, roof models. TLS data has proven its effectiveness in the geometric reconstruction of building façades. Although the operating algorithms used in the processing chain of these two kinds of data are quite similar, their combination should be more investigated. This study explores the possibility of combining ALS and TLS data for simultaneously producing 3D building models from bird point of view and pedestrian point of view. The geometric accuracy of roofs and façades models is different due to the acquisition techniques. In order to take these differences into account, the surfaces composing roofs and façades are extracted with the same algorithm of segmentation. Nevertheless the segmentation algorithm must be adapted to the properties of the different point clouds. It is based on the RANSAC algorithm, but has been applied in a sequential way in order to extract all potential planar clusters from airborne and terrestrial datasets. Surfaces are fitted to planar clusters, allowing edge detection and reconstruction of vector polygons. Models resulting from TLS data are obviously more accurate than those generated from ALS data. Therefore, the geometry of the roofs is corrected and adapted according to the geometry of the corresponding façades. Finally, the effects of the differences between raw ALS and TLS data on the results of the modeling process are analyzed. It is shown that such combination could be used to produce reliable 3D building models.

  17. New porcine test-model reveals remarkable differences between algorithms for spectrophotometrical haemoglobin saturation measurements with VLS

    DEFF Research Database (Denmark)

    Gade, John; Greisen, Gorm


    UNLABELLED: The study created an 'ex vivo' model to test different algorithms for measurements of mucosal haemoglobin saturation with visible light spectrophotometry (VLS). The model allowed comparison between algorithms, but it also allowed comparison with co-oximetry using a 'gold standard......-oxygenated state ranged from  -32.8 to  +29.9 percentage points and from  -5.0 to  +9.2 percentage points, respectively. CONCLUSION: the algorithms showed remarkable in-between differences when tested on raw-spectra from an 'ex vivo' model. All algorithms had bias, more marked at high oxygenation than low...

  18. Comparative reactivity of human sera to recombinant VlsE and other Borrelia burgdorferi antigens in class-specific enzyme-linked immunosorbent assays for Lyme borreliosis. (United States)

    Magnarelli, Louis A; Lawrenz, Matthew; Norris, Steven J; Fikrig, Erol


    A comparative study of human sera was conducted to determine which purified preparations of 11 recombinant antigens of Borrelia burgdorferi sensu stricto were diagnostically most important in enzyme-linked immunosorbent assays (ELISAs). To assess sensitivity, 20 serum samples obtained 1-6 weeks after onset of illness from 20 persons who had physician-diagnosed erythema migrans (EM) were tested for IgM and IgG antibodies. In tests for IgM antibody, seropositivity of > or = 25% was recorded when ELISAs had separate preparations of protein (p) 37, p41-G, outer-surface protein (Osp) C, OspE, OspF or VlsE antigens. Sera reacted most frequently (80% positive) with VlsE antigen in analyses for IgG antibodies. When results of both class-specific assays were considered for VlsE, OspC or OspF, 90% of the EM cases were serologically confirmed. Results of specificity testing with a further 59 sera from persons who had syphilis, louse-borne relapsing fever, oral infections, rheumatoid arthritis or human granulocytic ehrlichiosis and 28 normal sera indicated no false positive reactions when VlsE antigen was used in tests for IgM antibody. One of the 11 louse-borne relapsing fever sera cross-reacted with VlsE antigen in tests for IgG antibodies. Minor cross-reactivity also occurred when p37, OspC, OspE or OspF antigens were used. Overall, VlsE was the most suitable antigen for laboratory diagnosis of Lyme borreliosis during the early weeks of B. burgdorferi infection because of its high sensitivity and specificity.

  19. A review of III-V planar nanowire arrays: selective lateral VLS epitaxy and 3D transistors (United States)

    Zhang, Chen; Miao, Xin; Chabak, Kelson D.; Li, Xiuling


    Nanowires have long been regarded as a promising architecture for beyond Si CMOS logic, future III-V RF electronics, next generation optoelectronic applications, as well as heterogeneous integration. The inherent 3D structure also enables new device concepts that are otherwise not accessible with conventional technology. Nanowires grown using bottom-up epitaxial methods such as metalorganic chemical vapor deposition are free of ion-induced damage, which is especially critical for III-V because of the irreversibility of such damage, and can be scaled to dimensions smaller than lithographically defined. The challenges for nanowire based devices have been the controllability and compatibility with Si CMOS manufacturing. The discovery of parallel arrays of planar III-V nanowire growth mode provides an in-plane nanowire configuration that is perfectly compatible with existing planar processing technology for industry. The selective lateral epitaxy nature guided by the metal nanoparticles via the vapor-liquid-solid (VLS) mechanism opens up a new paradigm of crystal growth and consequently enabled in situ lateral and radial junctions. In this article, we review the planar nanowire based transistor development, particularly, planar III-As compound semiconductor based transistors enabled by this bottom-up self-assembled selective lateral VLS mechanism. We first review the characteristics and mechanism of planar nanowire growth, then focus on the growth, fabrication, and DC and RF performance of metal-semiconductor field-effect transistors, metal-oxide semiconductor field-effect transistors, and high electron mobility transistors (HEMTs), before providing our perspective on future development.

  20. Birefringence Bragg Binary (3B) grating, quasi-Bragg grating and immersion gratings (United States)

    Ebizuka, Noboru; Morita, Shin-ya; Yamagata, Yutaka; Sasaki, Minoru; Bianco, Andorea; Tanabe, Ayano; Hashimoto, Nobuyuki; Hirahara, Yasuhiro; Aoki, Wako


    A volume phase holographic (VPH) grating achieves high angular dispersion and very high diffraction efficiency for the first diffraction order and for S or P polarization. However the VPH grating could not achieve high diffraction efficiency for non-polarized light at a large diffraction angle because properties of diffraction efficiencies for S and P polarizations are different. Furthermore diffraction efficiency of the VPH grating extinguishes toward a higher diffraction order. A birefringence binary Bragg (3B) grating is a thick transmission grating with optically anisotropic material such as lithium niobate or liquid crystal. The 3B grating achieves diffraction efficiency up to 100% for non-polarized light by tuning of refractive indices for S and P polarizations, even in higher diffraction orders. We fabricated 3B grating with liquid crystal and evaluated the performance of the liquid crystal grating. A quasi-Bragg (QB) grating, which consists long rectangle mirrors aligned in parallel precisely such as a window shade, also achieves high diffraction efficiency toward higher orders. We fabricated QB grating by laminating of silica glass substrates and glued by pressure fusion of gold films. A quasi-Bragg immersion (QBI) grating has smooth mirror hypotenuse and reflector array inside the hypotenuse, instead of step-like grooves of a conventional immersion grating. An incident beam of the QBI grating reflects obliquely at a reflector, then reflects vertically at the mirror surface and reflects again at the same reflector. We are going to fabricate QBI gratings by laminating of mirror plates as similar to fabrication of the QB grating. We will also fabricate silicon and germanium immersion gratings with conventional step-like grooves by means of the latest diamond machining methods. We introduce characteristics and performance of these gratings.

  1. Holographic Grating Study. Volume 1 (United States)


    EFFICIENCY GRATING ANALYSIS AND MEASUREMENT 167 4. 1 High-Efficiency Holographic Grating Desl ^ri Isaues .... 167 4.2 Computer Modeling of or more higher orders is maximized . This distinguishes them from low-efficiency gratings which utilize the zero order at hi^h efficiency

  2. Switchable Bragg gratings

    DEFF Research Database (Denmark)

    Marckmann, Carl Johan


    . Characterization of the third-order nonlinearities and the frozen-in field were performed using a new measurement method where the Bragg gratings were used as probes. Good coherence was obtained between this new measurement method and the traditional Mach-Zehnder interferometer method. In the project, several...

  3. Sensored fiber reinforced polymer grate (United States)

    Ross, Michael P.; Mack, Thomas Kimball


    Various technologies described herein pertain to a sensored grate that can be utilized for various security fencing applications. The sensored grate includes a grate framework and an embedded optical fiber. The grate framework is formed of a molded polymer such as, for instance, molded fiber reinforced polymer. Further, the grate framework includes a set of elongated elements, where the elongated elements are spaced to define apertures through the grate framework. The optical fiber is embedded in the elongated elements of the grate framework. Moreover, bending or breaking of one or more of the elongated elements can be detected based on a change in a characteristic of input light provided to the optical fiber compared to output light received from the optical fiber.

  4. Spherical tube hypersurfaces

    CERN Document Server

    Isaev, Alexander


    We examine Levi non-degenerate tube hypersurfaces in complex linear space which are "spherical," that is, locally CR-equivalent to the real hyperquadric. Spherical hypersurfaces are characterized by the condition of the vanishing of the CR-curvature form, so such hypersurfaces are flat from the CR-geometric viewpoint. On the other hand, such hypersurfaces are also of interest from the point of view of affine geometry. Thus our treatment of spherical tube hypersurfaces in this book is two-fold: CR-geometric and affine-geometric. As the book shows, spherical tube hypersurfaces possess remarkable properties. For example, every such hypersurface is real-analytic and extends to a closed real-analytic spherical tube hypersurface in complex space. One of our main goals is to provide an explicit affine classification of closed spherical tube hypersurfaces whenever possible. In this book we offer a comprehensive exposition of the theory of spherical tube hypersurfaces, starting with the idea proposed in the pioneering...

  5. Engineering scale development of the vapor-liquid-solid (VLS) process for the production of silicon carbide fibrils. Phase 2

    Energy Technology Data Exchange (ETDEWEB)

    Ohnsorg, R.W.; Hollar, W.E. Jr.; Lau, S.K. [Carborundum Co., Niagara Falls, NY (United States). Technology Div.; Ko, F.K.; Schatz, K. [Advanced Product Development, Bristol, PA (United States)


    As reinforcements for composites, VLS SiC fibrils have attractive mechanical properties including high-strength, high modulus, and excellent creep resistance. To make use of their excellent mechanical properties in a composite, a significant volume fraction (>10%) of aligned, long fibrils (>2 mm) needs to be consolidated in the ceramic matrix. The fibrils must be processed into an assembly that will allow for composite fabrication while maintaining fibril alignment and length. With Advanced Product Development (APD) as the yam fabrication subcontractor, Carborundum investigated several approaches to achieve this goaL including traditional yam-forming processes such as carding and air-vortex spinning and nontraditional processes such as tape forming and wet casting. Carborundum additionally performed an economic analysis for producing 500 and 10,000 pounds of SiC fibrils annually using both conservative and more aggressive processing parameters. With the aggressive approach, the projected costs for SiC fibril production for 500 and 10,000 pounds per year are $1,340/pound and $340/pound, respectively.

  6. Low crosstalk Arrayed Waveguide Grating with Cascaded Waveguide Grating Filter

    Energy Technology Data Exchange (ETDEWEB)

    Deng Yang; Liu Yuan; Gao Dingshan, E-mail: [Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074 (China)


    We propose a highly compact and low crosstalk arrayed waveguide grating (AWG) with cascaded waveguide grating (CWGF). The side lobes of the silicon nanowire AWG, which are normally introduced by fabrication errors, can be effectively suppressed by the CWGF. And the crosstalk can be improved about 15dB.

  7. Bragg Gratings in GIPOF


    Van Boxel, Roel


    Chapter 1: Optical Fibres 1.1 Optical Communication 1.2 Light 1.3 Refractive Index 1.4 Total Internal Reflection 1.5 Fibre Parameters 1.6 Ray Types 1.7 Mode concept 1.8 Fibre Modes 1.9 Number of Modes 1.10 Mode coupling and Mode conversion 1.11 Attenuation 1.12 Dispersion and Bandwidth 1.13 Types of fibres 1.14 Graded Index Polymer Optical Fibre (GIPOF) 1.15 Summary 1.16 References Chapter 2: Bragg Gratings 2.1 Theory 2.2 Photosensi...

  8. Spherically Actuated Motor (United States)

    Peeples, Steven


    A three degree of freedom (DOF) spherical actuator is proposed that will replace functions requiring three single DOF actuators in robotic manipulators providing space and weight savings while reducing the overall failure rate. Exploration satellites, Space Station payload manipulators, and rovers requiring pan, tilt, and rotate movements need an actuator for each function. Not only does each actuator introduce additional failure modes and require bulky mechanical gimbals, each contains many moving parts, decreasing mean time to failure. A conventional robotic manipulator is shown in figure 1. Spherical motors perform all three actuation functions, i.e., three DOF, with only one moving part. Given a standard three actuator system whose actuators have a given failure rate compared to a spherical motor with an equal failure rate, the three actuator system is three times as likely to fail over the latter. The Jet Propulsion Laboratory reliability studies of NASA robotic spacecraft have shown that mechanical hardware/mechanism failures are more frequent and more likely to significantly affect mission success than are electronic failures. Unfortunately, previously designed spherical motors have been unable to provide the performance needed by space missions. This inadequacy is also why they are unavailable commercially. An improved patentable spherically actuated motor (SAM) is proposed to provide the performance and versatility required by NASA missions.

  9. Spherical geodesic mesh generation

    Energy Technology Data Exchange (ETDEWEB)

    Fung, Jimmy [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Kenamond, Mark Andrew [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Burton, Donald E. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Shashkov, Mikhail Jurievich [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)


    In ALE simulations with moving meshes, mesh topology has a direct influence on feature representation and code robustness. In three-dimensional simulations, modeling spherical volumes and features is particularly challenging for a hydrodynamics code. Calculations on traditional spherical meshes (such as spin meshes) often lead to errors and symmetry breaking. Although the underlying differencing scheme may be modified to rectify this, the differencing scheme may not be accessible. This work documents the use of spherical geodesic meshes to mitigate solution-mesh coupling. These meshes are generated notionally by connecting geodesic surface meshes to produce triangular-prismatic volume meshes. This mesh topology is fundamentally different from traditional mesh topologies and displays superior qualities such as topological symmetry. This work describes the geodesic mesh topology as well as motivating demonstrations with the FLAG hydrocode.

  10. Picosecond Holographic-Grating Spectroscopy

    NARCIS (Netherlands)

    Duppen, K.


    Interfering light waves produce an optical interference pattern in any medium that interacts with light. This modulation of some physical parameter of the system acts as a classical holographic grating for optical radiation. When such a grating is produced through interaction of pulsed light waves

  11. Imaging properties of diffraction gratings

    NARCIS (Netherlands)

    Werner, W.


    For almost a century now diffraction gratings are being used as the dispersing element in spectroscopic systems. In the greater majority of cases this grating is of the reflecting type, which (among others) has the advantage that the radiation to be analysed need not pass absorbing material as is

  12. The Spherical Deformation Model

    DEFF Research Database (Denmark)

    Hobolth, Asgar


    Miller et al. (1994) describe a model for representing spatial objects with no obvious landmarks. Each object is represented by a global translation and a normal deformation of a sphere. The normal deformation is defined via the orthonormal spherical-harmonic basis. In this paper we analyse...... the spherical deformation model in detail and describe how it may be used to summarize the shape of star-shaped three-dimensional objects with few parameters. It is of interest to make statistical inference about the three-dimensional shape parameters from continuous observations of the surface and from...

  13. Optical Fiber Grating based Sensors

    DEFF Research Database (Denmark)

    Michelsen, Susanne


    In this thesis differenct optical fiber gratings are used for sensor purposes. If a fiber with a core concentricity error (CCE) is used, a directional dependent bend sensor can be produced. The CCE direction can be determined by means of diffraction. This makes it possible to produce long......-period gratings in a fiber with a CCE direction parallel or perpendicular to the writing direction. The maximal bending sensitivity is independent on the writing direction, but the detailed bending response is different in the two cases. A temperature and strain sensor, based on a long-period grating and two...... sampled gratings, was produced and investigated. It is based on the different temperature and strain response of these gratings. Both a transfer matrix method and an overlap calculation is performed to explain the sensor response. Another type of sensor is based on tuning and modulation of a laser...

  14. Engineering scale development of the vapor-liquid-solid (VLS) process for the production of silicon carbide fibrils and linear fibril assemblies

    Energy Technology Data Exchange (ETDEWEB)

    Tenhover, M.; Biernacki, J. [Carborundum Co., Niagara Falls, NY (United States); Schatz, K.; Ko, F. [Advanced Product Development, Inc., Bristol, PA (United States)


    In order to exploit the superior thermomechanical properties of the VLS fibril, the feasibility of scaled-up production of the SiC fibril is demonstrated in this study. Through time series study and computer simulation, the parameters affecting the growth process and properties of the fibrils were examined. To facilitate translation of the superior mechanical properties into higher level preform structures, conventional and unconventional processing methods were evaluated. As revealed by scanning electron microscopic examination and X-ray diffractometry, high level alignment of the fibrils was achieved by the wet-laid process.

  15. Fabrication of Polymer Optical Fibre (POF) Gratings (United States)

    Luo, Yanhua; Yan, Binbin; Zhang, Qijin; Peng, Gang-Ding; Wen, Jianxiang; Zhang, Jianzhong


    Gratings inscribed in polymer optical fibre (POF) have attracted remarkable interest for many potential applications due to their distinctive properties. This paper overviews the current state of fabrication of POF gratings since their first demonstration in 1999. In particular we summarize and discuss POF materials, POF photosensitivity, techniques and issues of fabricating POF gratings, as well as various types of POF gratings. PMID:28273844

  16. Sensational spherical shells (United States)

    Lee, M. C.; Kendall, J. M., Jr.; Bahrami, P. A.; Wang, T. G.


    Fluid-dynamic and capillary forces can be used to form nearly perfect, very small spherical shells when a liquid that can solidify is passed through an annular die to form an annular jet. Gravity and certain properties of even the most ideal materials, however, can cause slight asymmetries. The primary objective of the present work is the control of this shell formation process in earth laboratories rather than space microgravity, through the development of facilities and methods that minimize the deleterious effects of gravity, aerodynamic drag, and uncontrolled cooling. The spherical shells thus produced can be used in insulation, recyclable filter materials, fire retardants, explosives, heat transport slurries, shock-absorbing armor, and solid rocket motors.

  17. Bragg gratings: Optical microchip sensors (United States)

    Watts, Sam


    A direct UV writing technique that can create multiple Bragg gratings and waveguides in a planar silica-on-silicon chip is enabling sensing applications ranging from individual disposable sensors for biotechnology through to multiplexed sensor networks in pharmaceutical manufacturing.

  18. Encapsulation process for diffraction gratings. (United States)

    Ratzsch, Stephan; Kley, Ernst-Bernhard; Tünnermann, Andreas; Szeghalmi, Adriana


    Encapsulation of grating structures facilitates an improvement of the optical functionality and/or adds mechanical stability to the fragile structure. Here, we introduce novel encapsulation process of nanoscale patterns based on atomic layer deposition and micro structuring. The overall size of the encapsulated structured surface area is only restricted by the size of the available microstructuring and coating devices; thus, overcoming inherent limitations of existing bonding processes concerning cleanliness, roughness, and curvature of the components. Finally, the process is demonstrated for a transmission grating. The encapsulated grating has 97.5% transmission efficiency in the -1st diffraction order for TM-polarized light, and is being limited by the experimental grating parameters as confirmed by rigorous coupled wave analysis.

  19. MEMS Bragg grating force sensor

    DEFF Research Database (Denmark)

    Reck, Kasper; Thomsen, Erik Vilain; Hansen, Ole


    We present modeling, design, fabrication and characterization of a new type of all-optical frequency modulated MEMS force sensor based on a mechanically amplified double clamped waveguide beam structure with integrated Bragg grating. The sensor is ideally suited for force measurements in harsh...... environments and for remote and distributed sensing and has a measured sensitivity of -14 nm/N, which is several times higher than what is obtained in conventional fiber Bragg grating force sensors. © 2011 Optical Society of America....

  20. Infants' responsiveness to rivalrous gratings. (United States)

    Kavšek, Michael


    The study investigated the early development of responsiveness to rivalrous gratings. Infants were tested weekly between 6 and 16 weeks of age for their ability to discriminate between interocularly identical (fusible) lines and interocularly orthogonal (unfusible, rivalrous) lines. The stimuli were presented on an autostereoscopic monitor equipped with a face-tracking device. Two psychophysical techniques, the forced-choice preferential looking (FPL) method and measurement of looking times, were employed. Contrary to earlier findings, infants at all ages avoided looking at the rivalrous gratings instead of showing a developmental shift from a relative preference for unfusible, rivalrous gratings to a relative preference for fusible gratings. Avoidance of the rivalrous gratings became significant at 8-9weeks of age, suggesting that infants clearly exhibit binocular rivalry from that age onwards. Control experiments secured that the infants' preference for the fusible gratings was not governed by a natural preference for less over more complex line patterns. Copyright © 2012 Elsevier Ltd. All rights reserved.

  1. Grating monochromator for soft X-ray self-seeding the European XFEL

    Energy Technology Data Exchange (ETDEWEB)

    Serkez, Svitozar; Kocharyan, Vitali; Saldin, Evgeni [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Geloni, Gianluca [European XFEL GmbH, Hamburg (Germany)


    Self-seeding is a promising approach to significantly narrow the SASE bandwidth of XFELs to produce nearly transform-limited pulses. The implementation of this method in the soft X-ray wavelength range necessarily involves gratings as dispersive elements. We study a very compact self-seeding scheme with a grating monochromator originally designed at SLAC, which can be straightforwardly installed in the SASE3 type undulator beamline at the European XFEL. The monochromator design is based on a toroidal VLS grating working at a fixed incidence angle mounting without entrance slit. It covers the spectral range from 300 eV to 1000 eV. The optical system was studied using wave optics method (in comparison with ray tracing) to evaluate the performance of the self-seeding scheme. Our wave optics analysis takes into account the actual beam wavefront of the radiation from the coherent FEL source, third order aberrations, and errors from each optical element. Wave optics is the only method available, in combination with FEL simulations, for the design of a self-seeding monochromator without exit slit. We show that, without exit slit, the self-seeding scheme is distinguished by the much needed experimental simplicity, and can practically give the same resolving power (about 7000) as with an exit slit. Wave optics is also naturally applicable to calculations of the self-seeding scheme efficiency, which include the monochromator transmittance and the effect of the mismatching between seed beam and electron beam. Simulations show that the FEL power reaches 1 TW and that the spectral density for a TW pulse is about two orders of magnitude higher than that for the SASE pulse at saturation.

  2. Fundamentals of spherical array processing

    CERN Document Server

    Rafaely, Boaz


    This book provides a comprehensive introduction to the theory and practice of spherical microphone arrays. It is written for graduate students, researchers and engineers who work with spherical microphone arrays in a wide range of applications.   The first two chapters provide the reader with the necessary mathematical and physical background, including an introduction to the spherical Fourier transform and the formulation of plane-wave sound fields in the spherical harmonic domain. The third chapter covers the theory of spatial sampling, employed when selecting the positions of microphones to sample sound pressure functions in space. Subsequent chapters present various spherical array configurations, including the popular rigid-sphere-based configuration. Beamforming (spatial filtering) in the spherical harmonics domain, including axis-symmetric beamforming, and the performance measures of directivity index and white noise gain are introduced, and a range of optimal beamformers for spherical arrays, includi...

  3. Holographic Spherically Symmetric Metrics (United States)

    Petri, Michael

    The holographic principle (HP) conjectures, that the maximum number of degrees of freedom of any realistic physical system is proportional to the system's boundary area. The HP has its roots in the study of black holes. It has recently been applied to cosmological solutions. In this article we apply the HP to spherically symmetric static space-times. We find that any regular spherically symmetric object saturating the HP is subject to tight constraints on the (interior) metric, energy-density, temperature and entropy-density. Whenever gravity can be described by a metric theory, gravity is macroscopically scale invariant and the laws of thermodynamics hold locally and globally, the (interior) metric of a regular holographic object is uniquely determined up to a constant factor and the interior matter-state must follow well defined scaling relations. When the metric theory of gravity is general relativity, the interior matter has an overall string equation of state (EOS) and a unique total energy-density. Thus the holographic metric derived in this article can serve as simple interior 4D realization of Mathur's string fuzzball proposal. Some properties of the holographic metric and its possible experimental verification are discussed. The geodesics of the holographic metric describe an isotropically expanding (or contracting) universe with a nearly homogeneous matter-distribution within the local Hubble volume. Due to the overall string EOS the active gravitational mass-density is zero, resulting in a coasting expansion with Ht = 1, which is compatible with the recent GRB-data.

  4. Imaging transmission grating spectrometer for magnetic fusion experiments (United States)

    Blagojević, B.; Stutman, D.; Finkenthal, M.; Moos, H. W.; Kaita, R.; Majeski, R.


    The Johns Hopkins Plasma Spectroscopy Group is developing a transmission grating based imaging spectrometer for the ultrasoft x-ray [(USXR), 10-300 Å] range. The spectrometer will be integrated into an impurity diagnostic package for magnetic fusion experiments, which provides time and space resolved information about radiation losses, Zeff profiles, and particle transport. The spectrometer has a simple layout, consisting of collimating and space resolving slits, a transmission grating, and a two-dimensional imaging USXR detector. We tested two types of detectors, a CsI coated multichannel plate and a phosphor P45 coated fiber optic plate, both with intensified charge-coupled-device image readout. The performance of the 5000 1/mm, 3:1 bar to open area ratio transmission grating has been evaluated in the laboratory using Kα lines from a Manson source and the emission from a Penning discharge. A prototype spectrometer equiped with the first type detector and optimized for 6 Å spectral resolution has been tested successfully on the CDX-U tokamak at the Princeton Plasma Physics Laboratory. A spectrometer using the second detector version has been developed for the NSTX spherical torus at Princeton. Spatially resolved spectra have been recorded with 25-250 ms time integration with both spectrometers. In both experiments, spectra are dominated by low-Z impurities, C, N, and O.

  5. Etched silicon gratings for NGST

    Energy Technology Data Exchange (ETDEWEB)

    Ge, J.; Ciarlo, D.; Kuzmenko, P.; Macintosh, B.; Alcock, C.; Cook, K.


    The authors have developed the world's first etched silicon grisms at LLNL in September 1999. The high optical surface quality of the grisms allows diffraction-limited spectral resolution in the IR wavelengths where silicon has good transmission. They estimated that the scattering light level is less than 4% at 2.2 {micro}m. Silicon can significantly increase the dispersive power of spectroscopic instruments for NGST due to its very large refractive index (n = 3.4). For example, a silicon grism with 40 mm clear entrance aperture and a 46 wedge angle can provide R = 10,000--100,000 in {approximately} 1--10 {micro}m. The same grating working in the immersed reflection mode can provide {approximately} three times higher spectral resolution than in the transmission mode. To achieve a desired spectral resolution for NGST, the spectrograph size and weight can be significantly reduced if silicon gratings are used instead of conventional gratings.

  6. The ETE spherical Tokamak project

    Energy Technology Data Exchange (ETDEWEB)

    Ludwig, Gerson Otto; Andrade, Maria Celia Ramos de; Barbosa, Luis Filipe Wiltgen [Instituto Nacional de Pesquisas Espaciais (INPE), Sao Jose dos Campos, SP (Brazil). Lab. Associado de Plasma] [and others]. E-mail:


    This paper describes the general characteristics of spherical tokamaks, with a brief overview of work in the area of spherical torus already performed or in progress at several institutions. The paper presents also the historical development of the ETE (Spherical Tokamak Experiment) project, its research program, technical characteristics and status of construction in September, 1998 at the Associated plasma Laboratory (LAP) of the National Institute for Space Research (INPE) in Brazil. (author)

  7. Spherical tokamak development in Brazil

    Energy Technology Data Exchange (ETDEWEB)

    Ludwig, Gerson Otto; Bosco, Edson Del; Ferreira, Julio Guimaraes [Instituto Nacional de Pesquisas Espaciais (INPE), Sao Jose dos Campos, SP (Brazil). Lab. Associado de Plasma] (and others)


    The general characteristics of spherical tokamaks, or spherical tori, with a brief view of work in this area already performed or in progress at several institutions worldwide are described. The paper presents also the steps in the development of the ETE (Experiment Tokamak spheric) project, its research program, technical characteristics and operating conditions as of December, 2002 a the Associated Plasma Laboratory (LAP) of the National Space Research Institute (INPE) in Brazil. (author)

  8. Engineered plasmon focusing on functional gratings

    NARCIS (Netherlands)

    Offerhaus, Herman L.; van den Bergen, B; van Hulst, N.F.


    We report on the engineering of plasmon propagation and focusing by dedicated curved gratings and noncollinear phasematching. Gratings were created on gold by focused ion beam milling and plasmons were measured using phase sensitive PSTM.

  9. High Efficiency Low Scatter Echelle Grating Project (United States)

    National Aeronautics and Space Administration — A high efficiency low scatter echelle grating will be developed using a novel technique of multiple diamond shaving cuts. The grating will have mirror surfaces on...

  10. Polymer optical fiber bragg grating sensors

    DEFF Research Database (Denmark)

    Stefani, Alessio; Yuan, Scott Wu; Andresen, Søren


    Fiber-optical accelerometers based on polymer optical fiber Bragg gratings are reported. We have written fiber Bragg gratings for 1550 nm and 850 nm operations, characterized their temperature and strain response, and tested their performance in a prototype accelerometer....

  11. Computational spherical astronomy (United States)

    Taff, Laurence G.

    The subject of the considered volume is the applied mathematics of spherical astronomy. The book is intended to aid those scientists and engineers, not trained in astrometry, to rapidly master the computational aspects of positional astronomy. Celestial coordinate systems are considered, taking into account the celestial sphere, the horizon system, the equatorial systems, the ecliptic system, the rotational transformations of celestial coordinates, position angle and distance, and special star positions. Other subjects discussed are related to general precession and proper motion, the parallax, the computation of the topocentric place, time systems, photographic astrometry, celestial mechanics, and astronomical catalogs. Attention is given to the power series method for the combined effects of general precession and proper motion, atomic time, the gravitational force, perturbation theory, solar system objects, stars, nonstellar objects, and the linear plate model.

  12. Pairing in spherical nanograins

    Energy Technology Data Exchange (ETDEWEB)

    Kuzmenko, N.K., E-mail: kuzmenko@NK9433.spb.ed [V.G. Khlopin Radium Institute, 2-nd Murinsky avenue 28, 194021 St.-Petersburg (Russian Federation); Mikhajlov, V.M. [Institute of Physics, St.-Petersburg State University, Ul' yanovskaya 3, 198904 Petergof (Russian Federation)


    Conditions are ascertained when the pairing and other thermodynamic properties of spherical nanograins with numbers of delocalized electrons N<10{sup 5} can be investigated by using the Single Shell Model (SSM) that gives the eigenvalues of the pairing Hamiltonian for a solitary shell. In the frame of SSM the exact canonical and grand canonical descriptions are employed first to analyze the absence of the abrupt superconducting-normal phase transition in finite systems in which an increase of the pairing and BCS critical temperature can be observed and secondly to study such new phenomena as the temperature re-entrance of the pairing in postcritical magnetic fields and also low temperature oscillations of the magnetic susceptibility and electronic heat capacity in an increasing uniform magnetic field.

  13. Tunable grating with active feedback (United States)

    Rosset, Samuel; O'Brien, Benjamin M.; Gisby, Todd; Xu, Daniel; Shea, Herbert R.; Anderson, Iain A.


    We report on the use of capacitive self-sensing to operate a DEA-based tunable grating in closed-loop mode. Due to their large strain capabilities, DEAs are key candidates for tunable optics applications. However, the viscoelasticity of elastomers is detrimental for applications that require long-term stability, such as tunable gratings and lenses. We show that capacitive sensing of the electrode strain can be used to suppress the strain drift and increase the response speed of silicone-based actuators. On the other hand, VHB actuators exhibit a time-dependent permittivity, which causes a drift between the device capacitance and its strain.

  14. Fabrication of Polymer Optical Fibre (POF Gratings

    Directory of Open Access Journals (Sweden)

    Yanhua Luo


    Full Text Available Gratings inscribed in polymer optical fibre (POF have attracted remarkable interest for many potential applications due to their distinctive properties. This paper overviews the current state of fabrication of POF gratings since their first demonstration in 1999. In particular we summarize and discuss POF materials, POF photosensitivity, techniques and issues of fabricating POF gratings, as well as various types of POF gratings.

  15. Surface plasmons on zig-zag gratings. (United States)

    Constant, Thomas J; Taphouse, Tim S; Rance, Helen J; Kitson, Stephen C; Hibbins, Alastair P; Sambles, J Roy


    Optical excitation of surface plasmons polaritons (SPPs) on a 'zig-zag diffraction grating' is explored. The fabricated silver grating consists of sub-wavelength grooves 'zig-zagged' along their length, providing a diffractive periodicity to visible radiation. SPPs propagating in the diffraction plane and scattered by an odd number of grating vectors are only excited by TE polarized radiation, whereas for TM polarized light, which also induces surface charge, SPP excitation is forbidden by the grating's broken-mirror symmetry.

  16. Advanced Fibre Bragg Grating and Microfibre Bragg Grating Fabrication Techniques (United States)

    Chung, Kit Man

    Fibre Bragg gratings (FBGs) have become a very important technology for communication systems and fibre optic sensing. Typically, FBGs are less than 10-mm long and are fabricated using fused silica uniform phase masks which become more expensive for longer length or non-uniform pitch. Generally, interference UV laser beams are employed to make long or complex FBGs, and this technique introduces critical precision and control issues. In this work, we demonstrate an advanced FBG fabrication system that enables the writing of long and complex gratings in optical fibres with virtually any apodisation profile, local phase and Bragg wavelength using a novel optical design in which the incident angles of two UV beams onto an optical fibre can be adjusted simultaneously by moving just one optical component, instead of two optics employed in earlier configurations, to vary the grating pitch. The key advantage of the grating fabrication system is that complex gratings can be fabricated by controlling the linear movements of two translation stages. In addition to the study of advanced grating fabrication technique, we also focus on the inscription of FBGs written in optical fibres with a cladding diameter of several ten's of microns. Fabrication of microfibres was investigated using a sophisticated tapering method. We also proposed a simple but practical technique to filter out the higher order modes reflected from the FBG written in microfibres via a linear taper region while the fundamental mode re-couples to the core. By using this technique, reflection from the microfibre Bragg grating (MFBG) can be effectively single mode, simplifying the demultiplexing and demodulation processes. MFBG exhibits high sensitivity to contact force and an MFBG-based force sensor was also constructed and tested to investigate their suitability for use as an invasive surgery device. Performance of the contact force sensor packaged in a conforming elastomer material compares favourably to one

  17. Spherical wave rotation in spherical near-field antenna measurements

    DEFF Research Database (Denmark)

    Wu, Jian; Larsen, Flemming Holm; Lemanczyk, J.


    The rotation of spherical waves in spherical near-field antenna measurement is discussed. Considering the many difficult but interesting features of the rotation coefficients, an efficient rotation scheme is derived. The main feature of the proposed scheme is to ignore the calculation of the very...

  18. 3D Printed Terahertz Focusing Grating Couplers (United States)

    Jahn, David; Weidenbach, Marcel; Lehr, Jannik; Becker, Leonard; Beltrán-Mejía, Felipe; Busch, Stefan F.; Balzer, Jan C.; Koch, Martin


    We have designed, constructed and characterized a grating that focuses electromagnetic radiation at specific frequencies out of a dielectric waveguide. A simple theoretical model predicts the focusing behaviour of these chirped gratings, along with numerical results that support our assumptions and improved the grating geometry. The leaky waveguide was 3D printed and characterized at 120 GHz demonstrating its potential for manipulating terahertz waves.

  19. Hybrid grating reflectors: Origin of ultrabroad stopband

    DEFF Research Database (Denmark)

    Park, Gyeong Cheol; Taghizadeh, Alireza; Chung, Il-Sug


    Hybrid grating (HG) reflectors with a high-refractive-index cap layer added onto a high contrast grating (HCG) provide a high reflectance close to 100% over a broader wavelength range than HCGs. The combination of a cap layer and a grating layer brings a strong Fabry-Perot (FP) resonance as well ...

  20. Holographic Gratings for Slow-Neutron Optics (United States)

    Klepp, Juergen; Pruner, Christian; Tomita, Yasuo; Geltenbort, Peter; Drevenšek-Olenik, Irena; Gyergyek, Saso; Kohlbrecher, Joachim; Fally, Martin


    Recent progress in the development of holographic gratings for neutron-optics applications is reviewed. We summarize the properties of gratings recorded in deuterated (poly)methylmethacrylate, holographic polymer-dispersed liquid crystals and nanoparticle-polymer composites revealed by diffraction experiments with slow neutrons. Existing and anticipated neutron-optical instrumentations based on holographic gratings are discussed.

  1. Transmission grating based extreme ultraviolet imaging spectrometer for time and space resolved impurity measurements

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Deepak; Stutman, Dan; Tritz, Kevin; Finkenthal, Michael [Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, Maryland 21218 (United States); Tarrio, Charles; Grantham, Steven [Physics Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States)


    A free standing transmission grating based imaging spectrometer in the extreme ultraviolet range has been developed for the National Spherical Torus Experiment (NSTX). The spectrometer operates in a survey mode covering the approximate spectral range from 30 to 700 A and has a resolving capability of {delta}{lambda}/{lambda} on the order of 3%. Initial results from space resolved impurity measurements from NSTX are described in this paper.

  2. First results of spherical GEMs

    CERN Document Server

    Pinto, Serge Duarte; Brock, Ian; Croci, Gabriele; David, Eric; de Oliveira, Rui; Ropelewski, Leszek; van Stenis, Miranda; Taureg, Hans; Villa, Marco


    We developed a method to make GEM foils with a spherical geometry. Tests of this procedure and with the resulting spherical GEMs are presented. Together with a spherical drift electrode, a spherical conversion gap can be formed. This eliminates the parallax error for detection of x-rays, neutrons or UV photons when a gaseous converter is used. This parallax error limits the spatial resolution at wide scattering angles. Besides spherical GEMs, we have developed curved spacers to maintain accurate spacing, and a conical field cage to prevent edge distortion of the radial drift field up to the limit of the angular acceptance of the detector. With these components first tests are done in a setup with a spherical entrance window but a planar readout structure; results will be presented and discussed. A flat readout structure poses difficulties, however. Therefore we will show advanced plans to make a prototype of an entirely spherical double-GEM detector, including a spherical 2D readout structure. This detector w...

  3. Compact Imaging Spectrometer Utilizing Immersed Gratings

    Energy Technology Data Exchange (ETDEWEB)

    Chrisp, Michael P. (Danville, CA); Lerner, Scott A. (Corvallis, OR); Kuzmenko, Paul J. (Livermore, CA); Bennett, Charles L. (Livermore, CA)


    A compact imaging spectrometer with an immersive diffraction grating that compensates optical distortions. The imaging spectrometer comprises an entrance slit for transmitting light, a system for receiving the light and directing the light, an immersion grating, and a detector array. The entrance slit, the system for receiving the light, the immersion grating, and the detector array are positioned wherein the entrance slit transmits light to the system for receiving the light and the system for receiving the light directs the light to the immersion grating and the immersion grating receives the light and directs the light through an optical element to the detector array.

  4. Reflectivity-modulated grating-mirror

    DEFF Research Database (Denmark)


    The invention relates to vertical cavity lasers (VCL) incorporating a reflectivity-modulated grating mirror (1) for modulating the laser output. A cavity is formed by a bottom mirror (4), an active region (3), and an outcoupling top grating mirror (1) formed by a periodic refractive index grating...... region in a layer structure comprising a p- and a n-doped semiconductor layer with an electrooptic material layer (12) arranged there between. The grating region comprises a grating structure formed by periodic perforations to change the refractive index periodically in directions normal...... to the oscillation axis. A modulated voltage (91) is applied in reverse bias between the n- and p-doped layers to modulate the refractive index of the electrooptic material layer (12) and thereby the reflectivity spectrum of the grating mirror (1). The reflectivity of the grating mirror (1) can be modulated between...

  5. Curved VPH gratings for novel spectrographs (United States)

    Clemens, J. Christopher; O'Donoghue, Darragh; Dunlap, Bart H.


    The introduction of volume phase holographic (VPH) gratings into astronomy over a decade ago opened new possibilities for instrument designers. In this paper we describe an extension of VPH grating technology that will have applications in astronomy and beyond: curved VPH gratings. These devices can disperse light while simultaneously correcting aberrations. We have designed and manufactured two different kinds of convex VPH grating prototypes for use in off-axis reflecting spectrographs. One type functions in transmission and the other in reflection, enabling Offnerstyle spectrographs with the high-efficiency and low-cost advantages of VPH gratings. We will discuss the design process and the tools required for modelling these gratings along with the recording layout and process steps required to fabricate them. We will present performance data for the first convex VPH grating produced for an astronomical spectrograph.

  6. Point-by-point written fiber-Bragg gratings and their application in complex grating designs. (United States)

    Marshall, Graham D; Williams, Robert J; Jovanovic, Nemanja; Steel, M J; Withford, Michael J


    The point-by-point technique of fabricating fibre-Bragg gratings using an ultrafast laser enables complete control of the position of each index modification that comprises the grating. By tailoring the local phase, amplitude and spacing of the grating's refractive index modulations it is possible to create gratings with complex transmission and reflection spectra. We report a series of grating structures that were realized by exploiting these flexibilities. Such structures include gratings with controlled bandwidth, and amplitude- and phase-modulated sampled (or superstructured) gratings. A model based on coupled-mode theory provides important insights into the manufacture of such gratings. Our approach offers a quick and easy method of producing complex, non-uniform grating structures in both fibres and other mono-mode waveguiding structures.

  7. High Efficiency Germanium Immersion Gratings

    Energy Technology Data Exchange (ETDEWEB)

    Kuzmenko, P J; Davis, P J; Little, S L; Little, L M; Bixler, J V


    We have fabricated several germanium immersion gratings by single crystal, single point diamond flycutting on an ultra-precision lathe. Use of a dead sharp tool produces groove corners less than 0.1 micron in radius and consequently high diffraction efficiency. We measured first order efficiencies in immersion of over 80% at 10.6 micron wavelength. Wavefront error was low averaging 0.06 wave rms (at 633 nm) across the full aperture. The grating spectral response was free of ghosts down to our detection limit of 1 part in 10{sup 4}. Scatter should be low based upon the surface roughness. Measurement of the spectral line profile of a CO{sub 2} laser sets an upper bound on total integrated scatter of 0.5%.

  8. Fixational saccades during grating detection and discrimination. (United States)

    Spotorno, Sara; Masson, Guillaume S; Montagnini, Anna


    We investigated the patterns of fixational saccades in human observers performing two classical perceptual tasks: grating detection and discrimination. First, participants were asked to detect a vertical or tilted grating with one of three spatial frequencies and one of four luminance contrast levels. In the second experiment, participants had to discriminate the spatial frequency of two supra-threshold gratings. The gratings were always embedded in additive, high- or low-contrast pink noise. We observed that the patterns of fixational saccades were highly idiosyncratic among participants. Moreover, during the grating detection task, the amplitude and the number of saccades were inversely correlated with stimulus visibility. We did not find a systematic relationship between saccade parameters and grating frequency, apart from a slight decrease of saccade amplitude during grating discrimination with higher spatial frequencies. No consistent changes in the number and amplitude of fixational saccades with performance accuracy were reported. Surprisingly, during grating detection, saccade number and amplitude were similar in grating-with-noise and noise-only displays. Grating orientation did not affect substantially saccade direction in either task. The results challenge the idea that, when analyzing low-level spatial properties of visual stimuli, fixational saccades can be adapted in order to extract task-relevant information optimally. Rather, saccadic patterns seem to be overall modulated by task context, stimulus visibility and individual variability. Copyright © 2015 Elsevier Ltd. All rights reserved.

  9. Spherically symmetric perfect fluid solutions

    Energy Technology Data Exchange (ETDEWEB)

    Hajj-Boutros, J.


    Many exact solutions for the spherically symmetric perfect fluid distribution of matter with shear, acceleration, and expansion are obtained. One of them is expressed in terms of Painleve's third transcendent.

  10. Toroidal equilibria in spherical coordinates


    Tsui, K. H.


    The standard Grad-Shafranov equation for axisymmetric toroidal plasma equilibrium is customary expressed in cylindrical coordinates with toroidal contours, and through which benchmark equilibria are solved. An alternative approach to cast the Grad-Shafranov equation in spherical coordinates is presented. This equation, in spherical coordinates, is examined for toroidal solutions to describe low $\\beta$ Solovev and high $\\beta$ plasma equilibria in terms of elementary functions.

  11. Spherical tokamak development in Brazil

    Energy Technology Data Exchange (ETDEWEB)

    Ludwig, G.O.; Del Bosco, E.; Ferreira, J.G.; Berni, L.A.; Oliveira, R.M.; Andrade, M.C.R.; Shibata, C.S.; Ueda, M.; Barroso, J.J.; Castro, P.J. [Instituto Nacional de Pesquisas Espaciais (INPE), Sao Jose dos Campos, SP (Brazil). Lab. Associado de Plasma; Barbosa, L.F.W. [Universidade do Vale do Paraiba (UNIVAP), Sao Jose dos Campos, SP (Brazil). Faculdade de Engenharia, Arquitetura e Urbanismo; Patire Junior, H. [Instituto Nacional de Pesquisas Espaciais (INPE), Sao Jose dos Campos, SP (Brazil). Div. de Mecanica Espacial e Controle; The high-power microwave sources group


    This paper describes the general characteristics of spherical tokamaks, or spherical tori, with a brief overview of work in this area already performed or in progress at several institutions worldwide. The paper presents also the steps in the development of the ETE (Experimento Tokamak Esferico) project, its research program, technical characteristics and operating conditions as of December, 2002 at the Associated Plasma Laboratory (LAP) of the National Space Research Institute (INPE) in Brazil. (author)

  12. Nanoporous Polymeric Grating-Based Biosensors

    KAUST Repository

    Gao, Tieyu


    We demonstrate the utilization of an interferometrically created nanoporous polymeric gratings as a platform for biosensing applications. Aminopropyltriethoxysilane (APTES)-functionalized nanoporous polymeric gratings was fabricated by combining holographic interference patterning and APTES-functionalization of pre-polymer syrup. The successful detection of multiple biomolecules indicates that the biofunctionalized nanoporous polymeric gratings can act as biosensing platforms which are label-free, inexpensive, and applicable as high-throughput assays. Copyright © 2010 by ASME.

  13. Temperature tunable optical gratings in nematic elastomer

    Energy Technology Data Exchange (ETDEWEB)

    Sungur, Emel; Mager, Loic; Boeglin, Alex; Dorkenoo, Kokou D. [IPCMS-CNRS UMR 7504, 23 rue du Loess, BP 43, Strasbourg Cedex 2 (France); Li, Min-Hui; Keller, Patrick [Institut Curie, CNRS 168, Paris Cedex 5 (France)


    We have investigated the behaviour of temperature dependent periodic-index gratings fabricated in a nematic elastomer. The gratings have been obtained by photopolymerisation under a microscopy apparatus. Contraction properties, as well as diffraction properties, have been studied as a function of temperature. Unidirectional contraction has been demonstrated by means of circular figure deformation and the polarisation dependency of the diffraction by the gratings has been determined. (orig.)

  14. Large bandwidth, highly efficient optical gratings through high index materials

    NARCIS (Netherlands)

    Rathgen, H.; Offerhaus, Herman L.


    We analyze the diffraction characteristics of dielectric gratings that feature a high index grating layer, and devise, through rigorous numeri-cal calculations, large bandwidth, highly efficient, high dispersion dielectric gratings in reflection, transmission, and immersed transmission geometry. A

  15. Determination of stamp deformation during imprinting on semi-spherical surfaces

    DEFF Research Database (Denmark)

    Kafka, Jan; Matschuk, Maria; Pranov, Henrik

    We developed a process for double curved injection molding inserts presenting nanostructuredsurfaces. Line gratings with a line width and spacing of 500 nm as well as arrays of pillars,both up to an aspect ratio of unity, have been successfully transferred onto steel mold surfaces. A thin film...... of sol-gel was applied onto spherical injection mold inserts and subsequently imprinted using a flexible stamp. A hard curing step transformed the sol-gel into a quartz-like and durable material. As an example, we present theory and results regarding the imprint of pillar nanostructures on semi......-spherical mold surfaces. Imprints were realized on three different radii of circumferenceof the spherical mold: R = 0.5 mm, R = 1.0 mm, and R = 2 mm. After hard-curing of theimprinted sol-gel, the inserts were used for cold-mold as well as vario-therm injection molding.The polymer replicas and the inserts were...

  16. Fiber Bragg Grating Based Thermometry

    CERN Document Server

    Ahmed, Zeeshan; Guthrie, William; Quintavalle, John


    In recent years there has been considerable interest in developing photonic temperature sensors such as the Fiber Bragg gratings (FBG) as an alternative to resistance thermometry. In this study we examine the thermal response of FBGs over the temperature range of 233 K to 393 K. We demonstrate, in a hermetically sealed dry Argon environment, that FBG devices show a quadratic dependence on temperature with expanded uncertainties (k = 2) of ~500 mK. Our measurements indicate that the combined measurement uncertainty is dominated by uncertainty in determining the peak center fitting and by thermal aging of polyimide coated fibers.

  17. Spherical agglomeration of acetylsalicylic acid

    Directory of Open Access Journals (Sweden)

    Polowczyk Izabela


    Full Text Available In this paper spherical agglomeration of acetylsalicylic acid was described. In the first step, the system of good and poor solvents as well as bridging liquid was selected. As a result of a preliminary study, ethyl alcohol, water and carbon tetrachloride were used as the good solvent, poor one, and bridging liquid, respectively. Then, the amount of acetylsalicylic acid and the ratio of the solvents as well as the volume of the bridging liquid were examined. In the last step, the agglomeration conditions, such as mixing intensity and time, were investigated. The spherical agglomerates obtained under optimum conditions could be subjected to a tableting process afterwards.

  18. Basketballs as spherical acoustic cavities (United States)

    Russell, Daniel A.


    The sound field resulting from striking a basketball is found to be rich in frequency content, with over 50 partials in the frequency range of 0-12 kHz. The frequencies are found to closely match theoretical expectations for standing wave patterns inside a spherical cavity. Because of the degenerate nature of the mode shapes, explicit identification of the modes is not possible without internal investigation with a microphone probe. A basketball proves to be an interesting application of a boundary value problem involving spherical coordinates.

  19. The Flexibility of Pusher Furnace Grate

    Directory of Open Access Journals (Sweden)

    Słowik J.A.


    Full Text Available The lifetime of guide grates in pusher furnaces for heat treatment could be increased by raising the flexibility of their structure through, for example, the replacement of straight ribs, parallel to the direction of grate movement, with more flexible segments. The deformability of grates with flexible segments arranged in two orientations, i.e. crosswise (perpendicular to the direction of compression and lengthwise (parallel to the direction of compression, was examined. The compression process was simulated using SolidWorks Simulation program. Relevant regression equations were also derived describing the dependence of force inducing the grate deformation by 0.25 mm ‒ modulus of grate elasticity ‒ on the number of flexible segments in established orientations. These calculations were made in Statistica and Scilab programs. It has been demonstrated that, with the same number of segments, the crosswise orientation of flexible segments increases the grate structure flexibility in a more efficient way than the lengthwise orientation. It has also been proved that a crucial effect on the grate flexibility has only the quantity and orientation of segments (crosswise / lengthwise, while the exact position of segments changes the grate flexibility by less than 1%.

  20. Straw combustion on slow-moving grates

    DEFF Research Database (Denmark)

    Kær, Søren Knudsen


    Combustion of straw in grate-based boilers is often associated with high emission levels and relatively poor fuel burnout. A numerical grate combustion model was developed to assist in improving the combustion performance of these boilers. The model is based on a one-dimensional ‘‘walking...

  1. Overview on grating developments at ESA (United States)

    Guldimann, B.; Deep, A.; Vink, R.; Harnisch, B.; Kraft, S.; Sierk, B.; Bazalgette, G.; Bézy, J.-L.


    In the frame of recent studies and missions, ESA has been performing various pre-developments of optical gratings for instruments operating at wavelengths from the UV up to the SWIR. The instrument requirements of Sentinel-4, Sentinel-5, CarbonSat and FLEX are driving the need for advanced designs and technologies leading to gratings with high efficiency, high spectral resolution, low stray light and low polarization sensitivities. Typical ESA instruments (e.g. Sciamachy, GOME, MERIS, OLCI, NIRSpec) were and are based on ruled gratings or gratings manufactured with one holographic photoresist mask layer which is transferred to an optical substrate (e.g. glass, glass ceramic) with dry etching methods and subsequently either coated with a reflective coating or used as a mold for replication. These manufacturing methods lead to blazed grating profiles with a metallic reflective surface. The vast majority of spectrometers on ground are still based on such gratings. In general, gratings based on grooved metallic surfaces tend for instance to polarize the incoming light significantly and are therefore not always suitable for ESA's needs of today. Gratings made for space therefore evolved to many other designs and concepts which will be reported in this paper.

  2. New generation DWDM fibre grating devices


    Zervas, M.N.


    Using a recently developed inverse scattering layer-peeling algorithm and a modified stroboscopic grating writing technique, we have designed and successfully demonstrated novel grating devices, such as 50GHz-bandwidth dispersion compensators and square dispersionless filters, suitable for future high performance DWDM optical systems.

  3. Diffractive Optics of Anisotropic Polarization Gratings

    NARCIS (Netherlands)

    Xu, M.


    Diffraction gratings are being used to manipulate light in many different applications, such as in flat panel display systems, modern lighting systems, and optical recording. Diffraction gratings can be made polarization selective due to form birefringence. An alternative approach to polarization

  4. High order Bragg grating microfluidic dye laser

    DEFF Research Database (Denmark)

    Balslev, Søren; Kristensen, Anders


    We demonstrate a single mode distributed feedback liquid dye laser, based on a short 133 'rd order Bragg grating defined in a single polymer layer between two glass substrates.......We demonstrate a single mode distributed feedback liquid dye laser, based on a short 133 'rd order Bragg grating defined in a single polymer layer between two glass substrates....

  5. Compact imaging spectrometer utilizing immersed gratings

    Energy Technology Data Exchange (ETDEWEB)

    Chrisp, Michael P. (Danville, CA); Lerner, Scott A. (Corvallis, OR); Kuzmenko, Paul J. (Livermore, CA); Bennett, Charles L. (Livermore, CA)


    A compact imaging spectrometer with an immersive diffraction grating that compensates optical distortions. The imaging spectrometer comprises an entrance slit for transmitting light, means for receiving the light and directing the light, an immersion grating, and a detector array. The entrance slit, the means for receiving the light, the immersion grating, and the detector array are positioned wherein the entrance slit transmits light to the means for receiving the light and the means for receiving the light directs the light to the immersion grating and the immersion grating receives the light and directs the light to the means for receiving the light, and the means for receiving the light directs the light to the detector array.

  6. Chirped polymer optical fiber Bragg grating sensors (United States)

    Marques, Carlos A. F.; Pereira, L.; Antunes, P.; Mergo, P.; Webb, D. J.; Pinto, J. L.; André, P.


    We report chirped fiber Bragg gratings (CFBGs) photo-inscribed in undoped PMMA polymer optical fibre (POF) for the first time. The chirped polymer optical fiber Bragg gratings (CPOFBGs) were inscribed using an UV KrF excimer laser operating at 248 nm. The rectangular gauss laser beam was expanded to 25 mm in horizontal direction along the fiber core by a cylindrical lens, giving a total of 25 mm grating length. A 25 mm long chirped phase mask chosen for 1550 nm grating inscription was used. The laser frequency was 1 Hz with an energy of 5 mJ per exposure, exposing few pulses for each grating inscription. The reflection amplitude spectrum evolution of a CPOFBG is investigated as a function of the applied strain and temperature. Also, some results regarding to group delay are collected and discussed. These results pave the way to further developments in different fields, where POFs could present some advantages preferably replacing their silica counterparts.

  7. Flat dielectric grating reflectors with focusing abilities (United States)

    Fattal, David; Li, Jingjing; Peng, Zhen; Fiorentino, Marco; Beausoleil, Raymond G.


    Sub-wavelength dielectric gratings have emerged recently as a promising alternative to distributed Bragg reflection dielectric stacks for broadband, high-reflectivity filtering applications. Such a grating structure composed of a single dielectric layer with the appropriate patterning can sometimes perform as well as 30 or 40 dielectric distributed Bragg reflection layers, while providing new functionalities such as polarization control and near-field amplification. In this Letter, we introduce an interesting property of grating mirrors that cannot be realized by their distributed Bragg reflection counterpart: we show that a non-periodic patterning of the grating surface can give full control over the phase front of reflected light while maintaining a high reflectivity. This new feature of dielectric gratings allows the creation of miniature planar focusing elements that could have a substantial impact on a number of applications that depend on low-cost, compact optical components, from laser cavities to CD/DVD read/write heads.

  8. Vapor-liquid-solid (VLS) synthesis of alpha-monoclinic selenium and antimony selenide nanowires and sonication synthesis of blue photoluminescent zero-dimensional nanoparticles (United States)

    Farfan Mendoza, Willinton

    Semiconducting nanostructures such as nanowires and 0-D nanoparticles have received great interest due to their improved properties in comparison with macroscopic materials. Therefore, these nanostructures have attracted considerable attention for optoelectronics and biological applications, among others. In this way, this thesis reports the synthesis of alpha-monoclinic selenium and antimony selenide (Sb2Se3) semiconducting nanowires using a physical vapor-liquid-solid (VLS) process for the first time. In addition, synthesis of naturally dispersed Sb2Se 3 0-D nanoparticles using a sonication process is also reported here for the first time. Crystalline alpha-monoclinic selenium nanowires with diameters in the range between 20 nm and 1im and lengths up to 30 mum were synthesized. The majority of these VLS synthesized nanowires have a diameter of ~50 nm. As-obtained nanowires grew perpendicular to the (053) plane and exhibit an energy band-gap of 2.20 +/- 0.05 eV, showing a blue shift of 0.18 eV relative to the bulk than is attributed to quantum confinement from the most abundant produced nanowires (~50 nm). Crystalline Sb2Se3 nanowires with diameters in the range between 20 nm and 2mum and lengths up to 30 mum were synthesized. The diameter of the most abundant produced nanowires is ~800 nm. Our nanowires are oriented along the [010] crystallographic direction. Growth along this orientation is being reported for the first time. Due to the anisotropy of the lattice, [010] oriented nanowires have properties different to the ones produced by the other methods that are [001] oriented. This thesis also analyses the controversial band gap energy results reported in the literature and conclude that is due to incorrect interpretation of experimental measurements. Photoluminescence (PL) measurements of powdered crystalline bulk Sb2Se3 at room temperature and under UV excitation are reported here for the first time. The PL spectra show that Sb2Se3 crystalline exhibits high

  9. Spherical Pendulum, Actions, and Spin

    NARCIS (Netherlands)

    Richter, Peter H.; Dullin, Holger R.; Waalkens, Holger; Wiersig, Jan


    The classical and quantum mechanics of a spherical pendulum are worked out, including the dynamics of a suspending frame with moment of inertia θ. The presence of two separatrices in the bifurcation diagram of the energy-momentum mapping has its mathematical expression in the hyperelliptic nature of

  10. Strichartz Estimates in Spherical Coordinates


    Cho, Yonggeun; Lee, Sanghyuk


    In this paper we study Strichartz estimates for dispersive equations which are defined by radially symmetric pseudo-differential operators, and of which initial data belongs to spaces of Sobolev type defined in spherical coordinates. We obtain the space time estimates on the best possible range including the endpoint cases.

  11. VEP vernier, VEP grating, and behavioral grating acuity in patients with cortical visual impairment. (United States)

    Watson, Tonya; Orel-Bixler, Deborah; Haegerstrom-Portnoy, Gunilla


    Cortical visual impairment (CVI) is a leading cause of bilateral vision impairment. Because many patients with CVI cannot perform an optotype test, their acuity is often measured with a grating stimulus using a preferential looking (PL) test or the visual-evoked potential (VEP) recording. The purpose of this study is to determine the relationship among VEP vernier acuity, VEP grating acuity, and behavioral grating acuity in patients with CVI. Sweep VEP vernier acuity, sweep VEP grating acuity, and behavioral grating acuity (measured with PL cards) were measured in 29 patients with CVI. The patients ranged in age from 3.2 to 22.7 years (mean: 12.3; SD: 5.3). Because the measures of vernier acuity and grating acuity have different units, the results were expressed as the log deficit (with normal being 30 cycles per degrees and 0.5 arc min, respectively). VEP grating acuity loss and VEP vernier acuity loss were significantly related (r = 0.70) with a slope of 1.31, indicating that indicating that on average, vernier acuity showed a 0.2 log unit deficit compared with VEP grating acuity. Behavioral grating acuity loss and VEP grating acuity loss were also significantly related (r = 0.64) with a slope of 1.55, indicating that behavioral acuity was more reduced (by approximately 0.3 log unit). VEP vernier acuity loss and behavioral grating acuity loss were significantly related (r = 0.66) with a slope of 0.85, indicating that behavioral acuity and VEP vernier acuity showed a similar magnitude of reduction. A Bland-Altman comparison between the VEP vernier acuity method and the behavioral acuity method showed a flat slope (0.30), indicating that the two measures produce similar visual acuity measures across the range of acuity levels. In patients with CVI, VEP vernier acuity showed greater deficits than VEP grating acuity and was more similar to the behavioral measures of grating acuity.

  12. Fiber Bragg Grating Sensors for Harsh Environments

    Directory of Open Access Journals (Sweden)

    Stephen J. Mihailov


    Full Text Available Because of their small size, passive nature, immunity to electromagnetic interference, and capability to directly measure physical parameters such as temperature and strain, fiber Bragg grating sensors have developed beyond a laboratory curiosity and are becoming a mainstream sensing technology. Recently, high temperature stable gratings based on regeneration techniques and femtosecond infrared laser processing have shown promise for use in extreme environments such as high temperature, pressure or ionizing radiation. Such gratings are ideally suited for energy production applications where there is a requirement for advanced energy system instrumentation and controls that are operable in harsh environments. This paper will present a review of some of the more recent developments.

  13. Optical Fiber Grating Hydrogen Sensors: A Review. (United States)

    Dai, Jixiang; Zhu, Li; Wang, Gaopeng; Xiang, Feng; Qin, Yuhuan; Wang, Min; Yang, Minghong


    In terms of hydrogen sensing and detection, optical fiber hydrogen sensors have been a research issue due to their intrinsic safety and good anti-electromagnetic interference. Among these sensors, hydrogen sensors consisting of fiber grating coated with sensitive materials have attracted intensive research interests due to their good reliability and distributed measurements. This review paper mainly focuses on optical fiber hydrogen sensors associated with fiber gratings and various materials. Their configurations and sensing performances proposed by different groups worldwide are reviewed, compared and discussed in this paper. Meanwhile, the challenges for fiber grating hydrogen sensors are also addressed.

  14. Speed enhancement in VCSELs employing grating mirrors

    DEFF Research Database (Denmark)

    Chung, Il-Sug; Mørk, Jesper


    In recent years, various approaches to improve the speed of directly modulated vertical-cavity surface-emitting lasers (VCSELs) have been reported and demonstrated good improvement. In this paper, we propose and numerically investigate a new possibility of using high-index-contrast grating (HCG......) as mirror for VCSELs. By changing the grating design, one can control the reflection delay of the grating mirror, enabling the control of cavity photon lifetime. On the other hand, short energy penetration depth of the HCG results in smaller modal volume, compared to DBR VCSELs. An example structure shows...... that the HCG VCSEL has a 30-% higher 3-dB bandwidth than the DBR VCSEL....

  15. Advanced experimental applications for x-ray transmission gratings spectroscopy using a novel grating fabrication method

    Energy Technology Data Exchange (ETDEWEB)

    Hurvitz, G.; Ehrlich, Y.; Shpilman, Z.; Levy, I.; Fraenkel, M. [Plasma Physics Department, Applied Physics Division, Soreq NRC, Yavne (Israel); Strum, G. [Solid State Department, Applied Physics Division, Soreq NRC, Yavne (Israel)


    A novel fabrication method for soft x-ray transmission grating and other optical elements is presented. The method uses focused-ion-beam technology to fabricate high-quality free standing grating bars on transmission electron microscopy grids. High quality transmission gratings are obtained with superb accuracy and versatility. Using these gratings and back-illuminated CCD camera, absolutely calibrated x-ray spectra can be acquired for soft x-ray source diagnostics in the 100-3000 eV spectral range. Double grating combinations of identical or different parameters are easily fabricated, allowing advanced one-shot application of transmission grating spectroscopy. These applications include spectroscopy with different spectral resolutions, bandwidths, dynamic ranges, and may serve for identification of high-order contribution, and spectral calibrations of various x-ray optical elements.

  16. Miniaturization of Spherical Magnetodielectric Antennas

    DEFF Research Database (Denmark)

    Hansen, Troels Vejle

    The fundamental limitations in performance of electrically small antennas (ESAs) - and how far these may be approached - have been of great interest for over a century. Particularly over the past few decades, it has become increasingly relevant and important, to approach these limits in view...... to the important antenna parameters of radiation efficiency e and impedance bandwidth. For single-mode antennas the fundamental minimum Q is the Chu lower bound. In this Ph.D. dissertation, the topic is miniaturization of spherical antennas loaded by an internal magnetodielectric core. The goal is to determine......, quantify, and assess the effects of an internal material loading upon antenna performance, including its potentials towards miniaturization. Emphasis have been upon performing an exhaustive and exact analysis of rigorous validity covering a large class of spherical antennas. In the context of this study...

  17. Access Platforms for Offshore Wind Turbines Using Gratings

    DEFF Research Database (Denmark)

    Andersen, Thomas Lykke; Rasmussen, Michael R.


    The paper deals with forces generated by a stationary jet on different types of gratings and a solid plate. The force reduction factors for the different gratings compared to the solid plate mainly depend on the porosity of the gratings, but the geometry of the grating is also of some importance........ The derived reduction factors are expected to be applicable to design of offshore wind turbine access platforms with gratings where slamming also is an important factor....

  18. Liquid crystal on subwavelength metal gratings

    Energy Technology Data Exchange (ETDEWEB)

    Palto, S. P.; Barnik, M. I.; Artemov, V. V.; Shtykov, N. M.; Geivandov, A. R.; Yudin, S. G.; Gorkunov, M. V. [Shubnikov Institute of Crystallography of Russian Academy of Sciences, Leninsky pr. 59, 119333 Moscow (Russian Federation)


    Optical and electrooptical properties of a system consisting of subwavelength metal gratings and nematic liquid crystal layer are studied. Aluminium gratings that also act as interdigitated electrodes are produced by focused ion beam lithography. It is found that a liquid crystal layer strongly influences both the resonance and light polarization properties characteristic of the gratings. Enhanced transmittance is observed not only for the TM-polarized light in the near infrared spectral range but also for the TE-polarized light in the visible range. Although the electrodes are separated by nanosized slits, and the electric field is strongly localized near the surface, a pronounced electrooptical effect is registered. The effect is explained in terms of local reorientation of liquid crystal molecules at the grating surface and propagation of the orientational deformation from the surface into the bulk of the liquid crystal layer.

  19. Hydraulic Capacity of an ADA Compliant Street Drain Grate

    Energy Technology Data Exchange (ETDEWEB)

    Lottes, Steven A. [Argonne National Lab. (ANL), Argonne, IL (United States); Bojanowski, Cezary [Argonne National Lab. (ANL), Argonne, IL (United States)


    Resurfacing of urban roads with concurrent repairs and replacement of sections of curb and sidewalk may require pedestrian ramps that are compliant with the American Disabilities Act (ADA), and when street drains are in close proximity to the walkway, ADA compliant street grates may also be required. The Minnesota Department of Transportation ADA Operations Unit identified a foundry with an available grate that meets ADA requirements. Argonne National Laboratory’s Transportation Research and Analysis Computing Center used full scale three dimensional computational fluid dynamics to determine the performance of the ADA compliant grate and compared it to that of a standard vane grate. Analysis of a parametric set of cases was carried out, including variation in longitudinal, gutter, and cross street slopes and the water spread from the curb. The performance of the grates was characterized by the fraction of the total volume flow approaching the grate from the upstream that was captured by the grate and diverted into the catch basin. The fraction of the total flow entering over the grate from the side and the fraction of flow directly over a grate diverted into the catch basin were also quantities of interest that aid in understanding the differences in performance of the grates. The ADA compliant grate performance lagged that of the vane grate, increasingly so as upstream Reynolds number increased. The major factor leading to the performance difference between the two grates was the fraction of flow directly over the grates that is captured by the grates.

  20. Influence of spherical aberration, stimulus spatial frequency, and pupil apodisation on subjective refractions (United States)

    Bradley, Arthur; Xu, Renfeng; Thibos, Larry; Marin, Gildas; Hernandez, Martha


    Purpose To test competing hypotheses (Stiles Crawford pupil apodising or superior imaging of high spatial frequencies by the central pupil) for the pupil size independence of subjective refractions in the presence of primary spherical aberration. Methods Subjective refractions were obtained with a variety of test stimuli (high contrast letters, urban cityscape, high and low spatial frequency gratings) while modulating pupil diameter, levels of primary spherical aberration and pupil apodisation. Subjective refractions were also obtained with low-pass and high-pass stimuli and using “darker” and “sharper” subjective criteria. Results Subjective refractions for stimuli containing high spatial frequencies focus a near paraxial region of the pupil and are affected only slightly by level of Seidel spherical aberration, degree of pupil apodisation and pupil diameter, and generally focused a radius of about 1 to 1.5 mm from the pupil centre. Low spatial frequency refractions focus a marginal region of the pupil, and are significantly affected by level of spherical aberration, amount of pupil apodisation, and pupil size. Clinical refractions that employ the “darker” or “sharper” subjective criteria bias the patient to use lower or higher spatial frequencies respectively. Conclusions In the presence of significant levels of spherical aberration, the pupil size independence of subjective refractions occurs with or without Stiles Crawford apodisation for refractions that optimise high spatial frequency content in the image. If low spatial frequencies are optimised by a subjective refraction, spherical refractive error varies with spherical aberration, pupil size, and level of apodisation. As light levels drop from photopic to scotopic, therefore, we expect a shift from pupil size independent to pupil size dependent subjective refractions. Emphasising a “sharper” criterion during subjective refractions will improve image quality for high spatial frequencies

  1. Image Processing and Cell Phone Microscopy to Analyze the Immunomagnetic Beads on Micro-Contact Printed Gratings

    Directory of Open Access Journals (Sweden)

    Kutay İçöz


    Full Text Available In this paper we report an ultra-low-cost spherical ball lens based cell phone microscopy and image processing algorithms to analyze the amount of immunomagnetic beads on micro-contact printed gratings. The spherical ball lens provides approximately 100× magnification but the recorded images are not clear and are noisy. By using the image-processing algorithms, the noise can be reduced and the images can be enhanced to quantify the amount of immunomagnetic beads on micro-contact printed lines. This method, which is portable and low-cost, can be an alternative read out mechanism for biosensing applications using immunomagnetic beads on micro-contact printed surface receptors. Further, 0.0335 mg/mL was the lowest magnetic bead concentration that could be detected above the inherent noise level of the spherical ball lens.

  2. A novel single-order diffraction grating: Random position rectangle grating (United States)

    Zuhua, Yang; Qiangqiang, Zhang; Jing, Wang; Quanping, Fan; Yuwei, Liu; Lai, Wei; Leifeng, Cao


    Spectral diagnosis of radiation from laser plasma interaction and monochromation of radiation source are hot and important topics recently. Grating is one of the primary optical elements to do this job. Although easy to fabricate, traditional diffraction grating suffers from multi-order diffraction contamination. On the other hand, sinusoidal amplitude grating has the nonharmonic diffraction property, but it is too difficult to fabricate, especially for x-ray application. A novel nonharmonic diffraction grating named random position rectangle grating (RPRG) is proposed in this paper. Theoretical analysis and experiment results show that the RPRG is both higher order diffraction suppressing and not difficult to fabricate. Additionally, it is highly efficient; its first order absolute theoretical diffraction efficiency reaches 4.1%. Our result shows that RPRG is a novel tool for radiation diagnosis and monochromation. Project supported by the National Natural Science Foundation of China (Grant No. 11375160) and the National Science Instruments Major Project of China (Grant No. 2012YQ130125).

  3. Hybrid grating reflector with high reflectivity and broad bandwidth

    DEFF Research Database (Denmark)

    Taghizadeh, Alireza; Park, Gyeong Cheol; Mørk, Jesper


    We suggest a new type of grating reflector denoted hybrid grating (HG) which shows large reflectivity in a broad wavelength range and has a structure suitable for realizing a vertical cavity laser with ultra-small modal volume. The properties of the grating reflector are investigated numerically...... and explained. The HG consists of an un-patterned III-V layer and a Si grating. The III-V layer has a thickness comparable to the grating layer, introduces more guided mode resonances and significantly increases the bandwidth of the reflector compared to the well-known high-index-contrast grating (HCG...

  4. Progress in octahedral spherical hohlraum study

    Directory of Open Access Journals (Sweden)

    Ke Lan


    Full Text Available In this paper, we give a review of our theoretical and experimental progress in octahedral spherical hohlraum study. From our theoretical study, the octahedral spherical hohlraums with 6 Laser Entrance Holes (LEHs of octahedral symmetry have robust high symmetry during the capsule implosion at hohlraum-to-capsule radius ratio larger than 3.7. In addition, the octahedral spherical hohlraums also have potential superiority on low backscattering without supplementary technology. We studied the laser arrangement and constraints of the octahedral spherical hohlraums, and gave a design on the laser arrangement for ignition octahedral hohlraums. As a result, the injection angle of laser beams of 50°–60° was proposed as the optimum candidate range for the octahedral spherical hohlraums. We proposed a novel octahedral spherical hohlraum with cylindrical LEHs and LEH shields, in order to increase the laser coupling efficiency and improve the capsule symmetry and to mitigate the influence of the wall blowoff on laser transport. We studied on the sensitivity of the octahedral spherical hohlraums to random errors and compared the sensitivity among the octahedral spherical hohlraums, the rugby hohlraums and the cylindrical hohlraums, and the results show that the octahedral spherical hohlraums are robust to these random errors while the cylindrical hohlraums are the most sensitive. Up till to now, we have carried out three experiments on the spherical hohlraum with 2 LEHs on Shenguang(SG laser facilities, including demonstration of improving laser transport by using the cylindrical LEHs in the spherical hohlraums, spherical hohlraum energetics on the SGIII prototype laser facility, and comparisons of laser plasma instabilities between the spherical hohlraums and the cylindrical hohlraums on the SGIII laser facility.

  5. Hyperspectral grating optimization and manufacturing considerations (United States)

    Ziph-Schatzberg, Leah; Swartz, Barry; Warren, Chris; Santman, Jeff; Saleh, Mohammad; Wiggins, Richard; Crifasi, Joe; Comstock, Lovell; Taylor, Kevan


    Hyperspectral imaging systems are finding broader applications in both the commercial and aerospace markets. It is becoming clear that to optimize the performance of these systems, their instrument transfer function needs to be tailored for each application. Vis-SWIR systems in the full 400nm to 2500nm waveband present particular design and manufacturing challenges. A single blazed grating is inadequate for a system operating in the full vis-SWIR wavelength range. In addition, optical materials and broad band coatings present a challenge for non-reflective systems. An understanding of the application and wavelengths of interest, combined with a judicious choice of a focal plane array, can then lead to an optimized system for the specific application. The ability to tailor the grating and manufacture a wide variety of grating profiles and substrate shapes becomes a significant performance enabler. This paper will discuss how the use of optical, coating, and grating design/analysis software, combined with grating manufacturing techniques assure meeting high performance requirements for different applications.

  6. Scanning for piecewise holographic grating generation (United States)

    Miler, Miroslav; Kostka, František; Dvořák, Martin


    Holographic gratings that are recorded as a whole in a single exposition are limited in size because of the available power of suitable laser sources and nonlinear response of and/or reciprocity effects in a recording medium. A sequential-illumination technique can help in this case. This technique relies on piecewise grating recording that consists in scanning with a relatively narrow laser beam, a pencil, across the grating surface employing an appropriate optical set up. The contribution describes a method utilizing a small parallel displacement of the laser pencil by turning a plane-parallel plate, which is then transferred to a larger angular deflection by a short focus lens. Simultaneously, the beam is expanded angularly. This all can take place either before light enters the beam-splitter or along paths of both the interfering beams. In this way, uniform diffraction efficiency gratings that are much larger than the cross-section of the beam can be achieved. The laser pencil can be moved in polar or rectangular coordinates. Recording of larger gratings supposes large precise collimating mirrors. If they are not available e.g. due to their high price, they can be replaced by long propagating homocentric beams with their origins in the same distance from the recording plate.

  7. Optically tunable chirped fiber Bragg grating. (United States)

    Li, Zhen; Chen, Zhe; Hsiao, V K S; Tang, Jie-Yuan; Zhao, Fuli; Jiang, Shao-Ji


    This work presents an optically tunable chirped fiber Bragg grating (CFBG). The CFBG is obtained by a side-polished fiber Bragg grating (SPFBG) whose thickness of the residual cladding layer in the polished area (D(RC)) varies with position along the length of the grating, which is coated with a photoresponsive liquid crystal (LC) overlay. The reflection spectrum of the CFBG is tuned by refractive index (RI) modulation, which comes from the phase transition of the overlaid photoresponsive LC under ultraviolet (UV) light irradiation. The broadening in the reflection spectrum and corresponding shift in the central wavelength are observed with UV light irradiation density of 0.64mW/mm. During the phase transition of the photoresponsive LC, the RI increase of the overlaid LC leads to the change of the CFBG reflection spectrum and the change is reversible and repeatable. The optically tunable CFBGs have potential use in optical DWDM system and an all-fiber telecommunication system.

  8. Diffusion of solid fuelon a vibrating grate

    DEFF Research Database (Denmark)

    Sabelström, Hanna Katarina

    of vibrations can be incorporated into a numerical model. The chosen model approach has been to separate the gas and solid phases into two independent models related to each other through the bed porosity. By treating the bed as a porous media and using Ergun's equation for the gas flow, the numerical work...... is simplified and the computational time shortened. The vibrations are affecting the transport and mixing of the fuel and incorporated into the model through the diffusion coefficient in the conservation equation of the solid phase. Experimental work has been carried out with the aim to study the behaviour...... of wood pellets on a vibrating grate and deriving the diffusion coefficient to be used in the numerical model. Three different grate designs are used and the particle trajectories have been captured by a camera placed above the grate. The diffusion coefficient is defined as the deviation from the mean...

  9. Spherical sila- and germa-homoaromaticity. (United States)

    Chen, Zhongfang; Hirsch, Andreas; Nagase, Shigeru; Thiel, Walter; Schleyer, Paul von Ragué


    Guided by the 2(N + 1)2 electron-counting rule for spherical aromatic molecules, we have designed various spherical sila- and germa-homoaromatic systems rich in group 14 elements. Their aromaticity is revealed by density-functional computations of their structures and the nucleus-independent chemical shifts (NICS). Besides the formerly used endohedral inclusion strategy, spherical homoaromaticity is another way to stabilize silicon and germanium clusters.

  10. The ETE spherical Tokamak project. IAEA report

    Energy Technology Data Exchange (ETDEWEB)

    Ludwig, Gerson Otto; Del Bosco, E.; Berni, L.A.; Ferreira, J.G.; Oliveira, R.M.; Andrade, M.C.R.; Shibata, C.S.; Barroso, J.J.; Castro, P.J.; Patire Junior, H. [Instituto Nacional de Pesquisas Espaciais (INPE), Sao Jose dos Campos, SP (Brazil). Lab. Associado de Plasma]. E-mail:


    This paper describes the general characteristics of spherical tokamaks, or spherical tori, with a brief overview of work in this area already performed or in progress at several institutions worldwide. The paper presents also the historical development of the ETE (Spherical Tokamak Experiment) project, its research program, technical characteristics and operating conditions as of October, 2002 at the Associated Plasma Laboratory (LAP) of the National Space Research Institute (INPE) in Brazil. (author)

  11. Measuring Spherical Harmonic Coefficients on a Sphere

    Energy Technology Data Exchange (ETDEWEB)

    Pollaine, S; Haan, S W


    The eigenfunctions of Rayleigh-Taylor modes on a spherical capsule are the spherical harmonics Y{sub l,m} These can be measured by measuring the surface perturbations along great circles and fitting them to the first few modes by a procedure described in this article. For higher mode numbers, it is more convenient to average the Fourier power spectra along the great circles, and then transform them to spherical harmonic modes by an algorithm derived here.

  12. Spherical Collapse in Chameleon Models

    CERN Document Server

    Brax, Ph; Steer, D A


    We study the gravitational collapse of an overdensity of nonrelativistic matter under the action of gravity and a chameleon scalar field. We show that the spherical collapse model is modified by the presence of a chameleon field. In particular, we find that even though the chameleon effects can be potentially large at small scales, for a large enough initial size of the inhomogeneity the collapsing region possesses a thin shell that shields the modification of gravity induced by the chameleon field, recovering the standard gravity results. We analyse the behaviour of a collapsing shell in a cosmological setting in the presence of a thin shell and find that, in contrast to the usual case, the critical density for collapse depends on the initial comoving size of the inhomogeneity.

  13. Towards Non-spherical Radio Models (United States)

    Ribeiro, V. A. R. M.; Steffen, W.; Chomiuk, L.; Koning, N.; O'Brien, T. J.; Woudt, P. A.


    Radio observations of novae in outburst are of particular interest due to the physical parameters that may be retrieved from fitting the radio light curves. Most models that have fitted previous data assumed spherical symmetry however, it is becoming more and more clear that this is not the case. We explore morpho-kinematical techniques to retrieve the free-free radio light curves of non-spherical models and explore the effects of a non-spherical outburst on the physical parameters. In particular, we find that we may have been over estimating the ejected masses in the outburst of non-spherical novae.

  14. The geometry of spherical space form groups

    CERN Document Server

    Gilkey, Peter B


    In this volume, the geometry of spherical space form groups is studied using the eta invariant. The author reviews the analytical properties of the eta invariant of Atiyah-Patodi-Singer and describes how the eta invariant gives rise to torsion invariants in both K-theory and equivariant bordism. The eta invariant is used to compute the K-theory of spherical space forms, and to study the equivariant unitary bordism of spherical space forms and the Pin c and Spin c equivariant bordism groups for spherical space form groups. This leads to a complete structure theorem for these bordism and K-theor

  15. Recording multiple holographic gratings in silver-doped ...

    Indian Academy of Sciences (India)

    -wave transmission gratings were stored in the same location of silver-doped photopolymer film using peristrophic multiplexing techniques. Constant and variable exposure scheduling methods were adopted for storing gratings in the film using ...

  16. Interferometric fiber Bragg grating shift demodulation (United States)

    Stepien, Karol; Jóźwik, Michalina; Nasilowski, Tomasz


    In this paper we present a fiber Bragg grating shift demodulator with changeable resolution based on an unbalanced fiber Mach-Zehnder interferometer. Preliminary research proves phase sensitivity to Bragg wavelength changes of 6,83 rad/mɛ. Phase sensitivity can be modified by changing the optical path difference witch is only limited by the coherence length of light reflected by the fiber Bragg grating. This solution can be used as a single sensor or as a part of a more complex system.

  17. Silicon immersion gratings and their spectroscopic applications (United States)

    Ge, Jian; Zhao, Bo; Powell, Scott; Fletcher, Adam; Wan, Xiaoke; Chang, Liang; Jakeman, Hali; Koukis, Dimitrios; Tanner, David B.; Ebbets, Dennis; Weinberg, Jonathan; Lipscy, Sarah; Nyquist, Rich; Bally, John


    Silicon immersion gratings (SIGs) offer several advantages over the commercial echelle gratings for high resolution infrared (IR) spectroscopy: 3.4 times the gain in dispersion or ~10 times the reduction in the instrument volume, a multiplex gain for a large continuous wavelength coverage and low cost. We present results from lab characterization of a large format SIG of astronomical observation quality. This SIG, with a 54.74 degree blaze angle (R1.4), 16.1 l/mm groove density, and 50x86 mm2 grating area, was developed for high resolution IR spectroscopy (R~70,000) in the near IR (1.1-2.5 μm). Its entrance surface was coated with a single layer of silicon nitride antireflection (AR) coating and its grating surface was coated with a thin layer of gold to increase its throughput at 1.1-2.5 μm. The lab measurements have shown that the SIG delivered a spectral resolution of R=114,000 at 1.55 μm with a lab testing spectrograph with a 20 mm diameter pupil. The measured peak grating efficiency is 72% at 1.55 μm, which is consistent with the measurements in the optical wavelengths from the grating surface at the air side. This SIG is being implemented in a new generation cryogenic IR spectrograph, called the Florida IR Silicon immersion grating spectrometer (FIRST), to offer broad-band high resolution IR spectroscopy with R=72,000 at 1.4-1.8 um under a typical seeing condition in a single exposure with a 2kx2k H2RG IR array at the robotically controlled Tennessee State University 2-meter Automatic Spectroscopic Telescope (AST) at Fairborn Observatory in Arizona. FIRST is designed to provide high precision Doppler measurements (~4 m/s) for the identification and characterization of extrasolar planets, especially rocky planets in habitable zones, orbiting low mass M dwarf stars. It will also be used for other high resolution IR spectroscopic observations of such as young stars, brown dwarfs, magnetic fields, star formation and interstellar mediums. An optimally designed

  18. Multiwavelength optical scatterometry of dielectric gratings

    KAUST Repository

    Yashina, Nataliya P.


    Modern scatterometry problems arising in the lithography production of periodic gratings are in the focus of the work. The performance capabilities of a novel theoretical and numerical modeling oriented to these problems are considered. The approach is based on rigorous solutions of 2-D initial boundary value problems of the gratings theory. The quintessence and advantage of the method is the possibility to perform an efficient analysis simultaneously and interactively both for steady state and transient processes of the resonant scattering of electromagnetic waves by the infinite and compact periodic structures. © 2012 IEEE.

  19. Demonstration of three-port grating phase relations


    Bunkowski, A.; Burmeister, O.; Danzmann, K.; Schnabel, R.; Clausnitzer, T; Kley, E.; Tünnermann, A.


    We experimentally demonstrate the phase relations of three-port gratings by investigating three-port coupled Fabry-Perot cavities. Two different gratings that have the same first-order diffraction efficiency but differ substantially in their second-order diffraction efficiency have been designed and manufactured. Using the gratings as couplers to Fabry-Perot cavities, we could validate the results of an earlier theoretical description of the phases at a three-port grating [Opt. Lett. 30, 1183...

  20. Transmission grating stretcher for contrast enhancement of high power lasers. (United States)

    Tang, Yunxin; Hooker, Chris; Chekhlov, Oleg; Hawkes, Steve; Collier, John; Rajeev, P P


    We propose, for the first time, a transmission grating stretcher for high power lasers and demonstrate its superiority over conventional, reflective gold grating stretchers in terms of pulse temporal quality. We show that, compared to a conventional stretcher with the same stretching factor, the transmission-grating based stretcher yields more than an order of magnitude improvement in the contrast pedestal. We have also quantitatively characterized the roughness of the grating surfaces and estimated its impact on the contrast pedestal.

  1. Laser-induced transient grating setup with continuously tunable period

    Energy Technology Data Exchange (ETDEWEB)

    Vega-Flick, A. [Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Applied Physics Department, CINVESTAV-Unidad Mérida, Carretera Antigua a Progreso Km 6, Cordemex, Mérida, Yucatán 97310 Mexico (Mexico); Eliason, J. K.; Maznev, A. A.; Nelson, K. A., E-mail: [Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Khanolkar, A.; Abi Ghanem, M.; Boechler, N. [Department of Mechanical Engineering, University of Washington, Seattle, Washington 98195 (United States); Alvarado-Gil, J. J. [Applied Physics Department, CINVESTAV-Unidad Mérida, Carretera Antigua a Progreso Km 6, Cordemex, Mérida, Yucatán 97310 Mexico (Mexico)


    We present a modification of the laser-induced transient grating setup enabling continuous tuning of the transient grating period. The fine control of the period is accomplished by varying the angle of the diffraction grating used to split excitation and probe beams. The setup has been tested by measuring dispersion of bulk and surface acoustic waves in both transmission and reflection geometries. The presented modification is fully compatible with optical heterodyne detection and can be easily implemented in any transient grating setup.

  2. Slow light via a tapered grating: transfer matrix approach

    NARCIS (Netherlands)

    Valkering, T.P.


    Reflection properties of a nonuniform apodized Bragg grating connecting a homogeneous medium with a (half-infinite) uniform grating are investigated for system parameters such that the group velocity in the uniform grating is low. In particular a smooth polynomial transition of the index profile to

  3. 21 CFR 133.147 - Grated American cheese food. (United States)


    ... 21 Food and Drugs 2 2010-04-01 2010-04-01 false Grated American cheese food. 133.147 Section 133...) FOOD FOR HUMAN CONSUMPTION CHEESES AND RELATED CHEESE PRODUCTS Requirements for Specific Standardized Cheese and Related Products § 133.147 Grated American cheese food. (a)(1) Grated American cheese food is...

  4. Design and development of long-period grating sensors for ...

    Indian Academy of Sciences (India)

    Abstract. Long Period Gratings (LPGs) have been developed using carbon diox- ide laser in a standard optical fibre. LPGs with a periodicity of 600 μm and grating length of 24 mm have been inscribed on standard single mode fibre. Such gratings have been used in designing temperature sensors and temperature is ...

  5. Theory of optimal beam splitting by phase gratings. I. One-dimensional gratings. (United States)

    Romero, Louis A; Dickey, Fred M


    We give an analytical basis for the theory of optimal beam splitting by one-dimensional gratings. In particular, we use methods from the calculus of variations to derive analytical expressions for the optimal phase function.

  6. How Spherical Is a Cube (Gravitationally)? (United States)

    Sanny, Jeff; Smith, David


    An important concept that is presented in the discussion of Newton's law of universal gravitation is that the gravitational effect external to a spherically symmetric mass distribution is the same as if all of the mass of the distribution were concentrated at the center. By integrating over ring elements of a spherical shell, we show that the…

  7. Sharp Strichartz estimates in spherical coordinates


    Schippa, Robert


    We prove almost Strichartz estimates found after adding regularity in the spherical coordinates for Schr\\"odinger-like equations. The estimates are sharp up to endpoints. The proof relies on estimates involving spherical averages. Sharpness is discussed making use of a modified Knapp-type example.

  8. Plasmonic Transmission Gratings – Fabrication and Characterization

    DEFF Research Database (Denmark)

    Sierant, Aleksandra; Jany, Benedykt; Bartoszek-Bober, Dobrosława

    the proposed plasmonic transmission gratings via near-field optical scanning microscopy (NSOM) and goniometric far field measurements. We support the evidence of our analyses with numerical calculations, carried out via rigorous coupled wave analysis (RCWA) and finite-difference in time-domain (FDTD...

  9. Smart photogalvanic running-grating interferometer

    DEFF Research Database (Denmark)

    Kukhtarev, N. V.; Kukhtareva, T.; Edwards, M. E.


    Photogalvanic effect produces actuation of periodic motion of macroscopic LiNbO3 crystal. This effect was applied to the development of an all-optical moving-grating interferometer usable for optical trapping and transport of algae chlorella microorganisms diluted in water with a concentration...

  10. Etched multimode fiber Bragg gratings based refractometer (United States)

    Tiwari, Umesh; Kaushik, Siddharth


    A Multimode Fiber Bragg Gratings for refractive index sensing has been demonstrated experimentally. The fabrication of Bragg gratings in the Standard step-index multimode fiber with a core diameter of 50 μm and a numerical aperture of 0.20 is carried out by phase mask method. The period of the phase mask is 1064 nm. The etching of cladding portion of grating region (2 cm) is carried out by Hydrofluoric acid (48%) for 15 minutes. The etching process causes reduction of cladding diameter by 55 μm which further enhances the interaction of light propagating in core mode with higher cladding modes. Solutions of varied concentrations of glycerol were prepared having corresponding refractive index. Shift in wavelength in the reflection peak of high-order mode L1 is observed when glycerol solution is passed over the cladding surface of grating region. The proposed sensor with 1-pm resolution was successfully employed for sensing of different glycerol solutions. The sensitivity of proposed sensor is 15000 pm/RIU and it can be used as potential sensing platform for bio-chemical applications.

  11. Undergraduate Experiment with Fractal Diffraction Gratings (United States)

    Monsoriu, Juan A.; Furlan, Walter D.; Pons, Amparo; Barreiro, Juan C.; Gimenez, Marcos H.


    We present a simple diffraction experiment with fractal gratings based on the triadic Cantor set. Diffraction by fractals is proposed as a motivating strategy for students of optics in the potential applications of optical processing. Fraunhofer diffraction patterns are obtained using standard equipment present in most undergraduate physics…

  12. Hybrid grating reflectors: Origin of ultrabroad stopband

    Energy Technology Data Exchange (ETDEWEB)

    Park, Gyeong Cheol; Taghizadeh, Alireza; Chung, Il-Sug, E-mail: [DTU Fotonik, Department of Photonics Engineering, Technical University of Denmark, DK-2800 Kgs. Lyngby (Denmark)


    Hybrid grating (HG) reflectors with a high-refractive-index cap layer added onto a high contrast grating (HCG) provide a high reflectance close to 100% over a broader wavelength range than HCGs. The combination of a cap layer and a grating layer brings a strong Fabry-Perot (FP) resonance as well as a weak guided mode (GM) resonance. Most of the reflected power results from the FP resonance, while the GM resonance plays a key role in achieving a reflectance close to 100% as well as broadening the stopband. An HG sample with 7 InGaAlAs quantum wells included in the cap layer has been fabricated by directly wafer-bonding a III-V cap layer onto a Si grating layer. Its reflection property has been characterized. This heterogeneously integrated HG reflector may allow for a hybrid III-V on Si laser to be thermally efficient, which has promising prospects for silicon photonics light sources and high-speed operation.

  13. Fiber Bragg Grating Filter High Temperature Sensors (United States)

    Lyons, Donald R.; Brass, Eric D.; Pencil, Eric (Technical Monitor)


    We present a scaled-down method for determining high temperatures using fiber-based Bragg gratings. Bragg gratings are distributed along the length of the optical fiber, and have high reflectivities whenever the optical wavelength is twice the grating spacing. These spatially distinct Bragg regions (located in the core of a fiber) are sensitive to local temperature changes. Since these fibers are silica-based they are easily affected by localized changes in temperature, which results in changes to both the grating spacing and the wavelength reflectivity. We exploit the shift in wavelength reflectivity to measure the change in the local temperature. Note that the Bragg region (sensing area) is some distance away from where the temperature is being measured. This is done so that we can measure temperatures that are much higher than the damage threshold of the fiber. We do this by affixing the fiber with the Bragg sensor to a material with a well-known coefficient of thermal expansion, and model the heat gradient from the region of interest to the actual sensor. The research described in this paper will culminate in a working device as well as be the second portion of a publication pending submission to Optics Letters.

  14. 21 CFR 133.146 - Grated cheeses. (United States)


    ... 21 Food and Drugs 2 2010-04-01 2010-04-01 false Grated cheeses. 133.146 Section 133.146 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) FOOD FOR HUMAN... 101 and 130 of this chapter, except that: (1) Enzymes of animal, plant, or microbial origin may be...

  15. Statistical mechanics of thin spherical shells

    CERN Document Server

    Kosmrlj, Andrej


    We explore how thermal fluctuations affect the mechanics of thin amorphous spherical shells. In flat membranes with a shear modulus, thermal fluctuations increase the bending rigidity and reduce the in-plane elastic moduli in a scale-dependent fashion. This is still true for spherical shells. However, the additional coupling between the shell curvature, the local in-plane stretching modes and the local out-of-plane undulations, leads to novel phenomena. In spherical shells thermal fluctuations produce a radius-dependent negative effective surface tension, equivalent to applying an inward external pressure. By adapting renormalization group calculations to allow for a spherical background curvature, we show that while small spherical shells are stable, sufficiently large shells are crushed by this thermally generated "pressure". Such shells can be stabilized by an outward osmotic pressure, but the effective shell size grows non-linearly with increasing outward pressure, with the same universal power law expone...

  16. Scaling of a fast spherical discharge (United States)

    Antsiferov, P. S.; Dorokhin, L. A.


    The influence of the discharge cavity dimensions on the properties of the spherical plasma formed in a fast discharge was studied experimentally. The passage of a current pulse with an amplitude of 30-40 kA and a rise rate of 1012 A/s (a fast discharge) through a spherical ceramic (Al2O3) cavity with an inner diameter of 11 mm filled with argon at a pressure of 80 Pa results in the formation of a 1- to 2-mm-diameter spherical plasma with an electron temperature of several tens of electronvolts and a density of 1018-1019 cm-3. It is shown that an increase in the inner diameter of the discharge cavity from 11 to 21 mm leads to the fourfold increase in the formation time of the spherical plasma and a decrease in the average ion charge. A decrease in the cavity diameter to 7 mm makes the spherical plasma unstable.

  17. CMB Anisotropy of Spherical Spaces

    CERN Document Server

    Aurich, Ralf; Steiner, Frank


    The first-year WMAP data taken at their face value hint that the Universe might be slightly positively curved and therefore necessarily finite, since all spherical (Clifford-Klein) space forms M^3 = S^3/Gamma, given by the quotient of S^3 by a group Gamma of covering transformations, possess this property. We examine the anisotropy of the cosmic microwave background (CMB) for all typical groups Gamma corresponding to homogeneous universes. The CMB angular power spectrum and the temperature correlation function are computed for the homogeneous spaces as a function of the total energy density parameter Omega_tot in the large range [1.01, 1.20] and are compared with the WMAP data. We find that out of the infinitely many homogeneous spaces only the three corresponding to the binary dihedral group T*, the binary octahedral group O*, and the binary icosahedral group I* are in agreement with the WMAP observations. Furthermore, if Omega_tot is restricted to the interval [1.00, 1.04], the space described by T* is excl...

  18. Spherically symmetric charged compact stars

    Energy Technology Data Exchange (ETDEWEB)

    Maurya, S.K. [University of Nizwa, Department of Mathematical and Physical Sciences, College of Arts and Science, Nizwa (Oman); Gupta, Y.K. [Jaypee Institute of Information Technology University, Department of Mathematics, Noida, Uttar Pradesh (India); Ray, Saibal [Government College of Engineering and Ceramic Technology, Department of Physics, Kolkata, West Bengal (India); Chowdhury, Sourav Roy [Seth Anandaram Jaipuria College, Department of Physics, Kolkata, West Bengal (India)


    In this article we consider the static spherically symmetric metric of embedding class 1. When solving the Einstein-Maxwell field equations we take into account the presence of ordinary baryonic matter together with the electric charge. Specific new charged stellar models are obtained where the solutions are entirely dependent on the electromagnetic field, such that the physical parameters, like density, pressure etc. do vanish for the vanishing charge. We systematically analyze altogether the three sets of Solutions I, II, and III of the stellar models for a suitable functional relation of ν(r). However, it is observed that only the Solution I provides a physically valid and well-behaved situation, whereas the Solutions II and III are not well behaved and hence not included in the study. Thereafter it is exclusively shown that the Solution I can pass through several standard physical tests performed by us. To validate the solution set presented here a comparison has also been made with that of the compact stars, like RX J 1856 - 37, Her X - 1, PSR 1937+21, PSRJ 1614-2230, and PSRJ 0348+0432, and we have shown the feasibility of the models. (orig.)

  19. Fundamental limit of light trapping in grating structures

    KAUST Repository

    Yu, Zongfu


    We use a rigorous electromagnetic approach to analyze the fundamental limit of light-trapping enhancement in grating structures. This limit can exceed the bulk limit of 4n 2, but has significant angular dependency. We explicitly show that 2D gratings provide more enhancement than 1D gratings. We also show the effects of the grating profile’s symmetry on the absorption enhancement limit. Numerical simulations are applied to support the theory. Our findings provide general guidance for the design of grating structures for light-trapping solar cells.

  20. Fiber-bragg grating-loop ringdown method and apparatus (United States)

    Wang, Chuji [Starkville, MS


    A device comprising a fiber grating loop ringdown (FGLRD) system of analysis is disclosed. A fiber Bragg grating (FBG) or Long-Period grating (LPG) written in a section of single mode fused silica fiber is incorporated into a fiber loop. By utilizing the wing areas of the gratings' bandwidth as a wavelength dependent attenuator of the light transmission, a fiber grating loop ringdown concept is formed. One aspect of the present invention is temperature sensing, which has been demonstrated using the disclosed device. Temperature measurements in the areas of accuracy, stability, high temperature, and dynamic range are also described.

  1. Metrology measurements for large-aperture VPH gratings (United States)

    Zheng, Jessica R.; Gers, Luke; Heijmans, Jeroen


    The High Efficiency and Resolution Multi Element Spectrograph (HERMES) for the Australian Astronomical Observatory (AAO) uses four large aperture, high angle of incidence volume phase holographic gratings (VPHG) for high resolution `Galactic archaeology' spectroscopy. The large clear aperture, the high diffraction efficiency, the line frequency homogeneity, and mosaic alignment made manufacturing and testing challenging. We developed new metrology systems at the AAO to verify the performance of these VPH gratings. The measured diffraction efficiencies and line frequency of the VPH gratings received so far meet the vendor's provided data. The wavefront quality for the Blue VPH grating is good but the Green and Red VPH gratings need to be post polishing.

  2. Fast calculation of spherical computer generated hologram using spherical wave spectrum method. (United States)

    Jackin, Boaz Jessie; Yatagai, Toyohiko


    A fast calculation method for computer generation of spherical holograms in proposed. This method is based on wave propagation defined in spectral domain and in spherical coordinates. The spherical wave spectrum and transfer function were derived from boundary value solutions to the scalar wave equation. It is a spectral propagation formula analogous to angular spectrum formula in cartesian coordinates. A numerical method to evaluate the derived formula is suggested, which uses only N(logN)2 operations for calculations on N sampling points. Simulation results are presented to verify the correctness of the proposed method. A spherical hologram for a spherical object was generated and reconstructed successfully using the proposed method.

  3. Performance characteristics of continuously grated multicore sensor fiber (United States)

    Westbrook, Paul S.; Kremp, Tristan; Feder, Kenneth S.; Ko, Wing; Monberg, Eric M.; Wu, Hongchao; Simoff, Debra A.; Shenk, Scott; Ortiz, Roy M.


    We describe the fabrication and performance of a continuously grated twisted multicore fiber sensor array. The grated fiber sensor comprises nearly continuous Bragg gratings along its entire length. The gratings are inscribed over lengths in excess of 10m in fibers with UV transparent coating using a flexible and scalable reel to reel processing system. The arrays are tested using optical frequency domain reflectometry (OFDR). We report on automated analysis routines applied to these OFDR measurements that allow for characterization of 100s of individual grating exposures that make up a continuously grated fiber length. We also report on the spectral loss of the continuously grated fiber, showing that it is suitable for applications with sensors in excess of 100m. Finally, we report on the fiber sensing characteristics by performing measurements of fiber bend using a fiber shape reconstruction algorithm on OFDR traces obtained from four of the fiber cores.

  4. Spherical aberration in contact lens wear. (United States)

    Lindskoog Pettersson, A; Jarkö, C; Alvin, A; Unsbo, P; Brautaset, R


    The aim of the present studies was to investigate the effect on spherical aberration of different non custom-made contact lenses, both with and without aberration control. A wavefront analyser (Zywave, Bausch & Lomb) was used to measure the aberrations in each subject's right eye uncorrected and with the different contact lenses. The first study evaluated residual spherical aberration with a standard lens (Focus Dailies Disposable, Ciba Vision) and with an aberration controlled contact lens (ACCL) (Definition AC, Optical Connection Inc.). The second study evaluated the residual spherical aberrations with a monthly disposable silicone hydrogel lens with aberration reduction (PureVision, Bausch & Lomb). Uncorrected spherical aberration was positive for all pupil sizes in both studies. In the first study, residual spherical aberration was close to zero with the standard lens for all pupil sizes whereas the ACCL over-corrected spherical aberration. The results of the second study showed that the monthly disposable lens also over-corrected the aberration making it negative. The changes in aberration were statistically significant (plenses. Since the amount of aberration varies individually we suggest that aberrations should be measured with lenses on the eye if the aim is to change spherical aberration in a certain direction.

  5. Novel Electrically Small Spherical Electric Dipole Antenna

    DEFF Research Database (Denmark)

    Kim, Oleksiy S.


    This paper introduces a novel electrically small spherical meander antenna. Horizontal sections of the meander are composed of wire loops, radii of which are chosen so that the whole structure is conformal to a sphere of radius a. To form the meander the loops are connected by wires at a meridian...... plane. The antenna operates as an electric dipole, i.e. it radiates the TM10 spherical mode. The antenna is self-resonant and can be matched to a wide range of input feed lines without an external matching network. In this paper, a spherical meander antenna of the size ka = 0.27 and the input impedance...

  6. Optical Properties of Topological Insulator Bragg Gratings

    CERN Document Server

    Crosse, J A


    Using the transfer matrix formalism, we study the transmission properties of a Bragg grating constructed from a layered axionic material. Such a material can be realized by a topological insulator subject to a time-symmetry breaking perturbation, such as an external magnetic field or surface magnetic impurities. Whilst the reflective properties of the structure are only negligibly changed by the presence of the axionic material, the grating induces Faraday and Kerr rotations in the transmitted and reflected light, respectively. These rotations are proportional to the number of layers and the strength of the time-symmetry breaking perturbation. In areas of low reflectivity the rotation angle of TE polarization decreases with increasing incidence angle while the TM polarization increases with increasing incidence angle with the converse occurring in areas of high reflectivity. The formalism and results will be useful in the development of optical and photonic devices based on topological insulators, devices whi...

  7. Spherically symmetric inhomogeneous dust collapse in higher ...

    Indian Academy of Sciences (India)

    We consider a collapsing spherically symmetric inhomogeneous dust cloud in higher dimensional space-time. We show that the central singularity of collapse can be a strong curvature or a weak curvature naked singularity depending on the initial density distribution.

  8. Novel gratings for next-generation instruments of astronomical observations (United States)

    Ebizuka, N.; Okamoto, T.; Takeda, M.; Hosobata, T.; Yamagata, Y.; Sasaki, M.; Uomoto, M.; Shimatsu, T.; Sato, S.; Hashimoto, N.; Tanaka, I.; Hattori, T.; Ozaki, S.; Aoki, W.


    We will introduce current status of development of a birefringence volume phase holographic (B-VPH) grating, volume binary (VB) grating and reflector facet transmission (RFT) grating developing as the novel dispersive optical element for astronomical instruments for the 8.2m Subaru Telescope, for next generation 30 m class huge ground-based telescopes and for next generation large space-bone telescopes. We will also introduce a hybrid grism developed for MOIRCS (Multi-Object InfraRed Camera and Spectrograph) of the Subaru Telescope and a quasi-Bragg (QB) immersion grating. Test fabrication of B-VPH gratings with a liquid crystal (LC) of UV curable and normal LCs or a resin of visible light curable are performed. We successfully fabricated VB gratings of silicon as a mold with ridges of a high aspect ratio by means of the cycle etching process, oxidation and removal of silicon oxide. The RFT grating which is a surface-relief (SR) transmission grating with sawtooth shaped ridges of an acute vertex angle. The hybrid grism, as a prototype of the RFT grating, combines a high-index prism and SR transmission grating with sawtooth shape ridges of an acute vertex angle. The mold of the SR grating for the hybrid grism on to a work of Ni-P alloy of non-electrolysic plating successfully fabricated by using our ultra-precision machine and a single-crystal diamond bite. The QB immersion grating was fabricated by a combination of an inclined QB grating, Littrow prism and surface reflection mirror.


    African Journals Online (AJOL)

    Dr Obe


    Sep 1, 1984 ... shaft of this gear (D) is connected by a 1:2 chain drive ... of the handle produces half a rotation of gear (D). This means that for one rotation of the handle, the grating drum rotates. 115/(2x11) or 5.23 times. Fig. 1 Photograph of Prototype ... If the top surface of the wedge were projected to intersect the.

  10. High-index-contrast subwavelength grating VCSEL

    DEFF Research Database (Denmark)

    Gilet, Philippe; Olivier, Nicolas; Grosse, Philippe


    In this article, we report our results on 980nm high-index-contrast subwavelength grating (HCG) VCSELs for optical interconnection applications. In our structure, a thin undoped HCG layer replaces a thick p-type Bragg mirror. The HCG mirror can feasibly achieve polarization-selective reflectivities...... structures. These results build a bridge between a standard VCSEL and a hybrid laser on silicon, making them of potential use for the realization of silicon photonics....

  11. 1550 nm high contrast grating VCSEL. (United States)

    Chase, Christopher; Rao, Yi; Hofmann, Werner; Chang-Hasnain, Connie J


    We demonstrate an electrically pumped high contrast grating (HCG) VCSEL operating at 1550 nm incorporating a proton implant-defined aperture. Output powers of >1 mW are obtained at room temperature under continuous wave operation. Devices operate continuous wave at temperatures exceeding 60 degrees C. The novel device design, which is grown in a single epitaxy step, may enable lower cost long wavelength VCSELs.

  12. Detailed Investigations of Load Coefficients on Grates

    DEFF Research Database (Denmark)

    Andersen, Thomas Lykke; Rasmussen, Michael R.; Frigaard, Peter

    In this report is presented the results of model tests carried out at Dept. of Civil Engineering, aalborg University (AAU) on behalf of DONG Energy A/S and Vattenfall A/S, Denmark. The objective of the tests was to investigate the load coefficient on different grates and a solid plate for designi...... offshore windmill access platforms against run-up generated forces with special attention to the influence of air entrainment and the angle of attack....


    Levey, R.P. Jr.; Smith, A.E.


    This patent relates to the preparation of high-density, spherical UO/sub 2/ particles 80 to 150 microns in diameter. Sinterable UO/sub 2/ powder is wetted with 3 to 5 weight per cent water and tumbled for at least 48 hours. The resulting spherical particles are then sintered. The sintered particles are useful in dispersion-type fuel elements for nuclear reactors. (AEC)

  14. 3D Printing Electrically Small Spherical Antennas

    DEFF Research Database (Denmark)

    Kim, Oleksiy S.


    3D printing is applied for rapid prototyping of an electrically small spherical wire antenna. The model is first printed in plastic and subsequently covered with several layers of conductive paint. Measured results are in good agreement with simulations.......3D printing is applied for rapid prototyping of an electrically small spherical wire antenna. The model is first printed in plastic and subsequently covered with several layers of conductive paint. Measured results are in good agreement with simulations....

  15. Grating THz laser with optical pumping (United States)

    Khoury, Jed; Haji-saeed, Bahareh; Woods, Charles; Kierstead, John


    In this paper, we present a design for a widely tunable solid-state optically and electrically pumped THz laser based on the Smith-Purcell free-electron laser. In the free-electron laser, an energetic electron beam pumps a metallic grating to generate surface plasmons. Our solid-state optically pumped design consists of a thin layer of dielectic, such as SiNx, sandwiched between a corrugated structure and a thin metal or semiconductor layer. The lower layer is for current streaming, and replaces the electron beam in the original design. The upper layer consists of one micro-grating for coupling the electromagnetic field in, another for coupling out, and a nano-grating for coupling with the current in the lower layer for electromagnetic field generation. The surface plasmon waves generated from the upper layer by an external electromagnetic field, and the lower layer by the applied current, are coupled. Emission enhancement occurs when the plasmonic waves in both layers are resonantly coupled.

  16. Grating Spectroscopes and How to Use Them

    CERN Document Server

    Harrison, Ken M


    Transmission grating spectroscopes look like simple filters and are designed to screw into place on the eyepiece tube of a telescope for visual use, or into a camera adapter for digicam or CCD imaging. They are relatively inexpensive and by far the easiest type of astronomical spectroscope to use, and so are the starting point for most beginners. Using the most popular commercially made filter gratings - from Rainbow Optics in the United States to Star Analyser in the United Kingdon - as examples, the book provides all the information needed to set up and use the grating to obtain stellar spectra. It also presents methods of analyzing the results. No heavy mathematics or formulas are involved, although a reasonable level of proficiency in using an astronomic telescope and, if relevant, imaging camera, is assumed. This book contains many practical hints and tips - something that is almost essential to success when starting out. It encourages new users to get quick results, and by following the worked examples,...

  17. Spherical cows in dark matter indirect detection (United States)

    Bernal, Nicolás; Necib, Lina; Slatyer, Tracy R.


    Dark matter (DM) halos have long been known to be triaxial, but in studies of possible annihilation and decay signals they are often treated as approximately spherical. In this work, we examine the asymmetry of potential indirect detection signals of DM annihilation and decay, exploiting the large statistics of the hydrodynamic simulation Illustris. We carefully investigate the effects of the baryons on the sphericity of annihilation and decay signals for both the case where the observer is at 8.5 kpc from the center of the halo (exemplified in the case of Milky Way-like halos), and for an observer situated well outside the halo. In the case of Galactic signals, we find that both annihilation and decay signals are expected to be quite symmetric, with axis ratios very different from 1 occurring rarely. In the case of extragalactic signals, while decay signals are still preferentially spherical, the axis ratio for annihilation signals has a much flatter distribution, with elongated profiles appearing frequently. Many of these elongated profiles are due to large subhalos and/or recent mergers. Comparing to gamma-ray emission from the Milky Way and X-ray maps of clusters, we find that the gamma-ray background appears less spherical/more elongated than the expected DM signal from the large majority of halos, and the Galactic gamma ray excess appears very spherical, while the X-ray data would be difficult to distinguish from a DM signal by elongation/sphericity measurements alone.

  18. Nanointaglio fabrication of optical lipid multilayer diffraction gratings with applications in biosensing (United States)

    Lowry, Troy Warren

    supramolecular remodeling such as vesicle formation from planar lipid bilayers or multilayers are needed to understand cellular self-organization. Presented next is a nanointaglio based method for quantitative measurements of lipid-protein interactions and its suitability for quantifying the membrane binding, inflation, and budding activity of the membrane-remodeling protein Sar1. Optical diffraction gratings composed of lipids are printed on surfaces using nanointaglio, resulting in lipid multilayer gratings. Exposure of lipid multilayer gratings to Sar1 results in the inflation of lipid multilayers into unilamellar structures, the kinetics of which can be detected in a label-free manner by monitoring the diffraction of white light through an optical microscope. Local variations in lipid multilayer volume on the surface can be used to vary substrate availability in a microarray format, allowing kinetic and thermodynamic data to be obtained from a single experiment without the need for varying enzyme concentration. A quantitative model is developed and fits to the data allow measurements of both binding affinity (KD) and kinetics (kon and koff). Importantly, this assay is uniquely capable of quantifying membrane remodeling. Upon Sar1 induced inflation of single bilayers from surface supported multilayers, the semi-cylindrical grating lines are observed to remodel into semi-spherical buds when a critical radius of curvature equal to 300 nm is reached, which is explained in terms of a Rayleigh type instability.

  19. Phasor analysis of binary diffraction gratings with different fill factors

    Energy Technology Data Exchange (ETDEWEB)

    MartInez, Antonio [Departamento de Ciencia de Materiales, Optica y TecnologIa Electronica, Universidad Miguel Hernandez, 03202 Elche (Spain); Sanchez-Lopez, Ma del Mar [Instituto de BioingenierIa y Departamento de Fisica y Arquitectura de Computadores, Universidad Miguel Hernandez, 03202 Elche (Spain); Moreno, Ignacio [Departamento de Ciencia de Materiales, Optica y TecnologIa Electronica, Universidad Miguel Hernandez, 03202 Elche (Spain)


    In this work, we present a simple analysis of binary diffraction gratings with different slit widths relative to the grating period. The analysis is based on a simple phasor technique directly derived from the Huygens principle. By introducing a slit phasor and a grating phasor, the intensity of the diffracted orders and the grating's resolving power can be easily obtained without applying the usual Fourier transform operations required for these calculations. The proposed phasor technique is mathematically equivalent to the Fourier transform calculation of the diffraction order amplitude, and it can be useful to explain binary diffraction gratings in a simple manner in introductory physics courses. This theoretical analysis is illustrated with experimental results using a liquid crystal device to display diffraction gratings with different fill factors.

  20. Coherently controlling Raman-induced grating in atomic media


    Arkhipkin, V. G.; Myslivets, S. A.; Timofeev, I. V.


    We consider dynamically controllable periodic structures, called Raman induced gratings, in three- and four-level atomic media, resulting from Raman interaction in a standing-wave pump. These gratings are due to periodic spatial modulation of the Raman nonlinearity and fundamentally differ from the ones based on electromagnetically induced transparency. The transmission and reflection spectra of such gratings can be simultaneously amplified and controlled by varying the pump field intensity. ...

  1. Diffraction Gratings for High-Intensity Laser Applications

    Energy Technology Data Exchange (ETDEWEB)

    Britten, J


    The scattering of light into wavelength-dependent discrete directions (orders) by a device exhibiting a periodic modulation of a physical attribute on a spatial scale similar to the wavelength of light has been the subject of study for over 200 years. Such a device is called a diffraction grating. Practical applications of diffraction gratings, mainly for spectroscopy, have been around for over 100 years. The importance of diffraction gratings in spectroscopy for the measurement of myriad properties of matter can hardly be overestimated. Since the advent of coherent light sources (lasers) in the 1960's, applications of diffraction gratings in spectroscopy have further exploded. Lasers have opened a vast application space for gratings, and apace, gratings have enabled entirely new classes of laser systems. Excellent reviews of the history, fundamental properties, applications and manufacturing techniques of diffraction gratings up to the time of their publication can be found in the books by Hutley (1) and more recently Loewen and Popov (2). The limited scope of this chapter can hardly do justice to such a comprehensive subject, so the focus here will be narrowly limited to characteristics required for gratings suitable for high-power laser applications, and methods to fabricate them. A particular area of emphasis will be on maximally-efficient large-aperture gratings for short-pulse laser generation.

  2. Strong phase-controlled fiber Bragg gratings for dispersion compensation (United States)

    Liu, Yisi; Dong, Liang; Pan, J. J.; Gu, Claire


    Dispersion-compensating fiber Bragg gratings with ~99.9% reflectivity that are made by continuous apodization and phase control are demonstrated. These strong dispersion-compensating gratings provide precision second-order, third-order, or even more complex dispersion compensation, as well as sufficient transmission isolation to be used at add-drop stages without additional filtering. A 99.84% grating with a constant -700-ps/nm dispersion and a 99.94% grating with dispersion varying linearly from 1000 to -1000 ps/nm are demonstrated.

  3. Photonic crystal fiber long-period gratings for biochemical sensing

    DEFF Research Database (Denmark)

    Rindorf, Lars Henning; Jensen, Jesper Bo; Dufva, Hans Martin


    -period grating it was possible to measure the thickness of the layer. The long-period gratings were inscribed in a large-mode area silica photonic crystal fiber with a CO2 laser. The thicknesses of a monolayer of poly-L-lysine and double-stranded DNA was measured using the device. We find that the grating has......We present experimental results showing that long-period gratings in photonic crystal fibers can be used as sensitive biochemical sensors. A layer of biomolecules was immobilized on the sides of the holes of the photonic crystal fiber and by observing the shift in the resonant wavelength of a long...

  4. Fiber facet gratings for high power fiber lasers (United States)

    Vanek, Martin; Vanis, Jan; Baravets, Yauhen; Todorov, Filip; Ctyroky, Jiri; Honzatko, Pavel


    We numerically investigated the properties of diffraction gratings designated for fabrication on the facet of an optical fiber. The gratings are intended to be used in high-power fiber lasers as mirrors either with a low or high reflectivity. The modal reflectance of low reflectivity polarizing grating has a value close to 3% for TE mode while it is significantly suppressed for TM mode. Such a grating can be fabricated on laser output fiber facet. The polarizing grating with high modal reflectance is designed as a leaky-mode resonant diffraction grating. The grating can be etched in a thin layer of high index dielectric which is sputtered on fiber facet. We used refractive index of Ta2O5 for such a layer. We found that modal reflectance can be close to 0.95 for TE polarization and polarization extinction ratio achieves 18 dB. Rigorous coupled wave analysis was used for fast optimization of grating parameters while aperiodic rigorous coupled wave analysis, Fourier modal method and finite difference time domain method were compared and used to compute modal reflectance of designed gratings.

  5. VCSELs and silicon light sources exploiting SOI grating mirrors

    DEFF Research Database (Denmark)

    Chung, Il-Sug; Mørk, Jesper


    grating works as a highly-reflective mirror as well as routes light into a Si in-plane output waveguide connected to the grating. In the vertical-cavity surface-emitting laser (VCSEL) version, there is no in-plane output waveguide connected to the grating. Thus, light is vertically emitted through...... the Bragg reflector. Numerical simulations show that both the silicon light source and the VCSEL exploiting SOI grating mirrors have superior performances, compared to existing silicon light sources and long wavelength VCSELs. These devices are highly adequate for chip-level optical interconnects as well...

  6. Gratings for Increasing Solid-State Laser Gain and Efficiency

    Energy Technology Data Exchange (ETDEWEB)

    Erlandson, A C; Britten, J A; Bonlie, J D


    We introduce new concepts for increasing the efficiency of solid state lasers by using gratings deposited on laser slabs or disks. The gratings improve efficiency in two ways: (1) by coupling out of the slab deleterious amplified spontaneous emission (ASE) and (2) by increasing the absorption efficiency of pump light. The gratings also serve as antireflective coatings for the extracting laser beam. To evaluate the potential for such coatings to improve laser performance, we calculated optical properties of a 2500 groove/mm, tantala-silica grating on a 1cm x 4cm x 8cm titanium-doped sapphire slab and performed ray-trace calculations for ASE and pump light. Our calculations show substantial improvements in efficiency due to grating ASE-coupling properties. For example, the gratings reduce pump energy required to produce a 0.6/cm gain coefficient by 9%, 20% and 35% for pump pulse durations of 0.5 {micro}s, 1{micro}s and 3{micro}s, respectively. Gratings also increase 532-nm pump-light absorption efficiency, particularly when the product slab overall absorption is small. For example, when the single-pass absorption is 1 neper, absorption efficiency increases from 66%, without gratings, to 86%, when gratings are used.

  7. Bragg Fibers with Soliton-like Grating Profiles

    Directory of Open Access Journals (Sweden)

    Bugaychuk S.


    Full Text Available Nonlinear dynamical system corresponding to the optical holography in a nonlocal nonlinear medium with dissipation contains stable localized spatio-temporal states, namely the grid dissipative solitons. These solitons display a non-uniform profile of the grating amplitude, which has the form of the dark soliton in the reflection geometry. The transformation of the grating amplitude gives rise many new atypical effects for the beams diffracted on such grating, and they are very suitable for the fiber Brass gratings. The damped nonlinear Schrodinger equation is derived that describes the properties of the grid dissipative soliton.

  8. Grating coupler on single-crystal lithium niobate thin film (United States)

    Chen, Zhihua; Wang, Yiwen; Jiang, Yunpeng; Kong, Ruirui; Hu, Hui


    The grating coupler on single-crystal lithium niobate thin film (lithium niobate on insulator, LNOI) was designed. A bottom reflector was added in the LNOI material to improve the coupling efficiency. The grating structure was optimized by FDTD method. The material parameters such as layer thickness of lithium niobate thin film, SiO2 thickness were discussed with respect to the coupling efficiency, and the tolerances of grating period, etch depth, groove width and fiber position were also studied systematically. The simulated maximum coupling efficiency from a grating coupler with (without) bottom reflector to a single-mode fiber is about 78% (40%) in z-cut LNOI for TE polarization.

  9. Increasing the field of view in grating based X-ray phase contrast imaging using stitched gratings. (United States)

    Meiser, J; Willner, M; Schröter, T; Hofmann, A; Rieger, J; Koch, F; Birnbacher, L; Schüttler, M; Kunka, D; Meyer, P; Faisal, A; Amberger, M; Duttenhofer, T; Weber, T; Hipp, A; Ehn, S; Walter, M; Herzen, J; Schulz, J; Pfeiffer, F; Mohr, J


    Grating based X-ray differential phase contrast imaging (DPCI) allows for high contrast imaging of materials with similar absorption characteristics. In the last years' publications, small animals or parts of the human body like breast, hand, joints or blood vessels have been studied. Larger objects could not be investigated due to the restricted field of view limited by the available grating area. In this paper, we report on a new stitching method to increase the grating area significantly: individual gratings are merged on a carrier substrate. Whereas the grating fabrication process is based on the LIGA technology (X-ray lithography and electroplating) different cutting and joining methods have been evaluated. First imaging results using a 2×2 stitched analyzer grating in a Talbot-Lau interferometer have been generated using a conventional polychromatic X-ray source. The image quality and analysis confirm the high potential of the stitching method to increase the field of view considerably.

  10. UV laser fabrication and modification of fiber Bragg gratings by stitching sub-gratings with in situ fluorescence monitoring. (United States)

    Leng, Yongzhang; Yun, Victor E; Goldhar, Julius


    We present a method for synthesizing complex fiber Bragg gratings using femtosecond UV laser pulses and image projection from a small phase mask. Fiber gratings with arbitrary spectral reflectivity can be achieved by stitching short grating segments with proper phases. The relative phase between neighboring sub-gratings is controlled using in situ UV-excited fluorescence monitoring. During the fabrication, we are able to monitor the amplitude and phase of each segment right after it was written. This is accomplished by scanning the phase mask with attenuated UV laser pulses and observing modulation in fluorescence. This information allows us to precisely set the position of fiber for the next segment. A fabricated grating segment can also be effectively erased with additional out-of-phase UV exposure. Bragg gratings over both telecom C-band and L-band can be conveniently achieved with this simple setup and a single phase mask.

  11. Recent Progress on Spherical Torus Research

    Energy Technology Data Exchange (ETDEWEB)

    Ono, Masayuki [PPPL; Kaita, Robert [PPPL


    The spherical torus or spherical tokamak (ST) is a member of the tokamak family with its aspect ratio (A = R0/a) reduced to A ~ 1.5, well below the normal tokamak operating range of A ≥ 2.5. As the aspect ratio is reduced, the ideal tokamak beta β (radio of plasma to magnetic pressure) stability limit increases rapidly, approximately as β ~ 1/A. The plasma current it can sustain for a given edge safety factor q-95 also increases rapidly. Because of the above, as well as the natural elongation κ, which makes its plasma shape appear spherical, the ST configuration can yield exceptionally high tokamak performance in a compact geometry. Due to its compactness and high performance, the ST configuration has various near term applications, including a compact fusion neutron source with low tritium consumption, in addition to its longer term goal of attractive fusion energy power source. Since the start of the two megaampere class ST facilities in 2000, National Spherical Torus Experiment (NSTX) in the US and Mega Ampere Spherical Tokamak (MAST) in UK, active ST research has been conducted worldwide. More than sixteen ST research facilities operating during this period have achieved remarkable advances in all of fusion science areas, involving fundamental fusion energy science as well as innovation. These results suggest exciting future prospects for ST research both near term and longer term. The present paper reviews the scientific progress made by the worldwide ST research community during this new mega-ampere-ST era.

  12. Scaling of a fast spherical discharge

    Energy Technology Data Exchange (ETDEWEB)

    Antsiferov, P. S., E-mail:; Dorokhin, L. A. [Russian Academy of Sciences, Institute of Spectroscopy (Russian Federation)


    The influence of the discharge cavity dimensions on the properties of the spherical plasma formed in a fast discharge was studied experimentally. The passage of a current pulse with an amplitude of 30–40 kA and a rise rate of ~10{sup 12} A/s (a fast discharge) through a spherical ceramic (Al{sub 2}O{sub 3}) cavity with an inner diameter of 11 mm filled with argon at a pressure of 80 Pa results in the formation of a 1- to 2-mm-diameter spherical plasma with an electron temperature of several tens of electronvolts and a density of 10{sup 18}–10{sup 19} cm{sup –3}. It is shown that an increase in the inner diameter of the discharge cavity from 11 to 21 mm leads to the fourfold increase in the formation time of the spherical plasma and a decrease in the average ion charge. A decrease in the cavity diameter to 7 mm makes the spherical plasma unstable.

  13. Spherical angular spectrum and the fractional order Fourier transform. (United States)

    Pellat-Finet, Pierre; Durand, Pierre-Emmanuel; Fogret, Eric


    The notion of a spherical angular spectrum leads to the decomposition of the field amplitude on a spherical emitter into a sum of spherical waves that converge onto the Fourier sphere of the emitter. Unlike the usual angular spectrum, the spherical angular spectrum is propagated as the field amplitude, in a way that can be expressed by a fractional order Fourier transform.

  14. Friction factor for water flow through packed beds of spherical and non-spherical particles

    Directory of Open Access Journals (Sweden)

    Kaluđerović-Radoičić Tatjana


    Full Text Available The aim of this work was the experimental evaluation of different friction factor correlations for water flow through packed beds of spherical and non-spherical particles at ambient temperature. The experiments were performed by measuring the pressure drop across the bed. Packed beds made of monosized glass spherical particles of seven different diameters were used, as well as beds made of 16 fractions of quartz filtration sand obtained by sieving (polydisperse non-spherical particles. The range of bed voidages was 0.359–0.486, while the range of bed particle Reynolds numbers was from 0.3 to 286 for spherical particles and from 0.1 to 50 for non-spherical particles. The obtained results were compared using a number of available literature correlations. In order to improve the correlation results for spherical particles, a new simple equation was proposed in the form of Ergun’s equation, with modified coefficients. The new correlation had a mean absolute deviation between experimental and calculated values of pressure drop of 9.04%. For non-spherical quartz filtration sand particles the best fit was obtained using Ergun’s equation, with a mean absolute deviation of 10.36%. Surface-volume diameter (dSV necessary for correlating the data for filtration sand particles was calculated based on correlations for dV = f(dm and Ψ = f(dm. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. ON172022

  15. Computer simulation of multiple dynamic photorefractive gratings

    DEFF Research Database (Denmark)

    Buchhave, Preben


    The benefits of a direct visualization of space-charge grating buildup are described. The visualization is carried out by a simple repetitive computer program, which simulates the basic processes in the band-transport model and displays the result graphically or in the form of numerical data....... The simulation sheds light on issues that are not amenable to analytical solutions, such as the spectral content of the wave forms, cross talk in three-beam interaction, and the range of applications of the band-transport model. (C) 1998 Optical Society of America....

  16. Background reduction of a spherical gaseous detector

    Energy Technology Data Exchange (ETDEWEB)

    Fard, Ali Dastgheibi [Laboratoire Souterrain de Modane, France (France); Loaiza, Pia; Piquemal, Fabrice [Laboratoire Souterrain de Modane (France); Giomataris, Ioannis; Gray, David; Gros, Michel; Magnier, Patrick; Navick, Xavier-François [CEA Saclay - IRFU/SEDI - 91191 Gif sur Yvette (France); Savvidis, Ilias [Aristotle University of Thessaloniki (Greece)


    The Spherical gaseous detector (or Spherical Proportional Counter, SPC) is a novel type of detector. It consists of a large spherical volume filled with gas, using a single detection readout channel. The detector allows 100 % detection efficiency. SEDINE is a low background version of SPC installed at the Laboratoire Souterrain de Modane (LSM) underground laboratory (4800 m.w.e) looking for rare events at very low energy threshold, below 100 eV. This work presents the details on the chemical cleaning to reduce internal {sup 210}Pb surface contamination on the copper vessel and the external radon reduction achieved via circulation of pure air inside anti-radon tent. It will be also show the radon measurement of pure gases (Ar, N, Ne, etc) which are used in the underground laboratory for the low background experiments.

  17. Low-Dispersion Fibre Bragg Gratings Written Using the Polarization Control Method

    DEFF Research Database (Denmark)

    Deyerl, Hans Jürgen; Plougmann, Nikolai; Jensen, Jesper Bo Damm


    We present two fibre Bragg gratings with reduced in-band dispersion for DWDM applications. The gratings were designed by the inverse scattering method and fabricated using the novel polarization control method for UV-writing of advanced gratings.......We present two fibre Bragg gratings with reduced in-band dispersion for DWDM applications. The gratings were designed by the inverse scattering method and fabricated using the novel polarization control method for UV-writing of advanced gratings....

  18. Overview of spherical tokamak research in Japan (United States)

    Takase, Y.; Ejiri, A.; Fujita, T.; Fukumoto, N.; Fukuyama, A.; Hanada, K.; Idei, H.; Nagata, M.; Ono, Y.; Tanaka, H.; Uchida, M.; Horiuchi, R.; Kamada, Y.; Kasahara, H.; Masuzaki, S.; Nagayama, Y.; Oishi, T.; Saito, K.; Takeiri, Y.; Tsuji-Iio, S.


    Nationally coordinated research on spherical tokamak is being conducted in Japan. Recent achievements include: (i) plasma current start-up and ramp-up without the use of the central solenoid by RF waves (in electron cyclotron and lower hybrid frequency ranges), (ii) plasma current start-up by AC Ohmic operation and by coaxial helicity injection, (iii) development of an advanced fuelling technique by compact toroid injection, (iv) ultra-long-pulse operation and particle control using a high temperature metal wall, (v) access to the ultra-high-β regime by high-power reconnection heating, and (vi) improvement of spherical tokamak plasma stability by externally applied helical field.


    Directory of Open Access Journals (Sweden)



    Full Text Available Polaron states in cylindrical and spherical quantum dots with parabolic confinement potentials are investigated applying the Feynman variational principle. It is observed that for both kinds of quantum dots the polaron energy and mass increase with the increase of Frohlich electron-phonon coupling constant and confinement frequency. In the case of a spherical quantum dot, the polaron energy for the strong coupling is found to be greater than that of a cylindrical quantum dot. The energy and mass are found to be monotonically increasing functions of the coupling constant and the confinement frequency.

  20. Compact Bragg Gratings for Long-Range Surface Plasmon Polaritons

    DEFF Research Database (Denmark)

    Boltasseva, Alexandra; Bozhevolnyi, Sergey I; Nikolajsen, Thomas


    By introducing periodic thickness-modulation of thin metal stripes embedded in a dielectric, we realize compact and efficient Bragg gratings for long-range surface plasmon polaritons (LR-SPPs) operating around 1550 nm. We measure reflection and transmission spectra of the gratings having different...

  1. Holographic gratings in photorefractive polymers without external electric field

    DEFF Research Database (Denmark)

    Kukhtarev, N.; Lyuksyutov, S.; Buchhave, Preben


    Using anomalous large diffusion we report a recording of reflection type gratings in a PVK-based photorefractive polymer without any external electric field. The diffraction efficiency of the gratings was measured to be 7%. An efficient modulation of beams during two-beam coupling up to 12...

  2. Transmission gratings for beam sampling and beam splitting. (United States)

    Popov, E K; Loewen, E G; Neviére, M


    Transmission gratings have rarely been used for beam sampling because they require special properties from dielectric overcoatings, which, to the best of our knowledge, are described here for the first time. Although such gratings are often used as beam splitters, their nature can be modified along the same principles with thin metal coatings, which are described.

  3. Analysis of the optical parameters of phase holographic gratings

    Directory of Open Access Journals (Sweden)

    Є.О. Тихонов


    Full Text Available  Suitability of 2- wave approximation of the coupled waves theory tor description of holographic phase gratings recorded on photopolymer compound ФПК-488 is proved. Using the basic formulas of the theory, main grating optical parameters - a depth of modulation and finished thickness are not measured immediately are determined.

  4. Transversely loaded fiber optic grating strain sensors for aerospace applications (United States)

    Udd, Eric; Schulz, Whitten L.; Seim, John M.; Trego, Angela; Haugse, Eric D.; Johnson, Patrick E.


    Most fiber grating sensor technology that has been developed to support strain sensing involves the measurement of axial strain. Fiber grating sensors are however capable of monitoring transverse as well as axial strain. This paper reviews a series of applications of this technology that are of particular interest to aerospace applications.

  5. Investigations on birefringence effects in polymer optical fiber Bragg gratings

    DEFF Research Database (Denmark)

    Hu, Xiaolian; Saez-Rodriguez, D.; Bang, Ole


    Step-index polymer optical fiber Bragg gratings (POFBGs) and microstructured polymer optical fiber Bragg gratings (mPOFBGs) present several attractive features, especially for sensing purposes. In comparison to FBGs written in silica fibers, they are more sensitive to temperature and pressure bec...

  6. Wave-front-engineered grating mirrors for VCSELs

    DEFF Research Database (Denmark)

    Carletti, Luca; Malureanu, Radu; Mørk, Jesper


    High-index-contrast grating mirrors featuring beam steering abilities for the transmitted beam as well as high reflectivity over a broad bandwidth are suggested. Gratings designed to provide control over the wave front of the transmitted beam are numerically investigated. The proposed structures ...

  7. Development of tilted fibre Bragg gratings using highly coherent 255 ...

    Indian Academy of Sciences (India)


    Feb 6, 2014 ... very efficient source for writing FBGs using phase mask as well as interferometers [4–7]. In this paper, we ... Figure 1 shows the experimental set-up for writing the tilted fibre Bragg grating. High spatial coherent UV .... [1] R Kashyap, Fibre Bragg grating (Academic Press, New York, 1999). [2] T Erdogan and ...

  8. Electromagnetically induced two-dimensional grating assisted by incoherent pump

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Yu-Yuan; Liu, Zhuan-Zhuan; Wan, Ren-Gang, E-mail:


    We propose a scheme for realizing electromagnetically induced two-dimensional grating in a double-Λ system driven simultaneously by a coherent field and an incoherent pump field. In such an atomic configuration, the absorption is suppressed owing to the incoherent pumping process and the probe can be even amplified, while the refractivity is mainly attributed to the dynamically induced coherence. With the help of a standing-wave pattern coherent field, we obtain periodically modulated refractive index without or with gain, and therefore phase grating or gain-phase grating which diffracts a probe light into high-order direction efficiently can be formed in the medium via appropriate manipulation of the system parameters. The diffraction efficiency attainable by the present gratings can be controlled by tuning the coherent field intensity or the interaction length. Hence, the two-dimensional grating can be utilized as all-optical splitter or router in optical networking and communication. - Highlights: • Two-dimensional grating is coherently induced in four-level atoms. • Phase and gain-phase gratings are obtained assisted by incoherent pump. • The diffraction power is improved due to the enhanced refraction modulation. • The gratings can be utilized as multi-channel all-optical splitter and router.

  9. Development of tilted fibre Bragg gratings using highly coherent 255 ...

    Indian Academy of Sciences (India)


    Feb 6, 2014 ... This paper reports the study on development of tilted fibre Bragg gratings using highly coherent 255 nm radiation, obtained from the second harmonic generation (SHG) of copper vapour laser (CVL). The transmission and reflection spectra of the tilted fibre Bragg gratings (TFBG) were studied for the tilt ...

  10. The Off-plane Grating Rocket Experiment (United States)

    Donovan, Benjamin


    The next generation of X-ray spectrometers necessitate significant increases in both resolution and effective area to achieve the science goals set forth in the 2010 Decadal Survey and the 2013 Astrophysics Roadmap. The Off-plane Grating Rocket Experiment (OGRE), an X-ray spectroscopy suborbital rocket payload currently scheduled for launch in Q3 2020, will serve as a testbed for several key technologies which can help achieve the desired performance increases of future spectrometers. OGRE will be the first instrument to fly mono-crystalline silicon X-ray mirrors developed at NASA Goddard Space Flight Center. The payload will also utilize an array of off-plane gratings manufactured at The Pennsylvania State University. Additionally, the focal plane will be populated with an array of four electron-multiplying CCDs developed by the Open University and XCAM Ltd. With these key technologies, OGRE hopes to achieve the highest resolution on-sky soft X-ray spectrum to date. We discuss the optical design, expected performance, and the current status of the payload.

  11. 130-nm tunable grating-mirror VCSEL

    DEFF Research Database (Denmark)

    Chung, Il-Sug; Mørk, Jesper


    We have reported that a combination of the high-index-contrast grating (HCG) mirror as movable mirror and the extended cavity configuration with an antireflection layer can provide a tuning wavelength range of 100 nm for tunable VCSELs. Here, we report that using the air-coupled cavity configurat......We have reported that a combination of the high-index-contrast grating (HCG) mirror as movable mirror and the extended cavity configuration with an antireflection layer can provide a tuning wavelength range of 100 nm for tunable VCSELs. Here, we report that using the air-coupled cavity...... configuration instead of the extended cavity configuration can bring 130-nm tuning range around 1330-nm wavelength. The air-coupled cavity is known to reduce the quantum confinement factor in VCSELs, increasing threshold. In our air-coupled cavity HCG VCSEL case, the very short power penetration length...... in the HCG minimizes this reduction of the quantum confinement factor, not as significant as in the air-coupled cavity DBR VCSEL....

  12. Modern Theory of Gratings Resonant Scattering: Analysis Techniques and Phenomena

    CERN Document Server

    Sirenko, Yuriy K


    Diffraction gratings are one of the most popular objects of analysis in electromagnetic theory. The requirements of applied optics and microwave engineering lead to many new problems and challenges for the theory of diffraction gratings, which force us to search for new methods and tools for their resolution. In Modern Theory of Gratings, the authors present results of the electromagnetic theory of diffraction gratings that will constitute the base of further development of this theory, which meet the challenges provided by modern requirements of fundamental and applied science. This volume covers: spectral theory of gratings (Chapter 1) giving reliable grounds for physical analysis of space-frequency and space-time transformations of the electromagnetic field in open periodic resonators and waveguides; authentic analytic regularization procedures (Chapter 2) that, in contradistinction to the traditional frequency-domain approaches, fit perfectly for the analysis of resonant wave scattering processes; paramet...

  13. Mode conversion and coupling in a slanted grating. (United States)

    Li, Shubin; Zhou, Changhe; Cao, Hongchao; Wu, Jun; Yu, Junjie


    We have proposed a novel transmission slanted grating at the central wavelength of 1550 nm, which can be used in optical communication. We have presented an approximate analytical expression that provides an insightful physical description of the simplified modal method for the slanted grating. The odd grating mode, which only exists in the asymmetric structure under normal incidence, plays the positive role of enhancing the -1st order diffraction efficiency. The analytic expressions of mode conversion and coupling can be obtained to explain the asymmetric field distribution, which cannot occur in the rectangular grating region. Numerical results achieved by the rigorous wave analysis verify the validity of the simplified modal method. We expect that the theoretical modal method set forth in this work will be helpful for the tremendous potential application of the slanted grating.

  14. Grate-firing of biomass for heat and power production

    DEFF Research Database (Denmark)

    Yin, Chungen; Rosendahl, Lasse; Kær, Søren Knudsen


    bed on the grate, and the advanced secondary air supply (a real breakthrough in this technology) are highlighted for grate-firing systems. Amongst all the issues or problems associated with grate-fired boilers burning biomass, primary pollutant formation and control, deposition formation and corrosion......As a renewable and environmentally friendly energy source, biomass (i.e., any organic non-fossil fuel) and its utilization are gaining an increasingly important role worldwide Grate-firing is one of the main competing technologies in biomass combustion for heat and power production, because it can...... fire a wide range of fuels of varying moisture content, and requires less fuel preparation and handling. The basic objective of this paper is to review the state-of-the-art knowledge on grate-fired boilers burning biomass: the key elements in the firing system and the development, the important...

  15. Self Referencing Heterodyne Transient Grating Spectroscopy with Short Wavelength

    Directory of Open Access Journals (Sweden)

    Jakob Grilj


    Full Text Available Heterodyning by a phase stable reference electric field is a well known technique to amplify weak nonlinear signals. For short wavelength, the generation of a reference field in front of the sample is challenging because of a lack of suitable beamsplitters. Here, we use a permanent grating which matches the line spacing of the transient grating for the creation of a phase stable reference field. The relative phase among the two can be changed by a relative translation of the permanent and transient gratings in direction orthogonal to the grating lines. We demonstrate the technique for a transient grating on a VO2 thin film and observe constructive as well as destructive interference signals.

  16. Electromagnetically Induced Grating Without Absorption Using Incoherent Pump (United States)

    Chen, Yu-Yuan; Liu, Zhuan-Zhuan; Wan, Ren-Gang


    We propose a scheme for creating electromagnetically induced grating in a four-level double- Λ atomic system driven by a coupling field and an incoherent pump field. Owing to the incoherent pumping process, large refractivity accompanied with vanishing absorption or even gain across the probe field can be built up in the atoms, thus phase grating or gain-phase grating, which diffracts a probe light into different directions, can be formed with the help of a standing-wave coupling field. The diffraction efficiency of the gratings can be tuned by the coupling field intensity and the incoherent pump rate, hence the proposed gratings should be suitable for beam splitter and optical switching in optical communication and networking.

  17. Spherical Horn Array for Wideband Propagation Measurements

    DEFF Research Database (Denmark)

    Franek, Ondrej; Pedersen, Gert Frølund


    A spherical array of horn antennas designed to obtain directional channel information and characteristics is introduced. A dual-polarized quad-ridged horn antenna with open flared boundaries and coaxial feeding for the frequency band 600 MHz–6 GHz is used as the element of the array. Matching...... for a wideband multipath propagation studies....

  18. Exact solutions of the spherically symmetric multidimensional ...

    African Journals Online (AJOL)

    The complete orthonormalised energy eigenfunctions and the energy eigenvalues of the spherically symmetric isotropic harmonic oscillator in N dimensions, are obtained through the methods of separation of variables. Also, the degeneracy of the energy levels are examined. KEY WORDS: - Schrödinger Equation, Isotropic ...

  19. Spherical projections and liftings in geometric tomography

    DEFF Research Database (Denmark)

    Goodey, Paul; Kiderlen, Markus; Weil, Wolfgang


    We consider a variety of integral transforms arising in Geometric Tomography. It will be shown that these can be put into a common framework using spherical projection and lifting operators. These operators will be applied to support functions and surface area measures of convex bodies and to rad...

  20. Noncommutative spherically symmetric spacetimes at semiclassical order (United States)

    Fritz, Christopher; Majid, Shahn


    Working within the recent formalism of Poisson-Riemannian geometry, we completely solve the case of generic spherically symmetric metric and spherically symmetric Poisson-bracket to find a unique answer for the quantum differential calculus, quantum metric and quantum Levi-Civita connection at semiclassical order O(λ) . Here λ is the deformation parameter, plausibly the Planck scale. We find that r, t, d r, d t are all forced to be central, i.e. undeformed at order λ, while for each value of r, t we are forced to have a fuzzy sphere of radius r with a unique differential calculus which is necessarily nonassociative at order λ2 . We give the spherically symmetric quantisation of the FLRW cosmology in detail and also recover a previous analysis for the Schwarzschild black hole, now showing that the quantum Ricci tensor for the latter vanishes at order λ. The quantum Laplace-Beltrami operator for spherically symmetric models turns out to be undeformed at order λ while more generally in Poisson-Riemannian geometry we show that it deforms to □f+λ2ωαβ(Ricγα-Sγα)(∇^βdf)γ+O(λ2) in terms of the classical Levi-Civita connection \\widehat\

  1. Spherical Tolman-Bondi Models in Cosmology (United States)

    Bochicchio, I.; Laserra, E.


    Spherical symmetry is considered and exact solutions of Tolman-Bondi equations are studied taking advantage from Ricci principal curvature depending on the radial coordinate. Moreover an expansion of the exact solutions in fractional Puiseux series in considered to compare Euclidean and not Euclidean cases.

  2. Determining a Sonographic Nomogram for Gallbladder Spherical ...

    African Journals Online (AJOL)

    Kurtosis and skewness values (0.991 and 0.152 respectively) showed even distribution . This study establishes a normogram for the population using the model formula and could be used in the assessment of gallbladder in conditions giving rise to gallbladder hydrops. Keywords: Sonography, Gallbladder Spherical index, ...

  3. A Generalization of the Spherical Inversion (United States)

    Ramírez, José L.; Rubiano, Gustavo N.


    In the present article, we introduce a generalization of the spherical inversion. In particular, we define an inversion with respect to an ellipsoid, and prove several properties of this new transformation. The inversion in an ellipsoid is the generalization of the elliptic inversion to the three-dimensional space. We also study the inverse images…

  4. Spherically symmetric inhomogeneous dust collapse in higher ...

    Indian Academy of Sciences (India)

    Higher dimensional space-time; naked singularity; cosmic censorship. PACS Nos 04.20.Dw; 04.50. ... The existence of strong curvature naked singularities in gravitational collapse of spherically symmetric space-times ..... distributions (in an appropriate metric space) can be discussed along the lines of [16]. 3. Strength of the ...

  5. Spherical hashing: binary code embedding with hyperspheres. (United States)

    Heo, Jae-Pil; Lee, Youngwoon; He, Junfeng; Chang, Shih-Fu; Yoon, Sung-Eui


    Many binary code embedding schemes have been actively studied recently, since they can provide efficient similarity search, and compact data representations suitable for handling large scale image databases. Existing binary code embedding techniques encode high-dimensional data by using hyperplane-based hashing functions. In this paper we propose a novel hypersphere-based hashing function, spherical hashing, to map more spatially coherent data points into a binary code compared to hyperplane-based hashing functions. We also propose a new binary code distance function, spherical Hamming distance, tailored for our hypersphere-based binary coding scheme, and design an efficient iterative optimization process to achieve both balanced partitioning for each hash function and independence between hashing functions. Furthermore, we generalize spherical hashing to support various similarity measures defined by kernel functions. Our extensive experiments show that our spherical hashing technique significantly outperforms state-of-the-art techniques based on hyperplanes across various benchmarks with sizes ranging from one to 75 million of GIST, BoW and VLAD descriptors. The performance gains are consistent and large, up to 100 percent improvements over the second best method among tested methods. These results confirm the unique merits of using hyperspheres to encode proximity regions in high-dimensional spaces. Finally, our method is intuitive and easy to implement.

  6. Collapsing spherical null shells in general relativity

    Directory of Open Access Journals (Sweden)

    S Khakshournia


    Full Text Available In this work, the gravitational collapse of a spherically symmetric null shell with the flat interior and a charged Vaidya exterior spacetimes is studied. There is no gravitational impulsive wave present on the null hypersurface which is shear-free and contracting. It follows that there is a critical radius at which the shell bounces and starts expanding.

  7. Spherical crystallization: direct spherical agglomeration of salicylic Acid crystals during crystallization. (United States)

    Kawashima, Y; Okumura, M; Takenaka, H


    Direct spherical agglomeration of salicylic acid crystals during crystallization is described. The needle-like salicylic acid crystals simultaneously form and agglomerate in a mixture of three partially miscible liquids, such as water, ethanol, and chloroform, with agitation. The agglomerates can be made directly into tablets because of their excellent flowability. Spherical crystallization could eliminate the usual separate agglomeration step after crystallization and may be adaptable to other pharmaceutical and chemical systems.

  8. MEMS tunable grating micro-spectrometer (United States)

    Tormen, Maurizio; Lockhart, R.; Niedermann, P.; Overstolz, T.; Hoogerwerf, A.; Mayor, J.-M.; Pierer, J.; Bosshard, C.; Ischer, R.; Voirin, G.; Stanley, R. P.


    The interest in MEMS based Micro-Spectrometers is increasing due to their potential in terms of flexibility as well as cost, low mass, small volume and power savings. This interest, especially in the Near-Infrared and Mid- Infrared, ranges from planetary exploration missions to astronomy, e.g. the search for extra solar planets, as well as to many other terrestrial fields of application such as, industrial quality and surface control, chemical analysis of soil and water, detection of chemical pollutants, exhausted gas analysis, food quality control, process control in pharmaceuticals, to name a few. A compact MEMS-based Spectrometer for Near- Infrared and Mid-InfraRed operation have been conceived, designed and demonstrated. The design based on tunable MEMS blazed grating, developed in the past at CSEM [1], achieves state of the art results in terms of spectral resolution, operational wavelength range, light throughput, overall dimensions, and power consumption.

  9. Robust topology design of periodic grating surfaces

    DEFF Research Database (Denmark)

    Friis, Kasper Storgaard; Sigmund, Ole


    depending on the purpose. This work details the use of topology optimization for designing periodic polymer grating surfaces with complex optical properties. A method based on robust topology optimization is formulated for designing the nanostructure of plastic surfaces with extreme reflection......Modern nanoscale manufacturing techniques allow for a high degree of flexibility in designing surface microstructures and nanostructures. Injection molding of nanosized features allows for mass production of plastic components with a tailored nanostructure producing specific optical effects...... or transmission properties. Topology optimization allows for free distribution of material but a mechanical constraint based on the fundamental free mechanical vibration frequency ensures connected structures. Several examples are given to illustrate the efficiency of the method....

  10. Blazed Gratings Recorded in Absorbent Photopolymers

    Directory of Open Access Journals (Sweden)

    Roberto Fernández


    Full Text Available Phase diffractive optical elements, which have many interesting applications, are usually fabricated using a photoresist. In this paper, they were made using a hybrid optic-digital system and a photopolymer as recording medium. We analyzed the characteristics of the input and recording light and then simulated the generation of blazed gratings with different spatial periods in different types of photopolymers using a diffusion model. Finally, we analyzed the output and diffraction efficiencies of the 0 and 1st order so as to compare the simulated values with those measured experimentally. We evaluated the effects of index matching in a standard PVA/AA photopolymer, and in a variation of Biophotopol, a more biocompatible photopolymer. Diffraction efficiencies near 70%, for a wavelength of 633 nm, were achieved for periods longer than 300 µm in this kind of materials.

  11. Grating-based tomography of human tissues (United States)

    Müller, Bert; Schulz, Georg; Mehlin, Andrea; Herzen, Julia; Lang, Sabrina; Holme, Margaret; Zanette, Irene; Hieber, Simone; Deyhle, Hans; Beckmann, Felix; Pfeiffer, Franz; Weitkamp, Timm


    The development of therapies to improve our health requires a detailed knowledge on the anatomy of soft tissues from the human body down to the cellular level. Grating-based phase contrast micro computed tomography using synchrotron radiation provides a sensitivity, which allows visualizing micrometer size anatomical features in soft tissue without applying any contrast agent. We show phase contrast tomography data of human brain, tumor vessels and constricted arteries from the beamline ID 19 (ESRF) and urethral tissue from the beamline W2 (HASYLAB/DESY) with micrometer resolution. Here, we demonstrate that anatomical features can be identified within brain tissue as well known from histology. Using human urethral tissue, the application of two photon energies is compared. Tumor vessels thicker than 20 μm can be perfectly segmented. The morphology of coronary arteries can be better extracted in formalin than after paraffin embedding.

  12. High-resolution diffraction grating interferometric transducer of linear displacements (United States)

    Shang, Ping; Xia, Haojie; Fei, Yetai


    A high-resolution transducer of linear displacements is presented. The system is based on semiconductor laser illumination and a diffraction grating applied as a length master. The theory of the optical method is formulated using Doppler description. The relationship model among the interference strips, measurement errors, grating deflection around the X, Y and Z axes and translation along the Z axis is built. The grating interference strips' direction and space is not changed with movement along the X (direction of grating movement), Y (direction of grating line), Z axis, and the direction and space has a great effect when rotating around the X axis. Moreover the space is little affected by deflection around the Z axis however the direction is changed dramatically. In addition, the strips' position shifted rightward or downwards respectively for deflection around the X or Y axis. Because the emitted beams are separated on the grating plane, the tilt around the X axis error of the stage during motion will lead to the optical path difference of the two beams resulting in phase shift. This study investigates the influence of the tilt around the X axis error. Experiments show that after yaw error compensation, the high-resolution diffraction grating interferometric transducer readings can be significantly improved. The error can be reduced from +/-80 nm to +/-30 nm in maximum.

  13. Synchronously pumped optical parametric oscillator with diffraction-grating tuning

    Energy Technology Data Exchange (ETDEWEB)

    Hanna, D.C. [Optoelectronics Research Centre, University of Southampton, Highfield, Southampton (United Kingdom)]. E-mail:; O' Connor, M.V.; Watson, M.A.; Shepherd, D.P. [Optoelectronics Research Centre, University of Southampton, Highfield, Southampton (United Kingdom)


    The operating characteristics of a synchronously pumped optical parametric oscillator, based on periodically poled lithium niobate (PPLN), with a diffraction grating as the tuning element, are described and compared with design expectations. Operation at average signal output power levels of up to 2.0 W has been achieved and signal/idler tuning in the range 1.466-3.663 {mu}m has been investigated using the tilt of the diffraction grating, while keeping the temperature of the PPLN fixed. A detailed investigation has been made of the operating characteristics that might be influenced by the presence of pulse tilt caused by the grating. It is shown that any adverse effects of tilt on beam quality can be small, with the main observed effect being an excess loss. An observed tendency to oscillate in higher-order transverse modes on the long-wavelength side of the tuning range is ascribed to non-collinear phase-matching. This higher-order-mode oscillation is easily prevented by the insertion of an aperture. The analysis presented here includes a grating loss calculation and the calculation of the tuning range achievable with a diffraction grating. The effects of cavity-length change on oscillator performance are also examined and it is found that the grating can give a valuable stabilizing influence by suppressing cavity-length-induced frequency-pulling effects. Extension of the use of gratings from the picosecond to the femtosecond regime is also considered.(author)

  14. Fast tunable blazed MEMS grating for external cavity lasers (United States)

    Tormen, Maurizio; Niedermann, Philippe; Hoogerwerf, Arno; Shea, Herbert; Stanley, Ross


    Diffractive MEMS are interesting for a wide range of applications, including displays, scanners or switching elements. Their advantages are compactness, potentially high actuation speed and in the ability to deflect light at large angles. We have designed and fabricated deformable diffractive MEMS grating to be used as tuning elements for external cavity lasers. The resulting device is compact, has wide tunability and a high operating speed. The initial design is a planar grating where the beams are free-standing and attached to each other using leaf springs. Actuation is achieved through two electrostatic comb drives at either end of the grating. To prevent deformation of the free-standing grating, the device is 10 μm thick made from a Silicon on Insulator (SOI) wafer in a single mask process. At 100V a periodicity tuning of 3% has been measured. The first resonant mode of the grating is measured at 13.8 kHz, allowing high speed actuation. This combination of wide tunability and high operating speed represents state of the art in the domain of tunable MEMS filters. In order to improve diffraction efficiency and to expand the usable wavelength range, a blazed version of the deformable MEMS grating has been designed. A key issue is maintaining the mechanical properties of the original device while providing optically smooth blazed beams. Using a process based on anisotropic KOH etching, blazed gratings have been obtained and preliminary characterization is promising.

  15. Surface relief gratings in azobenzene supramolecular systems based on polyimides (United States)

    Schab-Balcerzak, Ewa; Sobolewska, Anna; Stumpe, Joachim; Hamryszak, Lukasz; Bujak, Piotr


    The paper describes formation of new supramolecular azopolymers based on hydrogen bonds as perspective materials for laser induced surface relief gratings (SRGs) and for polarization gratings. Supramolecular films were built on the basis of hydrogen bonds between the functional groups of polymer and azobenzene derivatives, that is 4-[4-(3-hydroxypropyloxy)phenylazo]-pyridine and 4-[4-(6-hydroxyhexyloxy)phenylazo]pyridine. Polymers with imide rings, i.e., poly(esterimide)s and poly(etherimide)s, with phenolic hydroxyl or carboxylic groups were applied as matrixes for polymer-dye supramolecular systems. They revealed glass transition temperatures (Tg) in the range of 170-260 °C, whereas supramolecular systems exhibited lower Tg (88-187 °C). The polymers were easily soluble in aprotic polar solvents and exhibited remarkable good film forming properties. Moreover, new chromophore 4-[4-(3-hydroxypropyloxy)phenylazo]pyridine was synthesized and characterized. The light induced SRGs formation and simultaneous formation of the polarization gratings were explored in prepared polymer-chromophore assembles films using a holographic grating recording technique. First time to the best of our knowledge SRGs were formed in hydrogen-bonded supramolecular systems based on polyimides. The highest SRG amplitude and thus the highest diffraction efficiency were obtained in poly(esterimide)s with the hydroxyl functional group. Additionally, the thermal stability of the photoinduced surface gratings and polarization gratings were tested revealing in the case of the SRGs partial stability and almost complete erasure of the polarization gratings.

  16. Design of compressors for FEL pulses using deformable gratings (United States)

    Bonora, Stefano; Fabris, Nicola; Frassetto, Fabio; Giovine, Ennio; Miotti, Paolo; Quintavalla, Martino; Poletto, Luca


    We present the optical layout of soft X-rays compressors using reflective grating specifically designed to give both positive or negative group-delay dispersion (GDD). They are tailored for chirped-pulse-amplification experiments with FEL sources. The optical design originates from an existing compressor with plane gratings already realized and tested at FERMI, that has been demonstrated capable to introduce tunable negative GDD. Here, we discuss two novel designs for compressors using deformable gratings capable to give both negative and positive GDD. Two novel designs are discussed: 1) a design with two deformable gratings and an intermediate focus between the twos, that is demonstrated capable to introduce positive GDD; 2) a design with one deformable grating giving an intermediate focus, followed by a concave mirror and a plane grating, that is capable to give both positive and negative GDD depending on the distance between the second mirror and the second grating. Both the designs are tunable in wavelength and GDD, by acting on the deformable gratings, that are rotated to tune the wavelength and the GDD and deformed to introduce the radius required to keep the spectral focus. The deformable gratings have a laminar profile and are ruled on a thin silicon plane substrate. A piezoelectric actuator is glued on the back of the substrate and is actuated to give a radius of curvature that is varying from infinite (plane) to few meters. The ruling procedure, the piezoelectric actuator and the efficiency measurements in the soft X-rays will be presented. Some test cases are discussed for wavelengths shorter than 12 nm.

  17. Enhanced surface plasmon polariton propagation length using a buried metal grating

    NARCIS (Netherlands)

    Jose, J.; Segerink, Franciscus B.; Korterik, Jeroen P.; Gomez Casado, A.; Huskens, Jurriaan; Herek, Jennifer Lynn; Offerhaus, Herman L.


    We report an enhancement in the propagation length of surface plasmon polaritons (SPPs) on a metallic grating when the grating is buried in the substrate. A template-stripping technique has been used to fabricate the buried grating. Near-field measurements on the buried and an exposed grating show

  18. Numerical modelling of a straw-fired grate boiler

    DEFF Research Database (Denmark)

    Kær, Søren Knudsen


    The paper presents a computational fluid dynamics (CFD) analysis of a 33 MW straw-fired grate boiler. Combustion on the grate plays akey-role in the analysis of these boilers and in this work a stand-alone code was used to provide inlet conditions for the CFD analysis. Modelpredictions were...... compared with available gas temperature and species concentration measurements showing good agreement. Combustionof biomass in grate-based boilers is often associated with high emission levels and relatively high amounts of unburnt carbon in the fly ash.Based on the CFD analysis, it is suggested that poor...

  19. Bragg grating chemical sensor with hydrogel as sensitive element (United States)

    Liu, Xiaomei; Zheng, Shilie; Zhang, Xianmin; Cong, Jun; Chen, Kangsheng; Xu, Jian


    A novel fiber Bragg grating (FBG) based chemical sensor using hydrogel, a swellable polymer, as sensitive element is demonstrated. The sensing mechanism relies on the shift of Bragg wavelength due to the stress resulted from volume change of sensitive swellable hydrogel responding to the change of external environment. A polyacrylamide hydrogel fiber grating chemical sensor is made, and the experiments on its sensitivity to the salinity are performed. The sensitivity is low due to the less stress from the shrinking or swelling of hydrogels. Reducing the cross diameter of the grating through etching with hydrofluoric acid can greatly improve the sensitivity of the sensor.

  20. Temporal differentiation of optical signals using resonant gratings. (United States)

    Bykov, Dmitry A; Doskolovich, Leonid L; Soifer, Viktor A


    We study theoretically the possibility of performing temporal differentiation of optical signals using a resonant diffraction grating. We demonstrate that the resonant grating allows the calculation of the first-order derivative of an optical signal envelope in the vicinity of waveguide resonant frequencies in the zeroth transmitted diffraction order. The grating is shown to allow the calculation of the fractional derivative of order 1/2 in the vicinity of Rayleigh-Wood anomalies. Numerical simulations based on the rigorous coupled-wave analysis of Maxwell's equations demonstrate the high-quality differentiation of optical signals with temporal features in the picosecond range.

  1. Grating-coupled surface plasmon resonance on bulk stainless steel. (United States)

    Seo, Minseok; Lee, Jeeyoung; Lee, Myeongkyu


    Grating-coupled surface plasmon resonance (SPR) is demonstrated with one-dimensional gratings fabricated on the surface of bulk stainless steel using imprinting combined with electrochemical etching. The extent of light coupling and the wavelengths of SPR peaks were characterized with respect to the incident angle and polarization states of the light. When the plane of incidence was orthogonal to the grating grooves, only TM polarization was absorbed at two different wavelengths. In the plane of incidence parallel to the grooves, a single resonance peak was observed only when the incident light was TE-polarized. The dependence of SPR wavelengths on the incident angle was in good agreement with theoretical consideration.

  2. POF based glucose sensor incorporating grating wavelength filters

    DEFF Research Database (Denmark)

    Hassan, Hafeez Ul; Aasmul, Søren; Bang, Ole


    , improve the mechanical stabilization of assay compartment by exploring the side excitation and side coupling method, ease of manufacturing and feasibility of Polymer Fiber Bragg gratings as filters. During the project, fibers will be drawn and fiber bragg gratings will be inscribed at DTU Fotonik...... AND RESEARCH IN POLYMER OPTICAL DEVICES; TRIPOD. Within the domain of TRIPOD, research is conducted on "Plastic Optical Fiber based Glucose Sensors Incorporating Grating Wavelength Filters". Research will be focused to optimized fiber tips for better coupling efficiency, reducing the response time of sensor...

  3. Resonance phenomena in one-dimensional grating-based structures

    Directory of Open Access Journals (Sweden)

    I.Ya. Yaremchuk


    Full Text Available Enhanced optical transmission through metallic 1-D grating-based structures has been studied using the rigorous coupled wave analysis. The results have shown that optical transmission is determined by waveguide properties of the grating slit, and there is a minimum width of slit for TE polarization, when high transmission occurs due to waveguide effect. In contrast, this limitation doesn’t exist for TM polarization, and extraordinary transmission is obtained at the sub-wavelength slit. As a result, high transmission is reached due to resonance of electromagnetic field inside the grating slit.

  4. Fiber Bragg grating inscription in optical multicore fibers (United States)

    Becker, Martin; Elsmann, Tino; Lorenz, Adrian; Spittel, Ron; Kobelke, Jens; Schuster, Kay; Rothhardt, Manfred; Latka, Ines; Dochow, Sebastian; Bartelt, Hartmut


    Fiber Bragg gratings as key components in telecommunication, fiber lasers, and sensing systems usually rely on the Bragg condition for single mode fibers. In special applications, such as in biophotonics and astrophysics, high light coupling efficiency is of great importance and therefore, multimode fibers are often preferred. The wavelength filtering effect of Bragg gratings in multimode fibers, however is spectrally blurred over a wide modal spectrum of the fiber. With a well-designed all solid multicore microstructured fiber a good light guiding efficiency in combination with narrow spectral filtering effect by Bragg gratings becomes possible.

  5. Optical properties of spherical gold mesoparticles

    DEFF Research Database (Denmark)

    Evlyukhin, A. B.; Kuznetsov, A. I.; Novikov, S. M.


    Optical properties of spherical gold particles with diameters of 150-650 nm (mesoparticles) are studied by reflectance spectroscopy. Particles are fabricated by laser-induced transfer of metallic droplets onto metal and dielectric substrates. Contributions of higher multipoles (beyond the quadrup......Optical properties of spherical gold particles with diameters of 150-650 nm (mesoparticles) are studied by reflectance spectroscopy. Particles are fabricated by laser-induced transfer of metallic droplets onto metal and dielectric substrates. Contributions of higher multipoles (beyond...... results obtained in homogeneous environment is demonstrated. Multipole resonance features in the experimental reflection spectra of particles located on a gold substrate, in the wavelength range of 500-1000 nm, are discussed and theoretically analyzed on the basis of finite-difference time...

  6. Sparse acoustic imaging with a spherical array

    DEFF Research Database (Denmark)

    Fernandez Grande, Efren; Xenaki, Angeliki


    In recent years, a number of methods for sound source localization and sound field reconstruction with spherical microphone arrays have been proposed. These arrays have properties that are potentially very useful, e.g. omni-directionality, robustness, compensable scattering, etc. This paper...... proposes a plane wave expansion method based on measurements with a spherical microphone array, and solved in the framework provided by Compressed Sensing. The proposed methodology results in a sparse solution, i.e. few non-zero coefficients, and it is suitable for both source localization and sound field...... reconstruction. In general it provides fine spatial resolution for localization (delta-like functions), and robust reconstruction (the noisy components are naturally suppressed). The validity and performance of the proposed method is examined, and its limitations as well as the underlying assumptions...

  7. Imaging with spherically bent crystals or reflectors (United States)

    Bitter, M.; Delgado Aparicio, L. F.; Hill, K. W.; Scott, S.; Ince-Cushman, A.; Reinke, M.; Podpaly, Y.; Rice, J. E.; Beiersdorfer, P.; Wang, E.


    This paper consists of two parts: part I describes the working principle of a recently developed x-ray imaging crystal spectrometer, where the astigmatism of spherically bent crystals is being used with advantage to record spatially resolved spectra of highly charged ions for Doppler measurements of the ion-temperature and toroidal plasma-rotation-velocity profiles in tokamak plasmas. This type of spectrometer was thoroughly tested on NSTX and Alcator C-Mod, and its concept was recently adopted for the design of the ITER crystal spectrometers. Part II describes imaging schemes, where the astigmatism has been eliminated by the use of matched pairs of spherically bent crystals or reflectors. These imaging schemes are applicable over a wide range of the electromagnetic radiation, which includes microwaves, visible light, EUV radiation and x-rays. Potential applications with EUV radiation and x-rays are the diagnosis of laser-produced plasmas, imaging of biological samples with synchrotron radiation and lithography.

  8. Quality metric for spherical panoramic video (United States)

    Zakharchenko, Vladyslav; Choi, Kwang Pyo; Park, Jeong Hoon


    Virtual reality (VR)/ augmented reality (AR) applications allow users to view artificial content of a surrounding space simulating presence effect with a help of special applications or devices. Synthetic contents production is well known process form computer graphics domain and pipeline has been already fixed in the industry. However emerging multimedia formats for immersive entertainment applications such as free-viewpoint television (FTV) or spherical panoramic video require different approaches in content management and quality assessment. The international standardization on FTV has been promoted by MPEG. This paper is dedicated to discussion of immersive media distribution format and quality estimation process. Accuracy and reliability of the proposed objective quality estimation method had been verified with spherical panoramic images demonstrating good correlation results with subjective quality estimation held by a group of experts.

  9. Technical notes. Spherical harmonics approximations of neutron transport

    Energy Technology Data Exchange (ETDEWEB)

    Demeny, A.; Dede, K.M.; Erdei, K.


    A double-range spherical harmonics approximation obtained by expanding the angular flux separately in the two regions combined with the conventional single-range spherical harmonics is found to give superior description of neutron transport.

  10. Dynamics and control of vibratory gyroscopes with special spherical symmetry

    CSIR Research Space (South Africa)

    Shatalov, M


    Full Text Available are obtained in the spherical Bessel and the associated Legendre functions, the effects of rotation are investigated and scales factors are determined for different vibrating modes of the spherical body, spheroidal and torsional. Corresponding scales factors...

  11. Optimization of grating duty cycle in non-interferometric grating-based X-ray phase contrast imaging (United States)

    Luo, Ronghui; Wu, Zhao; Xiong, Ying; Wei, Chenxi; Zhang, Xiaobo; Hu, Renfang; Wang, Lei; Guo, Liang; Liu, Gang; Tian, Yangchao


    Grating-based X-ray phase contrast imaging technology is one of the most potential imaging methods in real applications. It can be classified into two categories: interferometry and non-interferometric imaging. The non-interferometric grating-based X-ray phase contrast imaging (NIGPCI) instrument has a great advantage in the forthcoming commercial applications for the flexible system design and the use of large periodic gratings. The performance of the NIGPCI instrument depends on its angular sensitivity to a great extent. Therefore, good angular sensitivity is mandatory in order to obtain high quality phase-contrast images. Several parameters, such as the X-ray spectrum, the inter-grating distances, and the parameters of the three gratings, influence the angular sensitivity of the imaging system. However, the quantitative relationship between the angular sensitivity and grating duty cycle is unclear. Therefore, this paper is devoted to revealing their internal relation by theoretical deduction and emulation of the imaging process with the theories of linear system and Fourier optics. Furthermore, a quantitative analysis method to optimize the duty cycles of gratings is proposed and its applicability to a general NIGPCI system is verified.

  12. Spherical Cancer Models in Tumor Biology

    Directory of Open Access Journals (Sweden)

    Louis-Bastien Weiswald


    Full Text Available Three-dimensional (3D in vitro models have been used in cancer research as an intermediate model between in vitro cancer cell line cultures and in vivo tumor. Spherical cancer models represent major 3D in vitro models that have been described over the past 4 decades. These models have gained popularity in cancer stem cell research using tumorospheres. Thus, it is crucial to define and clarify the different spherical cancer models thus far described. Here, we focus on in vitro multicellular spheres used in cancer research. All these spherelike structures are characterized by their well-rounded shape, the presence of cancer cells, and their capacity to be maintained as free-floating cultures. We propose a rational classification of the four most commonly used spherical cancer models in cancer research based on culture methods for obtaining them and on subsequent differences in sphere biology: the multicellular tumor spheroid model, first described in the early 70s and obtained by culture of cancer cell lines under nonadherent conditions; tumorospheres, a model of cancer stem cell expansion established in a serum-free medium supplemented with growth factors; tissue-derived tumor spheres and organotypic multicellular spheroids, obtained by tumor tissue mechanical dissociation and cutting. In addition, we describe their applications to and interest in cancer research; in particular, we describe their contribution to chemoresistance, radioresistance, tumorigenicity, and invasion and migration studies. Although these models share a common 3D conformation, each displays its own intrinsic properties. Therefore, the most relevant spherical cancer model must be carefully selected, as a function of the study aim and cancer type.

  13. Marching Cubes in Cylindrical and Spherical Coordinates (United States)

    Goldsmith, J.; Jacobson, A. S.


    Isosurface extraction is a common analysis and visualization technique for three-dimensional scalar data. Marching Cubes is the most commonly-used algorithm for finding polygonal representations of isosurfaces in such data. We extend Marching Cubes to produce geometry for data sets that lie in spherical and cylindrical coordinate systems as well as show the steps for derivation of transformations for other coordinate systems.

  14. Indentation of pressurized viscoplastic polymer spherical shells

    DEFF Research Database (Denmark)

    Tvergaard, Viggo; Needleman, A.


    The indentation response of polymer spherical shells is investigated. Finite deformation analyses are carried out with the polymer characterized as a viscoelastic/viscoplastic solid. Both pressurized and unpressurized shells are considered. Attention is restricted to axisymmetric deformations...... large strains are attained. The transition from an indentation type mode of deformation to a structural mode of deformation involving bending that occurs as the indentation depth increases is studied. The results show the effects of shell thickness, internal pressure and polymer constitutive...

  15. The Quest for the Most Spherical Bubble

    CERN Document Server

    Obreschkow, Danail; Dorsaz, Nicolas; Kobel, Philippe; de Bosset, Aurele; Farhat, Mohamed


    We describe a recently realized experiment producing the most spherical cavitation bubbles today. The bubbles grow inside a liquid from a point-plasma generated by a nanosecond laser pulse. Unlike in previous studies, the laser is focussed by a parabolic mirror, resulting in a plasma of unprecedented symmetry. The ensuing bubbles are sufficiently spherical that the hydrostatic pressure gradient caused by gravity becomes the dominant source of asymmetry in the collapse and rebound of the cavitation bubbles. To avoid this natural source of asymmetry, the whole experiment is therefore performed in microgravity conditions (ESA, 53rd and 56th parabolic flight campaign). Cavitation bubbles were observed in microgravity (~0g), where their collapse and rebound remain spherical, and in normal gravity (1g) to hyper-gravity (1.8g), where a gravity-driven jet appears. Here, we describe the experimental setup and technical results, and overview the science data. A selection of high-quality shadowgraphy movies and time-res...

  16. Fusion potential for spherical and compact tokamaks

    Energy Technology Data Exchange (ETDEWEB)

    Sandzelius, Mikael


    The tokamak is the most successful fusion experiment today. Despite this, the conventional tokamak has a long way to go before being realized into an economically viable power plant. In this master thesis work, two alternative tokamak configurations to the conventional tokamak has been studied, both of which could be realized to a lower cost. The fusion potential of the spherical and the compact tokamak have been examined with a comparison of the conventional tokamak in mind. The difficulties arising in the two configurations have been treated from a physical point of view concerning the fusion plasma and from a technological standpoint evolving around design, materials and engineering. Both advantages and drawbacks of either configuration have been treated relative to the conventional tokamak. The spherical tokamak shows promising plasma characteristics, notably a high {beta}-value but have troubles with high heat loads and marginal tritium breeding. The compact tokamak operates at a high plasma density and a high magnetic field enabling it to be built considerably smaller than any other tokamak. The most notable down-side being high heat loads and neutron transport problems. With the help of theoretical reactor studies, extrapolating from where we stand today, it is conceivable that the spherical tokamak is closer of being realized of the two. But, as this study shows, the compact tokamak power plant concept offers the most appealing prospect.

  17. Spherically symmetric thick branes cosmological evolution (United States)

    Bernardini, A. E.; Cavalcanti, R. T.; da Rocha, Roldão


    Spherically symmetric time-dependent solutions for the 5D system of a scalar field canonically coupled to gravity are obtained and identified as an extension of recent results obtained by Ahmed et al. (JHEP 1404:061. arXiv:1312.3576 [hep-th], 2014). The corresponding cosmology of models with regularized branes generated by such a 5D scalar field scenario is also investigated. It has been shown that the anisotropic evolution of the warp factor and consequently the Hubble like parameter are both driven by the radial coordinate on the brane, which leads to an emergent thick brane-world scenario with spherically symmetric time dependent warp factor. Meanwhile, the separability of variables depending on fifth dimension, , which is exhibited by the equations of motion, allows one to recover the extra dimensional profiles obtained in Ahmed et al. (2014), namely the extra dimensional part of the scale (warp) factor and the scalar field dependence on . Therefore, our results are mainly concerned with the time dependence of a spherically symmetric warp factor. Besides evincing possibilities for obtaining asymmetric stable brane-world scenarios, the extra dimensional profiles here obtained can also be reduced to those ones investigated in Ahmed et al. (2014).

  18. Spherical Arrays for Wireless Channel Characterization and Emulation

    DEFF Research Database (Denmark)

    Franek, Ondrej; Pedersen, Gert Frølund


    Three types of spherical arrays for use in wireless communication research are presented. First, a spherical array of 32 monopoles with beam steering in arbitrary direction and with arbitrary polarization is described. Next, a spherical array with 16 quad-ridged open-flared horns is introduced...


    Directory of Open Access Journals (Sweden)

    G. Ch. Shushkevich


    Full Text Available An analytical solution of the boundary problem describing the process of penetration of thesound field of a spherical emitter located inside a thin unclosed spherical shell through a permeable multilayered spherical shell is considered. The influence of some parameters of the problem on the value of the sound field weakening (screening coefficient is studied via a numerical simulation.

  20. Grate Firing of Biomass: Measurements, Validation and Demonstration

    DEFF Research Database (Denmark)

    Yin, Chungen; Rosendahl, Lasse; Kær, Søren Knudsen

    The worldwide concern about global warming because of the emission of CO2 and other greenhouse gases and the limited availability of fossil fuels has increased the interest in using biomass as a fuel for energy production. In Denmark, to use biomass (mainly straw) as a fuel for energy production......, the development of combustion technology has followed two specific paths: grate firing and co-firing in conventional fossil fuel fired plants. Over the past decade, the research and development work related to biomass grate firing and co-firing has been extensive and the two technologies have now been developed...... to the complexity of the solid biomass fuel bed on the grate, the turbulent reacting flow in the combustion chamber and the intensive interaction between them. Therefore, development and test of biomass fuel bed models is one of the major concerns in this report, as well as the methodology of modelling grate...

  1. Broadband back grating design for thin film solar cells

    KAUST Repository

    Janjua, Bilal


    In this paper, design based on tapered circular grating structure was studied, to provide broadband enhancement in thin film amorphous silicon solar cells. In comparison to planar structure an absorption enhancement of ~ 7% was realized.

  2. UV writing of advanced Bragg gratings in optical waveguides

    DEFF Research Database (Denmark)

    Jensen, Jesper Bo Damm


    The subject of this ph.d. thesis is the fabrication of Bragg gratings in optical waveguides. During the study Bragg gratings were written in both planar waveguides and optical fibers using pulsed or continuous-wave lasers operating in the ultraviolet (UV) range. The main result is the development...... of the novel polarization control method for UV writing of Bragg gratings with advanced apodization profiles including phase shifts. The principle of the polarization control method relies on a spatial separation of the s- and p-polarized components of a linearly polarized UV beam corresponding to half...... were then translated into a polarizer angle profile and the Bragg grating were written using a pulsed excimer laser. Only optical fibers were used in this part of the thesis. The high quality planar waveguides used during the study were produced in the cleanroom facility at the Microelectronic Center...

  3. Reconfigurable terahertz grating with enhanced transmission of TE polarized light

    Directory of Open Access Journals (Sweden)

    J. W. He


    Full Text Available We demonstrate an optically reconfigurable grating with enhanced transmission of TE-polarized waves in the terahertz (THz waveband. This kind of grating is realized by projecting a grating image onto a thin Si wafer with a digital micromirror device (DMD. The enhanced transmission is caused by a resonance of the electromagnetic fields between the photoexcited strips. The position of the transmission peak shifts with the variation of the period and duty cycle of the photoinduced grating, which can be readily controlled by the DMD. Furthermore, a flattened Gaussian model was applied to describe the distribution of the photoexcited free carriers in the Si wafer, and the simulated transmittance spectra are shown to be in good agreement with the experimental results. In future, the photoexcited carriers could also be used to produce THz diffractive elements with reconfigurable functionality.

  4. Blazed Grating Resonance Conditions and Diffraction Efficiency Optical Transfer Function

    KAUST Repository

    Stegenburgs, Edgars


    We introduce a general approach to study diffraction harmonics or resonances and resonance conditions for blazed reflecting gratings providing knowledge of fundamental diffraction pattern and qualitative understanding of predicting parameters for the most efficient diffraction.

  5. Structural Health Monitoring Using Fiber Bragg Grating Sensor Matrix Project (United States)

    National Aeronautics and Space Administration — Fiber Bragg Grating had been identified as very important elements, especially for strain measurements in smart structures. In many applications, arrays of FBG...

  6. High-refractive-index gratings for spectroscopic and laser applications (United States)

    Zeitner, Uwe D.; Fuchs, Frank; Kley, E.-Bernhard; Tünnermann, Andreas


    Fabrication of high performance gratings may significantly benefit from the use of high index materials such as Ta2O5, TiO 2 or Al2O3. However, these materials can typically not be patterned with the required quality by common etching processes. To overcome this limitation we developed novel grating fabrication technologies based on a combination of conventional lithography with Atomic-Layer-Deposition. For that the basic structure of the grating is first realized in a fused-silica substrate or a SiO2-layer. This template is then functionalized by an ALD-coating in a specific pre-defined manner. The new approach opens up a huge variety of new options for the realization of gratings whose fabrication would otherwise not be possible.

  7. Reconfigurable terahertz grating with enhanced transmission of TE polarized light (United States)

    He, J. W.; Wang, X. K.; Xie, Z. W.; Xue, Y. Z.; Wang, S.; Zhang, Y.


    We demonstrate an optically reconfigurable grating with enhanced transmission of TE-polarized waves in the terahertz (THz) waveband. This kind of grating is realized by projecting a grating image onto a thin Si wafer with a digital micromirror device (DMD). The enhanced transmission is caused by a resonance of the electromagnetic fields between the photoexcited strips. The position of the transmission peak shifts with the variation of the period and duty cycle of the photoinduced grating, which can be readily controlled by the DMD. Furthermore, a flattened Gaussian model was applied to describe the distribution of the photoexcited free carriers in the Si wafer, and the simulated transmittance spectra are shown to be in good agreement with the experimental results. In future, the photoexcited carriers could also be used to produce THz diffractive elements with reconfigurable functionality.

  8. MEMS Tunable Diffraction Grating for Spaceborne Imaging Spectroscopic Applications

    Directory of Open Access Journals (Sweden)

    Sanathanan S. Muttikulangara


    Full Text Available Diffraction gratings are among the most commonly used optical elements in applications ranging from spectroscopy and metrology to lasers. Numerous methods have been adopted for the fabrication of gratings, including microelectromechanical system (MEMS fabrication which is by now mature and presents opportunities for tunable gratings through inclusion of an actuation mechanism. We have designed, modeled, fabricated and tested a silicon based pitch tunable diffraction grating (PTG with relatively large resolving power that could be deployed in a spaceborne imaging spectrometer, for example in a picosatellite. We have carried out a detailed analytical modeling of PTG, based on a mass spring system. The device has an effective fill factor of 52% and resolving power of 84. Tuning provided by electrostatic actuation results in a displacement of 2.7 μ m at 40 V . Further, we have carried out vibration testing of the fabricated structure to evaluate its feasibility for spaceborne instruments.

  9. Reannealed Fiber Bragg Gratings Demonstrated High Repeatability in Temperature Measurements (United States)

    Adamovsky, Grigory; Juergens, Jeffrey R.


    Fiber Bragg gratings (FBGs) are formed by periodic variations of the refractive index of an optical fiber. These periodic variations allow an FBG to act as an embedded optical filter, passing the majority of light propagating through a fiber while reflecting back a narrow band of the incident light. The peak reflected wavelength of the FBG is known as the Bragg wavelength. Since the period and width of the refractive index variation in the fiber determines the wavelengths that are transmitted and reflected by the grating, any force acting on the fiber that alters the physical structure of the grating will change the wavelengths that are transmitted and reflected by it. Both thermal and mechanical forces acting on the grating will alter its physical characteristics, allowing the FBG sensor to detect both the temperature variations and the physical stresses and strains placed upon it. This ability to sense multiple physical forces makes the FBG a versatile sensor. To assess the feasibility of using Bragg gratings as temperature sensors for propulsion applications, researchers at the NASA Glenn Research Center evaluated the performance of Bragg gratings at elevated temperatures for up to 300 C. For these purposes, commercially available polyimide-coated high-temperature gratings were used that were annealed by the manufacturer to 300 C. To assure the most thermally stable gratings at the operating temperatures, we reannealed the gratings to 400 C at a very slow rate for 12 to 24 hr until their reflected optical powers were stabilized. The reannealed gratings were then subjected to periodic thermal cycling from room temperature to 300 C, and their peak reflected wavelengths were monitored. The setup shown is used for reannealing and thermal cycling the FBGs. Signals from the photodetectors and the spectrum analyzer were fed into a computer equipped with LabVIEW software. The software synchronously monitored the oven/furnace temperature and the optical spectrum analyzer

  10. A phase mask fiber grating and sensing applications

    Directory of Open Access Journals (Sweden)

    Preecha P. Yupapin


    Full Text Available This paper presents an investigation of a fabricated fiber grating device characteristics and its applications, using a phase mask writing technique. The use of a most common UV phase laser (KrF eximer laser, with high intensity light source was focussed to the phase mask for writing on a fiber optic sample. The device (i.e. grating characteristic especially, in sensing application, was investigated. The possibility of using such device for temperature and strain sensors is discussed.

  11. Higher-speed demodulation of fiber grating sensors (United States)

    Seim, John M.; Schulz, Whitten L.; Udd, Eric; Morrell, Mike


    For very high-speed events, such as ballistics testing, strain measurement speed is not limited by the response of the fiber grating sensor, but rather the demodulation system used. This paper focuses on a current 10 kHz fiber grating demodulator used to support impact and ballistics testing of a composite panel. It also explores the next generation demodulator, pushing the emits of speed upwards of 3 Mhz.

  12. Zeonex Microstructured Polymer Optical Fibre Bragg Grating Sensor

    DEFF Research Database (Denmark)

    Woyessa, Getinet; Fasano, Andrea; Markos, Christos


    We fabricated an endlessly single mode and humidity insensitive Zeonex microstructured polymer optical fibre (mPOF) for fibre Bragg grating (FBG) temperature and strain sensors. We inscribed and characterise FBGs in Zeonex mPOF for the first time.......We fabricated an endlessly single mode and humidity insensitive Zeonex microstructured polymer optical fibre (mPOF) for fibre Bragg grating (FBG) temperature and strain sensors. We inscribed and characterise FBGs in Zeonex mPOF for the first time....

  13. Analisis Perpindahan Panas Pada Grate Cooler Industri Semen




    This research aimed to find out heat transfer rate between cooling air supply and clinker in grate cooler ofcement industry. The method used field survey with two datas. Primary data by direct measure in researchobject and others from control room. Then for the secondary data, we got from manual book of company.Grate cooler was divided into 3 sections, and the analysis performed for each section based on the principleof heat transfer through a porous medium to obtain the heat transfer coeffic...

  14. The potential of diffraction grating for spatial applications (United States)

    Jourlin, Y.; Parriaux, O.; Pigeon, F.; Tischenko, A. V.


    Diffraction gratings are know, and have been fabricated for more than one century. They are now making a come back for two reasons: first, because they are now better understood which leads to the efficient exploitation of what was then called their "anomalies"; secondly, because they are now fabricable by means of the modern manufacturing potential of planar technologies. Novel grating can now perform better than conventional gratings, and address new application fields which were not expected to be theirs. This is the case of spatial applications where they can offer multiple optical functions, low size, low weight and mechanical robustness. The proposed contribution will briefly discuss the use of gratings for spatial applications. One of the most important applications is in the measurement of displacement. Usual translation and rotation sensors are bulky devices, which impose a system breakdown leading to cumbersome and heavy assemblies. We are proposing a miniaturized version of the traditional moving grating technique using submicron gratings and a specific OptoASIC which enables the measurement function to be non-obtrusively inserted into light and compact electro-mechanical systems. Nanometer resolution is possible with no compromise on the length of the measurement range. Another family of spatial application is in the field of spectrometers where new grating types allow a more flexible processing of the optical spectrum. Another family of applications addresses the question of inter-satellite communications: the introduction of gratings in laser cavities or in the laser mirrors enables the stabilization of the emitted polarization, the stabilization of the frequency as well as wide range frequency sweeping without mobile parts.

  15. Compact Refractive Imaging Spectrometer Designs Utilizing Immersed Gratings (United States)

    Lerner, Scott A.; Bennett, Charles L.; Bixler, Jay V.; Kuzmenko, Paul J.; Lewis, Isabella T.


    A compact imaging spectrometer comprising an entrance slit for directing light, a first means for receiving the light and focusing the light, an immersed diffraction grating that receives the light from the first means and defracts the light, a second means for receiving the light from the immersed diffraction grating and focusing the light, and an image plane that receives the light from the second means

  16. Minimizing Fizeau Fringes During the Contact Printing of Diffraction Gratings

    Energy Technology Data Exchange (ETDEWEB)

    Ciarlo, D; Rushford, M; Kuzmenko, P; Ge, J


    An index matching fluid has been used to minimize the effect of interference fringes which develop when contact printing diffraction gratings on silicon wafers. These fringes are the result of interference effects when there is a small but uneven gap between the photomask and resist surface. They are especially troublesome when printing and etching large area, coarse diffraction gratings on the surface of silicon wafers and silicon disks.

  17. Coupling polariton quantum boxes in sub-wavelength grating microcavities

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Bo; Wang, Zhaorong; Deng, Hui, E-mail: [Department of Physics, University of Michigan, Ann Arbor, Michigan 48109 (United States); Brodbeck, Sebastian; Kamp, Martin; Schneider, Christian [Technische Physik, Physikalisches Institut and Wilhelm Conrad Röntgen-Research Center for Complex Material Systems, Universität Würzburg, Am Hubland, D-97074 Würzburg (Germany); Höfling, Sven [Technische Physik, Physikalisches Institut and Wilhelm Conrad Röntgen-Research Center for Complex Material Systems, Universität Würzburg, Am Hubland, D-97074 Würzburg (Germany); SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews KY16 9SS (United Kingdom)


    We report the construction of decoupled, coupled, and quasi-one dimensional polariton systems from zero dimensional polariton quantum boxes using microcavities with sub-wavelength gratings as the top mirror. By designing the tethering patterns around the suspended sub-wavelength gratings, we control the coupling between individual quantum boxes through different optical potentials. Energy levels and real-space or momentum space distributions of the confined modes were measured, which agreed well with simulations.

  18. Nonuniform dynamic gratings in photorefractive media with nonlocal response (United States)

    Bugaychuk, S.; Kovács, L.; Mandula, G.; Polgár, K.; Rupp, R. A.


    The amplitude of the phase dynamic grating is a nonuniform space distributed in photorefractive crystals with nonlocal response as a result of energy transfer between the interacted waves. The dynamical process of grating formation in the case of transmission two- and four-wave mixing is described by the damped sine-Gordon equation that governs the soliton propagation. A stationary soliton solution for the grating amplitude profile was obtained. Experiments on observation of a nonuniform distribution of the grating amplitude through the crystal volume are presented. It is experimentally shown that the changes of the grating amplitude profile in dependence of input intensity ratio match the solutions of the damped sine-Gordon equation in steady state. The diffraction efficiency of energy transfer is determined by the value of the integral under the grating amplitude profile. The soliton profile is altered with changing input intensity ratio of recorded beams. It provides the effect of diffraction efficiency management by changing the half-width and the position of the soliton. The theory predicts a multisoliton behavior in reversible media with strong amplitifcaiton gain that leads to auto-oscillations of output wave intensities.

  19. Bulk silica NIR blazed transmission gratings made by Silios technologies (United States)

    Caillat, Amandine; Pascal, Sandrine; Tisserand, Stéphane; Dohlen, Kjetil; Grange, Robert; Sauget, Vincent; Gautier, Sophie


    In order to study the dark universe (energy and matter), EUCLID space mission will collect near infrared spectra and images of millions of galaxies. This massive measurement survey requires a slitless spectroscopic channel including GRISMs (for "Grating pRISMs") in NISP (Near Infrared SpectroPhotometer). Very special technical specifications are required for the grating manufacturing: large aperture, low groove frequency and blaze angle, line curvature. In addition, it has to withstand space environment. Therefore, in the frame of a R&D project funded by the CNES, we developed bulk silica gratings in close collaboration with the French company SILIOS Technologies. SILIOS delivered two resin-free blazed gratings with curved lines engraved directly into the fused silica substrate of 80mm and 108mm useful aperture. At LAM, we measured very high optical performances of these prototypes: theory and uniform over the useful aperture. In this paper, we give specifications of these gratings, we describe the manufacturing process developed by SILIOS Technologies, we present briefly optical setups and models allowing optical performances verifications at LAM and we show very encouraging results obtained on the two gratings.

  20. Slow light in fiber Bragg gratings and its applications (United States)

    Skolianos, George; Arora, Arushi; Bernier, Martin; Digonnet, Michel


    Slow-light fiber Bragg gratings (FBGs) belong to a class of gratings designed to exhibit one or more narrow resonances in their reflection and transmission spectra, produced either by introducing a π phase shift near the middle of the grating, or by increasing the index modulation so that the grating behaves like a Fabry-Perot interferometer. These resonances can have very narrow linewidths (lines, and sensing. This paper reviews the principle of these gratings, in particular the more recent slow-light gratings relying on a strong index modulation. It discusses in particular the requirements for achieving large group delays and high sensitivities in sensors, and the fabrication and annealing techniques used to meet these requirements (high index modulation, low loss, index-profile apodization, and optimized length). Several applications are presented, including record-breaking FBGs that exhibit a group delay of 42 ns and Q-factor of ~30 million over a 12.5 mm length, robust acoustic sensors with pressure resolution of ~50 µPa (√Hz)-1 in the few-kHz, and a strain sensor capable of resolving as little as 30 femtostrain (√Hz)-1.

  1. MEMS-based tunable gratings and their applications (United States)

    Yu, Yiting; Yuan, Weizheng; Qiao, Dayong


    The marriage of optics and MEMS has resulted in a new category of optical devices and systems that have unprecedented advantages compared with their traditional counterparts. As an important spatial light modulating technology, diffractive optical MEMS obtains a wide variety of successful commercial applications, e.g. projection displays, optical communication and spectral analysis, due to its features of highly compact, low-cost, IC-compatible, excellent performance, and providing possibilities for developing totally new, yet smart devices and systems. Three most successful MEMS diffraction gratings (GLVs, Polychromator and DMDs) are briefly introduced and their potential applications are analyzed. Then, three different MEMS tunable gratings developed by our group, named as micro programmable blazed gratings (μPBGs) and micro pitch-tunable gratings (μPTGs) working in either digital or analog mode, are demonstrated. The strategies to largely enhance the maximum blazed angle and grating period are described. Some preliminary application explorations based on the developed grating devices are also shown. For our ongoing research focus, we will further improve the device performance to meet the engineering application requirements.

  2. Addition theorems for spin spherical harmonics: II. Results

    Energy Technology Data Exchange (ETDEWEB)

    Bouzas, Antonio O, E-mail: [Departamento de Fisica Aplicada, CINVESTAV-IPN, Carretera Antigua a Progreso Km. 6, Apdo. Postal 73 ' Cordemex' , Merida 97310, Yucatan (Mexico)


    Based on the results of part I (2011 J. Phys. A: Math. Theor. 44 165301), we obtain the general form of the addition theorem for spin spherical harmonics and give explicit results in the cases involving one spin-s' and one spin-s spherical harmonics with s', s = 1/2, 1, 3/2, and |s' - s| = 0, 1. We also obtain a fully general addition theorem for one scalar and one tensor spherical harmonic of arbitrary rank. A variety of bilocal sums of ordinary and spin spherical harmonics are given in explicit form, including a general explicit expression for bilocal spherical harmonics.

  3. Feasibility of Fiber Bragg Grating and Long-Period Fiber Grating Sensors under Different Environmental Conditions

    Directory of Open Access Journals (Sweden)

    Jian-Neng Wang


    Full Text Available This paper presents the feasibility of utilizing fiber Bragg grating (FBG and long-period fiber grating (LPFG sensors for nondestructive evaluation (NDE of infrastructures using Portland cement concretes and asphalt mixtures for temperature, strain, and liquid-level monitoring. The use of hybrid FBG and LPFG sensors is aimed at utilizing the advantages of two kinds of fiber grating to implement NDE for monitoring strains or displacements, temperatures, and water-levels of infrastructures such as bridges, pavements, or reservoirs for under different environmental conditions. Temperature fluctuation and stability tests were examined using FBG and LPFG sensors bonded on the surface of asphalt and concrete specimens. Random walk coefficient (RWC and bias stability (BS were used for the first time to indicate the stability performance of fiber grating sensors. The random walk coefficients of temperature variations between FBG (or LPFG sensor and a thermocouple were found in the range of −0.7499 °C/ to −1.3548 °C/. In addition, the bias stability for temperature variations, during the fluctuation and stability tests with FBG (or LPFG sensors were within the range of 0.01 °C/h with a 15–18 h time cluster to 0.09 °C/h with a 3–4 h time cluster. This shows that the performance of FBG or LPFG sensors is comparable with that of conventional high-resolution thermocouple sensors under rugged conditions. The strain measurement for infrastructure materials was conducted using a packaged FBG sensor bonded on the surface of an asphalt specimen under indirect tensile loading conditions. A finite element modeling (FEM was applied to compare experimental results of indirect tensile FBG strain measurements. For a comparative analysis between experiment and simulation, the FEM numerical results agreed with those from FBG strain measurements. The results of the liquid-level sensing tests show the LPFG-based sensor could discriminate five stationary liquid

  4. Fiber Bragg grating based arterial localization device (United States)

    Ho, Siu Chun Michael; Li, Weijie; Razavi, Mehdi; Song, Gangbing


    A critical first step to many surgical procedures is locating and gaining access to a patients vascular system. Vascular access allows the deployment of other surgical instruments and also the monitoring of many physiological parameters. Current methods to locate blood vessels are predominantly based on the landmark technique coupled with ultrasound, fluoroscopy, or Doppler. However, even with experience and technological assistance, locating the required blood vessel is not always an easy task, especially with patients that present atypical anatomy or suffer from conditions such as weak pulsation or obesity that make vascular localization difficult. With recent advances in fiber optic sensors, there is an opportunity to develop a new tool that can make vascular localization safer and easier. In this work, the authors present a new fiber Bragg grating (FBG) based vascular access device that specializes in arterial localization. The device estimates the location towards a local artery based on the bending of a needle inserted near the tissue surrounding the artery. Experimental results obtained from an artificial circulatory loop and a mock artery show the device works best for lower angles of needle insertion and can provide an approximately 40° range of estimation towards the location of a pulsating source (e.g. an artery).

  5. Multipoint sensor based on fiber Bragg gratings

    Energy Technology Data Exchange (ETDEWEB)

    Mendez-Zepeda, O; Munoz-Aguirre, S; Beltran-Perez, G; Castillo-Mixcoatl, J, E-mail: [Facultad de Ciencias FIsico-Matematicas, BUAP Av. San Claudio y Rio Verde, Col. San Manuel, CU. C.P. 72570, Puebla, Puebla (Mexico)


    In some control and industrial measurement systems of physical variables (pressure, temperature, flow, etc) it is necessary one system and one sensor to control each process. On the other hand, there are systems such as PLC (Programmable Logic Control), which can process several signals simultaneously. However it is still necessary to use one sensor for each variable. Therefore, in the present work the use of a multipoint sensor to solve such problem has been proposed. The sensor consists of an optical fiber laser with two Fabry-Perot cavities constructed using fiber Bragg gratings (FBG). In the same system is possible to measure changes in two variables by detecting the intermodal separation frequency of each cavity and evaluate their amplitudes. The intermodal separation frequency depends on each cavity length. The sensor signals are monitored through an oscilloscope or a PCI card and after that acquired by PC, where they are analyzed and displayed. Results of the evaluation of the intermodal frequency separation peak amplitude behavior with FBG stretching are presented.

  6. Einstein-Vlasov system in spherical symmetry. II. Spherical perturbations of static solutions (United States)

    Gundlach, Carsten


    We reduce the equations governing the spherically symmetric perturbations of static spherically symmetric solutions of the Einstein-Vlasov system (with either massive or massless particles) to a single stratified wave equation -ψ,t t=H ψ , with H containing second derivatives in radius, and integrals over energy and angular momentum. We identify an inner product with respect to which H is symmetric, and use the Ritz method to approximate the lowest eigenvalues of H numerically. For two representative background solutions with massless particles we find a single unstable mode with a growth rate consistent with the universal one found by Akbarian and Choptuik in nonlinear numerical time evolutions.

  7. Compressive sensing with a spherical microphone array

    DEFF Research Database (Denmark)

    Fernandez Grande, Efren; Xenaki, Angeliki


    A wave expansion method is proposed in this work, based on measurements with a spherical microphone array, and formulated in the framework provided by Compressive Sensing. The method promotes sparse solutions via ‘1-norm minimization, so that the measured data are represented by few basis functions....... This results in fine spatial resolution and accuracy. This publication covers the theoretical background of the method, including experimental results that illustrate some of the fundamental differences with the “conventional” leastsquares approach. The proposed methodology is relevant for source localization...

  8. Static spherical metrics: a geometrical approach (United States)

    Tiwari, A. K.; Maharaj, S. D.; Narain, R.


    There exist several solution generating algorithms for static spherically symmetric metrics. Here we use the geometrical approach of Lie point symmetries to solve the condition of pressure isotropy by finding the associated five-dimensional Lie algebra of symmetry generators. For the non-Abelian subalgebras the underlying equation is solved to obtain a general solution. Contained within this class are vacuum models, constant density models, metrics with linear equations of state and the Buchdahl representation of the polytrope with index five. For a different particular symmetry generator the condition of pressure isotropy is transformed to a Riccati equation which admits particular solutions.

  9. Spherical conformal models for compact stars

    Energy Technology Data Exchange (ETDEWEB)

    Takisa, P.M.; Maharaj, S.D.; Manjonjo, A.M.; Moopanar, S. [University of KwaZulu-Natal, Astrophysics and Cosmology Research Unit, School of Mathematics, Statistics and Computer Science, Durban (South Africa)


    We consider spherical exact models for compact stars with anisotropic pressures and a conformal symmetry. The conformal symmetry condition generates an integral relationship between the gravitational potentials. We solve this condition to find a new anisotropic solution to the Einstein field equations. We demonstrate that the exact solution produces a relativistic model of a compact star. The model generates stellar radii and masses consistent with PSR J1614-2230, Vela X1, PSR J1903+327 and Cen X-3. A detailed physical examination shows that the model is regular, well behaved and stable. The mass-radius limit and the surface red shift are consistent with observational constraints. (orig.)

  10. The Spherical Bolometric Albedo of Planet Mercury


    Mallama, Anthony


    Published reflectance data covering several different wavelength intervals has been combined and analyzed in order to determine the spherical bolometric albedo of Mercury. The resulting value of 0.088 +/- 0.003 spans wavelengths from 0 to 4 {\\mu}m which includes over 99% of the solar flux. This bolometric result is greater than the value determined between 0.43 and 1.01 {\\mu}m by Domingue et al. (2011, Planet. Space Sci., 59, 1853-1872). The difference is due to higher reflectivity at wavelen...

  11. Inversion of band patterns in spherical tumblers. (United States)

    Chen, Pengfei; Lochman, Bryan J; Ottino, Julio M; Lueptow, Richard M


    Bidisperse granular mixtures in spherical tumblers segregate into three bands: one at each pole and one at the equator. For low fill levels, large particles are at the equator; for high fill levels, the opposite occurs. Segregation is robust, though the transition depends on fill level, particle size, and rotational speed. Discrete element method simulations reproduce surface patterns and reveal internal structures. Particle trajectories show that small particles flow farther toward the poles than large particles in the upstream portion of the flowing layer for low fill levels leading to a band of small particles at each pole. The opposite occurs for high fill levels, though more slowly.


    Directory of Open Access Journals (Sweden)

    В. Воскобійник


    Full Text Available The results of experimental researches of the forming features of the vortex flow which is formed at the turbulentflow above of the deep spherical dimple are presented. Visualization shows that inclined asymmetric large-scale vortices are generated inside the dimple. These vortex structures are switched from one tilt in other, exciting lowfrequencyoscillations. During an evolution the asymmetric vortices are broken up above an aft wall of the dimple andthe angle of their incline and break up is increased with the growth of Reynolds number.

  13. Discrete analogues in harmonic analysis: Spherical averages


    Magyar, A; Stein, E. M.; Wainger, S.


    In this paper we prove an analogue in the discrete setting of \\Bbb Z^d, of the spherical maximal theorem for \\Bbb R^d. The methods used are two-fold: the application of certain "sampling" techniques, and ideas arising in the study of the number of representations of an integer as a sum of d squares in particular, the "circle method". The results we obtained are by necessity limited to d \\ge 5, and moreover the range of p for the L^p estimates differs from its analogue in \\Bbb R^d.

  14. The dynamo bifurcation in rotating spherical shells

    CERN Document Server

    Morin, Vincent; 10.1142/S021797920906378X


    We investigate the nature of the dynamo bifurcation in a configuration applicable to the Earth's liquid outer core, i.e. in a rotating spherical shell with thermally driven motions. We show that the nature of the bifurcation, which can be either supercritical or subcritical or even take the form of isola (or detached lobes) strongly depends on the parameters. This dependence is described in a range of parameters numerically accessible (which unfortunately remains remote from geophysical application), and we show how the magnetic Prandtl number and the Ekman number control these transitions.

  15. Space Radiation Detector with Spherical Geometry (United States)

    Wrbanek, John D. (Inventor); Fralick, Gustave C. (Inventor); Wrbanek, Susan Y. (Inventor)


    A particle detector is provided, the particle detector including a spherical Cherenkov detector, and at least one pair of detector stacks. In an embodiment of the invention, the Cherenkov detector includes a sphere of ultraviolet transparent material, coated by an ultraviolet reflecting material that has at least one open port. The Cherenkov detector further includes at least one photodetector configured to detect ultraviolet light emitted from a particle within the sphere. In an embodiment of the invention, each detector stack includes one or more detectors configured to detect a particle traversing the sphere.

  16. Formability of spherical and large aluminum sheets (United States)

    Zimmermann, F.; Brosius, A.; Beyer, E.; Standfuß, J.; Jahn, A.


    The novel aluminum alloy AlMgSc (AA5028) shows a high potential for aeronautical applications, especially to replace the currently used material for structural components within metallic aircraft fuselages [1]. As AlMgSc sheets cannot be stretch formed at room temperature due to cracking in the clamping zones, an alternative technology called "creep-forming" was investigated by Jambu [2]. Nevertheless, creep-forming is only applicable for panels to be formed in moulds with small curvatures, because shaping double-curved geometries with small radii of curvature tends to buckling [3]. Hence, the formability of large spherical aluminum sheets as double-curved geometries is investigated.

  17. Fabrication of high edge-definition steel-tape gratings for optical encoders (United States)

    Ye, Guoyong; Liu, Hongzhong; Yan, Jiawei; Ban, Yaowen; Fan, Shanjin; Shi, Yongsheng; Yin, Lei


    High edge definition of a scale grating is the basic prerequisite for high measurement accuracy of optical encoders. This paper presents a novel fabrication method of steel tape gratings using graphene oxide nanoparticles as anti-reflective grating strips. Roll-to-roll nanoimprint lithography is adopted to manufacture the steel tape with hydrophobic and hydrophilic pattern arrays. Self-assembly technology is employed to obtain anti-reflective grating strips by depositing the graphene oxide nanoparticles on hydrophobic regions. A thin SiO2 coating is deposited on the grating to protect the grating strips. Experimental results confirm that the proposed fabrication process enables a higher edge definition in making steel-tape gratings, and the new steel tape gratings offer better performance than conventional gratings.

  18. Fabrication of high edge-definition steel-tape gratings for optical encoders. (United States)

    Ye, Guoyong; Liu, Hongzhong; Yan, Jiawei; Ban, Yaowen; Fan, Shanjin; Shi, Yongsheng; Yin, Lei


    High edge definition of a scale grating is the basic prerequisite for high measurement accuracy of optical encoders. This paper presents a novel fabrication method of steel tape gratings using graphene oxide nanoparticles as anti-reflective grating strips. Roll-to-roll nanoimprint lithography is adopted to manufacture the steel tape with hydrophobic and hydrophilic pattern arrays. Self-assembly technology is employed to obtain anti-reflective grating strips by depositing the graphene oxide nanoparticles on hydrophobic regions. A thin SiO 2 coating is deposited on the grating to protect the grating strips. Experimental results confirm that the proposed fabrication process enables a higher edge definition in making steel-tape gratings, and the new steel tape gratings offer better performance than conventional gratings.

  19. Contrast sensitivity to angular frequency gratings is not higher than to Cartesian gratings

    Directory of Open Access Journals (Sweden)

    Zana Y.


    Full Text Available When contrast sensitivity functions to Cartesian and angular gratings were compared in previous studies the peak sensitivity to angular stimuli was reported to be 0.21 log units higher. In experiments carried out to repeat this result, we used the same two-alternative forced-choice paradigm, but improved experimental control and precision by increasing contrast resolution from 8 to 12 bits, increasing the screen refresh rate from 30 Hz interlaced to 85 Hz non-interlaced, linearizing the voltage-luminance relation, modulating luminance in frequencies that minimize pixel aliasing, and improving control of the subject's exposure to the stimuli. The contrast sensitivity functions to Cartesian and angular gratings were similar in form and peak sensitivity (2.4 cycles per visual degree (c/deg and 32 c/360º, respectively to those reported in a previous study (3 c/deg and 32 c/360º, respectively, but peak sensitivity to angular stimuli was 0.13 log units lower than that to Cartesian stimuli. When the experiment was repeated, this time simulating the experimental control level used in the previous study, no difference between the peak sensitivity to Cartesian and angular stimuli was found. This result agrees with most current models that assume Cartesian filtering at the first visual processing stage. The discrepancy in the results is explained in part by differences in the degree of experimental control.

  20. Spherically symmetric conformal gravity and "gravitational bubbles"

    CERN Document Server

    Berezin, V A; Eroshenko, Yu N


    The general structure of the spherically symmetric solutions in the Weyl conformal gravity is described. The corresponding Bach equation are derived for the special type of metrics, which can be considered as the representative of the general class. The complete set of the pure vacuum solutions is found. It consists of two classes. The first one contains the solutions with constant two-dimensional curvature scalar of our specific metrics, and the representatives are the famous Robertson-Walker metrics. One of them we called the "gravitational bubbles", which is compact and with zero Weyl tensor. The second class is more general, with varying curvature scalar. We found its representative as the one-parameter family. It appears that it can be conformally covered by the thee-parameter Mannheim-Kazanas solution. We also investigated the general structure of the energy-momentum tensor in the spherical conformal gravity and constructed the vectorial equation that reveals clearly the same features of non-vacuum solu...

  1. Initial assessments of ignition spherical torus

    Energy Technology Data Exchange (ETDEWEB)

    Peng, Y.K.M.; Borowski, S.K.; Bussell, G.T.; Dalton, G.R.; Gorker, G.E.; Haines, J.R.; Hamilton, W.R.; Kalsi, S.S.; Lee, V.D.; Miller, J.B.


    Initial assessments of ignition spherical tori suggest that they can be highly cost effective and exceptionally small in unit size. Assuming advanced methods of current drive to ramp up the plasma current (e.g., via lower hybrid wave at modest plasma densities and temperatures), the inductive solenoid can largely be eliminated. Given the uncertainties in plasma energy confinement times and the effects of strong paramagnetism on plasma pressure, and allowing for the possible use of high-strength copper alloys (e.g., C-17510, Cu-Ni-Be alloy), ignition spherical tori with a 50-s burn are estimated to have major radii ranging from 1.0 to 1.6 m, aspect ratios from 1.4 to 1.7, vacuum toroidal fields from 2 to 3 T, plasma currents from 10 to 19 MA, and fusion power from 50 to 300 MW. Because of its modest field strength and simple poloidal field coil configuration, only conventional engineering approaches are needed in the design. A free-standing toroidal field coil/vacuum vessel structure is assessed to be feasible and relatively independent of the shield structure and the poloidal field coils. This exceptionally simple configuration depends significantly, however, on practical fabrication approaches of the center conductor post, about which there is presently little experience. 19 refs.

  2. Flow and scour around spherical bodies

    DEFF Research Database (Denmark)

    Truelsen, Christoffer


    near an erodible bed. In Chapter 2, a 3-D Reynolds-Average Navier-Stokes (RANS) flow solver has been used to simulate flow around and forces on a free and a near-wall sphere. Fluid forces are computed and validated against experimental data. A good agreement is found between the model and experimental...... results except in the critical flow regime. For flow around a near-wall sphere, a weak horseshoe vortex emerges as the gap ratio becomes less than or equal to 0.3. In Chapter 3, a RANS flow solver has been used to compute the bed shear stress for a near-wall sphere. The model results compare well......Spherical bodies placed in the marine environment may bury themselves due to the action of the waves and the current on the sediment in their immediate neighborhood. The present study addresses this topic by a numerical and an experimental investigation of the flow and scour around a spherical body...


    Energy Technology Data Exchange (ETDEWEB)

    Wereszczak, Andrew A [ORNL; Johanns, Kurt E [ORNL


    Instrumented Hertzian indentation testing was performed on several grades of SiCs and the results and preliminary interpretations are presented. The grades included hot-pressed and sintered compositions. One of the hot-pressed grades was additionally subjected to high temperature heat treatment to produce a coarsened grain microstructure to enable the examination of exaggerated grain size on indentation response. Diamond spherical indenters were used in the testing. Indentation load, indentation depth of penetration, and acoustic activity were continually measured during each indentation test. Indentation response and postmortem analysis of induced damage (e.g., ring/cone, radial and median cracking, quasi-plasticity) are compared and qualitatively as a function of grain size. For the case of SiC-N, the instrumented spherical indentation showed that yielding initiated at an average contact stress 12-13 GPa and that there was another event (i.e., a noticeable rate increase in compliance probably associated with extensive ring and radial crack formations) occurring around an estimated average contact stress of 19 GPa.

  4. Clusters of polyhedra in spherical confinement (United States)

    Teich, Erin G.; van Anders, Greg; Klotsa, Daphne; Dshemuchadse, Julia; Glotzer, Sharon C.


    Dense particle packing in a confining volume remains a rich, largely unexplored problem, despite applications in blood clotting, plasmonics, industrial packaging and transport, colloidal molecule design, and information storage. Here, we report densest found clusters of the Platonic solids in spherical confinement, for up to N=60 constituent polyhedral particles. We examine the interplay between anisotropic particle shape and isotropic 3D confinement. Densest clusters exhibit a wide variety of symmetry point groups and form in up to three layers at higher N. For many N values, icosahedra and dodecahedra form clusters that resemble sphere clusters. These common structures are layers of optimal spherical codes in most cases, a surprising fact given the significant faceting of the icosahedron and dodecahedron. We also investigate cluster density as a function of N for each particle shape. We find that, in contrast to what happens in bulk, polyhedra often pack less densely than spheres. We also find especially dense clusters at so-called magic numbers of constituent particles. Our results showcase the structural diversity and experimental utility of families of solutions to the packing in confinement problem. PMID:26811458

  5. Slip Potential for Commonly Used Inclined Grated Metal Walkways (United States)

    Pollard, Jonisha P.; Heberger, John R.; Dempsey, Patrick G.


    Background No specific guidelines or regulations are provided by the Mine Safety and Health Administration for the use of inclined grated metal walkways in mining plants. Mining and other companies may be using walkway materials that do not provide sufficient friction, contributing to slip and fall injuries. Purpose The purpose of this study was to determine if there are significant differences in the required friction for different grated metal walkways during walking in diverse conditions. Methods The normalized coefficients of friction were measured for 12 participants while walking up and down an instrumented walkway with different inclinations (0°, 5°, 10°, 15°, and 20°) and with and without the presence of a contaminant (glycerol). Self-reported slip events were recorded and the required coefficients of friction were calculated considering only the anterior/posterior components of the shear forces. Additionally, the available coefficients of friction for these walkway materials were measured at the 0° orientation using a tribometer, with and without the presence of the contaminant, using a boot heel as well as Neolite as the test feet. Results The number of slips increased when the inclination angle reached 10° and above. Of all materials tested, the diamond weave grating was found to have the best performance at all inclines and when contaminated or dry. A high number of slips occurred for the perforated grating and serrated bar grating at 20° when contaminated. Conclusions Results of this study suggest that the diamond weave grating provides significantly better friction compared to serrated bar and perforated gratings, especially at inclines greater than 10°. PMID:26779388

  6. High-performance arrayed waveguide grating (United States)

    Fondeur, Bart; Sala, Anca; Thekdi, Sanjay; Gopinathan, Niranjan; Nakamoto, David; Aghel, Masoud; Brainard, Bob; Vaidyanathan, Anant


    Planar technology and design have evolved significantly in the past decade, both in terms of performance and yield, reducing the cost/performance advantage of thin-film filters (TFF) over Array-Waveguide Grating (AWG) devices. This evolution is primarily due to two reasons. One of the reasons for this is the adoption of the latest in semi-conductor fabrication techniques with respect to wafer scale, process equipment automation, and yield engineering. The other reason is the many advancements made in the Planar Light Circuit (PLC) design front which have resulted in lower optical insertion loss, reduced crosstalk, increased channel bandwidth, decreased channel spacing, and minimal chromatic dispersion. We demonstrate here how such state-of-the-art fabrication technology in combination with advanced PLC designs can be effectively used to engineer the filter shape (ripple, bandwidth, and flatness) and chromatic dispersion of AWG's to match or exceed that of their thin-film counterparts. Low passband ripple is critical for cascading multiple nodes in ring network architecture whereas minimal chromatic dispersion (CD) is desired in high rate data systems to avoid signal distortion. The AWG device presented here has a 1dB bandwidth that exceeds 80% of the channel spacing awhile exhibiting a high flatness (25dB/1dB ratio < 1.7), both of which are at least a 50% improvement over generic flat-top AWG designs available in the market and are equivalent in performance to TFF devices. At 100 GHz spacing, AWG's have intrinsic low-dispersion, but narrowing the spacing to 50GHz leads to a four fold increase in the CD. Here, we have successfully overcome this limitation and have been able to design and fabricate a 50GHz wide-band AWG with less than 1ps/nm chromatic dispersion, which exceeds TFF performance.

  7. A comparison of brazed metal and epoxied fibre Bragg grating strain sensors under high strain regimes (United States)

    Mckeeman, I.; Niewczas, P.; Khan, S.


    Three different fibre Bragg grating strain sensors were tested for their suitability for measuring high strain. The sensor types were: a bare epoxied fibre Bragg grating, a standard fibre Bragg grating epoxied into a metal capillary and, finally, a metal coated fibre Bragg grating brazed into a metal capillary. The sensors were calibrated on a steel specimen up to 1400MPa (equivalent to 7.3mɛ). The results show that the bare epoxied Bragg grating and the metal packaged grating are suitable for measuring strains of this level.

  8. Materials and Fabrication Issues for Large Machined Germanium Immersion Gratings

    Energy Technology Data Exchange (ETDEWEB)

    Kuzmenko, P J; Davis, P J; Little, S L; Hale, L C


    LLNL has successfully fabricated small (1.5 cm{sup 2} area) germanium immersion gratings. We studied the feasibility of producing a large germanium immersion grating by means of single point diamond flycutting. Our baseline design is a 63.4o blaze echelle with a 6 cm beam diameter. Birefringence and refractive index inhomogeneity due to stresses produced by the crystal growth process are of concern. Careful selection of the grating blank and possibly additional annealing to relieve stress will be required. The Large Optics Diamond Turning Machine (LODTM) at LLNL is a good choice for the fabrication. It can handle parts up to 1.5 meter in diameter and 0.5 meter in length and is capable of a surface figure accuracy of better than 28 nm rms. We will describe the machine modifications and the machining process for a large grating. A next generation machine, the Precision Optical Grinder and Lathe (POGAL), currently under development has tighter specifications and could produce large gratings with higher precision.

  9. Measurement system for diffraction efficiency of convex gratings (United States)

    Liu, Peng; Chen, Xin-hua; Zhou, Jian-kang; Zhao, Zhi-cheng; Liu, Quan; Luo, Chao; Wang, Xiao-feng; Tang, Min-xue; Shen, Wei-min


    A measurement system for diffraction efficiency of convex gratings is designed. The measurement system mainly includes four components as a light source, a front system, a dispersing system that contains a convex grating, and a detector. Based on the definition and measuring principle of diffraction efficiency, the optical scheme of the measurement system is analyzed and the design result is given. Then, in order to validate the feasibility of the designed system, the measurement system is set up and the diffraction efficiency of a convex grating with the aperture of 35 mm, the curvature-radius of 72mm, the blazed angle of 6.4°, the grating period of 2.5μm and the working waveband of 400nm-900nm is tested. Based on GUM (Guide to the Expression of Uncertainty in Measurement), the uncertainties in the measuring results are evaluated. The measured diffraction efficiency data are compared to the theoretical ones, which are calculated based on the grating groove parameters got by an atomic force microscope and Rigorous Couple Wave Analysis, and the reliability of the measurement system is illustrated. Finally, the measurement performance of the system is analyzed and tested. The results show that, the testing accuracy, the testing stability and the testing repeatability are 2.5%, 0.085% and 3.5% , respectively.

  10. Quantitative phase imaging using grating-based quadrature phase interferometer (United States)

    Wu, Jigang; Yaqoob, Zahid; Heng, Xin; Cui, Xiquan; Yang, Changhuei


    In this paper, we report the use of holographic gratings, which act as the free-space equivalent of the 3x3 fiber-optic coupler, to perform full field phase imaging. By recording two harmonically-related gratings in the same holographic plate, we are able to obtain nontrivial phase shift between different output ports of the gratings-based Mach-Zehnder interferometer. The phase difference can be adjusted by changing the relative phase of the recording beams when recording the hologram. We have built a Mach-Zehnder interferometer using harmonically-related holographic gratings with 600 and 1200 lines/mm spacing. Two CCD cameras at the output ports of the gratings-based Mach-Zehnder interferometer are used to record the full-field quadrature interferograms, which are subsequently processed to reconstruct the phase image. The imaging system has ~12X magnification with ~420μmx315μm field-of-view. To demonstrate the capability of our system, we have successfully performed phase imaging of a pure phase object and a paramecium caudatum.

  11. Sensitivity analysis and optimization method for the fabrication of one-dimensional beam-splitting phase gratings

    National Research Council Canada - National Science Library

    Pacheco, Shaun; Brand, Jonathan F; Zaverton, Melissa; Milster, Tom; Liang, Rongguang


    .... Numerical results for three 1x9 beam splitting phase gratings are given. Two optimized gratings with low sensitivity to fabrication errors were compared with a grating designed for optimal efficiency...

  12. Energetic particles in spherical tokamak plasmas (United States)

    McClements, K. G.; Fredrickson, E. D.


    Spherical tokamaks (STs) typically have lower magnetic fields than conventional tokamaks, but similar mass densities. Suprathermal ions with relatively modest energies, in particular beam-injected ions, consequently have speeds close to or exceeding the Alfvén velocity, and can therefore excite a range of Alfvénic instabilities which could be driven by (and affect the behaviour of) fusion α-particles in a burning plasma. STs heated with neutral beams, including the small tight aspect ratio tokamak (START), the mega amp spherical tokamak (MAST), the national spherical torus experiment (NSTX) and Globus-M, have thus provided an opportunity to study toroidal Alfvén eigenmodes (TAEs), together with higher frequency global Alfvén eigenmodes (GAEs) and compressional Alfvén eigenmodes (CAEs), which could affect beam current drive and channel fast ion energy into bulk ions in future devices. In NSTX GAEs were correlated with a degradation of core electron energy confinement. In MAST pulses with reduced magnetic field, CAEs were excited across a wide range of frequencies, extending to the ion cyclotron range, but were suppressed when hydrogen was introduced to the deuterium plasma, apparently due to mode conversion at ion-ion hybrid resonances. At lower frequencies fishbone instabilities caused fast particle redistribution in some MAST and NSTX pulses, but this could be avoided by moving the neutral beam line away from the magnetic axis or by operating the plasma at either high density or elevated safety factor. Fast ion redistribution has been observed during GAE avalanches on NSTX, while in both NSTX and MAST fast ions were transported by saturated kink modes, sawtooth crashes, resonant magnetic perturbations and TAEs. The energy dependence of fast ion redistribution due to both sawteeth and TAEs has been studied in Globus-M. High energy charged fusion products are unconfined in present-day STs, but have been shown in MAST to provide a useful diagnostic of beam ion

  13. Upgrade of beamline BL08B at Taiwan Light Source from a photon-BPM to a double-grating SGM beamline. (United States)

    Yuh, Jih Young; Lin, Shan Wei; Huang, Liang Jen; Fung, Hok Sum; Lee, Long Life; Chen, Yu Joung; Cheng, Chiu Ping; Chin, Yi Ying; Lin, Hong Ji


    During the last 20 years, beamline BL08B has been upgraded step by step from a photon beam-position monitor (BPM) to a testing beamline and a single-grating beamline that enables experiments to record X-ray photo-emission spectra (XPS) and X-ray absorption spectra (XAS) for research in solar physics, organic semiconductor materials and spinel oxides, with soft X-ray photon energies in the range 300-1000 eV. Demands for photon energy to extend to the extreme ultraviolet region for applications in nano-fabrication and topological thin films are increasing. The basic spherical-grating monochromator beamline was again upgraded by adding a second grating that delivers photons of energy from 80 to 420 eV. Four end-stations were designed for experiments with XPS, XAS, interstellar photoprocess systems (IPS) and extreme-ultraviolet lithography (EUVL) in the scheduled beam time. The data from these experiments show a large count rate in core levels probed and excellent statistics on background normalization in the L-edge adsorption spectrum.

  14. Crystal growth of drug materials by spherical crystallization (United States)

    Szabó-Révész, P.; Hasznos-Nezdei, M.; Farkas, B.; Göcző, H.; Pintye-Hódi, K.; Erős, I.


    One of the crystal growth processes is the production of crystal agglomerates by spherical crystallization. Agglomerates of drug materials were developed by means of non-typical (magnesium aspartate) and typical (acetylsalicylic acid) spherical crystallization techniques. The growth of particle size and the spherical form of the agglomerates resulted in formation of products with good bulk density, flow, compactibility and cohesivity properties. The crystal agglomerates were developed for direct capsule-filling and tablet-making.

  15. Spherical Location Problems with Restricted Regions and Polygonal Barriers


    Dedigama Dewage, Mangalika Jayasundara


    This thesis investigates the constrained form of the spherical Minimax location problem and the spherical Weber location problem. Specifically, we consider the problem of locating a new facility on the surface of the unit sphere in the presence of convex spherical polygonal restricted regions and forbidden regions such that the maximum weighted distance from the new facility on the surface of the unit sphere to m existing facilities is minimized and the sum of the weighted distance from the n...

  16. Regularised reconstruction of sound fields with a spherical microphone array

    DEFF Research Database (Denmark)

    Granados Corsellas, Alba; Jacobsen, Finn; Fernandez Grande, Efren


    Spherical near field acoustic holography with microphones mounted on a rigid spherical surface is used to reconstruct the incident sound field. However, reconstruction outside the sphere is an ill-posed inverse problem, and since this is very sensitive to the measurement noise, straightforward...... become apparent. Hence, a number of regularisation methods, including truncated singular value decomposition, standard Tikhonov, constrained Tikhonov, iterative Tikhonov, Landweber and Rutishauser, have been adapted for spherical near field acoustic holography. The accuracy of the methods is examined...

  17. Geometric inequalities in spherically symmetric spacetimes (United States)

    Csukás, Károly Z.


    In geometric inequalities ADM mass plays more fundamental role than the concept of quasi-local mass. This paper is to demonstrate that using the quasi-local mass some new insights can be acquired. In spherically symmetric spacetimes the Misner-Sharp mass and the concept of the Kodama vector field provides an ideal setting to the investigations of geometric inequalities. We applying the proposed new techniques to investigate the spacetimes containing black hole or cosmological horizons but we shall also apply them in context of normal bodies. Most of the previous investigations applied only the quasi-local charges and the area. Our main point is to include the quasi-local mass in the corresponding geometrical inequalities. This way we recover some known relations but new inequalities are also derived.

  18. Stability of Spherical Vesicles in Electric Fields (United States)


    The stability of spherical vesicles in alternating (ac) electric fields is studied theoretically for asymmetric conductivity conditions across their membranes. The vesicle deformation is obtained from a balance between the curvature elastic energies and the work done by the Maxwell stresses. The present theory describes and clarifies the mechanisms for the four types of morphological transitions observed experimentally on vesicles exposed to ac fields in the frequency range from 500 to 2 × 107 Hz. The displacement currents across the membranes redirect the electric fields toward the membrane normal to accumulate electric charges by the Maxwell−Wagner mechanism. These accumulated electric charges provide the underlying molecular mechanism for the morphological transitions of vesicles as observed on the micrometer scale. PMID:20575588

  19. Spherically-Convergent, Advanced-Fuel Systems (United States)

    Barnes, D. C.; Nebel, R. A.; Schauer, M. M.; Umstadter, K. R.


    Combining nonneutral electron confinement with spherical ion convergence leads to a cm sized reactor volume with high power density.(R. A. Nebel and D. C. Barnes, Fusion Technol.), to appear (1998); D. C. Barnes and R. A. Nebel, Phys. of Plasmas 5, 2498 (1998). This concept is being investigated experimentally,(D. C. Barnes, T. B. Mitchell, and M. M. Schauer, Phys. Plasmas) 4, 1745 (1997). and results will be reported. We argue that D-D operation of such a system offers all the advantages of aneutronic fusion cycles. In particular, no breeding or large tritium inventory is required, and material problems seem tractable based on previous LWR experience. In addition the extremely small unit size leads to a massively modular system which is easily maintained and repaired, suggesting a very high availability. It may also be possible to operate such a system with low or aneutronic fuels. Preliminary work in this direction will be presented.

  20. Effects of coating spherical iron oxide nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Milosevic, Irena; Motte, Laurence; Aoun, Bachir; Li, Tao; Ren, Yang; Sun, Chengjun; Saboungi, Marie-Louise


    We investigate the effect of several coatings applied in biomedical applications to iron oxide nanoparticles on the size, structure and composition of the particles. The four structural techniques employed - TEM, DLS, VSM, SAXS and EXAFS - show no significant effects of the coatings on the spherical shape of the bare nanoparticles, the average sizes or the local order around the Fe atoms. The NPs coated with hydroxylmethylene bisphosphonate or catechol have a lower proportion of magnetite than the bare and citrated ones, raising the question whether the former are responsible for increasing the valence state of the oxide on the NP surfaces and lowering the overall proportion of magnetite in the particles. VSM measurements show that these two coatings lead to a slightly higher saturation magnetization than the citrate. This article is part of a Special Issue entitled "Science for Life" Guest Editor: Dr. Austen Angell, Dr. Salvatore Magazu and Dr. Federica Migliardo.

  1. Laser Pulse Heating of Spherical Metal Particles

    Directory of Open Access Journals (Sweden)

    Michael I. Tribelsky


    Full Text Available We consider the general problem of laser pulse heating of spherical metal particles with the sizes ranging from nanometers to millimeters. We employ the exact Mie solution of the diffraction problem and solve the heat-transfer equation to determine the maximum temperature rise at the particle surface as a function of optical and thermometric parameters of the problem. Primary attention is paid to the case when the thermal diffusivity of the particle is much larger than that of the environment, as it is in the case of metal particles in fluids. We show that, in this case, for any given duration of the laser pulse, the maximum temperature rise as a function of the particle size reaches a maximum at a certain finite size of the particle. We suggest simple approximate analytical expressions for this dependence, which cover the entire parameter range of the problem and agree well with direct numerical simulations.

  2. Simple spherical ablative-implosion model

    Energy Technology Data Exchange (ETDEWEB)

    Mayer, F.J.; Steele, J.T.; Larsen, J.T.


    A simple model of the ablative implosion of a high-aspect-ratio (shell radius to shell thickness ratio) spherical shell is described. The model is similar in spirit to Rosenbluth's snowplow model. The scaling of the implosion time was determined in terms of the ablation pressure and the shell parameters such as diameter, wall thickness, and shell density, and compared these to complete hydrodynamic code calculations. The energy transfer efficiency from ablation pressure to shell implosion kinetic energy was examined and found to be very efficient. It may be possible to attach a simple heat-transport calculation to our implosion model to describe the laser-driven ablation-implosion process. The model may be useful for determining other energy driven (e.g., ion beam) implosion scaling.

  3. Volume phase holographic gratings for the Subaru Prime Focus Spectrograph: performance measurements of the prototype grating set (United States)

    Barkhouser, Robert H.; Arns, James; Gunn, James E.


    The Prime Focus Spectrograph (PFS) is a major instrument under development for the 8.2 m Subaru telescope on Mauna Kea. Four identical, fixed spectrograph modules are located in a room above one Nasmyth focus. A 55 m fiber optic cable feeds light into the spectrographs from a robotic fiber positioner mounted at the telescope prime focus, behind the wide field corrector developed for Hyper Suprime-Cam. The positioner contains 2400 fibers and covers a 1.3 degree hexagonal field of view. Each spectrograph module will be capable of simultaneously acquiring 600 spectra. The spectrograph optical design consists of a Schmidt collimator, two dichroic beamsplitters to separate the light into three channels, and for each channel a volume phase holographic (VPH) grating and a dual- corrector, modified Schmidt reimaging camera. This design provides a 275 mm collimated beam diameter, wide simultaneous wavelength coverage from 380 nm to 1.26 µm, and good imaging performance at the fast f/1.1 focal ratio required from the cameras to avoid oversampling the fibers. The three channels are designated as the blue, red, and near-infrared (NIR), and cover the bandpasses 380-650 nm (blue), 630-970 nm (red), and 0.94-1.26 µm (NIR). A mosaic of two Hamamatsu 2k×4k, 15 µm pixel CCDs records the spectra in the blue and red channels, while the NIR channel employs a 4k×4k, substrate-removed HAWAII-4RG array from Teledyne, with 15 µm pixels and a 1.7 µm wavelength cutoff. VPH gratings have become the dispersing element of choice for moderate-resolution astronomical spectro- graphs due their potential for very high diffraction efficiency, low scattered light, and the more compact instru- ment designs offered by transmissive dispersers. High quality VPH gratings are now routinely being produced in the sizes required for instruments on large telescopes. These factors made VPH gratings an obvious choice for PFS. In order to reduce risk to the project, as well as fully exploit the performance

  4. Spherical microwave confinement and ball lightning (United States)

    Robinson, William Richard

    This dissertation presents the results of research done on unconventional energy technologies from 1995 to 2009. The present civilization depends on an infrastructure that was constructed and is maintained almost entirely using concentrated fuels and ores, both of which will run out. Diffuse renewable energy sources rely on this same infrastructure, and hence face the same limitations. I first examined sonoluminescence directed toward fusion, but demonstrated theoretically that this is impossible. I next studied Low Energy Nuclear Reactions and developed methods for improving results, although these have not been implemented. In 2000, I began Spherical Microwave Confinement (SMC), which confines and heats plasma with microwaves in a spherical chamber. The reactor was designed and built to provide the data needed to investigate the possibility of achieving fusion conditions with microwave confinement. A second objective was to attempt to create ball lightning (BL). The reactor featured 20 magnetrons, which were driven by a capacitor bank and operated in a 0.2 s pulse mode at 2.45 GHz. These provided 20 kW to an icosahedral array of 20 antennas. Video of plasmas led to a redesign of the antennas to provide better coupling of the microwaves to the plasma. A second improvement was a grid at the base of the antennas, which provided corona electrons and an electric field to aid quick formation of plasmas. Although fusion conditions were never achieved and ball lightning not observed, experience gained from operating this basic, affordable system has been incorporated in a more sophisticated reactor design intended for future research. This would use magnets that were originally planned. The cusp geometry of the magnetic fields is suitable for electron cyclotron resonance in the same type of closed surface that in existing reactors has generated high-temperature plasmas. Should ball lightning be created, it could be a practical power source with nearly ideal

  5. Explosive fragmentation of liquids in spherical geometry (United States)

    Milne, A.; Longbottom, A.; Frost, D. L.; Loiseau, J.; Goroshin, S.; Petel, O.


    Rapid acceleration of a spherical shell of liquid following central detonation of a high explosive causes the liquid to form fine jets that are similar in appearance to the particle jets that are formed during explosive dispersal of a packed layer of solid particles. Of particular interest is determining the dependence of the scale of the jet-like structures on the physical parameters of the system, including the fluid properties (e.g., density, viscosity, and surface tension) and the ratio of the mass of the liquid to that of the explosive. The present paper presents computational results from a multi-material hydrocode describing the dynamics of the explosive dispersal process. The computations are used to track the overall features of the early stages of dispersal of the liquid layer, including the wave dynamics, and motion of the spall and accretion layers. The results are compared with new experimental results of spherical charges surrounded by a variety of different fluids, including water, glycerol, ethanol, and vegetable oil, which together encompass a significant range of fluid properties. The results show that the number of jet structures is not sensitive to the fluid properties, but primarily dependent on the mass ratio. Above a certain mass ratio of liquid fill-to-explosive burster ( F / B), the number of jets is approximately constant and consistent with an empirical model based on the maximum thickness of the accretion layer. For small values of F / B, the number of liquid jets is reduced, in contrast with explosive powder dispersal, where small F / B yields a larger number of particle jets. A hypothetical explanation of these features based on the nucleation of cavitation is explored numerically.

  6. ICPP: Results from the MAST Spherical Tokamak (United States)

    Sykes, Alan


    The MAST (Mega-Amp Spherical Tokamak) experiment is now fully operational, producing 1MA plasmas with MW level auxiliary heating from Neutral Beam Injection and 60GHz Electron Cyclotron Resonance Heating. Central electron and ion temperatures are both of order 1keV (measured by 30-point Thomson Scattering, Neutral Particle Analyzer and Charge-Exchange spectroscopy respectively). Following boronisation, the Greenwald density limit has been exceeded in double-null divertor discharges by 50operation has been achieved in both Ohmic and NBI heated plasmas. In addition to conventional plasma induction, MAST can employ the `merging-compression' scheme (pioneered on START) producing initial spherical tokamak plasmas of up to 0.5MA without use of flux from the central solenoid. The central solenoid can then be applied to further increase the current at ramp rates of up to 13MA/s; plasma current of 1MA is reached at only one-half of the full solenoid swing. Studies of strike point power loading in both Ohmic and beam heated plasmas have confirmed the result from START that the fraction of power loading on the inboard strike point is lower than predicted from simple models. Comprehensive arrays of halo detectors indicate tolerable levels of halo currents with low asymmetries; an encouraging result for the ST concept, and providing key data to test models. Results from MAST will be used both to extend the conventional tokamak database, and to determine the potential of the ST as a route to fusion power in its own right. Acknowledgement: this work is funded jointly by the UK Department of Trade and Industry and EURATOM. The NBI equipment is on loan from ORNL, the NPA from PPPL.

  7. Dynamical systems and spherically symmetric cosmological models (United States)

    He, Yanjing


    In this thesis we present a study of the timelike self-similar spherically symmetric cosmological models with two scalar fields with exponential potentials. We first define precisely the timelike self-similar spherically symmetric (TSS) spacetimes. We write the TSS metric in a conformally isometric form in a coordinate system adapted to the geometry of the spacetime manifold. In this coordinate system, both the metric functions of the TSS spacetimes and the potential functions of the scalar fields can be simplified to four undetermined functions of a single coordinate. As a result, the Einstein field equations reduce to an autonomous system of first-order ODEs and polynomial constraints in terms of these undetermined functions. By introducing new bounded variables as well as a new independent variable and solving the constraints, we are able to apply the theory of dynamical systems to study the properties of the TSS solutions. By finding invariant sets and associated monotonic functions, by applying the LaSalle Invariance Principle and the Monotonicity Principle, by applying the [straight phi] t -connected property of a limit set, and using other theorems, we prove that all of the TSS trajectories are heteroclinic trajectories. In addition, we conduct numerical simulations to confirm and support the qualitative analysis. We obtain all possible types of TSS solutions, by analyzing the qualitative behavior of the original system of ODES from those of the reduced one. We obtain asymptotic expressions for the TSS solutions (e.g., the asymptotic expressions for the metric functions, the source functions and the Ricci scalar). In particular, self-similar flat Friedmann-Robertson-Walker spacetimes are examined in order to obtain insights into the issues related to the null surface in general TSS spacetimes in these coordinates. A discussion of the divergence of the spacetime Ricci scalar and the possible extension of the TSS solutions across the null boundary is presented

  8. Measurement of Turbulence Modulation by Non-Spherical Particles

    DEFF Research Database (Denmark)

    Mandø, Matthias; Rosendahl, Lasse


    The change in the turbulence intensity of an air jet resulting from the addition of particles to the flow is measured using Laser Doppler Anemometry. Three distinct shapes are considered: the prolate spheroid, the disk and the sphere. Measurements of the carrier phase and particle phase velocities......, the particle mass flow and the integral length scale of the flow. The expression developed on basis of spherical particles only is applied on the data for the non-spherical particles. The results suggest that non-spherical particles attenuate the carrier phase turbulence significantly more than spherical...

  9. A multiball read-out for the spherical proportional counter (United States)

    Giganon, A.; Giomataris, I.; Gros, M.; Katsioulas, I.; Navick, X. F.; Tsiledakis, G.; Savvidis, I.; Dastgheibi-Fard, A.; Brossard, A.


    We present a novel concept of proportional gas amplification for the read-out of the spherical proportional counter. The standard single-ball read-out presents limitations for large diameter spherical detectors and high-pressure operations. We have developed a multi-ball read-out system which consists of several balls placed at a fixed distance from the center of the spherical vessel. Such a module can tune the volume electric field at the desired value and can also provide detector segmentation with individual ball read-out. In the latter case, the large volume of the vessel becomes a spherical time projection chamber with 3D capabilities.

  10. Investigation of spherical and concentric mechanism of compound droplets

    Directory of Open Access Journals (Sweden)

    Meifang Liu


    Full Text Available Polymer shells with high sphericity and uniform wall thickness are always needed in the inertial confined fusion (ICF experiments. Driven by the need to control the shape of water-in-oil (W1/O compound droplets, the effects of the density matching level, the interfacial tension and the rotation speed of the continuing fluid field on the sphericity and wall thickness uniformity of the resulting polymer shells were investigated and the spherical and concentric mechanisms were also discussed. The centering of W1/O compound droplets, the location and movement of W1/O compound droplets in the external phase (W2 were significantly affected by the density matching level of the key stage and the rotation speed of the continuing fluid field. Therefore, by optimizing the density matching level and rotation speed, the batch yield of polystyrene (PS shells with high sphericity and uniform wall thickness increased. Moreover, the sphericity also increased by raising the oil/water (O/W2 interfacial tension, which drove a droplet to be spherical. The experimental results show that the spherical driving force is from the interfacial tension affected by the two relative phases, while the concentric driving force, as a resultant force, is not only affected by the three phases, but also by the continuing fluid field. The understanding of spherical and concentric mechanism can provide some guidance for preparing polymer shells with high sphericity and uniform wall thickness.

  11. Low-Q Electrically Small Spherical Magnetic Dipole Antennas

    DEFF Research Database (Denmark)

    Kim, Oleksiy S.


    Three novel electrically small antenna configurations radiating a TE10 spherical mode corresponding to a magnetic dipole are presented and investigated: multiarm spherical helix (MSH) antenna, spherical split ring resonator (S-SRR) antenna, and spherical split ring (SSR) antenna. All three antennas...... are self-resonant, with the input resistance tuned to 50 ohms by an excitation curved dipole/monopole. A prototype of the SSR antenna has been fabricated and measured, yielding results that are consistent with the numerical simulations. Radiation quality factors (Q) of these electrically small antennas (in...

  12. Model based control of grate combustion; Modellbaserad roststyrning

    Energy Technology Data Exchange (ETDEWEB)

    Broden, Henrik; Kjellstroem, Bjoern; Niklasson, Fredrik; Boecher Poulsen, Kristian


    An existing dynamic model for grate combustion has been further developed. The model has been used for studies of possible advantages that can be gained from utilisation of measurements of grate temperatures and fuel bed height for control of a boiler after disturbances caused by varying fuel moisture and fuel feeding. The objective was to asses the possibilities to develop a control system that would adjust for such disturbances quicker than measurements of steam output and oxygen in the exhaust. The model is based on dividing the fuel bed into three layers, where the different layers include fuel being dried, fuel being pyrolysed and char reacting with oxygen. The grate below the fuel bed is also considered. A mass balance, an energy balance and a volume balance is considered for each layer in 22 cells along the grate. The energy balances give the temperature distribution and the volume balances the bed height. The earlier version of the model could not handle layers that are consumed. This weakness has now been eliminated. Comparisons between predicted grate temperatures and measurements in a 25 MW boiler fuelled with biofuel have been used for validation of the model. The comparisons include effects of variations in primary air temperature, fuel moisture and output power. The model shows good agreement with observations for changes in the air temperature but the ability of the model to predict effects of changed fuel moisture is difficult to judge since the steam dome pressure control caused simultaneous changes of the primary air flow, which probably had a larger influence on the grate temperature. A linearised, tuned and reduced version of the model was used for design of a linear quadratic controller. This was used for studies of advantages of using measurements of grate temperatures and bed height for control of pusher velocity, grate speed, primary air flow and air temperature after disturbances of fuel moisture and fuel flow. Measurements of the grate

  13. Numerical simulation of a biomass fired grate boiler

    DEFF Research Database (Denmark)

    Yin, Chungen; Rosendahl, Lasse; Kær, Søren Knudsen


    Computational fluid dynamic (CFD) analysis of the thermal flow in the combustion furnace of a biomass-fired grate boiler provides crucial insight into the boiler's performance. Quite a few factors play important roles in a general CFD analysis, such as grid, models, discretization scheme and so on....... For a grate boiler, the modeling the interaction of the fuel bed and the gas phase above the bed is also essential. Much effort can be found in literature on developing bed models whose results are introduced into CFD simulations of freeboard as inlet conditions. This paper presents a CFD analysis...... of the largest biomass-fired grate boiler in Denmark. The focus of this paper is to study how significantly an accurate bed model can affect overall CFD results, i.e., how necessarily it is to develop an accurate bed model in terms of the reliability of CFD results. The ultimate purpose of the study is to obtain...

  14. EUV-multilayers on grating-like topographies

    Energy Technology Data Exchange (ETDEWEB)

    van Boogaard, A. J. R.; Louis, E.; Goldberg, K. A.; Mochi, I.; Bijkerk, F.


    In this study, multilayer morphology near the key anomalies in grating-like structures, namely sharp step-edges and steep walls, are examined. Different deposition schemes are employed. Based on cross section TEM analysis an explanatory model describing the morphology of the successive layers is developed. A further insight into the periodicity and the general performance of the multilayer is obtained by EUV microscopy. The main distortions in multilayer structure and hence EUV performance are found to be restricted to a region within a few hundred nanometers from the anomalies, which is very small compared to the proposed grating period (50-100 {micro}m). These multilayer coated blazed gratings can thus be considered a viable option for spectral purity enhancement of EUV light sources.

  15. Volume phase holographic gratings for astronomy based on solid photopolymers (United States)

    Zanutta, Alessio; Bianco, Andrea; Insausti, Maider; Garzón, Francisco


    Volume Phase Holographic Gratings (VPHG) are gaining more and more interest as optical dispersing elements in new astronomical spectrographs at low and medium resolution. A key point is the development of new photosensitive materials suitable to produce VPHGs that match the stringent requirements of the astronomical environment. Here we report on the performances of VPHG based on Bayfol®HX solid photopolymer films developed by Bayer MaterialScience AG. Parameters affecting the grating efficiency (e. g. photopolymer film thickness and refractive index modulation) are measured and linked to the performances of VPHG working in the VIS-NIR region. Moreover, the behavior at low temperature and the aging properties of such materials/gratings are reported. Substantial efficiency gains on a new VPHG installed at the Asiago's spectrograph are shown and proven on the observation of a standard star (hr5501).

  16. Applications of laser-induced gratings to spectroscopy and dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Rohlfing, E.A. [Sandia National Laboratories, Livermore, CA (United States)


    This program has traditionally emphasized two principal areas of research. The first is the spectroscopic characterization of large-amplitude motion on the ground-state potential surface of small, transient molecules. The second is the reactivity of carbonaceous clusters and its relevance to soot and fullerene formation in combustion. Motivated initially by the desire to find improved methods of obtaining stimulated emission pumping (SEP) spectra of transients, most of our recent work has centered on the use of laser-induced gratings or resonant four-wave mixing in free-jet expansions. These techniques show great promise for several chemical applications, including molecular spectroscopy and photodissociation dynamics. The author describes recent applications of two-color laser-induced grating spectroscopy (LIGS) to obtain background-free SEP spectra of transients and double resonance spectra of nonfluorescing species, and the use of photofragment transient gratings to probe photodissociation dynamics.

  17. Transition of refractive index contrast in course of grating growth. (United States)

    Sabel, Tina; Zschocher, Michael


    Studies on the dynamics of holographic pattern formation in photosensitive polymers, gaining deeper insight into the specific material transformations, are essential for improvements in holographic recording as well as in integrated optics. Here we investigate the kinetics of volume hologram formation in an organic cationic ring-opening polymerization system. The time evolution of the grating strength and the grating phase is presented. We found two steps of growth, separated by a depletion of the light diffraction. Capable to explore this growing behavior, a transition-theory of the refractive index contrast is established. Accordingly the growth curves appear to be ruled by the interplay of polymerization and diffusion. Hence the grating formation mechanisms can be qualified as competing effects regarding the contribution to the refractive index change. We investigate the influence of the preparation and exposure procedure on the transition and consider the usability for integrated wave guide functions.

  18. Electromagnetically induced grating in a crystal of molecular magnets system

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Jibing, E-mail: [College of Physics and Electronic Science and Institute for Advanced Materials, Hubei Normal University, Huangshi 435002 (China); Liu, Na; Shan, Chuanjia; Liu, Tangkun; Li, Hong [College of Physics and Electronic Science and Institute for Advanced Materials, Hubei Normal University, Huangshi 435002 (China); Zheng, Anshou, E-mail: [School of Mathematics and Physics, China University of Geosciences, Wuhan 430074 (China); Xie, Xiao-Tao, E-mail: [School of Physics and Information Technology, Shaanxi Normal University, Xi' an 710119 (China)


    We investigate the response of the molecular system to the magnetic field modulation. Molecular magnets are subjected to a strong standing ac magnetic field and a weak probe magnetic field. The transmission and absorption of the weak probe magnetic field can be changed due to quantum coherence and the spatially modulating of the standing field. And a electromagnetically induced grating is formed in the crystal of molecular magnets via electromagnetically induced transparency (EIT). The diffraction efficiency of the grating can be adjusted efficiently by tuning the intensity of the standing wave field and the single photon detuning. - Highlights: • We provide a scheme to generate electromagnetically induced grating in a crystal of molecular magnets. • The transmission and absorption of the probe magnetic field can be changed by the standing field. • The efficiency of diffraction is depended on the intensity of coupling and the single photon detuning.

  19. Engine optimization grate multipurpose analysis method with quality function deployment

    Directory of Open Access Journals (Sweden)



    Full Text Available The object that will be developed in this study is a simple technology shredding machine design, artificial and has been patented by Andi Patolla (1988. which is often used by people specifically to grate the coconut. The methods used for product development using QFD. This method is needed to analyze and evaluate the level of consumer desires in order to develop products grate machine. The subject matter of the research outlined in the distribution table discussion. The research instrument used when data collection is questionnaire technique, which is supported by the observation technique, documentation, and interviews. From the discussion that has been done, it can be concluded that the priority consumers are very stressed to do a modification component or an additional tool in the machine grater multipurpose namely Cover Safeguard Fan Belt, Exhaust, Priority Motor Driving Fuel Gasoline, layout position Mover, Motor Starter, Plastic cleaning brush Roll Grate, and Plate Cap. 2.

  20. High performance Si immersion gratings patterned with electron beam lithography (United States)

    Gully-Santiago, Michael A.; Jaffe, Daniel T.; Brooks, Cynthia B.; Wilson, Daniel W.; Muller, Richard E.


    Infrared spectrographs employing silicon immersion gratings can be significantly more compact than spectro- graphs using front-surface gratings. The Si gratings can also offer continuous wavelength coverage at high spectral resolution. The grooves in Si gratings are made with semiconductor lithography techniques, to date almost entirely using contact mask photolithography. Planned near-infrared astronomical spectrographs require either finer groove pitches or higher positional accuracy than standard UV contact mask photolithography can reach. A collaboration between the University of Texas at Austin Silicon Diffractive Optics Group and the Jet Propulsion Laboratory Microdevices Laboratory has experimented with direct writing silicon immersion grating grooves with electron beam lithography. The patterning process involves depositing positive e-beam resist on 1 to 30 mm thick, 100 mm diameter monolithic crystalline silicon substrates. We then use the facility JEOL 9300FS e-beam writer at JPL to produce the linear pattern that defines the gratings. There are three key challenges to produce high-performance e-beam written silicon immersion gratings. (1) E- beam field and subfield stitching boundaries cause periodic cross-hatch structures along the grating grooves. The structures manifest themselves as spectral and spatial dimension ghosts in the diffraction limited point spread function (PSF) of the diffraction grating. In this paper, we show that the effects of e-beam field boundaries must be mitigated. We have significantly reduced ghost power with only minor increases in write time by using four or more field sizes of less than 500 μm. (2) The finite e-beam stage drift and run-out error cause large-scale structure in the wavefront error. We deal with this problem by applying a mark detection loop to check for and correct out minuscule stage drifts. We measure the level and direction of stage drift and show that mark detection reduces peak-to-valley wavefront error

  1. Highly Sensitive Cadmium Concentration Sensor Using Long Period Grating

    Directory of Open Access Journals (Sweden)

    A. S. Lalasangi


    Full Text Available In this paper we have proposed a simple and effective Long Period Grating chemical sensor for detecting the traces of Cadmium (Cd++ in drinking water at ppm level. Long Period gratings (LPG were fabricated by point-by-point technique with CO2 laser. We have characterized the LPG concentration sensor sensitivity for different solutions of Cd concentrations varying from 0.01 ppm to 0.04 ppm by injecting white Light source and observed transmitted spectra using Optical Spectrum Analyzer (OSA. Proper reagents have been used in the solutions for detection of the Cd species. The overall shift in wavelength is 10 nm when surrounding medium gradually changed from water to 0.04 ppm of cadmium concentrations. A comparative study has been done using sophisticated spectroscopic atomic absorption spectrometer (AAS and Inductively Coupled Plasma (ICP instruments. The spectral sensitivity enhancement was done by modifying grating surface with gold nanoparticles.

  2. High Resolving Power Volume Diffractive Gratings for 400-2700 nm Spectral Range Project (United States)

    National Aeronautics and Space Administration — The main purpose of this NASA SBIR Phase II proposal is development of a novel type of high resolving power diffraction gratings based on volume Bragg gratings...

  3. High Resolving Power Volume Diffractive Gratings for 400-2700 nm Spectral Range Project (United States)

    National Aeronautics and Space Administration — The purpose of this NASA SBIR Phase I proposal is to develop a novel type of high resolving power diffraction gratings based on volume Bragg gratings technology. The...

  4. Genetic algorithm-based design method for multilevel anisotropic diffraction gratings (United States)

    Okamoto, Hiroyuki; Noda, Kohei; Sakamoto, Moritsugu; Sasaki, Tomoyuki; Wada, Yasuhiro; Kawatsuki, Nobuhiro; Ono, Hiroshi


    We developed a method for the design of multilevel anisotropic diffraction gratings based on a genetic algorithm. The method is used to design the multilevel anisotropic diffraction gratings based on input data that represent the output from the required grating. The validity of the proposed method was evaluated by designing a multilevel anisotropic diffraction grating using the outputs from an orthogonal circular polarization grating. The design results corresponded to the orthogonal circular polarization grating structures that were used to provide outputs to act as the input data for the process. Comparison with existing design methods shows that the proposed method can reduce the number of human processes that are required to design multilevel anisotropic diffraction gratings. Additionally, the method will be able to design complex structures without any requirement for subsequent examination by a human designer. The method can contribute to the development of optical elements by designing multilevel anisotropic diffraction gratings.

  5. Controlled angular redirection of light via nanoimprinted disordered gratings

    DEFF Research Database (Denmark)

    Buss, Thomas; Teisseire, Jérémie; Mazoyer, Simon


    Enhanced control of diffraction through transparent substrates is achieved via disordered gratings in a silica sol–gel film. Tailoring the degree of disorder allows tuning of the diffractive behavior from discrete orders into broad distributions over large angular range. Gratings of optical quality...... are formed by silica sol–gel nanoimprint lithography and an optical setup for the measurement of continuous diffraction patterns is presented. Sound agreement is found between measurements and simulation, validating both the approach for redirection of light and the fabrication process. The disordered...

  6. Laser-induced grating in ZnO

    DEFF Research Database (Denmark)

    Ravn, Jesper N.


    A simple approach for the calculation of self-diffraction in a thin combined phase and amplitude grating is presented. The third order nonlinearity, the electron-hole recombination time, and the ambipolar diffusion coefficient in a ZnO crystal are measured by means of laser-induced self-diffracti......A simple approach for the calculation of self-diffraction in a thin combined phase and amplitude grating is presented. The third order nonlinearity, the electron-hole recombination time, and the ambipolar diffusion coefficient in a ZnO crystal are measured by means of laser-induced self...

  7. Flexible PCPDTBT:PCBM solar cells with integrated grating structures

    DEFF Research Database (Denmark)

    Oliveira Hansen, Roana Melina de; Liu, Yinghui; Madsen, Morten


    spectra of the active layer. This optimized solar cell structure leads to an enhanced absorption in the active layer and thus improved short-circuit currents and power conversion efficiencies in the fabricated devices. Fabrication of the solar cells on thin polyimide substrates which are compatible......We report on development of flexible PCPDTBT:PCBM solar cells with integrated diffraction gratings on the bottom electrodes. The presented results address PCPDTBT:PCBM solar cells in an inverted geometry, which contains implemented grating structures whose pitch is tuned to match the absorption...

  8. Point-by-point inscription of apodized fiber Bragg gratings. (United States)

    Williams, Robert J; Voigtländer, Christian; Marshall, Graham D; Tünnermann, Andreas; Nolte, Stefan; Steel, M J; Withford, Michael J


    We demonstrate apodized fiber Bragg gratings (FBGs) inscribed with a point-by-point (PbP) technique. We tailor the grating phase and coupling amplitude through precise control over the longitudinal and transverse positions of each laser-inscribed modification. This method of apodization is facilitated by the highly localized, high-contrast modifications generated by focused IR femtosecond laser inscription. Our technique provides a simple method for the design and implementation of PbP FBGs with complex apodization profiles. © 2011 Optical Society of America

  9. Diffraction pattern of triangular grating in the resonance domain. (United States)

    Hoshino, Tetsuya; Banerjee, Saswatee; Itoh, Masahide; Yatagai, Toyohiko


    We propose a combination of ray optics and Fraunhofer multiple-slit diffraction theory for calculating the two-dimensional triangular periodic grating in the resonance domain. The peak of the envelope pattern of angular distribution of diffraction efficiency is calculated by ray optics while the peak width is calculated using Fraunhofer theory. It was clarified, using rigorous coupled-wave analysis and a nonstandard-finite-difference time-domain method, that the envelope pattern of the diffraction of the grating could be calculated easily and understood intuitively for the design of displays and lighting.

  10. Submicrometer grating light bar for a color-separation backlight. (United States)

    Liu, Chun-Wei; Lee, Chi-Hung; Yang, Tzu-Chun; Ting, Chia-Jen; Lin, Tsung-Hsin; Lin, Shih-Chieh


    A light bar patterned using a submicrometer grating was designed to replace conventional dye color filters for color liquid crystal displays. The light bar generates color rays by transmitting them from side-lit color light-emitting diodes through the submicrometer grating. These angular color rays are then redirected by a V-grooved light guide, and then converged by a lens array and mapped to corresponding subpixel positions to efficiently display color images. The results show that 106% of the National Television System Committee (NTSC) color space in a blue-green-red-green (B-G-R-G) repeating pattern display pixel layout can be achieved.

  11. Enhanced resolution of long-period grating bend sensor

    DEFF Research Database (Denmark)

    Glavind, Lars; Gao, S; Cook, K


    We present an optical fiber bend sensor with enhanced resolution based on the principle of a Mach-Zehnder interferometer in transmission. The sensor is based on two identical Long-Period Gratings separated by approximately 100 mm in a D-shaped single-mode optical fiber. The sensor provides a narrow...... resonance bandwidth compared to a typical resonance from a Long-Period Grating. The sensor was recoated with low refractive index polyimide and embedded on a fiber-glass base plate before it was characterized as a bending sensor....

  12. Color multiplexing using directional holographic gratings and linear polarization

    Energy Technology Data Exchange (ETDEWEB)

    Lugo, L I; Rodriguez, A; Ramirez, G; Guel, S; Nunez, O F, E-mail: [Instituto de Investigacion en Comunicacion Optica (IICO) Universidad Autonoma de San Luis Potosi, S.L.P. (UASLP) (Mexico)


    We propose a system of multiplexing and de-multiplexing, which uses a holographic diffraction grating to compel modulated light of different colors to be sent through an optical fiber. Diffraction gratings were fabricated specifically to pick the desired direction in which we wanted the light of different wavelengths to impinge the optic fiber, and also to be separated at the output. It was been found that the system preserves the polarization of light, which give us a one more freedom degree, allowing us to process twice the original information amount.

  13. Fiber-guided modes conversion using superposed helical gratings (United States)

    Ma, Yancheng; Fang, Liang; Wu, Guoan


    Optical fibers can support various modal forms, including vector modes, linear polarization (LP) modes, and orbital angular momentum (OAM) modes, etc. The modal correlation among these modes is investigated via Jones matrix, associated with polarization and helical phase corresponding to spin angular momentum (SAM) and OAM of light, respectively. We can generate different modal forms by adopting superposed helical gratings (SHGs) with opposite helix orientations. Detailed analysis and discussion on mode conversion is given as for mode coupling in optical fibers with both low and high contrast index, respectively. Our study may deepen the understanding for various fiber-guided modes and mode conversion among them via fiber gratings.

  14. Subwavelength grating-mirror VCSEL with a thin oxide gap

    DEFF Research Database (Denmark)

    Chung, Il-Sug; Mørk, Jesper; Gilet, Philippe


    A new vertical-cavity surface-emitting laser (VCSEL) structure based on a subwavelength grating mirror and a thin oxide gap is suggested and numerically investigated. The structure is shown to exhibit similar threshold gain, suppression of higher order transverse modes, and polarization stability...... as a grating-mirror VCSEL reported in the literature based on a thick air gap. The thin oxide gap structure has a number of advantages including easier fabrication, better mechanical stability, and very strong single-mode properties....

  15. Bragg grating filters in plasmonic V-groove waveguides

    DEFF Research Database (Denmark)

    Smith, Cameron; Desiatov, Boris; Goykhmann, Ilya


    We demonstrate spectral filtering via Bragg gratings in plasmonic V-groove waveguides. Transmission spectra of wafer-scale fabricated devices exhibit 8.2 dB extinction ratio with 39.9 nm bandwidth. Near-field measurements verify spectral rejection.......We demonstrate spectral filtering via Bragg gratings in plasmonic V-groove waveguides. Transmission spectra of wafer-scale fabricated devices exhibit 8.2 dB extinction ratio with 39.9 nm bandwidth. Near-field measurements verify spectral rejection....

  16. Fiber Bragg Grating Sensors for Mainstream Industrial Processes

    Directory of Open Access Journals (Sweden)

    Gary Allwood


    Full Text Available This paper reviews fiber Bragg grating sensing technology with respect to its use in mainstream industrial process applications. A review of the various types of sensors that have been developed for industries such as power generation, water treatment and services, mining, and the oil and gas sector has been performed. A market overview is reported as well as a discussion of some of the factors limiting their penetration into these markets. Furthermore, the author’s make recommendations for future work that would potentially provide significant opportunity for the advancement of fiber Bragg grating sensor networks in these mainstream industries.

  17. Deformable silicone grating fabricated with a photo-imprinted polymer mold (United States)

    Yamada, Itsunari; Nishii, Junji; Saito, Mitsunori


    A tunable transmission grating was fabricated by molding a silicone elastomer (polydimethylsiloxane). Its optical characteristics were then evaluated during compression. For fabrication, a glass plate with a photoimprinted polymer grating film was used as a mold. Both the grating period and diffraction transmittance of the molded elastomer were functions of the compressive stress. The grating period changed from 3.02 to 2.86 μm during compressing the elastomer in the direction perpendicular to the grooves.

  18. Thick plasma gratings using a local photorefractive effect in CdZnTe:In. (United States)

    Macdonald, R L; Linke, R A; Chadi, J D; Thio, T; Devlin, G E; Becla, P


    Diffraction gratings have been encoded in bulk Cd(0.8)Zn(0.2)Te:In samples by near-band-gap excitation. The photoinduced index change is associated with persistent photoconductivity resulting from ionization of DX centers. The gratings have a thickness of 1.7 mm, as evinced by Bragg selectivity during the readout process. Encoded grating are shown to be persistent for sufficiently low temperatures and are not erased by subsequent writing of more gratings.

  19. Improved thermal and strain performance of annealed polymer optical fiber Bragg gratings

    DEFF Research Database (Denmark)

    Yuan, Scott Wu; Stefani, Alessio; Bache, Morten


    We report on a detailed study of the inscription and characterization of fiber Bragg gratings (FBGs) in commercial step index polymer optical fibers (POFs). Through the growth dynamics of the gratings, we identify the effect of UV-induced heating during the grating inscription. We found that FBGs...

  20. Embedding silica and polymer fibre Bragg gratings (FBG) in plastic 3D-printed sensing patches

    DEFF Research Database (Denmark)

    Zubel, Michal G.; Sugden, Kate; Webb, David J.


    This paper reports the first demonstration of a silica fibre Bragg grating (SOFBG) embedded in an FDM 3-D printed housing to yield a dual grating temperature-compensated strain sensor. We also report the first ever integration of polymer fibre Bragg grating (POFBG) within a 3-D printed sensing...

  1. A set of innovative immersed grating based spectrometer designs for METIS

    NARCIS (Netherlands)

    Agócs, T.; Navarro, R.; Venema, L.; Amerongen, A.H. van; Tol, P.J.J.; Brug, H. van; Brandl, B.R.; Molster, F.; Todd, S.


    We present innovative, immersed grating based optical designs for the SMO (Spectrograph Main Optics) module of the Mid-infrared E-ELT Imager and Spectrograph, METIS. The immersed grating allows a significant reduction of SMO volume compared to conventional echelle grating designs, because the

  2. High-resolution and wide range displacement measurement based on planar grating (United States)

    Lin, Jie; Guan, Jian; Wen, Feng; Tan, Jiubin


    High/ultra-precision motion measurements for precision translation stages are highly desired in modern manufacturing systems and instruments. In this work, we introduce a wide range three-axis grating encoder with nanometric resolution, which can measure the x-, y- and z-axial translational motions of a stage simultaneously. The grating encoder is composed of a reflective-type planar scale grating with a period of 8 μm and an optical reading head. A planar reference grating, which is the same as the planar scale grating except the length and width, is employed in the optical reading head. The x- and y- directional ±1st order diffractive beams of the planar scale grating interfere with the corresponding diffractive beams of the planar reference grating, forming the measurement signals. The x- and y- directional ±1st order diffractive beams of the two planar gratings propagate against their original incident path, working as the autocollimatic diffractive beams. Therefore, the z-axial measurement range of the proposed grating encoder is greatly enhanced. The x- and y- axial measurement ranges depend on the size of the planar scale grating. To make the grating encoder more compact, a double grating beam-splitting (DGBS) unit and two diffractive optical elements (DOEs) are introduced. The experimental results indicate that the z-axial displacement resolution is as high as 4 nm with an electronic data division card of 80 segments developed by our lab.

  3. Acoustic radiation force control: Pulsating spherical carriers. (United States)

    Rajabi, Majid; Mojahed, Alireza


    The interaction between harmonic plane progressive acoustic beams and a pulsating spherical radiator is studied. The acoustic radiation force function exerted on the spherical body is derived as a function of the incident wave pressure and the monopole vibration characteristics (i.e., amplitude and phase) of the body. Two distinct strategies are presented in order to alter the radiation force effects (i.e., pushing and pulling states) by changing its magnitude and direction. In the first strategy, an incident wave field with known amplitude and phase is considered. It is analytically shown that the zero- radiation force state (i.e., radiation force function cancellation) is achievable for specific pulsation characteristics belong to a frequency-dependent straight line equation in the plane of real-imaginary components (i.e., Nyquist Plane) of prescribed surface displacement. It is illustrated that these characteristic lines divide the mentioned displacement plane into two regions of positive (i.e., pushing) and negative (i.e., pulling) radiation forces. In the second strategy, the zero, negative and positive states of radiation force are obtained through adjusting the incident wave field characteristics (i.e., amplitude and phase) which insonifies the radiator with prescribed pulsation characteristics. It is proved that zero radiation force state occurs for incident wave pressure characteristics belong to specific frequency-dependent circles in Nyquist plane of incident wave pressure. These characteristic circles divide the Nyquist plane into two distinct regions corresponding to positive (out of circles) and negative (in the circles) values of radiation force function. It is analytically shown that the maximum amplitude of negative radiation force is exactly equal to the amplitude of the (positive) radiation force exerted upon the sphere in the passive state, by the same incident field. The developed concepts are much more deepened by considering the required

  4. Characterizing Student Mathematics Teachers' Levels of Understanding in Spherical Geometry (United States)

    Guven, Bulent; Baki, Adnan


    This article presents an exploratory study aimed at the identification of students' levels of understanding in spherical geometry as van Hiele did for Euclidean geometry. To do this, we developed and implemented a spherical geometry course for student mathematics teachers. Six structured, "task-based interviews" were held with eight student…

  5. Cylindrical and spherical dust-acoustic wave modulations in dusty ...

    Indian Academy of Sciences (India)

    The nonlinear wave modulation of planar and non-planar (cylindrical and spherical) dust-acoustic waves (DAW) propagating in dusty plasmas, in the presence of non-extensive distributions for ions and electrons is investigated. By employing multiple scales technique, a cylindrically and spherically modified nonlinear ...

  6. Effect of the spherical Earth on a simple pendulum


    Burko, Lior M.


    We consider the period of a simple pendulum in the gravitational field of the spherical Earth. Effectively, gravity is enhanced compared with the often used flat Earth approximation, such that the period of the pendulum is shortened. We discuss the flat Earth approximation, and show when the corrections due to the spherical Earth may be of interest.

  7. Spherical dust acoustic solitary waves with two temperature ions

    CERN Document Server

    Eslami, Esmaeil


    The nonlinear dust acoustic waves in unmagnetized dusty plasma which consists of two temperature Boltzmann distributed ions and Boltzmann distributed electrons in spherical dimension investigated and obtained spherical Kadomtsev Petviashvili (SKP) equation and shown that the dust acoustic solitary wave can exist in the SKP equation.

  8. Rapid Prototyping of Electrically Small Spherical Wire Antennas

    DEFF Research Database (Denmark)

    Kim, Oleksiy S.


    It is shown how modern rapid prototyping technologies can be applied for quick and inexpensive, but still accurate, fabrication of electrically small wire antennas. A well known folded spherical helix antenna and a novel spherical zigzag antenna have been fabricated and tested, exhibiting the imp...

  9. demonstrating close-packing of atoms using spherical bubble gums

    African Journals Online (AJOL)


    ABSTRACT: In this paper, the use of spherical bubble gums (Gum Balls) to demonstrate the close-packing of atoms and ions is presented. Spherical bubble gums having distinctive colours were used to illustrate the different layers in variety of crystalline packing and the formation of tetrahedral and octahedral holes.

  10. Development of a spherical aerial vehicle for urban search (United States)

    Hou, Kang; Sun, Hanxu; Jia, Qingxuan; Zhang, Yanheng


    With the ability to provide close surveillance in narrow space or urban areas, spherical aerial vehicles have been of great interest to many scholars and researchers. The spherical aerial vehicle offers substantial design advantages over the conventional small aerial vehicles. As a kind of small aerial vehicles, spherical aerial vehicle is presented in this paper. Firstly, the unique structure of spherical aerial vehicle is presented in detail. And then as the key component of the spherical aerial vehicle, the meshed spherical shell is analyzed. The shell is made of carbon fiber and is used to protect the inner devices, so the deformation of the shell is analyzed and simulated. Then the experimental results verify the above analysis and the composite carbon fiber material makes the mesh spherical shell small deformation. Considering the whole vehicle has a shell outside, the lift affect of the meshed spherical shell is analyzed. The simulation and experiment results are basically consistent with theoretical analysis, and the impact of the meshed shell has small resistance for the airflow through the sphere.

  11. Some spherical analysis related to the pairs (U (n), Hn)

    Indian Academy of Sciences (India)

    In this paper, we define the normalized spherical transform associated with the generalized Gelfand pair ( U ( p , q ) , H n ) , where H n is the Heisenberg group 2 + 1-dimensional and + = . We show that the normalized spherical transform F ( f ) of a Schwartz function on H n restricted to the spectrum of the Gelfand ...

  12. Calculated scan characteristics of a large spherical reflector antenna (United States)

    Agrawal, P. K.; Croswell, W. F.; Kauffman, J. F.


    A previously published numerical method to calculate the radiation properties of parabolic reflectors has been modified to also include very large spherical reflectors. The method has been verified by comparing the calculated and the measured results for a 120-wavelength spherical reflector.

  13. Cylindrical and spherical dust-acoustic wave modulations in dusty ...

    Indian Academy of Sciences (India)

    Abstract. The nonlinear wave modulation of planar and non-planar (cylindrical and spherical) dust-acoustic waves (DAW) propagating in dusty plasmas, in the presence of non-extensive distribu- tions for ions and electrons is investigated. By employing multiple scales technique, a cylindrically and spherically modified ...

  14. On spherically symmetric singularity-free models in relativistic ...

    Indian Academy of Sciences (India)

    These observations led to the search of spherically symmetric singularity-free cosmo- logical models with a perfect fluid source characterized by isotropic pressure This search resulted in construction of two spherically symmetric singularity-free relativistic cosmo- logical models, describing universes filled with non-adiabatic ...

  15. A Robust Solution of the Spherical Burmester Problem

    DEFF Research Database (Denmark)

    Angeles, Jorge; Bai, Shaoping


    The problem of spherical four-bar linkage synthesis is revisited in this paper. The work is aimed at developing a robust synthesis method by taking into account both the formulation and the solution method. In addition, the synthesis of linkages with spherical prismatic joints is considered...

  16. Creep stresses in a spherical shell under steady state temperature (United States)

    Verma, Gaurav; Rana, Puneet


    The paper investigates the problem of creep of a spherical structure under the influence of steady state temperature. The problem of creep in spherical shell is solved by using the concept of generalized strain measures and transition hypothesis given by Seth. The problem has reduced to non-linear differential equation for creep transition. This paper deals with the non-linear behaviour of spherical shell under thermal condition. The spherical shell structures are easily vulnerable to creep, shrinkage and thermal effects; a thorough understanding of their time-dependent behaviour has been fully established. The paper aims to provide thermal creep analysis to enhance the effective design and long life of shells, and a theoretical model is developed for calculating creep stresses and strains in a spherical shell with purpose. Results obtained for the problem are depicted graphically.

  17. Theory and applications of spherical microphone array processing

    CERN Document Server

    Jarrett, Daniel P; Naylor, Patrick A


    This book presents the signal processing algorithms that have been developed to process the signals acquired by a spherical microphone array. Spherical microphone arrays can be used to capture the sound field in three dimensions and have received significant interest from researchers and audio engineers. Algorithms for spherical array processing are different to corresponding algorithms already known in the literature of linear and planar arrays because the spherical geometry can be exploited to great beneficial effect. The authors aim to advance the field of spherical array processing by helping those new to the field to study it efficiently and from a single source, as well as by offering a way for more experienced researchers and engineers to consolidate their understanding, adding either or both of breadth and depth. The level of the presentation corresponds to graduate studies at MSc and PhD level. This book begins with a presentation of some of the essential mathematical and physical theory relevant to ...

  18. Nanoimprinted reflecting gratings for long-range surface plasmon polaritons

    DEFF Research Database (Denmark)

    Pedersen, Rasmus Haugstrup; Boltasseva, Alexandra; Johansen, Dan Mario


    We present a novel design, fabrication, and characterization of reflecting gratings for long-range surface plasmon polaritons (LR-SPPs) at telecom wavelengths. LR-SPP waveguides consisting of a thin (12 nm) gold film embedded in a thick (45 μm) layer of dielectric polymer cladding are structured...

  19. Bragg gratings in index-guiding photonic crystal fibres

    DEFF Research Database (Denmark)

    Riishede, Jesper; Hougaard, Kristian G.; Libori, S.E. Barkou


    A numerical investigation of coupling coefficients of Bragg-gratings in index-guiding photonic crystal fibres is presented. It is shown that index-guiding photonic crystal fibres have larger coupling coefficients for fibres with small core areas than step-index fibres....

  20. A Manually Operated Cassava Grating Machine | Odigboh | Nigerian ...

    African Journals Online (AJOL)

    The design and development of a manually operated cassava grating machine prototype are presented. The prototype grater is shown to be easy to operate at 30 - 45 rpm to give a product whose quality is as good as that from motorized graters at a throughput of 125 - 185 kg/h. The prototype grater is a powerful alternative ...

  1. First Results of ISO-SWS Grating Observations of Saturn

    NARCIS (Netherlands)

    de Graauw, Th.; Encrenaz, Th.; Schaeidt, S.; Lellouch, E.; Feuchtgruber, H.; Beintema, D. A.; Bezard, B.; Drossart, P.; Griffin, M.; Heras, A.; Kessler, M.; Leech, K.; Morris, A.; Roelfsema, P. R.; Roos-Serote, M.; Salama, A.; Vandenbussche, B.; Valentijn, E. A.; Davies, G. R.; Naylor, D. A.


    The spectrum of Saturn has been recorded between 2.3 and 15 mu m, on June 13, 1996, with the grating mode of the Short-Wavelength Spectrometer of ISO (Infrared Space Observatory). The resolving power is about 1500 and the sensitivity is better than 1 Jy. As compared to Jupiter, the spectrum of

  2. Fresnel equations and transmission line analogues for diffraction gratings

    Energy Technology Data Exchange (ETDEWEB)

    Kaushik, S.


    A simple and intuitive formalism is presented to describe diffraction in multi-layered periodic structures. We use the well known results from scalar analysis (wave propagation in homogeneous layered media) and show that they can be generalized rather readily to vector problems such as diffraction analysis. Specifically, we derive: (1) generalized Fresnel equations appropriate for reflection and transmission from an infinitely thick grating, (2) a generalized Airy formula for thin-film to describe reflection and transmission of light through a lamellar grating and (3) a matrix propagation method akin to that used for multi-layer thin film analysis. The results developed here complement the recent work on R-matrix and S-matrix propagation algorithms that have been used in connection with modal and differential grating theories. These algorithms have proven to be numerically stable for calculating diffraction efficiencies from deep groove gratings. The formalism developed here expands upon the earlier literature by providing important details that are hitherto unavailable.

  3. Recording multiple holographic gratings in silver-doped ...

    Indian Academy of Sciences (India)

    Poly(vinyl alcohol) (PVA) acrylamide-based photopolymers have been widely studied because of their excellent properties like high sensitivity, high diffraction .... be due to the consumption of the dynamic range of the photopolymer film as each new grating is recorded. The dynamic range (M/#) was calculated using the.

  4. Tuning Fano resonances of graphene-based gratings (United States)

    de Ceglia, Domenico; Vincenti, Maria A.; Grande, Marco; Bianco, Giuseppe Valerio; Bruno, Giovanni; D'Orazio, Antonella; Scalora, Michael


    We present a strategy to control Fano resonances in hybrid graphene-silicon-on-insulator gratings. The presence of a mono- or few-layer graphene film allows to electrically and/or chemically tuning the Fano resonances that result from the interaction of narrow-band, quasi-normal modes and broad-band, Fabry-Perot-like modes. Transmission, reflection and absorption spectra undergo significant modulations under the application of a static voltage to the graphene film. In particular, for low values of the graphene chemical potential, the structure exhibits a symmetric Lorentzian resonance; when the chemical potential increases beyond a specific threshold, the grating resonance becomes Fano-like, hence narrower and asymmetric. This transition occurs when the graphene optical response changes from that of a lossy dielectric medium into that of a low-loss metal. Further increasing the chemical potential allows to blue-shift the Fano resonance, leaving its shape and linewidth virtually unaltered. We provide a thorough description of the underlying physics by resorting to the quasi-normal mode description of the resonant grating and retrieve perturbative expressions for the characteristic wavelength and linewidth of the resonance. The roles of number of graphene layers, waveguide-film thickness and graphene quality on the tuning abilities of the grating will be discussed. Although developed for infrared telecom wavelengths and silicon-on-insulator technology, the proposed structure can be easily designed for other wavelengths, including visible, far-infrared and terahertz, and other photonic platforms.

  5. Optical fibre Bragg grating recorded in TOPAS cyclic olefin copolymer

    DEFF Research Database (Denmark)

    Johnson, I.P.; Yuan, Scott Wu; Stefani, Alessio


    A report is presented on the inscription of a fibre Bragg grating into a microstructured polymer optical fibre fabricated from TOPAS cyclic olefin copolymer. This material offers two important advantages over poly (methyl methacrylate), which up to now has formed the basis for polymer fibre Bragg...

  6. Rational solitons in deep nonlinear optical Bragg grating

    NARCIS (Netherlands)

    Alatas, H.; Iskandar, A.A.; Tjia, M.O.; Valkering, T.P.


    We have examined the rational solitons in the Generalized Coupled Mode model for a deep nonlinear Bragg grating. These solitons are the degenerate forms of the ordinary solitons and appear at the transition lines in the parameter plane. A simple formulation is presented for the investigation of the

  7. Grating Lobes Prediction in 3D Array Antennas

    NARCIS (Netherlands)

    Bentum, Marinus Jan; Bosma, Sjoerd; Bruinsma, Wessel P.; Hes, Robin P.; Lager, Ioan E.


    This papers discusses an effective framework for determining the number and direction of all possible grating lobes in the case of three-dimensional (3D) array antennas. Illustrating examples support the introduced theoretical concepts. The analysis highlights some intrinsic benefits of using 3D

  8. High-sensitivity bend angle measurements using optical fiber gratings. (United States)

    Rauf, Abdul; Zhao, Jianlin; Jiang, Biqiang


    We present a high-sensitivity and more flexible bend measurement method, which is based on the coupling of core mode to the cladding modes at the bending region in concatenation with optical fiber grating serving as band reflector. The characteristics of a bend sensing arm composed of bending region and optical fiber grating is examined for different configurations including single fiber Bragg grating (FBG), chirped FBG (CFBG), and double FBGs. The bend loss curves for coated, stripped, and etched sections of fiber in the bending region with FBG, CFBG, and double FBG are obtained experimentally. The effect of separation between bending region and optical fiber grating on loss is measured. The loss responses for single FBG and CFBG configurations are compared to discover the effectiveness for practical applications. It is demonstrated that the sensitivity of the double FBG scheme is twice that of the single FBG and CFBG configurations, and hence acts as sensitivity multiplier. The bend loss response for different fiber diameters obtained through etching in 40% hydrofluoric acid, is measured in double FBG scheme that resulted in a significant increase in the sensitivity, and reduction of dead-zone.

  9. PDMS-based waveguides with surface relief Bragg grating (United States)

    Goraus, Matej; Pudis, Dusan; Jandura, Daniel; Berezina, Sofia


    In this paper we present fabrication process of waveguides with surface relief Bragg grating (SR-BG) embossed in poly dimethyl diphenyl siloxane (PDMDPS). Generally, the Bragg grating causes spectral selectivity of propagated light in optical fibers and optical waveguides. We prepared the original concept of fabrication of novel optical waveguides with SR-BG using the laser interference lithography in combination with embossing process of liquid polymer. We used laser interference lithography in Mach-Zehnder configuration to create a grating with period of 21 μm in thin photoresist layer. In this manner, we created an array of D-shaped waveguides of 10 μm wide and app. 2.5 μm high. SR-BG was created in the next step, where the one dimensional surface Bragg grating with period 1.64 μm was prepared by interference lithography. This period was designed to reflect narrow spectral band close the telecommunication wavelength of 1.55 μm. Quality of the prepared waveguides and SR-BG was confirmed from atomic force microscope analysis. Transmission and coupling properties of the prepared SR-BG waveguides were finally measured by spectral measurements in infrared spectral region.

  10. Design of vibration sensor based on fiber Bragg grating (United States)

    Zhang, Zhengyi; Liu, Chuntong


    Fiber grating is a kind of new type of fiber optic light source device which has been rapidly changing in the refractive index of the core in recent years. Especially, it can realize the high precision of the external parameters by means of the special structure design and the encapsulation technology [1, 2]. In this paper, a fiber grating vibration sensor which is suitable for vibration monitoring in key areas is designed based on the technical background of vibration monitoring system. The sensor uses a single beam structure and pastes the fiber Bragg grating (FBG) to measure the vibration wavelength on the surface. When the vibration is simply harmonic vibration, the Bragg reflection wavelength will change periodically, and the periodic variation of the wavelength curve can be measured by the fiber grating demodulator, then the correctness of the experimental results is verified. In this paper, through the analysis of the data measured by the demodulator, the MATLAB software is used to verify the data, and the different frequency domains, the modes, and the phase frequency curves are obtained. The measurement range is 0 Hz-100 Hz, and the natural frequency is 90.6 Hz.

  11. Development of generalised model for grate combustion of biomass

    DEFF Research Database (Denmark)

    Rosendahl, Lasse; Kær, Søren Knudsen; Sørensen, Henrik

    of the grate, and it is not likely that this is representative for the motion within the layer. Finally, as the model complexity grows, model turnover time increases to a level where it is comparable to that of the full furnace model. In order to proceed and address the goals of the first paragraph...

  12. Gratefulness as a Life Principle: Essence and Diagnostics (United States)

    Safronova, Elena M.; Beylinson, Lyubov S.; Zolotykh, Natalia V.; Shevchenko, Tatyana Yu.


    The objective of this paper is to present the results of the study detailing the essence of the "gratefulness" phenomenon as a quintessence of morality in the context of today's world and its values. The methods of the research were theoretical analysis of the works of philosophers, psychologists, philologists, and pedagogues on the…

  13. Polarization-Independent Wideband High-Index-Contrast Grating Mirror

    DEFF Research Database (Denmark)

    Bekele, Dagmawi Alemayehu; Park, Gyeong Cheol; Malureanu, Radu


    Island-type two-dimensional high-index-contrast grating mirror based on a standard silicon-on-insulator wafer have been experimentally demonstrated. The measured spectra shows a bandwidth of ∼192 nm with a reflectivity over 99% as well as polarization independence. Numerical simulations show...... that the designed mirror has large tolerance to fabrication errors....

  14. 21 CFR 133.148 - Hard grating cheeses. (United States)


    ... 21 Food and Drugs 2 2010-04-01 2010-04-01 false Hard grating cheeses. 133.148 Section 133.148 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) FOOD FOR... harmless preparation of enzymes of animal or plant origin capable of aiding in the curing or development of...

  15. Optimization for sinusoidal profiles in surface relief gratings ...

    Indian Academy of Sciences (India)


    Feb 7, 2014 ... sure for 90 s and chemical development for 15 s were observed to be optimum for the translation of the sinusoidal ... gratings for the development of next generation photonics devices [1,2] based on reso- ... may be chosen to be sinusoidal, rectangular or saw-tooth depending on the requirements of GWS ...


    NARCIS (Netherlands)

    Knoester, Jasper


    A theory is presented that microscopically accounts for the role of polariton propagation in the transient grating experiment. The basis of our theory is formed by coupled equations of motion for polariton amplitudes and coherences, in which we account for polariton-phonon scattering. It is

  17. Diffraction from relief gratings on a biomimetic elastomer cast

    Energy Technology Data Exchange (ETDEWEB)

    Guerrero, Raphael A., E-mail: [Department of Physics, Ateneo de Manila University, Loyola Heights, Quezon City (Philippines); Aranas, Erika B. [Department of Physics, Ateneo de Manila University, Loyola Heights, Quezon City (Philippines)


    Biomimetic optical elements combine the optimized designs of nature with the versatility of materials engineering. We employ a beetle carapace as the template for fabricating relief gratings on an elastomer substrate. Biological surface features are successfully replicated by a direct casting procedure. Far-field diffraction effects are discussed in terms of the Fraunhofer approximation in Fourier space.

  18. Investigations on birefringence effects in polymer optical fiber Bragg gratings (United States)

    Hu, X.; Sáez-Rodríguez, D.; Bang, O.; Webb, D. J.; Caucheteur, C.


    Step-index polymer optical fiber Bragg gratings (POFBGs) and microstructured polymer optical fiber Bragg gratings (mPOFBGs) present several attractive features, especially for sensing purposes. In comparison to FBGs written in silica fibers, they are more sensitive to temperature and pressure because of the larger thermo-optic coefficient and smaller Young's modulus of polymer materials. (M)POFBGs are most often photowritten in poly(methylmethacrylate) (PMMA) materials using a continuous-wave 325 nm HeCd laser. For the first time to the best of our knowledge, we study photoinduced birefringence effects in (m)POFBGs. To achieve this, highly reflective gratings were inscribed with the phase mask technique. They were then monitored in transmission with polarized light. For this, (m)POF sections a few cm in length containing the gratings were glued to angled silica fibers. Polarization dependent loss (PDL) and differential group delay (DGD) were computed from the Jones matrix eigenanalysis using an optical vector analyser. Maximum values exceeding several dB and a few picoseconds were obtained for the PDL and DGD, respectively. The response to lateral force was finally investigated. As it induces birefringence in addition to the photo-induced one, an increase of the PDL and DGD values were noticed.

  19. Nonperiodic metallic gratings transparent for broadband terahertz waves (United States)

    Fan, Ren-Hao; Ren, Xiao-Ping; Peng, Ru-Wen; Huang, Xian-Rong; Wang, Mu

    Recently, we demonstrate both theoretically and experimentally that nonperiodic metallic gratings can become transparent for broadband terahertz waves. Quasiperiodic and disordered metallic gratings effectively weaken and even eliminate Wood's anomalies, which are the diffraction-related characters of periodic gratings. Consequently, both the transparence bandwidth and transmission efficiency are significantly increased due to the structural aperiodicity. Furthermore, we show that for a specific light source, for example, a line source, a corresponding nonperiodic transparent grating can be also designed. We expect that our findings can be applied for transparent conducting panels, perfect white-beam polarizers, antireflective conducting solar cells, and beyond. References: X. P. Ren, R. H. Fan, R. W. Peng, X. R. Huang, D. H. Xu, Y. Zhou, and Mu Wang, Physical Review B, 91, 045111 (2015); R. H. Fan, R. W. Peng, X. R. Huang, J. Li, Y. Liu, Q. Hu, Mu. Wang, and X. Zhang, Advanced Materials, 24, 1980 (2012); and X. R. Huang, R. W. Peng, and R. H. Fan. Physical Review Letters, 105, 243901 (2010).

  20. ISO observations of Titan with SWS/grating (United States)

    Coustenis, A.; Encrenaz, T.; Salama, A.; Lellouch, E.; Gautier, D.; Kessler, M. F.; deGraauw, T.; Samuelson, R. E.; Bjoraker, G.; Orton, G.


    The observations of Titan performed by the Infrared Space Observatory (ISO) short wavelength spectrometer (SWS), in the 2 micrometer to 45 micrometer region using the grating mode, are reported on. Special attention is given to data from Titan concerning 7 micrometer to 45 micrometer spectral resolution. Future work for improving Titan's spectra investigation is suggested.

  1. Measurement of gas flow velocities by laser-induced gratings

    Energy Technology Data Exchange (ETDEWEB)

    Hemmerling, B.; Stampanoni-Panariello, A. [Paul Scherrer Inst. (PSI), Villigen (Switzerland); Kozlov, A.D.N. [General Physics Institute, Moscow (Russian Federation)


    Time resolved light scattering from laser-induced electrostrictive gratings was used for the determination of flow velocities in air at room temperature. By measuring the velocity profile across the width of a slit nozzle we demonstrated the high spatial resolution (about 200 mm) of this novel technique. (author) 3 figs., 1 ref.

  2. Single-Molecule Detection in Nanogap-Embedded Plasmonic Gratings

    Directory of Open Access Journals (Sweden)

    Biyan Chen


    Full Text Available We introduce nanogap-embedded silver plasmonic gratings for single-molecule (SM visualization using an epifluorescence microscope. This silver plasmonic platform was fabricated by a cost-effective nano-imprint lithography technique, using an HD DVD template. DNA/ RNA duplex molecules tagged with Cy3/Cy5 fluorophores were immobilized on SiO 2 -capped silver gratings. Light was coupled to the gratings at particular wavelengths and incident angles to form surface plasmons. The SM fluorescence intensity of the fluorophores at the nanogaps showed approximately a 100-fold mean enhancement with respect to the fluorophores observed on quartz slides using an epifluorescence microscope. This high level of enhancement was due to the concentration of surface plasmons at the nanogaps. When nanogaps imaged with epifluorescence mode were compared to quartz imaged using total internal reflection fluorescence (TIRF microscopy, more than a 30-fold mean enhancement was obtained. Due to the SM fluorescence enhancement of plasmonic gratings and the correspondingly high emission intensity, the required laser power can be reduced, resulting in a prolonged detection time prior to photobleaching. This simple platform was able to perform SM studies with a low-cost epifluorescence apparatus, instead of the more expensive TIRF or confocal microscopes, which would enable SM analysis to take place in most scientific laboratories.

  3. Effects of coating spherical iron oxide nanoparticles. (United States)

    Milosevic, Irena; Motte, Laurence; Aoun, Bachir; Li, Tao; Ren, Yang; Sun, Chengjun; Saboungi, Marie-Louise


    We investigate the effect of several coatings applied in biomedical applications to iron oxide nanoparticles on the size, structure and composition of the particles. The four structural techniques employed - TEM, DLS, VSM, SAXS and EXAFS - show no significant effects of the coatings on the spherical shape of the bare nanoparticles, the average sizes or the local order around the Fe atoms. The NPs coated with hydroxylmethylene bisphosphonate or catechol have a lower proportion of magnetite than the bare and citrated ones, raising the question whether the former are responsible for increasing the valence state of the oxide on the NP surfaces and lowering the overall proportion of magnetite in the particles. VSM measurements show that these two coatings lead to a slightly higher saturation magnetization than the citrate. This article is part of a Special Issue entitled "Science for Life" Guest Editor: Dr. Austen Angell, Dr. Salvatore Magazù and Dr. Federica Migliardo. Copyright © 2016 Elsevier B.V. All rights reserved.

  4. Spherical Process Models for Global Spatial Statistics

    KAUST Repository

    Jeong, Jaehong


    Statistical models used in geophysical, environmental, and climate science applications must reflect the curvature of the spatial domain in global data. Over the past few decades, statisticians have developed covariance models that capture the spatial and temporal behavior of these global data sets. Though the geodesic distance is the most natural metric for measuring distance on the surface of a sphere, mathematical limitations have compelled statisticians to use the chordal distance to compute the covariance matrix in many applications instead, which may cause physically unrealistic distortions. Therefore, covariance functions directly defined on a sphere using the geodesic distance are needed. We discuss the issues that arise when dealing with spherical data sets on a global scale and provide references to recent literature. We review the current approaches to building process models on spheres, including the differential operator, the stochastic partial differential equation, the kernel convolution, and the deformation approaches. We illustrate realizations obtained from Gaussian processes with different covariance structures and the use of isotropic and nonstationary covariance models through deformations and geographical indicators for global surface temperature data. To assess the suitability of each method, we compare their log-likelihood values and prediction scores, and we end with a discussion of related research problems.

  5. Natural melting within a spherical shell (United States)

    Bahrami, Parviz A.


    Fundamental heat transfer experiments were performed on the melting of a phase change medium in a spherical shell. Free expansion of the medium into a void space within the sphere was permitted. A step function temperature jump on the outer shell wall was imposed and the timewise evolution of the melting process and the position of the solid-liquid interface was photographically recorded. Numerical integration of the interface position data yielded information about the melted mass and the energy of melting. It was found that the rate of melting and the heat transfer were significantly affected by the movement of the solid medium to the base of the sphere due to gravity. The energy transfer associated with melting was substantially higher than that predicted by the conduction model. Furthermore, the radio of the measured values of sensible energy in the liquid melt to the energy of melting were nearly proportional to the Stefan number. The experimental results are in agreement with a theory set forth in an earlier paper.

  6. The Spherical Tokamak MEDUSA for Costa Rica (United States)

    Ribeiro, Celso; Vargas, Ivan; Guadamuz, Saul; Mora, Jaime; Ansejo, Jose; Zamora, Esteban; Herrera, Julio; Chaves, Esteban; Romero, Carlos


    The former spherical tokamak (ST) MEDUSA (Madison EDUcation Small Aspect.ratio tokamak, Rphysics /technical related issues which will help all tasks of the very low aspect ratio stellarator SCR-1(A≡R/>=3.6, under design[2]) and also the ongoing activities in low temperature plasmas. Courses in plasma physics at undergraduate and post-graduate joint programme levels are regularly conducted. The scientific programme is intend to clarify several issues in relevant physics for conventional and mainly STs, including transport, heating and current drive via Alfv'en wave, and natural divertor STs with ergodic magnetic limiter[3,4]. [1] G.D.Garstka, PhD thesis, University of Wisconsin at Madison, 1997 [2] L.Barillas et al., Proc. 19^th Int. Conf. Nucl. Eng., Japan, 2011 [3] C.Ribeiro et al., IEEJ Trans. Electrical and Electronic Eng., 2012(accepted) [4] C.Ribeiro et al., Proc. 39^th EPS Conf. Contr. Fusion and Plasma Phys., Sweden, 2012

  7. A spherical cavity model for quadrupolar dielectrics (United States)

    Dimitrova, Iglika M.; Slavchov, Radomir I.; Ivanov, Tzanko; Mosbach, Sebastian


    The dielectric properties of a fluid composed of molecules possessing both dipole and quadrupole moments are studied based on a model of the Onsager type (molecule in the centre of a spherical cavity). The dielectric permittivity ɛ and the macroscopic quadrupole polarizability αQ of the fluid are related to the basic molecular characteristics (molecular dipole, polarizability, quadrupole, quadrupolarizability). The effect of αQ is to increase the reaction field, to bring forth reaction field gradient, to decrease the cavity field, and to bring forth cavity field gradient. The effects from the quadrupole terms are significant in the case of small cavity size in a non-polar liquid. The quadrupoles in the medium are shown to have a small but measurable effect on the dielectric permittivity of several liquids (Ar, Kr, Xe, CH4, N2, CO2, CS2, C6H6, H2O, CH3OH). The theory is used to calculate the macroscopic quadrupolarizabilities of these fluids as functions of pressure and temperature. The cavity radii are also determined for these liquids, and it is shown that they are functions of density only. This extension of Onsager's theory will be important for non-polar solutions (fuel, crude oil, liquid CO2), especially at increased pressures.

  8. Scaling regimes in spherical shell rotating convection

    CERN Document Server

    Gastine, T; Aubert, J


    Rayleigh-B\\'enard convection in rotating spherical shells can be considered as a simplified analogue of many astrophysical and geophysical fluid flows. Here, we use three-dimensional direct numerical simulations to study this physical process. We construct a dataset of more than 200 numerical models that cover a broad parameter range with Ekman numbers spanning $3\\times 10^{-7} \\leq E \\leq 10^{-1}$, Rayleigh numbers within the range $10^3 < Ra < 2\\times 10^{10}$ and a Prandtl number unity. We investigate the scaling behaviours of both local (length scales, boundary layers) and global (Nusselt and Reynolds numbers) properties across various physical regimes from onset of rotating convection to weakly-rotating convection. Close to critical, the convective flow is dominated by a triple force balance between viscosity, Coriolis force and buoyancy. For larger supercriticalities, a subset of our numerical data approaches the asymptotic diffusivity-free scaling of rotating convection $Nu\\sim Ra^{3/2}E^{2}$ in ...

  9. Spherical collapse in νΛCDM (United States)

    LoVerde, Marilena


    The abundance of massive dark matter halos hosting galaxy clusters provides an important test of the masses of relic neutrino species. The dominant effect of neutrino mass is to lower the typical amplitude of density perturbations that eventually form halos, but for neutrino masses ≳0.4 eV the threshold for halo formation can be changed significantly as well. We study the spherical collapse model for halo formation in cosmologies with neutrino masses in the range mνi=0.05-1 eV and find that halo formation is differently sensitive to Ων and mν. That is, different neutrino hierarchies with a common Ων are in principle distinguishable. The added sensitivity to mν is small but potentially important for scenarios with heavier sterile neutrinos. Massive neutrinos cause the evolution of density perturbations to be scale dependent at high redshift which complicates the usual mapping between the collapse threshold and halo abundance. We propose one way of handling this and compute the correction to the halo mass function within this framework. For ∑mνi≲0.3 eV, our prescription for the halo abundance is only ≲15% different than the standard calculation. However for larger neutrino masses the differences approach 50-100% which, if verified by simulations, could alter neutrino mass constraints from cluster abundance.

  10. Drop impact on spherical soft surfaces (United States)

    Chen, Simeng; Bertola, Volfango


    The impact of water drops on spherical soft surfaces is investigated experimentally through high-speed imaging. The effect of a convex compliant surface on the dynamics of impacting drops is relevant to various applications, such as 3D ink-jet printing, where drops of fresh material impact on partially cured soft substrates with arbitrary shape. Several quantities which characterize the morphology of impacting drops are measured through image-processing, including the maximum and minimum spreading angles, length of the wetted curve, and dynamic contact angle. In particular, the dynamic contact angle is measured using a novel digital image-processing scheme based on a goniometric mask, which does not require edge fitting. It is shown that the surface with a higher curvature enhances the retraction of the spreading drop; this effect may be due to the difference of energy dissipation induced by the curvature of the surface. In addition, the impact parameters (elastic modulus, diameter ratio, and Weber number) are observed to significantly affect the dynamic contact angle during impact. A quantitative estimation of the deformation energy shows that it is significantly smaller than viscous dissipation.

  11. A nonlinear elasticity phantom containing spherical inclusions (United States)

    Pavan, Theo Z.; Madsen, Ernest L.; Frank, Gary R.; Jiang, Jingfeng; Carneiro, Antonio A. O.; Hall, Timothy J.


    The strain image contrast of some in vivo breast lesions changes with increasing applied load. This change is attributed to differences in the nonlinear elastic properties of the constituent tissues suggesting some potential to help classify breast diseases by their nonlinear elastic properties. A phantom with inclusions and long-term stability is desired to serve as a test bed for nonlinear elasticity imaging method development, testing, etc. This study reports a phantom designed to investigate nonlinear elastic properties with ultrasound elastographic techniques. The phantom contains four spherical inclusions and was manufactured from a mixture of gelatin, agar and oil. The phantom background and each of the inclusions have distinct Young's modulus and nonlinear mechanical behavior. This phantom was subjected to large deformations (up to 20%) while scanning with ultrasound, and changes in strain image contrast and contrast-to-noise ratio between inclusion and background, as a function of applied deformation, were investigated. The changes in contrast over a large deformation range predicted by the finite element analysis (FEA) were consistent with those experimentally observed. Therefore, the paper reports a procedure for making phantoms with predictable nonlinear behavior, based on independent measurements of the constituent materials, and shows that the resulting strain images (e.g., strain contrast) agree with that predicted with nonlinear FEA.

  12. Phase contrast microscopy with fringe contrast adjustable by using grating-based phase-shifter. (United States)

    Zheng, Juanjuan; Yao, Baoli; Gao, Peng; Ye, Tong


    In this paper a new phase contrast method with fringe contrast adjustable is proposed. In the Fourier plane of the object wave, two Ronchi gratings i.e., a central grating and a surrounding grating, are used to modulate the phases of the undiffracted and diffracted components, respectively. By loading the two gratings separately on spatial light modulator, the undiffracted and diffracted components can be measured independently, which simplify greatly the reconstruction process. Besides, the fringe contrast of the phase contrast interferogram can be adjusted by changing the modulation depth of the two gratings. The feasibility of the proposed method is verified by theoretical analysis and experiment.

  13. Development and optical performance tests of the Si immersed grating demonstrator for E-ELT METIS (United States)

    Navarro, Ramon; Agócs, Tibor; Venema, Lars; van Amerongen, Aaldert H.; Rodenhuis, Michiel; Hoogeveen, Ruud W. M.; Coppens, Tonny; Brandl, Bernhard R.; Vink, Ramon


    Immersed gratings offer several advantages over conventional gratings: more compact spectrograph designs, and by using standard semiconductor industry techniques, higher diffraction-efficiency and lower stray-light can be achieved. We present the optical tests of the silicon immersed grating demonstrator for the Mid-infrared E-ELT Imager and Spectrograph, METIS. We detail the interferometric tests that were done to measure the wavefront-error and present the results of the throughput and stray-light measurements. We also elaborate on the challenges encountered and lessons learned during the immersed grating demonstrator test campaign that helped us to improve the fabrication processes of the grating patterning on the wafer.

  14. Distributed delay-line interferometer based on a Bragg grating in transmission mode

    CERN Document Server

    Preciado, Miguel A; Shu, Xuewen; Sugden, Kate


    A novel approach for a delay line interferometer (DLI) based purely on forward Bragg scattering is proposed. We have numerically and experimentally demonstrated that a Bragg grating can deliver the functionality of a DLI in its transmission mode along a single common interfering optical path, instead of the conventional DLI implementation with two interfering optical paths. As a proof of concept, a fiber Bragg grating has been designed and fabricated, showing the desired functionality in the transmission mode of the Bragg grating. The proposed "Bragg-DLI" approach is applicable to any kind of Bragg grating technology, such as volume Bragg gratings, dielectric mirrors, silicon photonics, and other optical waveguide based Bragg structures.

  15. Development of an efficient large-aperture high damage-threshold sol-gel diffraction grating.

    Energy Technology Data Exchange (ETDEWEB)

    Ashley, Carol S.; Rambo, Patrick K.; Schwarz, Jens; Dunphy, Darren Robert; Branson, Eric D.; Smith, Ian Craig; Johnson, William Arthur; Reed, Scott T.; Cook, Adam W.


    In order to develop the next generation of high peak intensity lasers, new grating technology providing higher damage thresholds and large apertures is required. The current assumption is that this technical innovation will be multilayer dielectric gratings, wherein the uppermost layer of a thin film mirror is etched to create the desired binary phase grating. A variant of this is explored with the upper grating layer being a lower density gelatin-based volume phase grating in either sol-gel or dichromated gelatin. One key benefit is the elimination of the etching step.

  16. Imaging of Volume Phase Gratings in a Photosensitive Polymer, Recorded in Transmission and Reflection Geometry

    Directory of Open Access Journals (Sweden)

    Tina Sabel


    Full Text Available Volume phase gratings, recorded in a photosensitive polymer by two-beam interference exposure, are studied by means of optical microscopy. Transmission gratings and reflection gratings, with periods in the order of 10 μm down to 130 nm, were investigated. Mapping of holograms by means of imaging in sectional view is introduced to study reflection-type gratings, evading the resolution limit of classical optical microscopy. In addition, this technique is applied to examine so-called parasitic gratings, arising from interference from the incident reference beam and the reflected signal beam. The appearance and possible avoidance of such unintentionally recorded secondary structures is discussed.

  17. Ultracompact resonator with high quality-factor based on a hybrid grating structure

    DEFF Research Database (Denmark)

    Taghizadeh, Alireza; Mørk, Jesper; Chung, Il-Sug


    We numerically investigate the properties of a hybrid grating structure acting as a resonator with ultrahigh quality factor. This reveals that the physical mechanism responsible for the resonance is quite different from the conventional guided mode resonance (GMR). The hybrid grating consists...... of a subwavelength grating layer and an un-patterned high-refractive-index cap layer, being surrounded by low index materials. Since the cap layer may include a gain region, an ultracompact laser can be realized based on the hybrid grating resonator, featuring many advantages over high-contrast-grating resonator...

  18. Fabrication of thermal-resistant gratings for high-temperature measurements using geometric phase analysis. (United States)

    Zhang, Q; Liu, Z; Xie, H; Ma, K; Wu, L


    Grating fabrication techniques are crucial to the success of grating-based deformation measurement methods because the quality of the grating will directly affect the measurement results. Deformation measurements at high temperatures entail heating and, perhaps, oxidize the grating. The contrast of the grating lines may change during the heating process. Thus, the thermal-resistant capability of the grating becomes a point of great concern before taking measurements. This study proposes a method that combines a laser-engraving technique with the processes of particle spraying and sintering for fabricating thermal-resistant gratings. The grating fabrication technique is introduced and discussed in detail. A numerical simulation with a geometric phase analysis (GPA) is performed for a homogeneous deformation case. Then, the selection scheme of the grating pitch is suggested. The validity of the proposed technique is verified by fabricating a thermal-resistant grating on a ZrO2 specimen and measuring its thermal strain at high temperatures (up to 1300 °C). Images of the grating before and after deformation are used to obtain the thermal-strain field by GPA and to compare the results with well-established reference data. The experimental results indicate that this proposed technique is feasible and will offer good prospects for further applications.

  19. Fabrication of thermal-resistant gratings for high-temperature measurements using geometric phase analysis (United States)

    Zhang, Q.; Liu, Z.; Xie, H.; Ma, K.; Wu, L.


    Grating fabrication techniques are crucial to the success of grating-based deformation measurement methods because the quality of the grating will directly affect the measurement results. Deformation measurements at high temperatures entail heating and, perhaps, oxidize the grating. The contrast of the grating lines may change during the heating process. Thus, the thermal-resistant capability of the grating becomes a point of great concern before taking measurements. This study proposes a method that combines a laser-engraving technique with the processes of particle spraying and sintering for fabricating thermal-resistant gratings. The grating fabrication technique is introduced and discussed in detail. A numerical simulation with a geometric phase analysis (GPA) is performed for a homogeneous deformation case. Then, the selection scheme of the grating pitch is suggested. The validity of the proposed technique is verified by fabricating a thermal-resistant grating on a ZrO2 specimen and measuring its thermal strain at high temperatures (up to 1300 °C). Images of the grating before and after deformation are used to obtain the thermal-strain field by GPA and to compare the results with well-established reference data. The experimental results indicate that this proposed technique is feasible and will offer good prospects for further applications.

  20. Beam splitting of low-contrast binary gratings under second Bragg angle incidence. (United States)

    Zheng, Jiangjun; Zhou, Changhe; Wang, Bo; Feng, Jijun


    Beam splitting of low-contrast rectangular gratings under second Bragg angle incidence is studied. The grating period is between lambda and 2lambda. The diffraction behaviors of the three transmitted propagating orders are illustrated by analyzing the first three propagating grating modes. From a simplified modal approach, the design conditions of gratings as a high-efficiency element with most of its energy concentrated in the -2nd transmitted order (~90%) and of gratings as a 1 x 2 beam splitter with a total efficiency over 90% are derived. The grating parameters for achieving exactly the splitting pattern by use of rigorous coupled-wave analysis verified the design method. A 1 x 3 beam splitter is also demonstrated. Moreover, the polarization-dependent diffraction behaviors are investigated, which suggest the possibility of designing polarization-selective elements under such a configuration. The proposed concept of using the second Bragg angle should be helpful for developing new grating-based devices.

  1. Continuously tunable pulsed Ti:Sa laser self-seeded by an extended grating cavity

    CERN Document Server

    Li, Ruohong; Rothe, Sebastian; Teigelhöfer, Andrea; Mostamand, Maryam


    A continuously tunable titanium:sapphire (Ti:Sa) laser self-seeded by an extended grating cavity was demonstrated and characterized. By inserting a partially reflecting mirror inside the cavity of a classic single-cavity grating laser, two oscillators are created: a broadband power oscillator, and a narrowband oscillator with a prism beam expander and a diffraction grating in Littrow configuration. By coupling the grating cavity oscillation into the power oscillator, a power-enhanced narrow-linewidth laser oscillation is achieved. Compared to the classic grating laser, this simple modification significantly increases the laser output power without considerably broadening the linewidth. With most of the oscillating laser power confined inside the broadband power cavity and lower power incident onto the grating, the new configuration also allows higher pump power, which is typically limited by the thermal deformation of the grating coating at high oscillation power.

  2. Ultra-broadband and wide-angle perfect absorber based on composite metal-semiconductor grating (United States)

    Li, Xu; Wang, Zongpeng; Hou, Yumin


    In this letter, we present an ultra-broadband and wide-angle perfect absorber based on composite Ge-Ni grating. Near perfect absorption above 90% is achieved in a wide frequency range from 150 nm to 4200 nm, which covers almost the full spectrum of solar radiation. The absorption keeps robust in a wide range of incident angle from 0º to 60º. The upper triangle Ge grating works as an antireflection coating. The lower Ni grating works as a reflector and an effective energy trapper. The guided modes inside Ge grating are excited due to reflection of the lower Ni grating surface. In longer wavelength band, gap surface plasmons (GSPs) in the Ni grating are excited and couple with the guided modes inside the Ge grating. The coupled modes extend the perfect absorption band to the near-infrared region (150 nm-4200 nm). This design has potential application in photovoltaic devices and thermal emitters.

  3. Simplified analysis of sub-wavelength triangular gratings by simplified modal method. (United States)

    Sridharan, Gayathri; Bhattacharya, Shanti


    A phase-equivalence of a triangular grating and a "corresponding" blazed structure is proposed. This equivalence is used to simplify the analysis of the grating, which otherwise would require the repetitive application of the simplified modal method to each lamellar grating that constitutes the triangular grating. The concept is used to arrive at an equation for the phase introduced by the triangular grating. The proposed model is verified by finite element simulations. A method of fabricating a triangular grating in quartz is presented. The proposed theory, along with optical testing, can be used as a non-destructive means by which to estimate the height of the triangular grating during the dry etching process.

  4. Properties of diffraction gratings holographically recorded in poly(ethylene glycol)dimethacrylate-ionic liquid composites (United States)

    Ellabban, Mostafa A.; Glavan, Gašper; Flauger, Peter; Klepp, Jürgen; Fally, Martin


    We investigated recording and readout of transmission gratings in composites of poly(ethylene glycol) dimethacrylate (PEGDMA) and ionic liquids (IL) in detail. Gratings were recorded using a two-wave mixing technique for different grating periods, exposures and a series of film thicknesses. The recording kinetics as well as the post-exposure behavior of the gratings were studied by diffraction experiments. We found that - depending on the parameters - different grating types (pure phase or mixed) are generated, and at elevated thicknesses strong light-induced scattering develops. Gratings with thicknesses up to 85 micrometers are of the required quality with excellent optical properties, thicker gratings exhibit strong detrimental light-induced scattering. The obtained results are particularly valuable when considering PEGDMA-ionic liquid composites for applications as e.g., holographic storage materials or as neutron optic diffractive elements.

  5. Spherical Accretion in a Uniformly Expanding Universe (United States)

    Colpi, Monica; Shapiro, Stuart L.; Wasserman, Ira


    We consider spherically symmetric accretion of material from an initially homogeneous, uniformly expanding medium onto a Newtonian point mass M. The gas is assumed to evolve adiabatically with a constant adiabatic index F, which we vary over the range Γ ɛ [1, 5/3]. We use a one-dimensional Lagrangian code to follow the spherical infall of material as a function of time. Outflowing shells gravitationally bound to the point mass fall back, giving rise to a inflow rate that, after a rapid rise, declines as a power law in time. If there were no outflow initially, Bondi accretion would result, with a characteristic accretion time-scale ta,0. For gas initially expanding at a uniform rate, with a radial velocity U = R/t0 at radius R, the behavior of the flow at all subsequent times is determined by ta,0/t0. If ta,0/t0 ≫ 1, the gas has no time to respond to pressure forces, so the fluid motion is nearly collisionless. In this case, only loosely bound shells are influenced by pressure gradients and are pushed outward. The late-time evolution of the mass accretion rate Mdot is close to the result for pure dust, and we develop a semianalytic model that accurately accounts for the small effect of pressure gradients in this limit. In the opposite regime, ta,0/t0 ≪ 1, pressure forces significantly affect the motion of the gas. At sufficiently early times, t ≤ ttr, the flow evolved along a sequence of quasi-stationary, Bondi-like states, with a time-dependent Mdot determined by the slowly varying gas density at large distances. However, at later times, t ≥ ttr, the fluid flow enters a dustllke regime; ttr is the time when the instantaneous Bondi accretion radius reaches the marginally bound radius. The transition time ttr depends sensitively on ta,0/t0 for a given Γ and can greatly exceed t0. We show that there exists a critical value Γ = 11/9, below which the transition from fluid to ballistic motion disappears. As one application of our calculations, we consider the

  6. HFE and Spherical Cryostats MC Study

    Energy Technology Data Exchange (ETDEWEB)

    Brodsky, Jason P. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)


    The copper vessel containing the nEXO TPC is surrounded by a buffer of HFE, a liquid refrigerant with very low levels of radioactive element contamination. The HFE is contained within the cryostat’s inner vessel, which is in turn inside the outer vessel. While some HFE may be necessary for stable cooling of nEXO, it is possible that using substantially more than necessary for thermal reasons will help reduce backgrounds originating in the cryostats. Using a larger amount of HFE is accomplished by making the cryostat vessels larger. By itself, increasing the cryostat size somewhat increases the background rate, as the thickness of the cryostat wall must increase at larger sizes. However, the additional space inside the cryostat will be filled with HFE which can absorb gamma rays headed for the TPC. As a result, increasing the HFE reduces the number of backgrounds reaching the TPC. The aim of this study was to determine the relationship between HFE thickness and background rate. Ultimately, this work should support choosing a cryostat and HFE size that satisfies nEXO’s background budget. I have attempted to account for every consequence of changing the cryostat size, although naturally this remains a work in progress until a final design is achieved. At the moment, the scope of the study includes only the spherical cryostat design. This study concludes that increasing cryostat size reduces backgrounds, reaching neglible backgrounds originating from the cryostat at the largest sizes. It also shows that backgrounds originating from the inherent radioactivity of the HFE plateau quickly, so may be considered essentially fixed at any quantity of HFE.

  7. A quantum reduction to spherical symmetry in loop quantum gravity

    Directory of Open Access Journals (Sweden)

    N. Bodendorfer


    Full Text Available Based on a recent purely geometric construction of observables for the spatial diffeomorphism constraint, we propose two distinct quantum reductions to spherical symmetry within full 3+1-dimensional loop quantum gravity. The construction of observables corresponds to using the radial gauge for the spatial metric and allows to identify rotations around a central observer as unitary transformations in the quantum theory. Group averaging over these rotations yields our first proposal for spherical symmetry. Hamiltonians of the full theory with angle-independent lapse preserve this spherically symmetric subsector of the full Hilbert space. A second proposal consists in implementing the vanishing of a certain vector field in spherical symmetry as a constraint on the full Hilbert space, leading to a close analogue of diffeomorphisms invariant states. While this second set of spherically symmetric states does not allow for using the full Hamiltonian, it is naturally suited to implement the spherically symmetric midisuperspace Hamiltonian, as an operator in the full theory, on it. Due to the canonical structure of the reduced variables, the holonomy-flux algebra behaves effectively as a one parameter family of 2+1-dimensional algebras along the radial coordinate, leading to a diagonal non-vanishing volume operator on 3-valent vertices. The quantum dynamics thus becomes tractable, including scenarios like spherically symmetric dust collapse.

  8. Spherical warm shield design for infrared imaging systems (United States)

    Tian, Qijie; Chang, Songtao; He, Fengyun; Li, Zhou; Qiao, Yanfeng


    The F-number matching is the primary means to suppress stray radiation for infrared imaging systems. However, it is difficult to achieve exact F-number matching, owing to the restriction from detectors, or multiple F-number design. Hence, an additional shield is required to block the certain thermal radiation. Typical shield is called flat warm shield, which is flat and operates at room temperature. For flat warm shield, it cannot suppress stray radiation while achieving F-number matching. To overcome the restriction, a spherical reflective warm shield is required. First of all, the detailed theory of spherical warm shield design is developed on basis of the principle that stray radiation cannot directly reach the infrared focal plane array. According to the theory developed above, a polished spherical warm shield, whose radius is 18 mm, is designed to match an F/2 infrared detector with an F/4 infrared imaging system. Then, the performance and alignment errors of the designed spherical warm shield are analyzed by simulation. Finally, a contrast experiment between the designed spherical warm shield and two differently processed flat warm shields is performed in a chamber with controllable inside temperatures. The experimental results indicate that the designed spherical warm shield cannot only achieve F-number matching but suppress stray radiation sufficiently. Besides, it is demonstrated that the theory of spherical warm shield design developed in this paper is valid and can be employed by arbitrary infrared imaging systems.

  9. Non-Spherical Microcapsules for Increased Core Content Volume Delivery (United States)

    Oliva-Buisson, Yvette J.


    The goal of this project was to advance microencapsulation from the standard spherical microcapsule to a non-spherical, high-aspect ratio (HAR), elongated microcapsule. This was to be accomplished by developing reproducible methods of synthesizing or fabricating robust, non-spherical, HAR microcapsules. An additional goal of this project was to develop the techniques to the point where scale-up of these methods could be examined. Additionally, this project investigated ways to apply the microencapsulation techniques developed as part of this project to self-healing formulations.

  10. Diffraction model of peristrophic multiplexing with spherical reference wave. (United States)

    Yoshida, Shuhei; Takahata, Yosuke; Horiuchi, Shuma; Yamamoto, Manabu


    Multiplexing recording is a primary contributor to determining the recording density in holographic data storage. Therefore, many different kinds of recording methods have been proposed. Among them, the method that utilizes spherical waves as reference waves is characterized by the ability to enable multiplexing recording only by moving (shifting or rotating) the recording medium. In our research, we propose a theoretical diffraction model of peristrophic multiplexing with a spherical reference wave and evaluate the diffraction efficiency; this multiplexing recording method has incorporated spherical reference waves in rotation of the media. Additionally, we verify the effectiveness of the model by comparing it with experimental results.

  11. Next-Step Spherical Torus Experiment and Spherical Torus Strategy in the Fusion Energy Development Path

    Energy Technology Data Exchange (ETDEWEB)

    M. Ono; M. Peng; C. Kessel; C. Neumeyer; J. Schmidt; J. Chrzanowski; D. Darrow; L. Grisham; P. Heitzenroeder; T. Jarboe; C. Jun; S. Kaye; J. Menard; R. Raman; T. Stevenson; M. Viola; J. Wilson; R. Woolley; I. Zatz


    A spherical torus (ST) fusion energy development path which is complementary to proposed tokamak burning plasma experiments such as ITER is described. The ST strategy focuses on a compact Component Test Facility (CTF) and higher performance advanced regimes leading to more attractive DEMO and Power Plant scale reactors. To provide the physics basis for the CTF an intermediate step needs to be taken which we refer to as the ''Next Step Spherical Torus'' (NSST) device and examine in some detail herein. NSST is a ''performance extension'' (PE) stage ST with the plasma current of 5-10 MA, R = 1.5 m, and Beta(sub)T less than or equal to 2.7 T with flexible physics capability. The mission of NSST is to: (1) provide a sufficient physics basis for the design of CTF, (2) explore advanced operating scenarios with high bootstrap current fraction/high performance regimes, which can then be utilized by CTF, DEMO, and Power Plants, and (3) contribute to the general plasma/fusion science of high beta toroidal plasmas. The NSST facility is designed to utilize the Tokamak Fusion Test Reactor (or similar) site to minimize the cost and time required for the design and construction.

  12. State of the art in silicon immersed gratings for space (United States)

    van Amerongen, Aaldert; Krol, Hélène; Grèzes-Besset, Catherine; Coppens, Tonny; Bhatti, Ianjit; Lobb, Dan; Hardenbol, Bram; Hoogeveen, Ruud


    We present the status of our immersed diffraction grating technology, as developed at SRON and of their multilayer optical coatings as developed at CILAS. Immersion means that diffraction takes place inside the medium, in our case silicon. The high refractive index of the silicon medium boosts the resolution and the dispersion. Ultimate control over the groove geometry yields high efficiency and polarization control. Together, these aspects lead to a huge reduction in spectrometer volume. This has opened new avenues for the design of spectrometers operating in the short-wave-infrared wavelength band. Immersed grating technology for space application was initially developed by SRON and TNO for the short-wave-infrared channel of TROPOMI, built under the responsibility of SSTL. This space spectrometer will be launched on ESA's Sentinel 5 Precursor mission in 2015 to monitor pollution and climate gases in the Earth atmosphere. The TROPOMI immersed grating flight model has technology readiness level 8. In this program CILAS has qualified and implemented two optical coatings: first, an anti-reflection coating on the entrance and exit facet of the immersed grating prism, which reaches a very low value of reflectivity for a wide angular range of incidence of the transmitted light; second, a metal-dielectric absorbing coating for the passive facet of the prism to eliminate stray light inside the silicon prism. Dual Ion Beam Sputtering technology with in-situ visible and infrared optical monitoring guarantees the production of coatings which are nearly insensitive to temperature and atmospheric conditions. Spectral measurements taken at extreme temperature and humidity conditions show the reliability of these multi-dielectric and metal-dielectric functions for space environment. As part of our continuous improvement program we are presently developing new grating technology for future missions, hereby expanding the spectral range, the blaze angles and grating size, while

  13. Shell closure at {ital N}=164: Spherical or deformed?

    Energy Technology Data Exchange (ETDEWEB)

    Rigol, J. [Joint Institute for Nuclear Research, 141980 Dubna (Russia)


    Brenner {ital et al}. [1] recently reported the apparent evidence for a spherical shell at {ital N}=164. Some arguments are given which may make it necessary to reconsider this conclusion. {copyright} {ital 1997} {ital The American Physical Society}

  14. Aircraft navigation and surveillance analysis for a spherical earth (United States)


    This memorandum addresses a fundamental function in surveillance and navigation analysis : quantifying the geometry of two or more locations relative to each other and to a spherical earth. Here, geometry refers to: (a) points (idealized lo...

  15. Sound field reconstruciton using a spherical microphone array

    DEFF Research Database (Denmark)

    Fernandez Grande, Efren


    measurement area consisting of an array of spheres, and the sound field at any point of the source-free domain can be estimated, not being restricted to spherical surfaces. Because it is formulated as an elementary wave model, it allows for diverse solution strategies (least squares, ℓ1-norm minimization, etc......A method is presented that makes it possible to reconstruct an arbitrary sound field based on measurements with a spherical microphone array. The proposed method (spherical equivalent source method) makes use of a point source expansion to describe the sound field on the rigid spherical array, from...... which it is possible to reconstruct the sound field over a three-dimensional domain, inferring all acoustic quantities: sound pressure, particle velocity, and sound intensity. The problem is formulated using a Neumann Green's function that accounts for the presence of the rigid sphere in the medium. One...

  16. Modelling and Simulation Analysis of Rolling Motion of Spherical Robot (United States)

    Kamis, N. N.; Embong, A. H.; Ahmad, S.


    This paper presents the findings of modelling, control and analysis of the spherical rolling robot based on pendulum driven within the simulation environment. The spherical robot is modelled using Lagrange function based on the equation of rolling motion. PD-type Fuzzy logic controller (FLC) was designed to control the position of the spherical robot where 25 rules were constructed to control the rolling motion of spherical robot. It was then integrated with the model developed in Simulink-Matlab environment. The output scaling factor (output gain) of the FLC was heuristically tuned to improve the system performance. The simulation results show that the FLC managed to eliminate the overshoot response and demonstrated better performance with 29.67% increasing in settling time to reach 0.01% of steady state error.

  17. Development of a hydrothermal method to synthesize spherical ...

    African Journals Online (AJOL)

    Vis spectroscopy. Through these techniques, it was found that the pure ZnSe nanoparticles have a zinc blend structure and in a spherical form with average diameter of 30 nm. KEY WORDS: ZnSe, Nanosphere, Hydrothermal, Surfactant. Bull.

  18. Resonant vibrations and acoustic radiation of rotating spherical structures.

    CSIR Research Space (South Africa)

    Shatalov, M


    Full Text Available on nature of the modes, spheroidal or torsional and their numbers. Bryan’s factors of radiated spherical body are calculated and compared with corresponding factors of a free body....


    Directory of Open Access Journals (Sweden)

    G. Fangi


    Full Text Available For architectural metric documentation, Spherical Photogrammetry (SP has demonstrated its validity and efficiency in many projects already. The speed of surveying is high, the accuracy and completeness of the plotting are satisfactory. However, there are still many problems to be solved. The weakest point is the orientation procedure, which is rather difficult to perform, in the sense that only very experienced people can run it, and few people only make use of it. The old orientation steps are 1 model formation (limited to binocular panoramas couples; 2 link of all the models in a block adjustment with independent model triangulation; 3 block bundle adjustment with 4 parameters/pano (3 coord.+1 orientation bearing; 4 block bundle adjustment with 6 parameters/pano, say the previous 4 + 2 correction angles around the horizontal axes. The panoramas must be spherical and quasi-horizontal. In order to make easier the orientation, enabling more people to use SP, an improved approach has been set up. It consists in the combination of any possible model formed either by three and two panoramas. The trinocular vision, say the combination of three different panoramas to form a unique model, has the advantage to be much more robust in comparison to binocular vision in the sense that the trinocular model is likely to be more error-free than any of the three composing binocular models. It contains less model deformation, the model coordinates are validated by the mutual comparison of the three intersecting binocular models. In addition, the number of possible trinocular models is normally much larger than the one of binocular models. The steps for a semi-automatic orientation of a block of panoramas proceed as follows: - Form any possible trinocular models by combination of the panoramas; - in case that no trinocular model has been formed, form any possible binocular model; - run a block adjustment with the algorithm of independent model, to link together

  20. Development and Application of Fiber Bragg Grating Clinometer (United States)

    Guo, Xin; Li, Wen; Wang, Wentao; Feng, Xiaoyu


    Using FBG (fiber bragg grating) technology in clinometers can solve the technological problem facing by wireless transmission devices like big data transfer volume and poor stability, which has been receiving more and more attention. This paper discusses a new clinometer that is designed and transformed based on upgrading current clinometers, installing fiber grating strain gauges and fiber thermometers, and carrying out studies on such aspects as equipment upgrading, on-site setting, and data acquisition and analysis. In addition, it brings up the method of calculating displacement change based on wavelength change; this method is used in safety monitoring of the right side slope of Longyong Expressway ZK56+860 ~ ZK56+940 Section. Data shows that the device is operating well with a higher accuracy, and the slope is currently in a steady state. The equipment improvement and the method together provide reference data for safety analysis of the side slope.

  1. Planar Bragg Grating Sensors—Fabrication and Applications: A Review

    Directory of Open Access Journals (Sweden)

    I. J. G. Sparrow


    Full Text Available We discuss the background and technology of planar Bragg grating sensors, reviewing their development and describing the latest developments. The physical operating principles are discussed, relating device operation to user requirements. Recent performance of such devices includes a planar Bragg grating sensor design which allows refractive index resolution of 1.9×10−6 RIU and temperature resolution of 0.03∘C. This sensor design is incorporated into industrialised applications allowing the sensor to be used for real time sensing in intrinsically safe, high-pressure pipelines, or for insertion probe applications such as fermentation. Initial data demonstrating the ability to identify solvents and monitor long term industrial processes is presented. A brief review of the technology used to fabricate the sensors is given along with examples of the flexibility afforded by the technique.

  2. Grating angle magnification enhanced angular sensor and scanner (United States)

    Sun, Ke-Xun (Inventor); Byer, Robert L. (Inventor)


    An angular magnification effect of diffraction is exploited to provide improved sensing and scanning. This effect is most pronounced for a normal or near-normal incidence angle in combination with a grazing diffraction angle, so such configurations are preferred. Angular sensitivity can be further enhanced because the width of the diffracted beam can be substantially less than the width of the incident beam. Normal incidence configurations with two symmetric diffracted beams are preferred, since rotation and vertical displacement can be readily distinguished. Increased sensitivity to vertical displacement can be provided by incorporating an interferometer into the measurement system. Quad cell detectors can be employed to provide sensitivity to rotation about the grating surface normal. A 2-D grating can be employed to provide sensitivity to angular displacements in two different planes (e.g., pitch and yaw). Combined systems can provide sensitivity to vertical displacement and to all three angular degrees of freedom.

  3. Flexible organic solar cells including efficiency enhancing grating structures

    DEFF Research Database (Denmark)

    Oliveira Hansen, Roana Melina de; Liu, Yinghui; Madsen, Morten


    In this work, a new method for the fabrication of organic solar cells containing functional light-trapping nanostructures on flexible substrates is presented. Polyimide is spin-coated on silicon support substrates, enabling standard micro- and nanotechnology fabrication techniques......, such as photolithography and electron-beam lithography, besides the steps required for the bulk-heterojunction organic solar cell fabrication. After the production steps, the solar cells on polyimide are peeled off the silicon support substrates, resulting in flexible devices containing nanostructures for light absorption...... enhancement. Since the solar cells avoid using brittle electrodes, the performance of the flexible devices is not affected by the peeling process. We have investigated three different nanostructured grating designs and conclude that gratings with a 500 nm pitch distance have the highest light...

  4. Dense Wavelength Division (De Multiplexers Based on Fiber Bragg Gratings

    Directory of Open Access Journals (Sweden)



    Full Text Available This study is to measure the impact of demultiplexers based on Fiber Bragg Grating (FBG filter on performance of DWDM system for optical access network. An optical transmission link has been established in which we have inserted a demultiplexer based on four different FBG filters. The first step will be the characterization of FBG’s filters (i.e. uniform FBG, Gaussian apodized Grating, chirped FBG to explain their behavior in the optical link. The simulations were conducted for different fiber’s lengths, filter bandwidth and different received power to get the best system performance. This helped to assess their impact on the link performance in terms of Bit Error Rate (BER.

  5. High order integral equation method for diffraction gratings. (United States)

    Lu, Wangtao; Lu, Ya Yan


    Conventional integral equation methods for diffraction gratings require lattice sum techniques to evaluate quasi-periodic Green's functions. The boundary integral equation Neumann-to-Dirichlet map (BIE-NtD) method in Wu and Lu [J. Opt. Soc. Am. A 26, 2444 (2009)], [J. Opt. Soc. Am. A 28, 1191 (2011)] is a recently developed integral equation method that avoids the quasi-periodic Green's functions and is relatively easy to implement. In this paper, we present a number of improvements for this method, including a revised formulation that is more stable numerically, and more accurate methods for computing tangential derivatives along material interfaces and for matching boundary conditions with the homogeneous top and bottom regions. Numerical examples indicate that the improved BIE-NtD map method achieves a high order of accuracy for in-plane and conical diffractions of dielectric gratings. © 2012 Optical Society of America

  6. Green's function method to study thin diffraction gratings (United States)

    Travo, Daniel A.; Muniz, Rodrigo A.; Liscidini, M.; Sipe, J. E.


    The anomalous features in diffraction patterns first observed by Wood over a century ago have been the subject of many investigations, both experimental and theoretical. The sharp, narrow structures—and the large resonances with which they are sometimes associated—arise in numerous studies in optics and photonics. In this paper we present an analytical method to study diffracted fields of optically thin gratings that highlights the nonanalyticities associated with the anomalies. Using this approach we can immediately derive diffracted fields for any polarization in a compact notation. While our equations are approximate, they fully respect energy conservation in the electromagnetic field, and describe the large exchanges of energy between incident and diffracted fields that can arise even for thin gratings.

  7. Quadratic grating apodized photon sieves for simultaneous multiplane microscopy (United States)

    Cheng, Yiguang; Zhu, Jiangping; He, Yu; Tang, Yan; Hu, Song; Zhao, Lixin


    We present a new type of imaging device, named quadratic grating apodized photon sieve (QGPS), used as the objective for simultaneous multiplane imaging in X-rays. The proposed QGPS is structured based on the combination of two concepts: photon sieves and quadratic gratings. Its design principles are also expounded in detail. Analysis of imaging properties of QGPS in terms of point-spread function shows that QGPS can image multiple layers within an object field onto a single image plane. Simulated and experimental results in visible light both demonstrate the feasibility of QGPS for simultaneous multiplane imaging, which is extremely promising to detect dynamic specimens by X-ray microscopy in the physical and life sciences.

  8. Rectangular Relief Diffraction Gratings for Coherent Lidar Beam Deflection (United States)

    Cole, H. J.; Dixit, S. N.; Shore, B. W.; Chambers, D. M.; Britten, J. A.; Kavaya, M. J.


    LIDAR systems require a light transmitting system for sending a laser light pulse into space and a receiving system for collecting the retro-scattered light, separating it from the outgoing beam and analyzing the received signal for calculating wind velocities. Currently, a shuttle manifested coherent LIDAR experiment called SPARCLE (SPAce Readiness Coherent Lidar Experiment) includes a silicon wedge (or prism) in its design in order to deflect the outgoing beam 30 degrees relative to the incident direction. The intent of this paper is to present two optical design approaches that may enable the replacement of the optical wedge component (in future, larger aperture, post-SPARCLE missions) with a surface relief transmission diffraction grating. Such a grating could be etched into a lightweight, flat, fused quartz substrate. The potential advantages of a diffractive beam deflector include reduced weight, reduced power requirements for the driving scanning motor, reduced optical sensitivity to thermal gradients, and increased dynamic stability.

  9. Optical imaging using spatial grating effects in ferrofluids

    Energy Technology Data Exchange (ETDEWEB)

    Dave, Vishakha; Virpura, Hiral; Patel, Rajesh, E-mail: [Department of Physics, Maharaja Krishankumarsinhji Bhavnagar University, Bhavnagar. 364002. India (India)


    Under the effect of magnetic field the magnetic nanoparticles of the ferrofluid tend to align in the direction of the magnetic field. This alignment of the magnetic nanoparticles behaves as a spatial grating and diffract light, when light is propagating perpendicular to the direction of the applied magnetic field. The chains of the magnetic nanoparticles represents a linear series of fringes like those observed in a grating/wire. Under applied magnetic field the circular beam of light transforms into a prominent diffraction line in the direction perpendicular to the applied magnetic field. This diffracted light illuminates larger area on the screen. This behavior can be used as magneto controlled illumination of the object and image analysis.

  10. Fibre-grating sensors for the measurement of physiological pulsations (United States)

    Petrović, M. D.; Daničić, A.; Atanasoski, V.; Radosavljević, S.; Prodanović, V.; Miljković, N.; Petrović, J.; Petrović, D.; Bojović, B.; Hadžievski, Lj; Allsop, T.; Lloyd, G.; Webb, D. J.


    Mechanical physiological pulsations are movements of a body surface incited by the movements of muscles in organs inside the body. Here we demonstrate the use of long-period grating sensors in the detection of cardio-vascular pulsations (CVP), in particular apex and carotid pulsations. To calibrate the sensors, we use a mechanical tool designed specifically to measure the sensor response to a localized perturbation at different grating curvatures as working points. From the data we infer the amplitude of the CVP. Together with the electrophysiological signals, the CVP signals obtained from the sensors can provide significant information on heart function which is inaccessible to the electrocardiogram. The low cost and easy handling of the fibre sensors increase their prospects to become the sensors of choice for novel diagnostic devices.

  11. Multi-wavelength VCSEL arrays using high-contrast gratings (United States)

    Haglund, Erik; Gustavsson, Johan S.; Sorin, Wayne V.; Bengtsson, Jörgen; Fattal, David; Haglund, Àsa; Tan, Michael; Larsson, Anders


    The use of a high-contrast grating (HCG) as the top mirror in a vertical-cavity surface-emitting laser (VCSEL) allows for setting the resonance wavelength by the grating parameters in a post-epitaxial growth fabrication process. Using this technique, we demonstrate electrically driven multi-wavelength VCSEL arrays at 980 nm wavelength. The VCSELs are GaAs-based and the suspended GaAs HCGs were fabricated using electron-beam lithography, dry etching and selective removal of an InGaP sacrificial layer. The air-coupled cavity design enabled 4-channel arrays with 5 nm wavelength spacing and sub-mA threshold currents thanks to the high HCG reflectance.

  12. Flat acoustic lens by acoustic grating with curled slits

    KAUST Repository

    Peng, Pai


    We design a flat sub-wavelength lens that can focus acoustic wave. We analytically study the transmission through an acoustic grating with curled slits, which can serve as a material with tunable impedance and refractive index for acoustic waves. The effective parameters rely on the geometry of the slits and are independent of frequency. A flat acoustic focusing lens by such acoustic grating with gradient effective refractive index is designed. The focusing effect is clearly observed in simulations and well predicted by the theory. We demonstrate that despite the large impedance mismatch between the acoustic lens and the matrix, the intensity at the focal point is still high due to Fabry-Perot resonance.

  13. A Long-Period Grating Sensor for Wind Turbine Blades

    DEFF Research Database (Denmark)

    Glavind, Lars

    This PhD project concerns the applied research for providing a novel sensor for measurements on wind turbine blades, based on Long-Period Gratings. The idea is based on the utilization of a special asymmetrical optical fibre with Long-Period Gratings for directional sensitive bend sensing...... blade material, where a suitable process and recoating material were investigated. The sensor was implemented and tested on a full scale wind turbine blade placed on a test rig. This first prototype has demonstrated the capability of the sensor for wind turbine blade monitoring, particular...... the possibility to distinguish between the flap- and edge-wise bend directions on the wind turbine blade, providing a selective sensor. The sensor has proven to be very robust and suitable for this application....

  14. Fluorescence of molecules placed near a spherical particle: Rabi splitting

    Directory of Open Access Journals (Sweden)

    M.M. Dvoynenko


    Full Text Available Theoretical study of spontaneously emitted spectra of point-like source placed near spherical Ag particle was performed. It was shown that near-field electromagnetic interaction between a point-like emitter and spherical Ag particle leads to strong coupling between them at very small emitter-metal surface distances. It was shown that values of Rabi splitting are quantitatively close to that of emitter-flat substrate interaction.

  15. Design considerations in the development of a spherical mobile robot (United States)

    Das, Tuhin; Mukherjee, Ranjan; Yuksel, H.


    The design problems in the development of a spherical mobile robot are discussed in this paper. These problems include dynamics and design of the propulsion mechanism, motion planning and control problems, actuator selection and sensor placement, design and fabrication of the exo-skeleton, and other issues related to power management and computing. Each of the problems are discussed in brief and presented in relation to the spherical mobile robot currently under development at Michigan State University.

  16. Minimum Q Electrically Small Spherical Magnetic Dipole Antenna - Theory

    DEFF Research Database (Denmark)

    Breinbjerg, Olav; Kim, Oleksiy S.


    The stored energies, radiated power, and quality factor of a magnetic-dipole antenna, consisting of a spherical electrical surface current density enclosing a magnetic core, is obtained through direct spatial integration of the internally and externally radiated field expressed in terms...... of spherical vector waves. The obtained quality factor agrees with that of Wheeler and Thal for vanishing free-space electric radius but holds also for larger radii and facilitates the optimal choice of permeability in the presence of the resonances....

  17. Horizon Quantum Mechanics: spherically symmetric and rotating sources (United States)

    Giusti, Andrea


    In this paper we discuss some mathematical aspects of the horizon wave-function formalism, also known in the literature as horizon quantum mechanics. In particular, first we review the structure of both the global and local formalism for static spherically symmetric sources. Then, we present an extension of the global analysis for rotating black holes and we also point out some technical diffculties that arise while attempting the local analysis for non-spherically symmetric sources.

  18. Turbulent dynamos in spherical shell segments of varying geometrical extent


    Mitra, Dhrubaditya; Tavakol, Reza; Brandenburg, Axel; Moss, David


    We use three-dimensional direct numerical simulations of the helically forced magnetohydrodynamic equations in spherical shell segments in order to study the effects of changes in the geometrical shape and size of the domain on the growth and saturation of large-scale magnetic fields. We inject kinetic energy along with kinetic helicity in spherical domains via helical forcing using Chandrasekhar-Kendall functions. We take perfect conductor boundary conditions for the magnetic field to ensure...

  19. On-chip near-wavelength diffraction gratings for surface electromagnetic waves (United States)

    Bezus, Evgeni A.; Podlipnov, Vladimir V.; Morozov, Andrey A.; Doskolovich, Leonid L.


    In the present work, on-chip dielectric diffraction gratings for steering the propagation of surface plasmon polaritons (SPP) are theoretically, numerically and experimentally studied. The investigated plasmonic gratings consist of dielectric ridges located on the SPP propagation surface (on the metal surface). In contrast to Bragg gratings, at normal incidence the periodicity direction of the grating is perpendicular to the SPP propagation direction. The studied gratings are designed using a simple plane-wave grating model and rigorously simulated using the aperiodic Fourier modal method for numerical solution of Maxwell's equations. In particular, plasmonic grating-based beam splitter with subwavelength footprint in the propagation direction is presented. Along with the theoretical and numerical results, proof-of-concept experimental results are presented. The investigated grating-based plasmonic gratings were fabricated from resist on a silver film using electron beam lithography and characterized using the leakage radiation microscopy technique. The obtained experimental results are in good agreement with the performed numerical simulations. The proposed on-chip gratings may find application in the design of systems for optical information transmission and processing at the nanoscale.

  20. Design of polarization-independent transmission fused-silica grating with high diffraction efficiency (United States)

    Cheng, Yushui; Li, Chaoming; Chen, Xinrong; Yu, Jian; Tang, Yu; Wang, Rui; Xu, Haiyan; Hu, Zuyuan; Wu, Jianhong


    The high diffraction efficiency and high dispersion ability of diffraction grating plays a very important role in laser systems. Fused-silica transmission gratings not only have board band, high diffraction efficiency and high damage threshold, but also have the advantage of light path without shelter comparing to reflective gratings. In this paper, the study of polarization-independent transmission fused-silica grating is carried out, and the influence of rectangular and trapezoidal grating microstructures on the -1st diffraction efficiency of grating is analyzed. For trapezoidal groove structure, in the range of 80 to 90 degrees, the distributions of diffraction efficiency at different bottom angle are calculated and analyzed. The structure parameters of the grating are optimized by rigorous coupled wave theory. The designed grating groove density is 1440 lines/mm. The -1st diffraction efficiency of the grating is over 96% for both of TE and TM polarized waves at the Littrow angle (49.7 degrees) with the center wavelength of 1060nm. Within the bandwidth of 42nm (from 1039 to 1081nm), the -1st diffraction efficiency of the designed grating is theoretically greater than 90% for both of TE and TM polarized waves.


    National Research Council Canada - National Science Library

    I. V. Makeev; I. Y. Popov; I. V. Blinova


    .... We suggest exact particular solutions of Stokes and continuity equations with variable viscosity and density in spherical coordinates for the case of spherically symmetric viscosity and density distributions...

  2. V-groove gratings on silicon for infrared beam splitting. (United States)

    Rajkumar, N; McMullin, J N


    Infrared beam-splitting transmission gratings that utilize anisotropically etched v-grooves on silicon wafers are proposed. With scalar diffraction theory to find the amplitudes of the different diffraction orders, a numerical search is used to find optimum designs for 1:3, 1:5, and 1:7 splitters with efficiencies greater than 70% with a standard deviation in intensity of no more than 7%.

  3. Temporal coherence requirement in a symmetric-path grating interferometer. (United States)

    Cheng, Y S


    The depth of fringes is obtained for a polychromatic point source at an arbitrary incidence angle. The path difference, calculated by ray tracing, at the plane where the interference fringes vanish indicates that the temporal coherence length is the same as that in other interferometers. It is also found that the equivalent path difference, introduced by relative phase modulation on two interfering rays by two gratings, is as important as the actual path-length difference but in the opposite sign.

  4. Smart architecture for stable multipoint fiber Bragg grating sensor system (United States)

    Yeh, Chien-Hung; Tsai, Ning; Zhuang, Yuan-Hong; Huang, Tzu-Jung; Chow, Chi-Wai; Chen, Jing-Heng; Liu, Wen-Fung


    In this work, we propose and investigate an intelligent fiber Bragg grating (FBG)-based sensor system in which the proposed stabilized and wavelength-tunable single-longitudinal-mode erbium-doped fiber laser can improve the sensing accuracy of wavelength-division-multiplexing multiple FBG sensors in a longer fiber transmission distance. Moreover, we also demonstrate the proposed sensor architecture to enhance the FBG capacity for sensing strain and temperature, simultaneously.

  5. Progress in reflection grating spectrometers for X-ray astrophysics (United States)

    McEntaffer, Randall L.


    Soft X-ray spectroscopy can address future science goals pertaining to understanding the cycle of hot baryons in the universe. Detailing feedback processes in galaxies, mapping the distribution of baryons in the circum- and intergalactic medium, and unraveling unknowns in stellar life cycles places demanding requirements upon spectrometers. Here, we detail advancements in reflection grating technologies that can be used to help provide answers to these important questions. We also discuss possible applications including a configuration for the Lynx concept strategic mission.

  6. Study on the fiber grating sensors in concrete safety monitoring (United States)

    Liu, Hang; Li, Yang; Zhang, Yu-hong


    The concrete may be damaged because there are freeze-thaw cycles between winter and summer in cold regions. Strain is an alternative parameter which can be used to describe deformation. In this paper, the fiber bragg gratings(FBG) were used to concrete safety monitoring. The strain and temperature sensing properties have been studied. The fiber reinforced polymers (FRP) were used for the packaged techniques of FBG sensors. The neural network was applied to temperature compensation for FBG sensors.

  7. Snapshot imaging Mueller matrix polarimeter using polarization gratings


    Kudenov, Michael W.; Escuti, Michael J.; Hagen, Nathan; Dereniak, Eustace L.; Oka, Kazuhiko


    A snapshot imaging Mueller matrix polarimeter (SIMMP) is theoretically described and empirically demonstrated through simulation. Spatial polarization fringes are localized onto a sample by incorporating polarization gratings (PGs) into a polarization generator module. These fringes modulate the Mueller matrix (MM) components of the sample, which are subsequently isolated with PGs in an analyzer module. The MM components are amplitude modulated onto spatial carrier frequencies which, due to t...

  8. Load Coefficients on Grates used for Wind Turbine Access Platforms

    DEFF Research Database (Denmark)

    Andersen, Thomas Lykke; Rasmussen, Michael R.; Frigaard, Peter

    In this report is presented the results of tests carried out at Dept. of Civil Engineering, Aalborg University (AAU) on behalf of DONG Energy A/S and Vattenfall A/S, Denmark. The objective of the tests was to investigate the load coefficient on different platform grates and a solid plate for desi...... for designing offshore windmill access platforms against wave run-up generated forces....

  9. Humidity insensitive TOPAS polymer fiber Bragg grating sensor


    Yuan, Scott Wu; Khan, Lutul; Webb, David J.; Kalli, Kyriacos; Rasmussen, Henrik K.; Stefani, Alessio; Bang, Ole


    We report the first experimental demonstration of a humidity insensitive polymer optical fiber Bragg grating (FBG), as well as the first FBG recorded in a TOPAS polymer optical fiber in the important low loss 850nm spectral region. For the demonstration we have fabricated FBGs with resonance wavelength around 850 nm and 1550 nm in single-mode microstructured polymer optical fibers made of TOPAS and the conventional poly (methyl methacrylate) (PMMA). Characterization of the FBGs shows that the...

  10. Screening of grated cheese authenticity by nir spectroscopy

    Directory of Open Access Journals (Sweden)

    Chiara Cevoli


    Full Text Available Parmigiano–Reggiano (PR cheese is one of the oldest traditional cheeses produced in Europe, and it is still one of the most valuable Protected Designation of Origin (PDO cheeses of Italy. The denomination of origin is extended to the grated cheese when manufactured exclusively from whole Parmigiano-Reggiano cheese wheels that respond to the production standard. The grated cheese must be matured for a period of at least 12 months and characterized by a rind content not over 18%. In this investigation the potential of near infrared spectroscopy (NIR, coupled to different statistical methods, were used to estimate the authenticity of grated Parmigiano Reggiano cheese PDO. Cheese samples were classified as: compliance PR, competitors, non-compliance PR (defected PR, and PR with rind content greater then 18%. NIR spectra were obtained using a spectrophotometer Vector 22/N (Bruker Optics, Milan, Italy in the diffuse reflectance mode. Instrument was equipped with a rotating integrating sphere. Principal Component Analysis (PCA was conducted for an explorative spectra analysis, while the Artificial Neural Networks (ANN were used to classify spectra, according to different cheese categories. Subsequently the rind percentage and month of ripening were estimated by a Partial Least Squares regression (PLS. Score plots of the PCA show a clear separation between compliance PR samples and the rest of the sample was observed. Competitors samples and the defected PR samples were grouped together. The classification performance for all sample classes, obtained by ANN analysis, was higher of 90%, in test set validation. Rind content and month of ripening were predicted by PLS a with a determination coefficient greater then 0.95 (test set. These results showed that the method can be suitable for a fast screening of grated cheese authenticity.

  11. Sphericity estimation bias for repeated measures designs in simulation studies. (United States)

    Bono, Roser; Arnau, Jaume; Blanca, María J; Alarcón, Rafael


    In this study, we explored the accuracy of sphericity estimation and analyzed how the sphericity of covariance matrices may be affected when the latter are derived from simulated data. We analyzed the consequences that normal and nonnormal data generated from an unstructured population covariance matrix-with low (ε = .57) and high (ε = .75) sphericity-can have on the sphericity of the matrix that is fitted to these data. To this end, data were generated for four types of distributions (normal, slightly skewed, moderately skewed, and severely skewed or log-normal), four sample sizes (very small, small, medium, and large), and four values of the within-subjects factor (K = 4, 6, 8, and 10). Normal data were generated using the Cholesky decomposition of the correlation matrix, whereas the Vale-Maurelli method was used to generate nonnormal data. The results indicate the extent to which sphericity is altered by recalculating the covariance matrix on the basis of simulated data. We concluded that bias is greater with spherical covariance matrices, nonnormal distributions, and small sample sizes, and that it increases in line with the value of K. An interaction was also observed between sample size and K: With very small samples, the observed bias was greater as the value of K increased.

  12. Broken Ergodicity in MHD Turbulence in a Spherical Domain (United States)

    Shebalin, John V.; wang, Yifan


    Broken ergodicity (BE) occurs in Fourier method numerical simulations of ideal, homogeneous, incompressible magnetohydrodynamic (MHD) turbulence. Although naive statistical theory predicts that Fourier coefficients of fluid velocity and magnetic field are zero-mean random variables, numerical simulations clearly show that low-wave-number coefficients have non-zero mean values that can be very large compared to the associated standard deviation. In other words, large-scale coherent structure (i.e., broken ergodicity) in homogeneous MHD turbulence can spontaneously grow out of random initial conditions. Eigenanalysis of the modal covariance matrices in the probability density functions of ideal statistical theory leads to a theoretical explanation of observed BE in homogeneous MHD turbulence. Since dissipation is minimal at the largest scales, BE is also relevant for resistive magnetofluids, as evidenced in numerical simulations. Here, we move beyond model magnetofluids confined by periodic boxes to examine BE in rotating magnetofluids in spherical domains using spherical harmonic expansions along with suitable boundary conditions. We present theoretical results for 3-D and 2-D spherical models and also present computational results from dynamical simulations of 2-D MHD turbulence on a rotating spherical surface. MHD turbulence on a 2-D sphere is affected by Coriolus forces, while MHD turbulence on a 2-D plane is not, so that 2-D spherical models are a useful (and simpler) intermediate stage on the path to understanding the much more complex 3-D spherical case.

  13. Imperfection sensitivity of pressured buckling of biopolymer spherical shells. (United States)

    Zhang, Lei; Ru, C Q


    Imperfection sensitivity is essential for mechanical behavior of biopolymer shells [such as ultrasound contrast agents (UCAs) and spherical viruses] characterized by high geometric heterogeneity. In this work, an imperfection sensitivity analysis is conducted based on a refined shell model recently developed for spherical biopolymer shells of high structural heterogeneity and thickness nonuniformity. The influence of related parameters (including the ratio of radius to average shell thickness, the ratio of transverse shear modulus to in-plane shear modulus, and the ratio of effective bending thickness to average shell thickness) on imperfection sensitivity is examined for pressured buckling. Our results show that the ratio of effective bending thickness to average shell thickness has a major effect on the imperfection sensitivity, while the effect of the ratio of transverse shear modulus to in-plane shear modulus is usually negligible. For example, with physically realistic parameters for typical imperfect spherical biopolymer shells, the present model predicts that actual maximum external pressure could be reduced to as low as 60% of that of a perfect UCA spherical shell or 55%-65% of that of a perfect spherical virus shell, respectively. The moderate imperfection sensitivity of spherical biopolymer shells with physically realistic imperfection is largely attributed to the fact that biopolymer shells are relatively thicker (defined by smaller radius-to-thickness ratio) and therefore practically realistic imperfection amplitude normalized by thickness is very small as compared to that of classical elastic thin shells which have much larger radius-to-thickness ratio.

  14. SOI waveguide based planar reflective grating demultiplexer for FTTH (United States)

    Bidnyk, S.; Feng, D.; Balakrishnan, A.; Pearson, M.; Gao, M.; Liang, H.; Qian, W.; Kung, C.-C.; Fong, J.; Yin, J.; Asghari, M.


    Recent deployments of fiber-to-the-home (FTTH) represent the fastest growing sector of the telecommunication industry. The emergence of the silicon-on-insulator (SOI) photonics presents an opportunity to exploit the wide availability of silicon foundries and high-quality low-cost substrates for addressing the FTTH market. We have now demonstrated that a monolithically integrated FTTH demultiplexer can be built using the SOI platform. The SOI filter comprises a monolithically integrated planar reflective grating and a multi-stage Mach-Zehnder interferometer that were fabricated using a CMOS-compatible SOI process with the core thickness of 3.0 μm and optically insulating layer of silica with a thickness of 0.375 μm. The Mach-Zehnder interferometer was used to coarsely separate the 1310 nm channel from 1490 and 1550 nm channels. Subsequently, a planar reflective grating was used to demultiplex the 1490 and 1550 nm channels. The manufactured device showed the 1-dB bandwidth of 110 nm for the 1310 nm channel. For the 1490 nm and 1550 nm channels, the 1-dB bandwidth was measured to be 30 nm. The adjacent channel isolation between the 1490 nm and 1550 nm channels was better than 32 dB. The optical isolation between the 1310 nm and 1490 and 1550 nm channels was better than 45 dB. Applications of the planar reflective gratings in the FTTH networks are discussed.

  15. An optical fiber Bragg grating and piezoelectric ceramic voltage sensor (United States)

    Yang, Qing; He, Yanxiao; Sun, Shangpeng; Luo, Mandan; Han, Rui


    Voltage measurement is essential in many fields like power grids, telecommunications, metallurgy, railways, and oil production. A voltage-sensing unit, consisting of fiber Bragg gratings (FBGs) and piezoelectric ceramics, based on which an optical over-voltage sensor was proposed and fabricated in this paper. No demodulation devices like spectrometer or Fabry-Perot filter were needed to gain the voltage signal, and a relatively large sensing frequency range was acquired in this paper; thus, the cost of the sensing system is more acceptable in engineering application. The voltage to be measured was directly applied to the piezoelectric ceramic, and deformation of the ceramics and the grating would be caused because of the inverse piezoelectric effect. With a reference grating, the output light intensity change will be caused by the FBG center wavelength change; thus, the relationship between the applied voltage and the output light intensity was established. Validation of the sensor was accomplished in the frequency range from 50 Hz to 20 kHz and switching impulse waves with a test platform; good linearity of the input-output characteristic was achieved. A temperature validation test was completed, showing that the sensor maintains good temperature stability. Experimental results show that the optical over-voltage sensor can be used for voltage monitoring, and if applied with a voltage divider, the sensor can be used to measure high voltage.

  16. Unidirectional transmission in non-symmetric gratings containing metallic layers. (United States)

    Serebryannikov, A E; Ozbay, Ekmel


    The mechanism of achieving unidirectional transmission in the gratings, which only contain isotropic dielectric and metallic layers, is suggested and numerically validated. It is shown that significant transmission in one direction and nearly zero transmission in the opposite direction can be obtained in the same intrinsically isotropic gratings as those studied recently in A. E. Serebryannikov and E. Ozbay, Opt. Express 17, 278 (2009), but at a non-zero angle of incidence. The tilting, non-symmetric features of the grating and the presence of a metallic layer with a small positive real part of the index of refraction are the conditions that are necessary for obtaining the unidirectionality. Single- and multibeam operational regimes are demonstrated. The frequency and angle ranges of the unidirectional transmission can be estimated by using the conventional framework based on isofrequency dispersion contours and construction lines that properly take into account the periodic features of the interfaces, but should then be corrected because of the tunneling arising within the adjacent ranges. After proper optimization, this mechanism is expected to become an alternative to that based on the use of anisotropic materials.

  17. A highly sensitive fiber Bragg grating diaphragm pressure transducer (United States)

    Allwood, Gary; Wild, Graham; Lubansky, Alex; Hinckley, Steven


    In this work, a novel diaphragm based pressure transducer with high sensitivity is described, including the physical design structure, in-depth analysis of optical response to changes in pressure, and a discussion of practical implementation and limitations. A flat circular rubber membrane bonded to a cylinder forms the body of the transducer. A fiber Bragg grating bonded to the center of the diaphragm structure enables the fractional change in pressure to be determined by analyzing the change in Bragg wavelength of the reflected spectra. Extensive evaluation of the physical properties and optical characteristics of the transducer has been performed through experimentation, and modeling using small deformation theory. The results show the transducer has a sensitivity of 0.116 nm/kPa, across a range of 15 kPa. Ultra-low cost interrogation of the optical signal was achieved through the use of an optically mismatched Bragg grating acting as an edge filter to convert the spectral change into an intensity change. A numerical model of the intensity based interrogation was implemented in order to validate the experimental results. Utilizing this interrogation technique and housing both the sensing and reference Bragg gratings within the main body of the transducer means it is effectively temperature insensitive and easily connected to electronic systems.

  18. SDO-EVE multiple EUV grating spectrograph (MEGS) optical design (United States)

    Crotser, David A.; Woods, Thomas N.; Eparvier, Francis G.; Ucker, Greg; Kohnert, Richard A.; Berthiaume, Gregory D.; Weitz, David M.


    The NASA Solar Dynamics Observatory (SDO), scheduled for launch in 2008, incorporates a suite of instruments including the EUV Variability Experiment (EVE). The EVE instrument package contains grating spectrographs used to measure the solar extreme ultraviolet (EUV) irradiance from 0.1 to 105 nm. The Multiple EUV Grating Spectrograph (MEGS) channels use concave reflection gratings to image solar spectra onto CCDs that are operated at -100°C. MEGS provides 0.1nm spectral resolution between 5-105nm every 10 seconds with an absolute accuracy of better than 25% over the SDO 5-year mission. MEGS-A utilizes a unique grazing-incidence, off-Rowland circle (RC) design to minimize angle of incidence at the detector while meeting high resolution requirements. MEGS-B utilizes a double-pass, cross-dispersed double-Rowland circle design. MEGS-P, a Ly-α monitor, will provide a proxy model calibration in the 60-105 nm range. Finally, the Solar Aspect Monitor (SAM) channel will provide continual pointing information for EVE as well as low-resolution X-ray images of the sun. In-flight calibrations for MEGS will be provided by the on-board EUV Spectrophotometer (ESP) in the 0.1-7nm and 17-37nm ranges, as well as from annual under-flight rocket experiments. We present the methodology used to develop the MEGS optical design.

  19. Finite difference time domain analysis of chirped dielectric gratings (United States)

    Hochmuth, Diane H.; Johnson, Eric G.


    The finite difference time domain (FDTD) method for solving Maxwell's time-dependent curl equations is accurate, computationally efficient, and straight-forward to implement. Since both time and space derivatives are employed, the propagation of an electromagnetic wave can be treated as an initial-value problem. Second-order central-difference approximations are applied to the space and time derivatives of the electric and magnetic fields providing a discretization of the fields in a volume of space, for a period of time. The solution to this system of equations is stepped through time, thus, simulating the propagation of the incident wave. If the simulation is continued until a steady-state is reached, an appropriate far-field transformation can be applied to the time-domain scattered fields to obtain reflected and transmitted powers. From this information diffraction efficiencies can also be determined. In analyzing the chirped structure, a mesh is applied only to the area immediately around the grating. The size of the mesh is then proportional to the electric size of the grating. Doing this, however, imposes an artificial boundary around the area of interest. An absorbing boundary condition must be applied along the artificial boundary so that the outgoing waves are absorbed as if the boundary were absent. Many such boundary conditions have been developed that give near-perfect absorption. In this analysis, the Mur absorbing boundary conditions are employed. Several grating structures were analyzed using the FDTD method.

  20. Broadband Asymmetric Light Transmission at Metal/Dielectric Composite Grating. (United States)

    Zhu, Rui; Wu, Xuannan; Hou, Yidong; Zheng, Gaige; Zhu, Jianhua; Gao, Fuhua


    Optical diode-like effect has sparked growing interest in recent years due to its potential applications in integrated photonic systems. In this paper, we propose and numerically demonstrate a new type of easy-processing metal/dielectric cylinder composite grating on semi-sphere substrate, which can achieve high-contrast asymmetric transmission of unpolarized light for the sum of all diffraction modes in the entire visible region, and effectively guide the diffraction light transmitting out the substrate. The asymmetric light transmission (ALT) ratio is larger than 2 dB in the waveband from 380 nm to 780 nm and the maximum ALT ratio can reach to 13 dB at specified wavelengths. The thorough theoretical research reveals that the proposed metal/dielectric pillar composite grating structure, together with the substrate, can effectively excite localized surface plasmonic resonance (LSPR) effect and waveguide mode (WGM), and enlarge the diffraction difference between forward and backward transmission spaces, including both number of diffraction orders and diffraction efficiency, thus resulting in high-contrast broadband ALT phenomenon. In particular, lowering the symmetry of the grating can achieve polarization-dependent ALT. Such a type of easy-processing ALT device with high performance for both polarized and unpolarized light can be regarded as suitable candidates in practical applications.

  1. Surface plasmon interference lithography using Al grating structure on glass (United States)

    Kim, Yong Min; Choi, Kyung Cheol


    Photolithography is used in the important technologies of the device fabrication process in the semiconductor industry. However, photolithography has a pattern resolution limit because of the diffraction of light. Using surface plasmon (SP) is one of the ways to overcome this limit, which is a recently proposed nanolithography technology. Using SP, we developed a fabrication process using an Al grating structure on glass (glass/Al grating/PR structure). A perfect contact between the photoresist and the Al grating increased the effects of the SP because the contact gap was reduced in the photolithography process. The pattern pitch of lithography result was 120 nm (simulation results) and 115 nm (fabrication results). In surface plasmon interference lithography (SPIL) it is possible to use SP in the photolithography area. And we analyzed irregular pattern trends in the shape of random horizontal patterns and found that the patterns result from Al line edge roughness. Therefore, techniques that reduce the Al line edge roughness could enable clearer Al line patterns in SPIL.

  2. An optical fiber Bragg grating and piezoelectric ceramic voltage sensor. (United States)

    Yang, Qing; He, Yanxiao; Sun, Shangpeng; Luo, Mandan; Han, Rui


    Voltage measurement is essential in many fields like power grids, telecommunications, metallurgy, railways, and oil production. A voltage-sensing unit, consisting of fiber Bragg gratings (FBGs) and piezoelectric ceramics, based on which an optical over-voltage sensor was proposed and fabricated in this paper. No demodulation devices like spectrometer or Fabry-Perot filter were needed to gain the voltage signal, and a relatively large sensing frequency range was acquired in this paper; thus, the cost of the sensing system is more acceptable in engineering application. The voltage to be measured was directly applied to the piezoelectric ceramic, and deformation of the ceramics and the grating would be caused because of the inverse piezoelectric effect. With a reference grating, the output light intensity change will be caused by the FBG center wavelength change; thus, the relationship between the applied voltage and the output light intensity was established. Validation of the sensor was accomplished in the frequency range from 50 Hz to 20 kHz and switching impulse waves with a test platform; good linearity of the input-output characteristic was achieved. A temperature validation test was completed, showing that the sensor maintains good temperature stability. Experimental results show that the optical over-voltage sensor can be used for voltage monitoring, and if applied with a voltage divider, the sensor can be used to measure high voltage.

  3. A multi-wavelength fiber laser based on superimposed fiber grating and chirp fiber Bragg grating for wavelength selection (United States)

    Wang, Feng; Bi, Wei-hong; Fu, Xing-hu; Jiang, Peng; Wu, Yang


    In this paper, a new type of multi-wavelength fiber laser is proposed and demonstrated experimentally. Superimposed fiber grating (SIFG) and chirp fiber Bragg grating (CFBG) are used for wavelength selection. Based on gain equalization technology, by finely adjusting the stress device in the cavity, the gain and loss are equal, so as to suppress the modal competition and achieve multi-wavelength lasing at room temperature. The experimental results show that the laser can output stable multi-wavelength lasers simultaneously. The laser coupling loss is small, the structure is simple, and it is convenient for integration, so it can be widely used in dense wavelength division multiplexing (DWDM) system and optical fiber sensors.

  4. Spherical spacelike geometries in static spherically symmetric spacetimes: Generalized Painlevè–Gullstrand coordinates, foliation, and embedding

    Energy Technology Data Exchange (ETDEWEB)

    Akbar, M.M., E-mail:


    It is well known that static spherically symmetric spacetimes can admit foliations by flat spacelike hypersurfaces, which are best described in terms of the Painlevè–Gullstrand coordinates. The uniqueness and existence of such foliations were addressed earlier. In this paper, we prove, purely geometrically, that any possible foliation of a static spherically symmetric spacetime by an arbitrary codimension-one spherical spacelike geometry, up to time translation and rotation, is unique, and we find the algebraic condition under which it exists. This leads us to what can be considered as the most natural generalization of the Painlevè–Gullstrand coordinate system for static spherically symmetric metrics, which, in turn, makes it easy to derive generic conclusions on foliation and to study specific cases as well as to easily reproduce previously obtained generalizations as special cases. In particular, we note that the existence of foliation by flat hypersurfaces guarantees the existence of foliation by hypersurfaces whose Ricci curvature tensor is everywhere non-positive (constant negative curvature is a special case). The study of uniqueness and the existence concurrently solves the question of embeddability of a spherical spacelike geometry in one-dimensional higher static spherically symmetric spacetimes, and this produces known and new results geometrically, without having to go through the momentum and Hamiltonian constraints.

  5. Spherical spacelike geometries in static spherically symmetric spacetimes: Generalized Painlevè–Gullstrand coordinates, foliation, and embedding

    Directory of Open Access Journals (Sweden)

    M.M. Akbar


    Full Text Available It is well known that static spherically symmetric spacetimes can admit foliations by flat spacelike hypersurfaces, which are best described in terms of the Painlevè–Gullstrand coordinates. The uniqueness and existence of such foliations were addressed earlier. In this paper, we prove, purely geometrically, that any possible foliation of a static spherically symmetric spacetime by an arbitrary codimension-one spherical spacelike geometry, up to time translation and rotation, is unique, and we find the algebraic condition under which it exists. This leads us to what can be considered as the most natural generalization of the Painlevè–Gullstrand coordinate system for static spherically symmetric metrics, which, in turn, makes it easy to derive generic conclusions on foliation and to study specific cases as well as to easily reproduce previously obtained generalizations as special cases. In particular, we note that the existence of foliation by flat hypersurfaces guarantees the existence of foliation by hypersurfaces whose Ricci curvature tensor is everywhere non-positive (constant negative curvature is a special case. The study of uniqueness and the existence concurrently solves the question of embeddability of a spherical spacelike geometry in one-dimensional higher static spherically symmetric spacetimes, and this produces known and new results geometrically, without having to go through the momentum and Hamiltonian constraints.

  6. Spherical-shell model for the van der Waals coefficients between fullerenes and/or nearly spherical nanoclusters. (United States)

    Perdew, John P; Tao, Jianmin; Hao, Pan; Ruzsinszky, Adrienn; Csonka, Gábor I; Pitarke, J M


    Fullerene molecules such as C(60) are large nearly spherical shells of carbon atoms. Pairs of such molecules have a strong long-range van der Waals attraction that can produce scattering or binding into molecular crystals. A simplified classical-electrodynamics model for a fullerene is a spherical metal shell, with uniform electron density confined between outer and inner radii (just as a simplified model for a nearly spherical metallic nanocluster is a solid metal sphere or filled shell). For the spherical-shell model, the exact dynamic multipole polarizabilities are all known analytically. From them, we can derive exact analytic expressions for the van der Waals coefficients of all orders between two spherical metal shells. The shells can be identical or different, and hollow or filled. To connect the model to a real fullerene, we input the static dipole polarizability, valence electron number and estimated shell thickness t of the real molecule. Our prediction for the leading van der Waals coefficient C(6) between two C(60) molecules ((1.30 ± 0.22) × 10(5) hartree bohr(6)) agrees well with a prediction for the real molecule from time-dependent density functional theory. Our prediction is remarkably insensitive to t. Future work might include the prediction of higher-order (e.g. C(8) and C(10)) coefficients for C(60), applications to other fullerenes or nearly spherical metal clusters, etc. We also make general observations about the van der Waals coefficients.

  7. High efficiency geometric-phase polarization fan-out grating on silicon. (United States)

    Wan, Chenhao; Lombardo, David; Sarangan, Andrew; Zhan, Qiwen


    We report the design, fabrication and characterization of a 1-by-5 geometric-phase polarization fan-out grating for coherent beam combining at 1550 nm. The phase profile of the grating is accurately controlled by the local orientation of the binary subwavelength structure instead of the etching depth and profile empowering the grating to be more tolerant to fabrication errors. Deep-UV interference lithography on silicon offers an inexpensive, highly efficient and high damage threshold solution to fabricating large-area fan-out gratings than electron beam lithography (EBL) and photoalignment liquid crystals. The theoretical and experimental diffraction efficiency of the grating is 87% and 85.7% respectively. Such a fan-out grating may find application to high-power beam combining in the infrared regime.

  8. Surface plasmon resonance hydrogen sensor based on metallic grating with high sensitivity. (United States)

    Lin, Kaiqun; Lu, Yonghua; Chen, Junxue; Zheng, Rongsheng; Wang, Pei; Ming, Hai


    High sensitivity is obtained at larger resonant incident angle if negative diffraction order of metallic grating is used to excite the surface plasmon. A highly sensitive grating-based surface plasmon resonance (SPR) sensor is designed for the hydrogen detection. A thin palladium (Pd) film deposited on the grating surface is used as transducer. The influences of grating period and the thickness of Pd on the performance of sensor are investigated using rigorous coupled-wave analysis (RCWA) method. The sensitivity as well as the width of the SPR curves and reflective amplitude is considered simultaneously for designing the grating-based SPR hydrogen sensor, and a set of optimized structural parameters is presented. The performance of grating-based SPR sensor is also compared with that of conventional prism-based SPR sensor.

  9. Surface plasmon-polariton resonance at diffraction of THz radiation on semiconductor gratings (United States)

    Spevak, I. S.; Kuzmenko, A. A.; Tymchenko, M.; Gavrikov, V. K.; Shulga, V. M.; Feng, J.; Sun, H. B.; Kamenev, Yu. E.; Kats, A. V.


    Resonance diffraction of THz hidrogen cyanide laser radiation on a semiconductor (InSb) grating is studied both experimentally and theoretically. The specular reflectivity suppression due to the resonance excitation of the THz surface plasmon-polariton is observed on a pure semiconductor grating and on semiconductor gratings covered with a thin dielectric layer. The dielectric coating of the grating results in the resonance shift and widening depending both on the layer thickness and dielectric properties. A simple analytical theory of the resonance diffraction on rather shallow gratings covered with a dielectric layer is presented, and the results are in a good accordance with the experimental data. Analytical expressions for the resonance shift and broadening are essential for the resonance properties understanding and useful for sensing data interpretation of the agents deposited on the grating surface.

  10. Measurement accuracy of articulated arm CMMs with circular grating eccentricity errors (United States)

    Zheng, Dateng; Yin, Sanfeng; Luo, Zhiyang; Zhang, Jing; Zhou, Taiping


    The 6 circular grating eccentricity errors model attempts to improve the measurement accuracy of an articulated arm coordinate measuring machine (AACMM) without increasing the corresponding hardware cost. We analyzed the AACMM’s circular grating eccentricity and obtained the 6 joints’ circular grating eccentricity error model parameters by conducting circular grating eccentricity error experiments. We completed the calibration operations for the measurement models by using home-made standard bar components. Our results show that the measurement errors from the AACMM’s measurement model without and with circular grating eccentricity errors are 0.0834 mm and 0.0462 mm, respectively. Significantly, we determined that measurement accuracy increased by about 44.6% when the circular grating eccentricity errors were corrected. This study is significant because it promotes wider applications of AACMMs both in theory and in practice.

  11. [Research on the photoelectric conversion efficiency of grating antireflective layer solar cells]. (United States)

    Zhong, Hui; Gao, Yong-Yi; Zhou, Ren-Long; Zhou, Bing-ju; Tang, Li-qiang; Wu, Ling-xi; Li, Hong-jian


    A numerical investigation of the effect of grating antireflective layer structure on the photoelectric conversion efficiency of solar cells was carried out by the finite-difference time-domain method. The influence of grating shape, height and the metal film thickness coated on grating surface on energy storage was analyzed in detail. It was found that the comparison between unoptimized and optimized surface grating structure on solar cells shows that the optimization of surface by grating significantly increases the energy storage capability and greatly improves the efficiency, especially of the photoelectric conversion efficiency and energy storage of the triangle grating. As the film thickness increases, energy storage effect increases, while as the film thickness is too thick, energy storage effect becomes lower and lower.

  12. Asymptotic model for finite-element calculations of diffraction by shallow metallic surface-relief gratings. (United States)

    Rivas, Cinthya; Solano, Manuel E; Rodríguez, Rodolfo; Monk, Peter B; Lakhtakia, Akhlesh


    We have formulated an asymptotic model for implementation in the finite-element method to calculate diffraction from a planar multilayered structure having a shallow surface-relief grating. The thin grating layer containing the shallow grating is replaced by a planar interface with transmission conditions that differ from the standard continuity conditions, thereby eliminating the necessity of representing the grating layer by a fine mesh. The parameters defining the shallow surface-relief grating are thereby removed from the geometry to the transmission conditions. Adoption of the asymptotic model will considerably reduce the computational cost of optimizing the grating shape because there is no need to re-mesh at every optimization step.

  13. Correcting groove error in gratings ruled on a 500-mm ruling engine using interferometric control. (United States)

    Mi, Xiaotao; Yu, Haili; Yu, Hongzhu; Zhang, Shanwen; Li, Xiaotian; Yao, Xuefeng; Qi, Xiangdong; Bayinhedhig; Wan, Qiuhua


    Groove error is one of the most important factors affecting grating quality and spectral performance. To reduce groove error, we propose a new ruling-tool carriage system based on aerostatic guideways. We design a new blank carriage system with double piezoelectric actuators. We also propose a completely closed-loop servo-control system with a new optical measurement system that can control the position of the diamond relative to the blank. To evaluate our proposed methods, we produced several gratings, including an echelle grating with 79  grooves/mm, a grating with 768  grooves/mm, and a high-density grating with 6000  grooves/mm. The results show that our methods effectively reduce groove error in ruled gratings.

  14. Time-and-frequency domains approach to data processing in multiwavelength optical scatterometry of dielectric gratings

    KAUST Repository

    Granet, Gérard


    This paper focuses on scatterometry problems arising in lithography production of periodic gratings. Namely, the paper introduces a theoretical and numerical-modeling-oriented approach to scatterometry problems and discusses its capabilities. The approach allows for reliable detection of deviations in gratings\\' critical dimensions (CDs) during the manufacturing process. The core of the approach is the one-to-one correspondence between the electromagnetic (EM) characteristics and the geometric/material properties of gratings. The approach is based on highly accurate solutions of initial boundary-value problems describing EM waves\\' interaction on periodic gratings. The advantage of the approach is the ability to perform simultaneously and interactively both in frequency and time domains under conditions of possible resonant scattering of EM waves by infinite or finite gratings. This allows a detection of CDs for a wide range of gratings, and, thus is beneficial for the applied scatterometry. (C) 2013 Optical Society of America

  15. X-ray grating interferometry at photon energies over 180 keV

    Energy Technology Data Exchange (ETDEWEB)

    Ruiz-Yaniz, M., E-mail: [European Synchrotron Radiation Facility, 71 Rue des Martyrs, 38000 Grenoble (France); Lehrstuhl für Biomedizinische Physik, Physik-Department and Institut für Medizintechnik, Technische Universität München, James-Franck-Str. 1, 85748 Garching (Germany); Koch, F.; Meyer, P.; Kunka, D.; Mohr, J. [Institute of Microstructure Technology, Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany); Zanette, I. [Lehrstuhl für Biomedizinische Physik, Physik-Department and Institut für Medizintechnik, Technische Universität München, James-Franck-Str. 1, 85748 Garching (Germany); Diamond Light Source, Harwell Science and Innovation Campus, Didcot OX11 0DE (United Kingdom); Rack, A. [European Synchrotron Radiation Facility, 71 Rue des Martyrs, 38000 Grenoble (France); Hipp, A. [Institute of Materials Research, Helmholtz-Zentrum Geesthacht, Max-Plank Strasse 1, 21502 Geesthacht (Germany); Pfeiffer, F. [Lehrstuhl für Biomedizinische Physik, Physik-Department and Institut für Medizintechnik, Technische Universität München, James-Franck-Str. 1, 85748 Garching (Germany); Institut für diagnostische und interventionelle Radiologie, Klinikum rechts der Isar, Technische Universität München, 81675 München (Germany)


    We report on the implementation and characterization of grating interferometry operating at an x-ray energy of 183 keV. With the possibility to use this technique at high x-ray energies, bigger specimens could be studied in a quantitative way. Also, imaging strongly absorbing specimens will benefit from the advantages of the phase and dark-field signals provided by grating interferometry. However, especially at these high photon energies the performance of the absorption grating becomes a key point on the quality of the system, because the grating lines need to keep their small width of a couple of micrometers and exhibit a greater height of hundreds of micrometers. The performance of high aspect ratio absorption gratings fabricated with different techniques is discussed. Further, a dark-field image of an alkaline multicell battery highlights the potential of high energy x-ray grating based imaging.

  16. Three-port beam splitter for slow neutrons using holographic nanoparticle-polymer composite diffraction gratings

    Energy Technology Data Exchange (ETDEWEB)

    Klepp, J.; Fally, M. [Faculty of Physics, University of Vienna, 1090 Wien (Austria); Tomita, Y. [Department of Engineering Science, University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo 182 (Japan); Pruner, C. [Department of Materials Science and Physics, University of Salzburg, 5020 Salzburg (Austria); Kohlbrecher, J. [Laboratory for Neutron Scattering, Paul Scherrer Institut, 5232 Villigen PSI (Switzerland)


    Diffraction of slow neutrons by nanoparticle-polymer composite gratings has been observed. By carefully choosing grating parameters such as grating thickness and spacing, a three-port beam splitter operation for slow neutrons - splitting the incident neutron intensity equally into the {+-}1st and the 0th diffraction orders - has been realized. As a possible application, a Zernike three-path interferometer is briefly discussed.

  17. High-Average-Power Diffraction Pulse-Compression Gratings Enabling Next-Generation Ultrafast Laser Systems

    Energy Technology Data Exchange (ETDEWEB)

    Alessi, D. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)


    Pulse compressors for ultrafast lasers have been identified as a technology gap in the push towards high peak power systems with high average powers for industrial and scientific applications. Gratings for ultrashort (sub-150fs) pulse compressors are metallic and can absorb a significant percentage of laser energy resulting in up to 40% loss as well as thermal issues which degrade on-target performance. We have developed a next generation gold grating technology which we have scaled to the petawatt-size. This resulted in improvements in efficiency, uniformity and processing as compared to previous substrate etched gratings for high average power. This new design has a deposited dielectric material for the grating ridge rather than etching directly into the glass substrate. It has been observed that average powers as low as 1W in a compressor can cause distortions in the on-target beam. We have developed and tested a method of actively cooling diffraction gratings which, in the case of gold gratings, can support a petawatt peak power laser with up to 600W average power. We demonstrated thermo-mechanical modeling of a grating in its use environment and benchmarked with experimental measurement. Multilayer dielectric (MLD) gratings are not yet used for these high peak power, ultrashort pulse durations due to their design challenges. We have designed and fabricated broad bandwidth, low dispersion MLD gratings suitable for delivering 30 fs pulses at high average power. This new grating design requires the use of a novel Out Of Plane (OOP) compressor, which we have modeled, designed, built and tested. This prototype compressor yielded a transmission of 90% for a pulse with 45 nm bandwidth, and free of spatial and angular chirp. In order to evaluate gratings and compressors built in this project we have commissioned a joule-class ultrafast Ti:Sapphire laser system. Combining the grating cooling and MLD technologies developed here could enable petawatt laser systems to

  18. Moiré phase-shifted fiber Bragg gratings in polymer optical fibers

    DEFF Research Database (Denmark)

    Min, Rui; Marques, Carlos; Bang, Ole


    We demonstrate a simple way to fabricate phase-shifted fiber Bragg grating in polymer optical fibers as a narrowband transmission filter for a variety of applications at telecom wavelengths. The filters have been fabricated by overlapping two uniform fiber Bragg gratings with slightly different...... periods to create a Moiré grating with only two pulses (one pulse is 15 ns) of UV power. Experimental characterization of the filter is provided under different conditions where the strain and temperature sensitivities were measured....

  19. Holographic Recording and Applications of Multiplexed Volume Bragg Gratings in Photo-Thermo-Refractive Glass (United States)


    Common methods for creating angle/wavelength selectivity. a.) prism b.) thin transmitting diffraction grating c.) blazed grating in the Littrow...resolution tunable laser. A 3 dB coupler is used to determine alignment by monitoring the intensity of back reflection from the gratings rejection band...shows the separation of input light into different angular components using a simple prism . These angularly separated components are then accessible by

  20. Angle dependent Fiber Bragg grating inscription in microstructured polymer optical fibers


    Bundalo, Ivan-Lazar; Nielsen, Kristian; Bang, Ole


    We report on an incidence angle influence on inscription of the Fiber Bragg Gratings in Polymethyl methacrylate (PMMA) microstructured polymer optical fibers. We have shown experimentally that there is a strong preference of certain angles, labeled Gamma K, over the other ones. Angles close to Gamma K showed fast start of inscription, rapid inscription and stronger gratings. We have also shown that gratings can be obtained at almost any angle but their quality will be lower if they are not ar...

  1. Angled grating high-power semiconductor lasers: simulation of beam characteristics under thermal effects (United States)

    Sarangan, Andrew M.


    The angled grating laser has been successful in achieving high-power diffraction-limited beams. The laser cavity utilizes a grating inclined at an angle to the facet to filter out the filamented beams. As a result, all of the filamented beams except the primary beam will be transmitted through the grating. In this paper we present the cavity resonance equation, and study temperature sensitivity of this device.

  2. Slow-light effect via Rayleigh anomaly and the effect of finite gratings. (United States)

    Kim, Kyoung-Youm; Chong, Xinyuan; Ren, Fanghui; Wang, Alan X


    In this Letter, we investigate the slow-light effect of subwavelength diffraction gratings via the Rayleigh anomaly using a fully analytical approach without needing to consider specific grating structures. Our results show that the local group velocity of the transmitted light can be significantly reduced due to the optical vortex, which can inspire a new mechanism to enhance light-matter interactions for optical sensing and photodetection. However, the slow-light effect will diminish as the transmitted light propagates farther from the grating surface, and the slowdown factor decreases as the grating size shrinks.

  3. Long Period Gratings in Random Hole Optical Fibers for Refractive Index Sensing

    Directory of Open Access Journals (Sweden)

    Gary Pickrell


    Full Text Available We have demonstrated the fabrication of long period gratings in random hole optical fibers. The long period gratings are fabricated by a point-by-point technique using a CO2 laser. The gratings with a periodicity of 450 µm are fabricated and a maximum coupling efficiency of −9.81 dB has been achieved. Sensing of different refractive indices in the surrounding mediums is demonstrated by applying standard liquids with refractive indices from 1.400 to 1.440 to the long period grating.

  4. Gelator-doped liquid-crystal phase grating with multistable and dynamic modes (United States)

    Lin, Hui-Chi; Yang, Meng-Ru; Tsai, Sheng-Feng; Yan, Shih-Chiang


    We demonstrate a gelator-doped nematic liquid-crystal (LC) phase grating, which can be operated in both the multistable mode and the dynamic mode. Thermoreversible association and dissociation of the gelator molecules can vary and fix the multistable diffraction efficiencies of the gratings. A voltage (V) can also be applied to modulate dynamically the diffraction efficiencies of the grating, which behaves as a conventional LC grating. Experimental results show that the variations of the diffraction efficiencies in the multistable and dynamic modes are similar. The maximum diffraction efficiency is approximately 30% at V = 2 V.

  5. Gelator-doped liquid-crystal phase grating with multistable and dynamic modes

    Energy Technology Data Exchange (ETDEWEB)

    Lin, Hui-Chi, E-mail:; Yang, Meng-Ru; Tsai, Sheng-Feng; Yan, Shih-Chiang [Department of Electro-Optical Engineering, National Formosa University, Yunlin 632, Taiwan (China)


    We demonstrate a gelator-doped nematic liquid-crystal (LC) phase grating, which can be operated in both the multistable mode and the dynamic mode. Thermoreversible association and dissociation of the gelator molecules can vary and fix the multistable diffraction efficiencies of the gratings. A voltage (V) can also be applied to modulate dynamically the diffraction efficiencies of the grating, which behaves as a conventional LC grating. Experimental results show that the variations of the diffraction efficiencies in the multistable and dynamic modes are similar. The maximum diffraction efficiency is approximately 30% at V = 2 V.

  6. Photorefractive grating formation in piezoelectric La3Ga5SiO14:Pr3+ crystals

    DEFF Research Database (Denmark)

    Dam-Hansen, C.; Johansen, P.M.; Fridkin, V.M.


    Photorefractive grating formation and erasure in piezoelectric crystals of La3Ga5SiO14:Pr3+ are presented. The specific photoconductivity and the photorefractive sensitivity are determined. The polarization dependence of the grating formation due to the bulk photovoltaic effect is shown and compa......Photorefractive grating formation and erasure in piezoelectric crystals of La3Ga5SiO14:Pr3+ are presented. The specific photoconductivity and the photorefractive sensitivity are determined. The polarization dependence of the grating formation due to the bulk photovoltaic effect is shown...

  7. Polarization-independent light-dispersing optical device consisting of two diffraction gratings and a waveplate. (United States)

    Amako, J; Fujii, E


    We report on a light-dispersing device consisting of two transmission gratings and a waveplate. The gratings separate two orthogonal polarization components of light incident at the Bragg angle. The waveplate, which is sandwiched between the gratings, functions as a polarization converter for oblique light incidence. With these optical parts suitably integrated, the resulting device efficiently diffracts unpolarized light with high spectral resolution. Using coupled-wave theories and Mueller matrix analysis, we constructed a device for a wavelength range of 680±50  nm with a 400 nm grating period. From the characterization of this optical device, we validated the proposed polarization-independent, light-dispersing concept.

  8. Coherent control of light-pulse propagation in a Raman induced grating (United States)

    Arkhipkin, V. G.; Myslivets, S. A.


    We study light-pulse propagation in a dynamically controllable periodic structure (grating) resulting from Raman interaction of a weak probe pulse with a standing-wave pump and a second control laser field in N-type four-level atomic media. The grating is induced due to periodic spatial modulation of the Raman gain in a standing pump field (Raman gain grating). We show that it is possible to control both the probe pulse amplitude and the group velocity of the pulse from subluminal to superluminal by varying the pump or control field. Such a grating is of interest for all-optical switches and transistors.

  9. Holographically formed, acoustically switchable gratings based on polymer-dispersed liquid crystals. (United States)

    Liu, Yan Jun; Lu, Mengqian; Ding, Xiaoyun; Leong, Eunice S P; Lin, Sz-Chin Steven; Shi, Jinjie; Teng, Jing Hua; Wang, Lin; Bunning, Timothy J; Huang, Tony Jun


    We report holographic polymer-dispersed liquid crystal (H-PDLC) gratings driven by surface acoustic waves (SAWs). Our experiments show that upon applying SAWs, the H-PDLC grating exhibited switchable properties: The diffraction of the H-PDLC grating decreased, whereas the transmission increased. This acoustically switchable behavior is due to the acoustic streaming-induced realignment of liquid crystals as well as absorption-resulted thermal diffusion. Such SAW-driven H-PDLC gratings are potentially useful in many photonic applications, such as optical switches, spatial light modulators, and switchable add/drop filters.

  10. Theory and characteristics of holographic polymer dispersed liquid crystal transmission grating with scaffolding morphology. (United States)

    Huang, Wenbin; Liu, Yonggang; Diao, Zhihui; Yang, Chengliang; Yao, Lishuang; Ma, Ji; Xuan, Li


    We have performed a detailed characterization of the optical properties of a holographic polymer dispersed liquid crystal (LC) transmission grating with polymer scaffolding morphology, which was fabricated with conventional high-functionality acrylate monomer under low curing intensity. Temporal evolution of the grating formation was investigated, and the amount of phase-separated LC was determined by birefringence investigation. A grating model combined with anisotropic coupled-wave theory yielded good agreement with experimental data without any fitting parameter. The results in this study demonstrate the non droplet scaffolding morphology grating is characterized by a high degree of phase separation (70%), high anisotropy, low scattering loss (<6%), and high diffraction efficiency (95%).

  11. Transmission Grating and Optics Technology Development for the Arcus Explorer Mission (United States)

    Heilmann, Ralf; Arcus Team


    Arcus is a high-resolution x-ray spectroscopy MIDEX mission selected for a Phase A concept study. It is designed to explore structure formation through measurements of hot baryon distributions, feedback from black holes, and the formation and evolution of stars, disks, and exoplanet atmospheres. The design provides unprecedented sensitivity in the 1.2-5 nm wavelength band with effective area above 450 sqcm and spectral resolution R > 2500. The Arcus technology is based on 12 m-focal length silicon pore optics (SPO) developed for the European Athena mission, and critical-angle transmission (CAT) x-ray diffraction gratings and x-ray CCDs developed at MIT. The modular design consists of four parallel channels, each channel holding an optics petal, followed by a grating petal. CAT gratings are lightweight, alignment insensitive, high-efficiency x-ray transmission gratings that blaze into high diffraction orders, leading to high spectral resolution. Each optics petal represents an azimuthal sub-aperture of a full Wolter optic. The sub-aperturing effect increases spectral resolving power further. Two CCD readout strips receive photons from each channel, including higher-energy photons in 0th order. Each optics petal holds 34 SPO modules. Each grating petal holds 34 grating windows, and each window holds 4-6 grating facets. A grating facet consists of a silicon grating membrane, bonded to a flexure frame that interfaces with the grating window. We report on a sequence of tests with increasing complexity that systematically increase the Technology Readiness Level (TRL) for the combination of CAT gratings and SPOs towards TLR 6. CAT gratings have been evaluated in x rays for diffraction efficiency (> 30% at 2.5 nm) and for resolving power (R> 10,000). A CAT grating/SPO combination was measured at R ~ 3100 at blaze angles smaller than design values, exceeding Arcus requirements. Efficiency and resolving power were not impacted by vibration and thermal testing of gratings. A

  12. Femtosecond-pulse inscription of fiber Bragg gratings in multimode graded index fiber (United States)

    Dostovalov, Alexandr V.; Wolf, Alexey A.; Zlobina, Ekaterina A.; Kablukov, Sergey I.; Babin, Sergey A.


    Femtosecond-pulse modification of the refractive index in transparent materials enables the inscription of fiber Bragg gratings with new features and extended capabilities. In this study we present the results of fiber Bragg gratings inscription in Corning 62.5/125 multimode graded index fiber with IR femtosecond laser pulses. The specifics of point-by-point inscription including single and multiple Bragg grating inscription in limited fiber segment as well as different transverse modes excitation/suppression is discussed. Multimode fiber Bragg gratings inscribed with femtosecond radiation are investigated for the first time directly in the Raman fiber laser cavity.

  13. Fabrication of Bragg grating sensors in UV-NIL structured Ormocer waveguides (United States)

    Girschikofsky, Maiko; Förthner, Michael; Rommel, Mathias; Frey, Lothar; Hellmann, Ralf


    We report on the fabrication and characterization of Bragg gratings in UV-NIL structured Ormocer hybrid polymer rib-type waveguides using phase mask technology. The influence of fabrication parameters such as the applied laser fluence during the inscription process and the grating's length on the spectral behavior of the waveguide Bragg gratings was experimentally determined and compared to numerical simulations and calculations. To investigate potential sensor applications, the sensitivity of the thus fabricated optical devices towards refractive index changes of the gratings' surrounding (qualification for bio- and chemical sensing) as well as the sensitivity towards temperature and relative humidity were determined.

  14. Fabrication of advanced Bragg gratings with complex apodization profiles by use of the polarization control method

    DEFF Research Database (Denmark)

    Deyerl, Hans-Jürgen; Plougmann, Nikolai; Jensen, Jesper Bo Damm


    The polarization control method offers a flexible, robust, and low-cost route for the parallel fabrication of gratings with complex apodization profiles including several discrete phase shifts and chirp. The performance of several test gratings is evaluated in terms of their spectral response...... and compared with theoretical predictions. Short gratings with sidelobe-suppression levels in excess of 32 dB and transmission dips lower than 80 dB have been realized. Finally, most of the devices fabricated by the polarization control method show comparable quality to gratings manufactured by far more...... complex methods....

  15. An update on X-ray reflection gratings developed for future missions (United States)

    Miles, Drew


    X-ray reflection gratings are a key technology being studied for future X-ray spectroscopy missions, including the Lynx X-ray mission under consideration for the 2020 Decadal Survey. We present an update on the status of X-ray reflection gratings being developed at Penn State University, including current fabrication techniques and mass-replication processes and the latest diffraction efficiency results and resolving power measurements. Individual off-plane X-ray reflection gratings have exceeded the current Lynx requirements for both effective area and resolving power. Finally, we discuss internal projects that will advance the technology readiness level of these gratings.

  16. Transmitted wavefront error of a volume phase holographic grating at cryogenic temperature. (United States)

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


    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.

  17. Preparation of spherical particles by vibrating orifice technique (United States)

    Shibata, Shuichi; Tomizawa, Atsushi; Yoshikawa, Hidemi; Yano, Tetsuji; Yamane, Masayuki


    Preparation of micrometer-sized spherical particles containing Rhodamine 6G (R6G) has been investigated for the spherical cavity micro-laser. Using phenyl triethoxy silane (PTES) as a starting material, R6G-doped monodisperse spherical particles were prepared by the vibrating orifice technique. Processing consists of two major processes: (1) Hydrolysis and polymerization of PTES and (2) Droplet formation from PTES oligomers by vibrating orifice technique. A cylindrical liquid jet passing through the orifice of 10 and 20 micrometers in diameter breaks up into equal- sized droplets by mechanical vibration. Alcohol solvent of these droplets was evaporated during flying with carrier gas and subsequently solidified in ammonium water trap. For making smooth surface and god shaped particles, control of molecular weight of PTES oligomer was essential. R6G-doped hybrid spherical particles of 4 to 10 micrometers size of cavity structure were successfully obtained. The spherical particles were pumped by a second harmonic pulse of Q- switched Nd:YAG laser and laser emission peaks were observed at wavelengths which correspond to the resonance modes.

  18. Source distance determination based on the spherical harmonics (United States)

    Koutny, Adam; Jiricek, Ondrej; Thomas, Jean-Hugh; Brothanek, Marek


    This paper deals with the processing of signals measured by a spherical microphone array, focusing on the utilization of near-field information of such an array. The processing, based on the spherical harmonics decomposition, is performed in order to investigate the radial-dependent spherical functions and extract their argument - distance to the source. Using the low-frequency approximation of these functions, the source distance is explicitly expressed. The source distance is also determined from the original equation (using no approximation) by comparing both sides of this equation. The applicability of both methods is first presented in the noise-less data simulation, then validated with data contaminated by the additive white noise of different signal-to-noise ratios. Finally, both methods are tested for real data measured by a rigid spherical microphone array of radius 0.15 m, consisting of 36 microphones for a point source represented by a small speaker. The possibility of determination of the source distance using low-order spherical harmonics is shown.

  19. Templated nucleation of acetaminophen on spherical excipient agglomerates. (United States)

    Quon, Justin L; Chadwick, Keith; Wood, Geoffrey P F; Sheu, Iris; Brettmann, Blair K; Myerson, Allan S; Trout, Bernhardt L


    We investigated the effect of spherical agglomeration of heterogeneous crystalline substrates on the nucleation of acetaminophen (AAP). Optical and electron microscopy showed that the surface morphologies of single crystal triclinic lactose and D-mannitol differed significantly from their counterparts formed via spherical agglomeration. Spherical agglomerates of lactose were shown to enhance the nucleation rate of acetaminophen (AAP) by a factor of 11 compared to single crystal lactose; however, no such enhancement was observed for D-mannitol. X-ray powder diffraction identified the presence of new crystal faces of lactose present only in the spherical agglomerates However, D-mannitol did not show any significant change in crystal morphology. The new crystal faces of triclinic lactose were analyzed using geometric lattice matching software and molecular dynamics simulations to establish any new and significant epitaxial matches between lactose and AAP. A coincident lattice match and a large favorable energy interaction from hydrogen bonding were observed between the (141¯) and (001) crystal faces of lactose and AAP, respectively. The enhanced nucleation kinetics, X-ray data, and computational studies indicated that the spherical crystallization of lactose exposed the (141¯) face on the surface of the agglomerates, which subsequently enhanced the nucleation rate of AAP through geometric lattice matching and molecular functionality. This study highlights the importance of exploring different heterogeneous substrate morphologies for enhancing nucleation kinetics.

  20. Peripheral Defocus with Spherical and Multifocal Soft Contact Lenses (United States)

    Berntsen, David A.; Kramer, Carl E.


    Purpose To describe peripheral defocus when myopic eyes are corrected with spherical and center-distance multifocal soft contact lenses while looking at distance and near. Methods Twenty-five young adults with spherical contact lens-corrected refractive error of −0.50 to −6.00 D participated. Refractive error of each participant’s right eye was measured while it wore a spherical soft contact lens (Biofinity) and again while it wore a center-distance multifocal soft contact lens with a +2.50-D add (Biofinity Multifocal "D"). Measurements were made centrally and along the horizontal meridian at ±20°, ±30°, and ±40° from the line of sight at distance and near (3.33-D demand). Results The mean (±SD) age and spherical equivalent refractive error were 23.8 ± 1.3 years and −3.62 ± 1.56 D, respectively. At distance, the multifocal contact lens resulted in significantly more myopic defocus than the spherical contact lens at the 40° and 30° locations on the nasal retina and at the 20° and 30° locations on the temporal retina (pcontact lens in this study make it a good candidate for studies seeking to examine the effect of peripheral myopic defocus on myopia progression in children. PMID:24076542