WorldWideScience

Sample records for order harmonic generation

  1. High order harmonic generation in rare gases

    Budil, Kimberly Susan [Univ. of California, Davis, CA (United States)

    1994-05-01

    The process of high order harmonic generation in atomic gases has shown great promise as a method of generating extremely short wavelength radiation, extending far into the extreme ultraviolet (XUV). The process is conceptually simple. A very intense laser pulse (I ~1013-1014 W/cm2) is focused into a dense (~1017 particles/cm3) atomic medium, causing the atoms to become polarized. These atomic dipoles are then coherently driven by the laser field and begin to radiate at odd harmonics of the laser field. This dissertation is a study of both the physical mechanism of harmonic generation as well as its development as a source of coherent XUV radiation. Recently, a semiclassical theory has been proposed which provides a simple, intuitive description of harmonic generation. In this picture the process is treated in two steps. The atom ionizes via tunneling after which its classical motion in the laser field is studied. Electron trajectories which return to the vicinity of the nucleus may recombine and emit a harmonic photon, while those which do not return will ionize. An experiment was performed to test the validity of this model wherein the trajectory of the electron as it orbits the nucleus or ion core is perturbed by driving the process with elliptically, rather than linearly, polarized laser radiation. The semiclassical theory predicts a rapid turn-off of harmonic production as the ellipticity of the driving field is increased. This decrease in harmonic production is observed experimentally and a simple quantum mechanical theory is used to model the data. The second major focus of this work was on development of the harmonic "source". A series of experiments were performed examining the spatial profiles of the harmonics. The quality of the spatial profile is crucial if the harmonics are to be used as the source for experiments, particularly if they must be refocused.

  2. High order harmonic generation from plasma mirror

    Thaury, C.

    2008-09-01

    When an intense laser beam is focused on a solid target, its surface is rapidly ionized and forms a dense plasma that reflects the incident field. For laser intensities above few 10 15 W/cm 2 , high order harmonics of the laser frequency, associated in the time domain to a train of atto-second pulses (1 as = 10 18 s), can be generated upon this reflection. Because such a plasma mirror can be used with arbitrarily high laser intensities, this process should eventually lead to the production of very intense pulses in the X-ray domain. In this thesis, we demonstrate that for laser intensities about 10 19 W/cm 2 , two mechanisms can contribute to the generation of high order harmonics: the coherent wake emission and the relativistic emission. These two mechanisms are studied both theoretically and experimentally. In particular, we show that, thanks to very different properties, the harmonics generated by these two processes can be unambiguously distinguished experimentally. We then investigate the phase properties of the harmonic, in the spectral and in the spatial domain. Finally, we illustrate how to exploit the coherence of the generation mechanisms to get information on the dynamics of the plasma electrons. (author)

  3. High order harmonic generation from plasma mirrors

    George, H.

    2010-01-01

    When an intense laser beam is focused on a solid target, the target's surface is rapidly ionized and forms dense plasma that reflects the incident field. For laser intensities above few 10 to the power of 15 Wcm -2 , high order harmonics of the laser frequency, associated in the time domain to a train of atto-second pulses (1 as 10 -18 s), can be generated upon this reflection. In this thesis, we developed numerical tools to reveal original aspects of harmonic generation mechanisms in three different interaction regime: the coherent wake emission, the relativistic emission and the resonant absorption. In particular, we established the role of these mechanisms when the target is a very thin foil (thickness of the order of 100 nm). Then we study experimentally the spectral, spatial and coherence properties of the emitted light. We illustrate how to exploit these measurements to get information on the plasma mirror dynamics on the femtosecond and atto-second time scales. Last, we propose a technique for the single-shot complete characterization of the temporal structure of the harmonic light emission from the laser-plasma mirror interaction. (author)

  4. Theoretical description of high-order harmonic generation in solids

    Kemper, A F; Moritz, B; Devereaux, T P; Freericks, J K

    2013-01-01

    We consider several aspects of high-order harmonic generation in solids: the effects of elastic and inelastic scattering, varying pulse characteristics and inclusion of material-specific parameters through a realistic band structure. We reproduce many observed characteristics of high harmonic generation experiments in solids including the formation of only odd harmonics in inversion-symmetric materials, and the nonlinear formation of high harmonics with increasing field. We find that the harmonic spectra are fairly robust against elastic and inelastic scattering. Furthermore, we find that the pulse characteristics can play an important role in determining the harmonic spectra. (paper)

  5. High-order harmonics generation from overdense plasmas

    Quere, F.; Thaury, C.; Monot, P.; Martin, Ph.; Geindre, J.P.; Audebert, P.; Marjoribanks, R.

    2006-01-01

    Complete test of publication follows. When an intense laser beam reflects on an overdense plasma generated on a solid target, high-order harmonics of the incident laser frequency are observed in the reflected beam. This process provides a way to produce XUV femtosecond and attosecond pulses in the μJ range from ultrafast ultraintense lasers. Studying the mechanisms responsible for this harmonic emission is also of strong fundamental interest: just as HHG in gases has been instrumental in providing a comprehensive understanding of basic intense laser-atom interactions, HHG from solid-density plasmas is likely to become a unique tool to investigate many key features of laser-plasma interactions at high intensities. We will present both experimental and theoretical evidence that two mechanisms contribute to this harmonic emission: - Coherent Wake Emission: in this process, harmonics are emitted by plasma oscillations in te overdense plasma, triggered in the wake of jets of Brunel electrons generated by the laser field. - The relativistic oscillating mirror: in this process, the intense laser field drives a relativistic oscillation of the plasma surface, which in turn gives rise to a periodic phase modulation of the reflected beam, and hence to the generation of harmonics of the incident frequency. Left graph: experimental harmonic spectrum from a polypropylene target, obtained with 60 fs laser pulses at 10 19 W/cm 2 , with a very high temporal contrast (10 10 ). The plasma frequency of this target corresponds to harmonics 15-16, thus excluding the CWE mechanism for the generation of harmonics of higher orders. Images on the right: harmonic spectra from orders 13 et 18, for different distances z between the target and the best focus. At the highest intensity (z=0), harmonics emitted by the ROM mechanism are observed above the 15th order. These harmonics have a much smaller spectral width then those due to CWE (below the 15th order). These ROM harmonics vanish as soon

  6. Generation of intense high-order vortex harmonics.

    Zhang, Xiaomei; Shen, Baifei; Shi, Yin; Wang, Xiaofeng; Zhang, Lingang; Wang, Wenpeng; Xu, Jiancai; Yi, Longqiong; Xu, Zhizhan

    2015-05-01

    This Letter presents for the first time a scheme to generate intense high-order optical vortices that carry orbital angular momentum in the extreme ultraviolet region based on relativistic harmonics from the surface of a solid target. In the three-dimensional particle-in-cell simulation, the high-order harmonics of the high-order vortex mode is generated in both reflected and transmitted light beams when a linearly polarized Laguerre-Gaussian laser pulse impinges on a solid foil. The azimuthal mode of the harmonics scales with its order. The intensity of the high-order vortex harmonics is close to the relativistic region, with the pulse duration down to attosecond scale. The obtained intense vortex beam possesses the combined properties of fine transversal structure due to the high-order mode and the fine longitudinal structure due to the short wavelength of the high-order harmonics. In addition to the application in high-resolution detection in both spatial and temporal scales, it also presents new opportunities in the intense vortex required fields, such as the inner shell ionization process and high energy twisted photons generation by Thomson scattering of such an intense vortex beam off relativistic electrons.

  7. Enhanced high-order harmonic generation from Argon-clusters

    Tao, Yin; Hagmeijer, Rob; Bastiaens, Hubertus M.J.; Goh, S.J.; van der Slot, P.J.M.; Biedron, S.; Milton, S.; Boller, Klaus J.

    2017-01-01

    High-order harmonic generation (HHG) in clusters is of high promise because clusters appear to offer an increased optical nonlinearity. We experimentally investigate HHG from Argon clusters in a supersonic gas jet that can generate monomer-cluster mixtures with varying atomic number density and

  8. High-order harmonic generation in laser plasma plumes

    Ganeev, Rashid A

    2013-01-01

    This book represents the first comprehensive treatment of high-order harmonic generation in laser-produced plumes, covering the principles, past and present experimental status and important applications. It shows how this method of frequency conversion of laser radiation towards the extreme ultraviolet range matured over the course of multiple studies and demonstrated new approaches in the generation of strong coherent short-wavelength radiation for various applications. Significant discoveries and pioneering contributions of researchers in this field carried out in various laser scientific centers worldwide are included in this first attempt to describe the important findings in this area of nonlinear spectroscopy. "High-Order Harmonic Generation in Laser Plasma Plumes" is a self-contained and unified review of the most recent achievements in the field, such as the application of clusters (fullerenes, nanoparticles, nanotubes) for efficient harmonic generation of ultrashort laser pulses in cluster-containin...

  9. High-order harmonic generation in a capillary discharge

    Rocca, Jorge J.; Kapteyn, Henry C.; Mumane, Margaret M.; Gaudiosi, David; Grisham, Michael E.; Popmintchev, Tenio V.; Reagan, Brendan A.

    2010-06-01

    A pre-ionized medium created by a capillary discharge results in more efficient use of laser energy in high-order harmonic generation (HHG) from ions. It extends the cutoff photon energy, and reduces the distortion of the laser pulse as it propagates down the waveguide. The observed enhancements result from a combination of reduced ionization energy loss and reduced ionization-induced defocusing of the driving laser as well as waveguiding of the driving laser pulse. The discharge plasma also provides a means to spectrally tune the harmonics by tailoring the initial level of ionization of the medium.

  10. High-order harmonic generation with short-pulse lasers

    Schafer, K.J.; Krause, J.L.; Kulander, K.C.

    1992-12-01

    Recent progress in the understanding of high-order harmonic conversion from atoms and ions exposed to high-intensity, short-pulse optical lasers is reviewed. We find that ions can produce harmonics comparable in strength to those obtained from neutral atoms, and that the emission extends to much higher order. Simple scaling laws for the strength of the harmonic emission and the maximium observable harmonic are suggested. These results imply that the photoemission observed in recent experiments in helium and neon contains contributions from ions as well as neutrals

  11. Higher order harmonic generation in the intense laser pulse

    Parvizi, R.; Bahrampour, A.; Karimi, M.

    2006-01-01

    The high intensity pulse of laser field ionizes the atoms and electrons are going to the continuum states of atoms. electrons absorb energy from the strong laser field. The back ground electromagnetic field causes to come back the electrons to ground states of atoms and the absorbed energy is emitted as a high order odd harmonics of incident light. The intensity of emitted harmonics depends on the material atoms and the laser pulse shape. I this paper the effects of step pulse duration on the high order harmonic radiated by the Argon, Helium, and Hydrogen atoms are reported.

  12. Multi-order nonlinear diffraction in second harmonic generation

    Saltiel, S. M.; Neshev, D.; Krolikowski, Wieslaw

    We analyze the emission patterns in the process of second harmonic (SH) generation in χ(2) nonlinear gratings and identify for the first time, to the best of our knowledge, the evidence of Raman-Nath type nonlinear diffraction in frequency doubling processes.......We analyze the emission patterns in the process of second harmonic (SH) generation in χ(2) nonlinear gratings and identify for the first time, to the best of our knowledge, the evidence of Raman-Nath type nonlinear diffraction in frequency doubling processes....

  13. Intense multimicrojoule high-order harmonics generated from neutral atoms of In2O3 nanoparticles

    Elouga Bom, L. B.; Abdul-Hadi, J.; Vidal, F.; Ozaki, T.; Ganeev, R. A.

    2009-01-01

    We studied high-order harmonic generation from plasma that contains an abundance of indium oxide nanoparticles. We found that harmonics from nanoparticle-containing plasma are considerably more intense than from plasma produced on the In 2 O 3 bulk target, with high-order harmonic energy ranging from 6 μJ (for the ninth harmonic) to 1 μJ (for the 17th harmonic) in the former case. The harmonic cutoff from nanoparticles was at the 21st order, which is lower than that observed using indium oxide solid target. By comparing the harmonic spectra obtained from solid and nanoparticle indium oxide targets, we concluded that intense harmonics in the latter case are dominantly generated from neutral atoms of the In 2 O 3 nanoparticles

  14. High-brightness high-order harmonic generation at 13 nm with a long gas jet

    Kim, Hyung Taek; Kim, I Jong; Lee, Dong Gun; Park, Jong Ju; Hong, Kyung Han; Nam, Chang Hee

    2002-01-01

    The generation of high-order harmonics is well-known method producing coherent extreme-ultraviolet radiation with pulse duration in the femtosecond regime. High-order harmonics have attracted much attention due to their unique features such as coherence, ultrashort pulse duration, and table-top scale system. Due to these unique properties, high-order harmonics have many applications of atomic and molecular spectroscopy, plasma diagnostics and solid-state physics. Bright generation of high-order harmonics is important for actual applications. Especially, the generation of strong well-collimated harmonics at 13 nm can be useful for the metrology of EUV lithography optics because of the high reflectivity of Mo-Si mirrors at this wavelength. The generation of bright high-order harmonics is rather difficult in the wavelength region below 15nm. Though argon and xenon gases have large conversion efficiency, harmonic generation from these gases is restricted to wavelengths over 20 nm due to low ionization potential. Hence, we choose neon for the harmonic generation around 13 nm; it has larger conversion efficiency than helium and higher ionization potential than argon. In this experiment, we have observed enhanced harmonic generation efficiency and low beam divergence of high-order harmonics from a elongated neon gas jet by the enhancement of laser propagation in an elongated gas jet. A uniform plasma column was produced when the gas jet was exposed to converging laser pulses.

  15. Application of organic compounds for high-order harmonic generation of ultrashort pulses

    Ganeev, R. A.

    2016-02-01

    The studies of the high-order nonlinear optical properties of a few organic compounds (polyvinyl alcohol, polyethylene, sugar, coffee, and leaf) are reported. Harmonic generation in the laser-produced plasmas containing the molecules and large particles of above materials is demonstrated. These studies showed that the harmonic distributions and harmonic cutoffs from organic compound plasmas were similar to those from the graphite ablation. The characteristic feature of observed harmonic spectra was the presence of bluesided lobes near the lower-order harmonics.

  16. High-order harmonic generation in solid slabs beyond the single-active-electron approximation

    Hansen, Kenneth K.; Deffge, Tobias; Bauer, Dieter

    2017-11-01

    High-harmonic generation by a laser-driven solid slab is simulated using time-dependent density functional theory. Multiple harmonic plateaus up to very high harmonic orders are observed already at surprisingly low field strengths. The full all-electron harmonic spectra are, in general, very different from those of any individual Kohn-Sham orbital. Freezing the Kohn-Sham potential instead is found to be a good approximation for the laser intensities and harmonic orders considered. The origins of the plateau cutoffs are explained in terms of band gaps that can be reached by Kohn-Sham electrons and holes moving through the band structure.

  17. Frequency dependence of quantum path interference in non-collinear high-order harmonic generation

    Zhong Shi-Yang; He Xin-Kui; Teng Hao; Ye Peng; Wang Li-Feng; He Peng; Wei Zhi-Yi

    2016-01-01

    High-order harmonic generation (HHG) driven by two non-collinear beams including a fundamental and its weak second harmonic is numerically studied. The interference of harmonics from adjacent electron quantum paths is found to be dependent on the relative delay of the driving pulse, and the dependences are different for different harmonic orders. This frequency dependence of the interference is attributed to the spatial frequency chirp in the HHG beam resulting from the harmonic dipole phase, which in turn provides a potential way to gain an insight into the generation of high-order harmonics. As an example, the intensity dependent dipole phase coefficient α is retrieved from the interference fringe. (paper)

  18. Spatial properties of odd and even low order harmonics generated in gas.

    Lambert, G; Andreev, A; Gautier, J; Giannessi, L; Malka, V; Petralia, A; Sebban, S; Stremoukhov, S; Tissandier, F; Vodungbo, B; Zeitoun, Ph

    2015-01-14

    High harmonic generation in gases is developing rapidly as a soft X-ray femtosecond light-source for applications. This requires control over all the harmonics characteristics and in particular, spatial properties have to be kept very good. In previous literature, measurements have always included several harmonics contrary to applications, especially spectroscopic applications, which usually require a single harmonic. To fill this gap, we present here for the first time a detailed study of completely isolated harmonics. The contribution of the surrounding harmonics has been totally suppressed using interferential filtering which is available for low harmonic orders. In addition, this allows to clearly identify behaviors of standard odd orders from even orders obtained by frequency-mixing of a fundamental laser and of its second harmonic. Comparisons of the spatial intensity profiles, of the spatial coherence and of the wavefront aberration level of 5ω at 160 nm and 6ω at 135 nm have then been performed. We have established that the fundamental laser beam aberrations can cause the appearance of a non-homogenous donut-shape in the 6ω spatial intensity distribution. This undesirable effect can be easily controlled. We finally conclude that the spatial quality of an even harmonic can be as excellent as in standard generation.

  19. High-order harmonic generation in a laser plasma: a review of recent achievements

    Ganeev, R A

    2007-01-01

    A review of studies of high-order harmonic generation in plasma plumes is presented. The generation of high-order harmonics (up to the 101st order, λ = 7.9 nm) of Ti:sapphire laser radiation during the propagation of short laser pulses through a low-excited, low-ionized plasma produced on the surfaces of different targets is analysed. The observation of considerable resonance-induced enhancement of a single harmonic (λ = 61.2 nm) at the plateau region with 10 -4 conversion efficiency in the case of an In plume can offer some expectations that analogous processes can be realized in other plasma samples in the shorter wavelength range. Recent achievements of single-harmonic enhancement at mid- and end-plateau regions are discussed. Various methods for the optimization of harmonic generation are analysed, such as the application of the second harmonic of driving radiation and the application of prepulses of different durations. The enhancement of harmonic generation efficiency during the propagation of femtosecond pulses through a nanoparticle-containing plasma is discussed. (topical review)

  20. Laser plasma as a source of intense attosecond pulses via high-order harmonic generation

    Ozaki, T.

    2013-01-01

    The incredible progress in ultrafast laser technology and Ti:sapphire lasers have lead to many important applications, one of them being high-order harmonic generation (HHG). HHG is a source of coherent extreme ultraviolet (XUV) radiation, which has opened new frontiers in science by extending nonlinear optics and time-resolved spectroscopy to the XUV region, and pushing ultrafast science to the attosecond domain. Progress in attosecond science has revealed many new phenomena that have not been seen with femtosecond pulses. Clearly, the next frontier is to study nonlinear effects at the attosecond timescale and in the XUV. However, a problem with present-day attosecond pulses is that they are just too weak to induce measurable nonlinearities, which severely limits the application of this source. While HHG from solid targets has shown promise for higher conversion efficiency, there is no experiment so far that demonstrates isolated attosecond pulse generation. The generation of isolated, several 100-as pulses with few-µJ energy will enable us to enter a completely new phase in attoscience. In past works, we have demonstrated that high-order harmonics from lowly ionized plasma is a highly efficient method to generate coherent XUV pulses. For example, indium plasma has been shown to generate intense 13th harmonic of the Ti:sapphire laser, with conversion efficiency of 10-4. However, the quasi-monochromatic nature of indium harmonics would make it difficult to generate attosecond pulses. We have also demonstrated that one could increase the harmonic yield by using nanoparticle targets. Specifically, we showed that by using indium oxide nanoparticles or C60 film, we could obtain intense harmonics between wavelengths of 50 to 90 nm. The energy in each of these harmonic orders was measured to be a few µJ, which is sufficient for many applications. However, the problem of using nanoparticle or film targets is the rapid decrease in the harmonic intensity, due to the rapid

  1. High-Intensity High-order Harmonics Generated from Low-Density Plasma

    Ozaki, T.; Bom, L. B. Elouga; Abdul-Hadi, J.; Ganeev, R. A.; Haessler, S.; Salieres, P.

    2009-01-01

    We study the generation of high-order harmonics from lowly ionized plasma, using the 10 TW, 10 Hz laser of the Advanced Laser Light Source (ALLS). We perform detailed studies on the enhancement of a single order of the high-order harmonic spectrum generated in plasma using the fundamental and second harmonic of the ALLS beam line. We observe quasi-monochromatic harmonics for various targets, including Mn, Cr, Sn, and In. We identify most of the ionic/neutral transitions responsible for the enhancement, which all have strong oscillator strengths. We demonstrate intensity enhancements of the 13th, 17th, 29th, and 33rd harmonics from these targets using the 800 nm pump laser and varying its chirp. We also characterized the attosecond nature of such plasma harmonics, measuring attosecond pulse trains with 360 as duration for chromium plasma, using the technique of ''Reconstruction of Attosecond Beating by Interference of Two-photon Transitions''(RABBIT). These results show that plasma harmonics are intense source of ultrashort coherent soft x-rays.

  2. High-order harmonic generation in clusters irradiated by an infrared laser field of moderate intensity

    Zaretsky, D F; Korneev, Ph; Becker, W

    2010-01-01

    Extending the Lewenstein model of high-order harmonic generation (HHG) in a laser-irradiated atom, a model of HHG in a cluster is formulated. The constituent atoms of the cluster are assumed to be partly ionized. An electron freed through tunnelling may recombine either with its parent ion or with another ion in the vicinity. Harmonics due to the former process are coherent within the same cluster and may be coherent between different clusters, while harmonics due to the latter process are incoherent. Depending on the density of available ions, the incoherent mechanism may dominate the total harmonic yield, and the harmonic spectrum, which extends to higher energies, has a less distinct cutoff and an enhanced low-energy part.

  3. Enhancement of high-order harmonic generation in the presence of noise

    Yavuz, I; Altun, Z [Department of Physics, Marmara University, 34722 Ziverbey, Istanbul (Turkey); Topcu, T, E-mail: ilhan.yavuz@marmara.edu.tr [Department of Physics, Auburn University, AL 36849-5311 (United States)

    2011-07-14

    We report on our simulations of the generation of high-order harmonics from atoms driven by an intense femtosecond laser field in the presence of noise. We numerically solve the non-perturbative stochastic time-dependent Schroedinger equation and observe how varying noise levels affect the frequency components of the high harmonic spectrum. Our calculations show that when an optimum amount of noise is present in the driving laser field, roughly a factor of 45 net enhancement can be achieved in high-order harmonic yield, especially, around the cut-off region. We observe that, for a relatively weak noise, the enhancement mechanism is sensitive to the carrier-envelope phase. We also investigate the possibility of generating ultra-short intense attosecond pulses by combining the laser field and noise and observe that a roughly four orders of magnitude enhanced isolated attosecond burst can be generated.

  4. Enhancement of high-order harmonic generation in the presence of noise

    Yavuz, I; Altun, Z; Topcu, T

    2011-01-01

    We report on our simulations of the generation of high-order harmonics from atoms driven by an intense femtosecond laser field in the presence of noise. We numerically solve the non-perturbative stochastic time-dependent Schroedinger equation and observe how varying noise levels affect the frequency components of the high harmonic spectrum. Our calculations show that when an optimum amount of noise is present in the driving laser field, roughly a factor of 45 net enhancement can be achieved in high-order harmonic yield, especially, around the cut-off region. We observe that, for a relatively weak noise, the enhancement mechanism is sensitive to the carrier-envelope phase. We also investigate the possibility of generating ultra-short intense attosecond pulses by combining the laser field and noise and observe that a roughly four orders of magnitude enhanced isolated attosecond burst can be generated.

  5. Interplay between absorption, dispersion and refraction in high-order harmonic generation

    Dachraoui, H; Helmstedt, A; Bartz, P; Michelswirth, M; Mueller, N; Pfeiffer, W; Heinzmann, U; Auguste, T; Salieres, P

    2009-01-01

    We report a detailed experimental and theoretical study on high-order harmonic generation of a femtosecond Ti-sapphire laser focused at an intensity of around 10 15 W cm -2 onto a high-pressure (50-210 mbar) neon gas cell of variable length (1-3 mm). Using thorough three-dimensional simulations, we discuss the interplay between the different factors influencing the harmonic-generation efficiency, i.e. phase matching determined by the electronic and atomic dispersions, re-absorption of the harmonics by the medium and refraction of the generating laser beam. Generically, we find that, in our generation conditions, the emission yield of harmonics from the plateau region of the spectrum is absorption limited, whereas the emission from harmonics in the cut-off is strongly reduced due to both electron dispersion and ionization-induced refraction of the laser beam. A good agreement between the numerical results and the experimental data is obtained for the harmonic yield dependence on the various generation parameters (gas pressure, medium length and laser intensity).

  6. Optimization of multi-color laser waveform for high-order harmonic generation

    Jin, Cheng; Lin, C. D.

    2016-09-01

    With the development of laser technologies, multi-color light-field synthesis with complete amplitude and phase control would make it possible to generate arbitrary optical waveforms. A practical optimization algorithm is needed to generate such a waveform in order to control strong-field processes. We review some recent theoretical works of the optimization of amplitudes and phases of multi-color lasers to modify the single-atom high-order harmonic generation based on genetic algorithm. By choosing different fitness criteria, we demonstrate that: (i) harmonic yields can be enhanced by 10 to 100 times, (ii) harmonic cutoff energy can be substantially extended, (iii) specific harmonic orders can be selectively enhanced, and (iv) single attosecond pulses can be efficiently generated. The possibility of optimizing macroscopic conditions for the improved phase matching and low divergence of high harmonics is also discussed. The waveform control and optimization are expected to be new drivers for the next wave of breakthrough in the strong-field physics in the coming years. Project supported by the Fundamental Research Funds for the Central Universities of China (Grant No. 30916011207), Chemical Sciences, Geosciences and Biosciences Division, Office of Basic Energy Sciences, Office of Science, U. S. Department of Energy (Grant No. DE-FG02-86ER13491), and Air Force Office of Scientific Research, USA (Grant No. FA9550-14-1-0255).

  7. Enhancement of third-order harmonic generation by interaction of two IR femtosecond filaments

    Liu, Z Y; Ding, P J; Shi, Y C; Lu, X; Liu, Q C; Sun, S H; Ding, B W; Hu, B T; Liu, X L

    2012-01-01

    Three orders of magnitude in the enhancement of the third-order harmonic (TH) generation induced by the interaction of two femtosecond filaments crossing with small angles in the air is achieved. The dependences of the TH generation on the time delay, the relative polarization, the input laser intensity ratios between the probe and pump beam are measured with the crossing angle of 3.5deg , and the results with quasi-vertical crossing angle are also shown for comparison

  8. High-order-harmonic generation from H2+ molecular ions near plasmon-enhanced laser fields

    Yavuz, I.; Tikman, Y.; Altun, Z.

    2015-08-01

    Simulations of plasmon-enhanced high-order-harmonic generation are performed for a H2+ molecular cation near the metallic nanostructures. We employ the numerical solution of the time-dependent Schrödinger equation in reduced coordinates. We assume that the main axis of H2+ is aligned perfectly with the polarization direction of the plasmon-enhanced field. We perform systematic calculations on plasmon-enhanced harmonic generation based on an infinite-mass approximation, i.e., pausing nuclear vibrations. Our simulations show that molecular high-order-harmonic generation from plasmon-enhanced laser fields is possible. We observe the dispersion of a plateau of harmonics when the laser field is plasmon enhanced. We find that the maximum kinetic energy of the returning electron follows 4 Up . We also find that when nuclear vibrations are enabled, the efficiency of the harmonics is greatly enhanced relative to that of static nuclei. However, the maximum kinetic energy 4 Up is largely maintained.

  9. Direct interferometric measurement of the atomic dipole phase in high-order harmonic generation

    Chiara Corsi; Angela Pirri; Emiliano Sali

    2006-01-01

    Complete test of publication follows. For low gas densities and negligible ionization, the so-called atomic dipole phase, connected with the electronic dynamics involved in the generation process, is the main source of phase modulation and incoherence of high-order harmonics. To accurately determine these laser-intensity-induced phase shifts is therefore of great importance, both for the possible spectroscopic applications of harmonics and for the controlled generation of attosecond pulses. In a semiclassical description, only two electronic trajectories contribute to generate plateau harmonics during each pump optical half-cycle. Electrons appearing in the continuum by tunnel ionization may follow two different quantum paths, namely a long (l) and a short (s) trajectory before recombination. According to the SFA approximation, the harmonic of q th order acquires a phase proportional to the electronic classical action, and simply given by: ψ 0 j (r,t) -α q j I(r,t) with j = l, s where α q j are non-linear phase coefficients, roughly proportional to the time that the originating electron spends in the continuum before recombination. The space and time variation of the laser intensity (I(r,t), causes just a little phase modulation for the s-trajectory harmonic component, while the l-trajectory component becomes strongly chirped and spatially defocused; this gives rise to two spatially-separated regions having different temporal coherence. Here we report the first direct measurement of such atomic dipole phase in the process of high-order harmonic generation. Differently from previous measurements based in the most natural way, i.e., by interferometry. Two phase-locked pump pulses generate two phase-locked harmonic pulses in two nearby positions in a gas jet; one of them is used as a fixed phase reference while the generating intensity of the other is varied. The shift of the XUV interference fringes observed in the far field then gives a direct estimate of the

  10. Probe of Multielectron Dynamics in Xenon by Caustics in High-Order Harmonic Generation

    Faccialà, D.; Pabst, S.; Bruner, B. D.; Ciriolo, A. G.; De Silvestri, S.; Devetta, M.; Negro, M.; Soifer, H.; Stagira, S.; Dudovich, N.; Vozzi, C.

    2016-08-01

    We investigated the giant resonance in xenon by high-order harmonic generation spectroscopy driven by a two-color field. The addition of a nonperturbative second harmonic component parallel to the driving field breaks the symmetry between neighboring subcycles resulting in the appearance of spectral caustics at two distinct cutoff energies. By controlling the phase delay between the two color components it is possible to tailor the harmonic emission in order to amplify and isolate the spectral feature of interest. In this Letter we demonstrate how this control scheme can be used to investigate the role of electron correlations that give birth to the giant resonance in xenon. The collective excitations of the giant dipole resonance in xenon combined with the spectral manipulation associated with the two-color driving field allow us to see features that are normally not accessible and to obtain a good agreement between the experimental results and the theoretical predictions.

  11. Quantum-path control in high-order harmonic generation at high photon energies

    Zhang Xiaoshi; Lytle, Amy L; Cohen, Oren; Murnane, Margaret M; Kapteyn, Henry C

    2008-01-01

    We show through experiment and calculations how all-optical quasi-phase-matching of high-order harmonic generation can be used to selectively enhance emission from distinct quantum trajectories at high photon energies. Electrons rescattered in a strong field can traverse short and long quantum trajectories that exhibit differing coherence lengths as a result of variations in intensity of the driving laser along the direction of propagation. By varying the separation of the pulses in a counterpropagating pulse train, we selectively enhance either the long or the short quantum trajectory, and observe distinct spectral signatures in each case. This demonstrates a new type of coupling between the coherence of high-order harmonic beams and the attosecond time-scale quantum dynamics inherent in the process

  12. High order harmonic generation in noble gases using plasmonic field enhancement

    Ciappina, Marcelo F.; Shaaran, Tahir; Lewenstein, Maciej

    2013-01-01

    Theoretical studies of high-order harmonic generation (HHG) in rare gases driven by plasmonic field enhancement are presented. This kind of fields appears when plasmonic nanostructures are illuminated by an intense few-cycle laser and have a particular spatial dependency, depending on the geometrical shape of the nanostructure. It is demonstrated that the strong nonhomogeneous character of the laser enhanced field plays an important role in the HHG process and significantly extends the harmonic cutoff. The models are based on numerical solution of the time dependent Schroedinger equation (TDSE) and supported by classical and semiclassical calculations. (copyright 2012 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  13. Phase-locked high-order-harmonic and sub-100-as pulse generation from stretched molecules

    Lan Pengfei; Lu Peixiang; Cao Wei; Wang Xinlin; Yang Guang

    2006-01-01

    High harmonic generation from diatomic molecules in a linearly polarized intense laser field is investigated and the emission time of the harmonics is discussed with the time-frequency analysis method. It is shown that high harmonic generation from molecules at equilibrium distance is similar to that from atoms. Only the harmonics in the cutoff are synchronized, i.e., well phase-locked, whereas the other harmonics are not phase-locked. For the molecule stretched well beyond its equilibrium distance, the harmonics exhibit distinct time-frequency characteristics. The harmonic spectrum can be extended to I p +8U p , where I p and U p are the ionization and ponderomotive potential, and the harmonics with energies below I p +3.17U p are not phase-locked and the harmonics with energies beyond I p +3.17U p are well phase-locked. Thus a large range of harmonics which are well phase-locked are produced, and a train of clean attosecond (as) pulses with a single 90-as pulse in each half optical cycle can be generated with a multicycle laser pulse. Using a few-cycle laser pulse, an isolated attosecond pulse with a duration of about 95 as is obtained

  14. Dynamic and structural studies of molecular or atomic systems through the generation of high order harmonics

    Higuet, J.

    2010-10-01

    High harmonic generation is a well known phenomenon explained by a three step model: because of the high intensity field generated by an ultrashort laser pulse, an atom or a molecule can be tunnel ionized. The ejected electron is then accelerated by the intense electric field, and eventually can recombine on its parent ion, leading to the emission of a XUV photon. Because of the generating process in itself, this light source is a promising candidate to probe the electronic structure of atoms and molecules, with an atto-second/sub-nanometer potential resolution (1 as=10 -18 s). In this work, we have studied the sensitivity of the emitted light (in terms of amplitude, but also phase and polarization) towards the electronic structure of the generating medium. We have first worked on atomic medium, then on molecules (N 2 , CO 2 , O 2 ). Comparing the experimental results with numerical simulations shows the necessity to model finely the generation process and to go beyond commonly used approximations. We have also shown the possibility to perform high harmonic spectroscopy in order to measure dynamics of complex molecules, such as Nitrogen Dioxide (NO 2 ). This technic has obtained complementary results compared to classical spectroscopy and has revealed dynamics of the electronic wave packet along a conical intersection. In this experiment, we have adapted conventional optical spectroscopy technic to the XUV spectral area, which significantly improved the signal over noise ratio. (author)

  15. Single attosecond pulse from terahertz-assisted high-order harmonic generation

    Balogh, Emeric; Kovacs, Katalin; Dombi, Peter; Fulop, Jozsef A.; Farkas, Gyozo; Hebling, Janos; Tosa, Valer; Varju, Katalin

    2011-08-01

    High-order harmonic generation by few-cycle 800 nm laser pulses in neon gas in the presence of a strong terahertz (THz) field is investigated numerically with propagation effects taken into account. Our calculations show that the combination of THz fields with up to 12 fs laser pulses can be an effective gating technique to generate single attosecond pulses. We show that in the presence of the strong THz field only a single attosecond burst can be phase matched, whereas radiation emitted during other half cycles disappears during propagation. The cutoff is extended and a wide supercontinuum appears in the near-field spectra, extending the available spectral width for isolated attosecond pulse generation from 23 to 93 eV. We demonstrate that phase-matching effects are responsible for the generation of isolated attosecond pulses, even in conditions when single-atom response yields an attosecond pulse train.

  16. Single attosecond pulse from terahertz-assisted high-order harmonic generation

    Balogh, Emeric; Kovacs, Katalin; Dombi, Peter; Farkas, Gyozo; Fulop, Jozsef A.; Hebling, Janos; Tosa, Valer; Varju, Katalin

    2011-01-01

    High-order harmonic generation by few-cycle 800 nm laser pulses in neon gas in the presence of a strong terahertz (THz) field is investigated numerically with propagation effects taken into account. Our calculations show that the combination of THz fields with up to 12 fs laser pulses can be an effective gating technique to generate single attosecond pulses. We show that in the presence of the strong THz field only a single attosecond burst can be phase matched, whereas radiation emitted during other half cycles disappears during propagation. The cutoff is extended and a wide supercontinuum appears in the near-field spectra, extending the available spectral width for isolated attosecond pulse generation from 23 to 93 eV. We demonstrate that phase-matching effects are responsible for the generation of isolated attosecond pulses, even in conditions when single-atom response yields an attosecond pulse train.

  17. Single attosecond pulse from terahertz-assisted high-order harmonic generation

    Balogh, Emeric [Department of Optics and Quantum Electronics, University of Szeged, H-6701 Szeged (Hungary); Kovacs, Katalin [Department of Optics and Quantum Electronics, University of Szeged, H-6701 Szeged (Hungary); National Institute for R and D of Isotopic and Molecular Technologies, RO-400293 Cluj-Napoca (Romania); Dombi, Peter; Farkas, Gyozo [Research Institute for Solid State Physics and Optics, H-1525 Budapest (Hungary); Fulop, Jozsef A.; Hebling, Janos [Department of Experimental Physics, University of Pecs, H-7624 Pecs (Hungary); Tosa, Valer [National Institute for R and D of Isotopic and Molecular Technologies, RO-400293 Cluj-Napoca (Romania); Varju, Katalin [HAS Research Group on Laser Physics, University of Szeged, H-6701 Szeged (Hungary)

    2011-08-15

    High-order harmonic generation by few-cycle 800 nm laser pulses in neon gas in the presence of a strong terahertz (THz) field is investigated numerically with propagation effects taken into account. Our calculations show that the combination of THz fields with up to 12 fs laser pulses can be an effective gating technique to generate single attosecond pulses. We show that in the presence of the strong THz field only a single attosecond burst can be phase matched, whereas radiation emitted during other half cycles disappears during propagation. The cutoff is extended and a wide supercontinuum appears in the near-field spectra, extending the available spectral width for isolated attosecond pulse generation from 23 to 93 eV. We demonstrate that phase-matching effects are responsible for the generation of isolated attosecond pulses, even in conditions when single-atom response yields an attosecond pulse train.

  18. Magnetic field induced third order susceptibility of third order harmonic generation in a ZnMgSe strained quantum well

    Mark, J. Abraham Hudson, E-mail: a.john.peter@gmail.com; Peter, A. John, E-mail: a.john.peter@gmail.com [Dept. of Physics, SSM Institute of Engineering and Technology, Dindigul-624002 (India)

    2014-04-24

    Third order susceptibility of third order harmonic generation is investigated in a Zn{sub 0.1}Mg{sub 0.9}Se/Zn{sub 0.8}Mg{sub 0.2}Se/Zn{sub 0.1}Mg{sub 0.9}Se quantum well in the presence of magnetic field strength. The confinement potential is considered as the addition of energy offsets of the conduction band (or valence band) and the strain-induced potential in our calculations. The material dependent effective mass is followed throughout the computation because it has a high influence on the electron energy levels in low dimensional semiconductor systems.

  19. Propagation effects in the generation process of high-order vortex harmonics.

    Zhang, Chaojin; Wu, Erheng; Gu, Mingliang; Liu, Chengpu

    2017-09-04

    We numerically study the propagation of a Laguerre-Gaussian beam through polar molecular media via the exact solution of full-wave Maxwell-Bloch equations where the rotating-wave and slowly-varying-envelope approximations are not included. It is found that beyond the coexistence of odd-order and even-order vortex harmonics due to inversion asymmetry of the system, the light propagation effect results in the intensity enhancement of a high-order vortex harmonics. Moreover, the orbital momentum successfully transfers from the fundamental laser driver to the vortex harmonics which topological charger number is directly proportional to its order.

  20. High-order harmonic generation: A coherent ultrashort emission in the XUV range

    Salieres, Pascal; Hergott, Jean-Francois; Le Deroff, Laurent; Merdji, Hamed; Carre, Bertrand; Auguste, Thierry; Monot, Pascal; D'Oliveira, Pascal; Joyeux, Denis; Phalippou, Daniel

    2000-01-01

    We review the recent progress in theoretical and experimental understanding of harmonic generation by intense laser pulses. We present investigations on the spatial and temporal coherence properties of the harmonic emission, showing that they can be controlled. Finally, we give some examples of current applications of this XUV source, in particular in the diagnostic of dense plasmas

  1. Two-color phase control of high-order harmonic generation in intense laser fields

    Telnov, D.A.; Wang, J.; Chu, S.

    1995-01-01

    We present a time-independent generalized Floquet approach for nonperturbative treatment of high-order harmonic generation (HG) in intense onea (i) determination of the complex quasienergy eigenvalue and eigenfunction by means of the non-Hermitian Floquet formalism, wherein the Floquet Hamiltonian is discretized by the complex-scaling generalized pseudospectral technique [Wang, Chu, and Laughlin, Phys. Rev. A 50, 3208 (1994)], and (ii) calculation of the HG rates based on the approach that implies the classical treatment of the electromagnetic field and quantal treatment of the atom. The method is applied to the nonperturbative study of HG by the hydrogen atom in strong laser fields with the fundamental frequencies 532 and 775 nm and their third harmonics. The results show a strong dependence on the relative phase δ between the fundamental frequency field and its harmonic. For the intensities used in calculations (1x10 13 and 5x10 13 W/cm 2 for the fundamental frequency 532 nm and 1x10 13 and 3x10 13 W/cm 2 for the fundamental frequency 775 nm, the harmonic intensity being 10 and 100 times weaker), the total photon emission rate has its maximum at δ=0 and minimum at δ=π. However, this tendency, while valid for the first several HG peaks, is reversed for the higher HG peaks. The HG spectrum for δ=π is broader and the peak heights decrease more slowly compared to the case of δ=0. These results have their analog in the multiphoton above-threshold detachment study performed recently for H - ions [Telnov, Wang, and Chu, Phys. Rev. A 51, 4797 (1995)

  2. Frequency modulation of high-order harmonic generation in an orthogonally polarized two-color laser field.

    Li, Guicun; Zheng, Yinghui; Ge, Xiaochun; Zeng, Zhinan; Li, Ruxin

    2016-08-08

    We have experimentally investigated the frequency modulation of high-order harmonics in an orthogonally polarized two-color laser field consisting of a mid-infrared 1800nm fundamental pulse and its second harmonic pulse. It is demonstrated that the high harmonic spectra can be fine-tuned as we slightly change the relative delay of the two-color laser pulses. By analyzing the relative frequency shift of each harmonic at different two-color delays, the nonadiabatic spectral shift induced by the rapid variation of the intensity-dependent intrinsic dipole phase can be distinguished from the blueshift induced by the change of the refractive index during self-phase modulation (SPM). Our comprehensive analysis shows that the frequency modulation pattern is a reflection of the average emission time of high-order harmonic generation (HHG), thus offering a simple method to fine-tune the spectra of the harmonics on a sub-cycle time scale.

  3. High-order harmonic generation spectra and isolated attosecond pulse generation with a two-color time delayed pulse

    Feng Liqiang; Chu Tianshu

    2012-01-01

    Highlights: ► Investigation of HHG spectra and single isolated attosecond pulse generation. ► Irradiation from a model Ne atom by two-color time delayed pulse. ► Observation of time delay effect and relative phase effect. ► Revelation of the optimal condition for generating isolated attosecond pulse. ► Generation of a single isolated attosecond pulse of 45as. - Abstract: In this paper, we theoretically investigate the delay time effect on the high-order harmonic generation (HHG) when a model Ne atom is exposed to a two-color time delayed pulse, consisting of a 5fs/800 nm fundamental field and a 20fs/2000 nm controlling field. It shows that the HHG spectra are strongly sensitive to the delay time between the two laser fields, in particular, for the zero carrier-envelope phase (CEP) φ case (corresponding to the 800 nm fundamental field), the maximum cutoff energy has been achieved at zero delay time. However, with the introduction of the CEP (φ = 180°), the delay effect on HHG is changed, exhibiting a ‘U’ structure harmonic emission from −1 T to 1 T. In addition, the combinations of different controlling pulse frequencies and pulse intensities have also been considered, showing the similar results as the original controlling field case, but with some characteristics. Finally, by properly superposing the optimal harmonic spectrum, an isolated 45as pulse is generated without phase compensation.

  4. Wavelength and intensity dependence of recollision-enhanced multielectron effects in high-order harmonic generation

    Abanador, Paul M.; Mauger, François; Lopata, Kenneth; Gaarde, Mette B.; Schafer, Kenneth J.

    2018-04-01

    Using a model molecular system (A2) with two active electrons restricted to one dimension, we examine high-order harmonic generation (HHG) enhanced by rescattering. Our results show that even at intensities well below the single ionization saturation, harmonics generated from the cation (A2+ ) can be significantly enhanced due to the rescattering of the electron that is initially ionized. This two-electron effect is manifested by the appearance of a secondary plateau and cutoff in the HHG spectrum, extending beyond the predicted cutoff in the single active electron approximation. We use our molecular model to investigate the wavelength dependence of rescattering enhanced HHG, which was first reported in a model atomic system [I. Tikhomirov, T. Sato, and K. L. Ishikawa, Phys. Rev. Lett. 118, 203202 (2017), 10.1103/PhysRevLett.118.203202]. We demonstrate that the HHG yield in the secondary cutoff is highly sensitive to the available electron rescattering energies as indicated by a dramatic scaling with respect to driving wavelength.

  5. Theoretical analysis of dynamic chemical imaging with lasers using high-order harmonic generation

    Van-Hoang Le; Anh-Thu Le; Xie Ruihua; Lin, C. D.

    2007-01-01

    We report theoretical investigations of the tomographic procedure suggested by Itatani et al. [Nature (London) 432, 867 (2004)] for reconstructing highest occupied molecular orbitals (HOMOs) using high-order harmonic generation (HHG). Due to the limited range of harmonics from the plateau region, we found that even under the most favorable assumptions, it is still very difficult to obtain accurate HOMO wave functions using the tomographic procedure, but the symmetry of the HOMOs and the internuclear separation between the atoms can be accurately extracted, especially when lasers of longer wavelengths are used to generate the HHG. Since the tomographic procedure relies on approximating the continuum wave functions in the recombination process by plane waves, the method can no longer be applied upon the improvement of the theory. For future chemical imaging with lasers, we suggest that one may want to focus on how to extract the positions of atoms in molecules instead, by developing an iterative method such that the theoretically calculated macroscopic HHG spectra can best fit the experimental HHG data

  6. Dynamic modification of the fragmentation of COq+ excited states generated with high-order harmonics

    Cao, W.; De, S.; Singh, K. P.; Chen, S.; Laurent, G.; Ray, D.; Ben-Itzhak, I.; Cocke, C. L.; Schoeffler, M. S.; Belkacem, A.; Osipov, T.; Rescigno, T.; Alnaser, A. S.; Bocharova, I. A.; Zherebtsov, S.; Kling, M. F.; Litvinyuk, I. V.

    2010-01-01

    The dynamic process of fragmentation of CO q+ excited states is investigated using a pump-probe approach. EUV radiation (32-48 eV) generated by high-order harmonics was used to ionize and excite CO molecules and a time-delayed infrared (IR) pulse (800 nm) was used to influence the evolution of the dissociating multichannel wave packet. Two groups of states, separable experimentally by their kinetic-energy release (KER), are populated by the EUV and lead to C + -O + fragmentation: direct double ionization of the neutral molecule and fragmentation of the cation leading to C + -O*, followed by autoionization of O*. The IR pulse was found to modify the KER of the latter group in a delay-dependent way which is explained with a model calculation.

  7. High-order harmonic generation from a two-dimensional band structure

    Jin, Jian-Zhao; Xiao, Xiang-Ru; Liang, Hao; Wang, Mu-Xue; Chen, Si-Ge; Gong, Qihuang; Peng, Liang-You

    2018-04-01

    In the past few years, harmonic generation in solids has attracted tremendous attention. Recently, some experiments of two-dimensional (2D) monolayer or few-layer materials have been carried out. These studies demonstrated that harmonic generation in the 2D case shows a strong dependence on the laser's orientation and ellipticity, which calls for a quantitative theoretical interpretation. In this work, we carry out a systematic study on the harmonic generation from a 2D band structure based on a numerical solution to the time-dependent Schrödinger equation. By comparing with the 1D case, we find that the generation dynamics can have a significant difference due to the existence of many crossing points in the 2D band structure. In particular, the higher conduction bands can be excited step by step via these crossing points and the total contribution of the harmonic is given by the mixing of transitions between different clusters of conduction bands to the valence band. We also present the orientation dependence of the harmonic yield on the laser polarization direction.

  8. Polarization and ellipticity of high-order harmonics from aligned molecules generated by linearly polarized intense laser pulses

    Le, Anh-Thu; Lin, C. D.; Lucchese, R. R.

    2010-01-01

    We present theoretical calculations for polarization and ellipticity of high-order harmonics from aligned N 2 , CO 2 , and O 2 molecules generated by linearly polarized lasers. Within the rescattering model, the two polarization amplitudes of the harmonics are determined by the photo-recombination amplitudes for photons emitted with polarization parallel or perpendicular to the direction of the same returning electron wave packet. Our results show clear species-dependent polarization states, in excellent agreement with experiments. We further note that the measured polarization ellipse of the harmonic furnishes the needed parameters for a 'complete' experiment in molecules.

  9. Detecting order and lateral pressure at biomimetic interfaces using a mechanosensitive second-harmonic-generation probe.

    Licari, Giuseppe; Beckwith, Joseph S; Soleimanpour, Saeideh; Matile, Stefan; Vauthey, Eric

    2018-04-04

    A planarizable push-pull molecular probe with mechanosensitive properties was investigated at several biomimetic interfaces, consisting of different phospholipid monolayers located between dodecane and an aqueous buffer solution, using the interface-specific surface-second-harmonic-generation (SSHG) technique. Whereas the SSHG spectra recorded at liquid-disordered interfaces were similar to the absorption spectra in bulk solutions, those measured at liquid-ordered phases exhibited a remarkable shift towards lower energies to an extent depending on the surface pressure of the phospholipid monolayer. On the basis of quantum-chemical calculations, this effect was accounted for by the planarization of the mechanosensitive probe. Polarization-resolved SSHG measurements revealed that the average orientation of the probe at the interface is an even more sensitive reporter of lateral pressure and order than the spectral shape. Additionally, time-resolved SSHG measurements pointed to slower dynamics upon intercalation inside the phospholipid monolayer, most likely due to the more constrained environment. This study demonstrates that the concept of mechanosensitive optical probes can be further exploited when combined with a surface-selective nonlinear optical technique.

  10. Temporal and spectral studies of high-order harmonics generated by polarization-modulated infrared fields

    Sola, I. J.; Zaier, A.; Cormier, E.; Mevel, E.; Constant, E.; Lopez-Martens, R.; Johnsson, P.; Varju, K.; Mauritsson, J.; L'Huillier, A.; Strelkov, V.

    2006-01-01

    The temporal confinement of high harmonic generation (HHG) via modulation of the polarization of the fundamental pulse is studied in both temporal and spectral domains. In the temporal domain, a collinear cross-correlation setup using a 40 fs IR pump for the HHG and a 9 fs IR pulse to probe the generated emission is used to measure the XUV pulse duration. The observed temporal confinement is found to be consistent with theoretical predictions. An increased confinement is observed when a 9 fs pulse is used to generate the harmonics. An important spectral broadening, including a continuum background, is also measured. Theoretical calculations show that with 10 fs driving pulses, either one or two main attosecond pulses are created depending on the value of the carrier envelope phase

  11. Laser Requirements for High-Order Harmonic Generation by Relativistic Plasma Singularities

    Alexander S. Pirozhkov

    2018-03-01

    Full Text Available We discuss requirements on relativistic-irradiance (I0 > 1018 W/cm2 high-power (multi-terawatt ultrashort (femtosecond lasers for efficient generation of high-order harmonics in gas jet targets in a new regime discovered recently (Pirozhkov et al., 2012. Here, we present the results of several experimental campaigns performed with different irradiances, analyse the obtained results and derive the required laser parameters. In particular, we found that the root mean square (RMS wavefront error should be smaller than ~100 nm (~λ/8. Further, the angular dispersion should be kept considerably smaller than the diffraction divergence, i.e., μrad level for 100–300-mm beam diameters. The corresponding angular chirp should not exceed 10−2 μrad/nm for a 40-nm bandwidth. We show the status of the J-KAREN-P laser (Kiriyama et al., 2015; Pirozhkov et al., 2017 and report on the progress towards satisfying these requirements.

  12. Coherent Water Window X Ray by Phase-Matched High-Order Harmonic Generation in Neutral Media

    Takahashi, Eiji J.; Kanai, Tsuneto; Ishikawa, Kenichi L.; Nabekawa, Yasuo; Midorikawa, Katsumi

    2008-01-01

    We demonstrate the generation of a coherent water window x ray by extending the plateau region of high-order harmonics under a neutral-medium condition. The maximum harmonic photon energies attained are 300 and 450 eV in Ne and He, respectively. Our proposed generation scheme, combining a 1.6 μm laser driver and a neutral Ne gas medium, is efficient and scalable in output yields of the water window x ray. Thus, the precept of the design parameter for a single-shot live-cell imaging by contact microscopy is presented

  13. Study of third order nonlinearity of chalcogenide thin films using third harmonic generation measurements

    Rani, Sunita; Mohan, Devendra; Kumar, Manish; Sanjay

    2018-05-01

    Third order nonlinear susceptibility of (GeSe3.5)100-xBix (x = 0, 10, 14) and ZnxSySe100-x-y (x = 2, y = 28; x = 4, y = 20; x = 6, y = 12; x = 8, y = 4) amorphous chalcogenide thin films prepared using thermal evaporation technique is estimated. The dielectric constant at incident and third harmonic wavelength is calculated using "PARAV" computer program. 1064 nm wavelength of Nd: YAG laser is incident on thin film and third harmonic signal at 355 nm wavelength alongwith fundamental light is obtained in reflection that is separated from 1064 nm using suitable optical filter. Reflected third harmonic signal is measured to trace the influence of Bi and Zn on third order nonlinear susceptibility and is found to increase with increase in Bi and Zn content in (GeSe3.5)100-xBix, and ZnxSySe100-x-y chalcogenide thin films respectively. The excellent optical nonlinear property shows the use of chalcogenide thin films in photonics for wavelength conversion and optical data processing.

  14. Advances in high-order harmonic generation sources for time-resolved investigations

    Reduzzi, Maurizio [Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano (Italy); Institute of Photonics and Nanotechnologies, CNR-IFN, Piazza Leonardo da Vinci 32, 20133 Milano (Italy); Carpeggiani, Paolo [Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano (Italy); Kühn, Sergei [ELI-ALPS, ELI-Hu Kft., Dugonics ter 13, H-6720 Szeged (Hungary); Calegari, Francesca [Institute of Photonics and Nanotechnologies, CNR-IFN, Piazza Leonardo da Vinci 32, 20133 Milano (Italy); Nisoli, Mauro; Stagira, Salvatore [Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano (Italy); Institute of Photonics and Nanotechnologies, CNR-IFN, Piazza Leonardo da Vinci 32, 20133 Milano (Italy); Vozzi, Caterina [Institute of Photonics and Nanotechnologies, CNR-IFN, Piazza Leonardo da Vinci 32, 20133 Milano (Italy); Dombi, Peter [ELI-ALPS, ELI-Hu Kft., Dugonics ter 13, H-6720 Szeged (Hungary); Wigner Research Center for Physics, 1121 Budapest (Hungary); Kahaly, Subhendu [ELI-ALPS, ELI-Hu Kft., Dugonics ter 13, H-6720 Szeged (Hungary); Tzallas, Paris; Charalambidis, Dimitris [ELI-ALPS, ELI-Hu Kft., Dugonics ter 13, H-6720 Szeged (Hungary); Foundation for Research and Technology – Hellas, Institute of Electronic Structure and Lasers, P.O. Box 1527, GR-711 10 Heraklion, Crete (Greece); Varju, Katalin [ELI-ALPS, ELI-Hu Kft., Dugonics ter 13, H-6720 Szeged (Hungary); Department of Optics and Quantum Electronics, University of Szeged, Dóm tér 9, 6720 Szeged (Hungary); Osvay, Karoly [ELI-ALPS, ELI-Hu Kft., Dugonics ter 13, H-6720 Szeged (Hungary); and others

    2015-10-15

    We review the main research directions ongoing in the development of extreme ultraviolet sources based on high-harmonic generation for the synthesization and application of trains and isolated attosecond pulses to time-resolved spectroscopy. A few experimental and theoretical works will be discussed in connection to well-established attosecond techniques. In this context, we present the unique possibilities offered for time-resolved investigations on the attosecond timescale by the new Extreme Light Infrastructure Attosecond Light Pulse Source, which is currently under construction.

  15. Advances in high-order harmonic generation sources for time-resolved investigations

    Reduzzi, Maurizio; Carpeggiani, Paolo; Kühn, Sergei; Calegari, Francesca; Nisoli, Mauro; Stagira, Salvatore; Vozzi, Caterina; Dombi, Peter; Kahaly, Subhendu; Tzallas, Paris; Charalambidis, Dimitris; Varju, Katalin; Osvay, Karoly

    2015-01-01

    We review the main research directions ongoing in the development of extreme ultraviolet sources based on high-harmonic generation for the synthesization and application of trains and isolated attosecond pulses to time-resolved spectroscopy. A few experimental and theoretical works will be discussed in connection to well-established attosecond techniques. In this context, we present the unique possibilities offered for time-resolved investigations on the attosecond timescale by the new Extreme Light Infrastructure Attosecond Light Pulse Source, which is currently under construction.

  16. Development of a high-flux XUV source based on high-order harmonic generation

    Nefedova, Victoria; Albrecht, Martin; Kozlová, Michaela; Nejdl, Jaroslav

    2017-01-01

    Roč. 220, Oct (2017), s. 9-13 ISSN 0368-2048 R&D Projects: GA MŠk EF15_008/0000162; GA MŠk LQ1606 Grant - others:ELI Beamlines(XE) CZ.02.1.01/0.0/0.0/15_008/0000162 Institutional support: RVO:68378271 Keywords : optimization * high harmonic generation * HHG * laser * XUV radiation * phase-matching * conversion efficiency Subject RIV: BL - Plasma and Gas Discharge Physics OBOR OECD: Fluids and plasma physics (including surface physics) Impact factor: 1.661, year: 2016

  17. Comparison between length and velocity gauges in quantum simulations of high-order harmonic generation

    Han, Yong-Chang; Madsen, Lars Bojer

    2010-01-01

    , and acceleration forms, and two gauges, the length and velocity gauges. The relationships among the harmonic phases obtained from the Fourier transform of the three forms are discussed in detail. Although quantum mechanics is gauge invariant and the length and velocity gauges should give identical results, the two...... gauges present different computation efficiencies, which reflects the different behavior in terms of characteristics of the physical couplings acting in the two gauges. In order to obtain convergence, more angular momentum states are required in the length gauge, while more grid points are required...

  18. In-line production of a bi-circular field for generation of helically polarized high-order harmonics

    Kfir, Ofer, E-mail: ofertx@technion.ac.il, E-mail: oren@si.technion.ac.il; Bordo, Eliyahu; Ilan Haham, Gil; Lahav, Oren; Cohen, Oren, E-mail: ofertx@technion.ac.il, E-mail: oren@si.technion.ac.il [Solid State Institute and Physics Department, Technion, Haifa 32000 (Israel); Fleischer, Avner [Solid State Institute and Physics Department, Technion, Haifa 32000 (Israel); Department of Physics and Optical Engineering, Ort Braude College, Karmiel 21982 (Israel)

    2016-05-23

    The recent demonstration of bright circularly polarized high-order harmonics of a bi-circular pump field gave rise to new opportunities in ultrafast chiral science. In previous works, the required nontrivial bi-circular pump field was produced using a relatively complicated and sensitive Mach-Zehnder-like interferometer. We propose a compact and stable in-line apparatus for converting a quasi-monochromatic linearly polarized ultrashort driving laser field into a bi-circular field and employ it for generation of helically polarized high-harmonics. Furthermore, utilizing the apparatus for a spectroscopic spin-mixing measurement, we identify the photon spins of the bi-circular weak component field that are annihilated during the high harmonics process.

  19. Revival structures of linear molecules in a field-free alignment condition as probed by high-order harmonic generation

    Lee, G. H.; Kim, H. T.; Park, J. Y.; Nam, C. H.; Kim, T. K.; Lee, J. H.; Ihee, H.

    2006-01-01

    Revival structures (rotational coherence) of three linear molecules (N 2 , O 2 , and CO 2 ) in a field free alignment condition have been investigated using high-order harmonic generation. The harmonic yields of these molecules were measured in a pump-probe manner by using a weak femtosecond (fs) laser pulse for field-free alignment of molecules and another intense fs laser pulse for harmonic generation. The harmonic intensities from 23rd to 29th order with respect to the time delay between the pump and the probe pulses showed revival structures in the condition of a field-free alignment of molecules. While the revival structure of a N 2 molecule had one-fourth the period of the full revival time and different degrees of modulation among different fractional revival times, the revival structures of O 2 and CO 2 molecules showed one-eighth the periods of the full revival time and similar degrees of modulation among all fractional revival times. The revival structures could be interpreted in terms of the nature of the highest occupied molecular orbital and the total nuclear spin.

  20. Scaling high-order harmonic generation from laser-solid interactions to ultrahigh intensity.

    Dollar, F; Cummings, P; Chvykov, V; Willingale, L; Vargas, M; Yanovsky, V; Zulick, C; Maksimchuk, A; Thomas, A G R; Krushelnick, K

    2013-04-26

    Coherent x-ray beams with a subfemtosecond (scale length, which can strongly influence the harmonic generation mechanism. It is shown that for intensities in excess of 10(21)  W cm(-2) an optimum density ramp scale length exists that balances an increase in efficiency with a growth of parametric plasma wave instabilities. We show that for these higher intensities the optimal scale length is c/ω0, for which a variety of HOHG properties are optimized, including total conversion efficiency, HOHG divergence, and their power law scaling. Particle-in-cell simulations show striking evidence of the HOHG loss mechanism through parametric instabilities and relativistic self-phase modulation, which affect the produced spectra and conversion efficiency.

  1. Coherent Sources of XUV Radiation Soft X-Ray Lasers and High-Order Harmonic Generation

    Jaeglé, Pierre

    2006-01-01

    Extreme ultraviolet radiation, also referred to as soft X-rays or XUV, offers very special optical properties. The X-UV refractive index of matter is such that normal reflection cannot take place on polished surfaces whereas beam transmission through one micrometer of almost all materials reduces to zero. Therefore, it has long been a difficult task to imagine and to implement devices designed for complex optics experiments in this wavelength range. Thanks to new sources of coherent radiation - XUV-lasers and High Order Harmonics - the use of XUV radiation, for interferometry, holography, diffractive optics, non-linear radiation-matter interaction, time-resolved study of fast and ultrafast phenomena and many other applications, including medical sciences, is ubiquitous.

  2. Harmonic arbitrary waveform generator

    Roberts, Brock Franklin

    2017-11-28

    High frequency arbitrary waveforms have applications in radar, communications, medical imaging, therapy, electronic warfare, and charged particle acceleration and control. State of the art arbitrary waveform generators are limited in the frequency they can operate by the speed of the Digital to Analog converters that directly create their arbitrary waveforms. The architecture of the Harmonic Arbitrary Waveform Generator allows the phase and amplitude of the high frequency content of waveforms to be controlled without taxing the Digital to Analog converters that control them. The Harmonic Arbitrary Waveform Generator converts a high frequency input, into a precision, adjustable, high frequency arbitrary waveform.

  3. Second harmonic generation imaging

    2013-01-01

    Second-harmonic generation (SHG) microscopy has shown great promise for imaging live cells and tissues, with applications in basic science, medical research, and tissue engineering. Second Harmonic Generation Imaging offers a complete guide to this optical modality, from basic principles, instrumentation, methods, and image analysis to biomedical applications. The book features contributions by experts in second-harmonic imaging, including many pioneering researchers in the field. Written for researchers at all levels, it takes an in-depth look at the current state of the art and possibilities of SHG microscopy. Organized into three sections, the book: Provides an introduction to the physics of the process, step-by-step instructions on how to build an SHG microscope, and comparisons with related imaging techniques Gives an overview of the capabilities of SHG microscopy for imaging tissues and cells—including cell membranes, muscle, collagen in tissues, and microtubules in live cells—by summarizing experi...

  4. High-order harmonic and attosecond pulse generation for a few-cycle laser pulse in modulated hollow fibres

    Zhang Xiangyun; Sun Zhenrong; Wang Yufeng; Chen Guoliang; Wang Zugeng; Li Ruxin; Zeng Zhinan; Xu Zhizhan

    2007-01-01

    High harmonic generation from Ar and He atoms by a few-cycle laser pulse in periodic and chirped hollow fibres is investigated theoretically by a self-consistent model. Based on enhanced high harmonics in a periodic hollow fibre, a chirped hollow fibre is proposed to improve quasi-phase matching for the generated harmonics near the cutoff. The results show that the extended and enhanced harmonics near the cutoff are well phase-matched, and a single x-ray pulse with a duration of 279 as in Ar gas and 255 as in He gas can be achieved by frequency synthesizing of high harmonics in the well-selected cutoff bandwidth. The results show that this technique is a potential candidate to generate an intense isolated attosecond pulse in the 'water window' spectrum

  5. Control of quantum paths of high-order harmonics and attosecond pulse generation in the presence of a static electric field

    Hong Weiyi; Lu Peixiang; Cao Wei; Lan Pengfei; Wang Xinlin

    2007-01-01

    The time-frequency properties of high-order harmonic generation in the presence of a static electric field are investigated. It is found that the quantum paths contributing to the harmonics can be controlled by adding a static electric field. The highest photon energies of harmonics emitted in the adjacent half-cycles of the laser field are modulated by the static electric field, and then an attosecond pulse train with one burst per optical cycle can be extracted. For the ratio between the laser and the static field of 0.39, the harmonic spectrum is extended to I p + 9.1U p , and the harmonics above I p + 0.7U p are emitted almost in phase. The phase-locked harmonics covered by a broad bandwidth are produced, and then a regular attosecond pulse train with a pulse duration of 80 as is generated

  6. Optimization and phase matching of fiber-laser-driven high-order harmonic generation at high repetition rate.

    Cabasse, Amélie; Machinet, Guillaume; Dubrouil, Antoine; Cormier, Eric; Constant, Eric

    2012-11-15

    High-repetition-rate sources are very attractive for high-order harmonic generation (HHG). However, due to their pulse characteristics (low energy, long duration), those systems require a tight focusing geometry to achieve the necessary intensity to generate harmonics. In this Letter, we investigate theoretically and experimentally the optimization of HHG in this geometry, to maximize the extreme UV (XUV) photon flux and improve the conversion efficiency. We analyze the influence of atomic gas media (Ar, Kr, or Xe), gas pressure, and interaction geometries (a gas jet and a finite and a semi-infinite gas cell). Numerical simulations allow us to define optimal conditions for HHG in this tight focusing regime and to observe the signature of on-axis phase matching. These conditions are implemented experimentally using a high-repetition-rate Yb-doped fiber laser system. We achieve optimization of emission with a recorded XUV photon flux of 4.5×10(12) photons/s generated in Xe at 100 kHz repetition rate.

  7. High-order nonlinear optical processes in ablated carbon-containing materials: Recent approaches in development of the nonlinear spectroscopy using harmonic generation in the extreme ultraviolet range

    Ganeev, R. A.

    2017-08-01

    The nonlinear spectroscopy using harmonic generation in the extreme ultraviolet range became a versatile tool for the analysis of the optical, structural and morphological properties of matter. The carbon-contained materials have shown the advanced properties among other studied species, which allowed both the definition of the role of structural properties on the nonlinear optical response and the analysis of the fundamental features of carbon as the attractive material for generation of coherent short-wavelength radiation. We review the studies of the high-order harmonic generation by focusing ultrashort pulses into the plasmas produced during laser ablation of various organic compounds. We discuss the role of ionic transitions of ablated carbon-containing molecules on the harmonic yield. We also show the similarities and distinctions of the harmonic and plasma spectra of organic compounds and graphite. We discuss the studies of the generation of harmonics up to the 27th order (λ = 29.9 nm) of 806 nm radiation in the boron carbide plasma and analyze the advantages and disadvantages of this target compared with the ingredients comprising B4C (solid boron and graphite) by comparing plasma emission and harmonic spectra from three species. We also show that the coincidence of harmonic and plasma emission wavelengths in most cases does not cause the enhancement or decrease of the conversion efficiency of this harmonic.

  8. First-principles prediction of optical second-order harmonic generation in the endohedral N-C{sub 60} compound

    Zhang, G. P.; Strubbe, David A.; Louie, Steven G.; George, Thomas F. [Department of Physics, Indiana State University, Terre Haute, Indiana 47809 (United States); Department of Physics, University of California, Berkeley, California 94720 (United States) and Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Department of Chemistry and Biochemistry and Department of Physics and Astronomy, Office of the Chancellor and Center for Nanoscience, University of Missouri-St. Louis, St. Louis, Missouri 63121 (United States)

    2011-08-15

    Non-linear-optical properties in C{sub 60} have attracted enormous attention for over two decades. The endohedral complex N-C{sub 60}, with its remarkable thermal stability and spin-quartet ground state, is a candidate for future room-temperature quantum computing, but there has been no investigation of its non-linear-optical properties. Here, a first-principles calculation shows that N-C{sub 60} is a promising material for nanoscale and ultrafast modulations. Excitation by a pump laser pulse of the nitrogen-atom vibration inside the C{sub 60} cage transiently breaks inversion symmetry and can enable second-harmonic generation (SHG) from a probe pulse. Unlike the SHG observed in C{sub 60} thin films, this harmonic signal is switched on and off periodically every 345 fs. For an fcc crystal of N-C{sub 60}, the second-order susceptibility {chi}{sup (2)} is on the order of 10{sup -8} esu, similar to commercially used nonlinear materials.

  9. Influence of micro- and macro-processes on the high-order harmonic generation in laser-produced plasma

    Ganeev, R. A., E-mail: rashid-ganeev@mail.ru [Ophthalmology and Advanced Laser Medical Center, Saitama Medical University, 38 Morohongo, Moroyama-machi, Iruma-gun, Saitama 350-0495 (Japan); Physical Department, Voronezh State University, Voronezh 394006 (Russian Federation)

    2016-03-21

    We compare the resonance-induced enhancement of single harmonic and the quasi-phase-matching-induced enhancement of the group of harmonics during propagation of the tunable mid-infrared femtosecond pulses through the perforated laser-produced indium plasma. We show that the enhancement of harmonics using the macro-process of quasi-phase-matching is comparable with the one using micro-process of resonantly enhanced harmonic. These studies show that joint implementation of the two methods of the increase of harmonic yield could be a useful tool for generation of strong short-wavelength radiation in different spectral regions. We compare these effects in indium, as well as in other plasmas.

  10. Next generation data harmonization

    Armstrong, Chandler; Brown, Ryan M.; Chaves, Jillian; Czerniejewski, Adam; Del Vecchio, Justin; Perkins, Timothy K.; Rudnicki, Ron; Tauer, Greg

    2015-05-01

    Analysts are presented with a never ending stream of data sources. Often, subsets of data sources to solve problems are easily identified but the process to align data sets is time consuming. However, many semantic technologies do allow for fast harmonization of data to overcome these problems. These include ontologies that serve as alignment targets, visual tools and natural language processing that generate semantic graphs in terms of the ontologies, and analytics that leverage these graphs. This research reviews a developed prototype that employs all these approaches to perform analysis across disparate data sources documenting violent, extremist events.

  11. Interaction of relativistic electrons with an intense laser pulse: High-order harmonic generation based on Thomson scattering

    Hack, Szabolcs; Varró, Sándor; Czirják, Attila

    2016-01-01

    We investigate nonlinear Thomson scattering as a source of high-order harmonic radiation with the potential to enable attosecond light pulse generation. We present a new analytic solution of the electron’s relativistic equations of motion in the case of a short laser pulse with a sine-squared envelope. Based on the single electron emission, we compute and analyze the radiated amplitude and phase spectrum for a realistic electron bunch, with special attention to the correct initial values. These results show that the radiation spectrum of an electron bunch in head-on collision with a sufficiently strong laser pulse of sine-squared envelope has a smooth frequency dependence to allow for the synthesis of attosecond light pulses.

  12. Interaction of relativistic electrons with an intense laser pulse: High-order harmonic generation based on Thomson scattering

    Hack, Szabolcs [ELI-ALPS, ELI-HU Non-Profit Ltd., Dugonics tér 13, H-6720 Szeged (Hungary); Department of Theoretical Physics, University of Szeged, Tisza L. krt. 84-86, H-6720 Szeged (Hungary); Varró, Sándor [ELI-ALPS, ELI-HU Non-Profit Ltd., Dugonics tér 13, H-6720 Szeged (Hungary); Wigner Research Center for Physics, SZFI, PO Box 49, H-1525 Budapest (Hungary); Czirják, Attila [ELI-ALPS, ELI-HU Non-Profit Ltd., Dugonics tér 13, H-6720 Szeged (Hungary); Department of Theoretical Physics, University of Szeged, Tisza L. krt. 84-86, H-6720 Szeged (Hungary)

    2016-02-15

    We investigate nonlinear Thomson scattering as a source of high-order harmonic radiation with the potential to enable attosecond light pulse generation. We present a new analytic solution of the electron’s relativistic equations of motion in the case of a short laser pulse with a sine-squared envelope. Based on the single electron emission, we compute and analyze the radiated amplitude and phase spectrum for a realistic electron bunch, with special attention to the correct initial values. These results show that the radiation spectrum of an electron bunch in head-on collision with a sufficiently strong laser pulse of sine-squared envelope has a smooth frequency dependence to allow for the synthesis of attosecond light pulses.

  13. Mechanism of equivalent electric dipole oscillation for high-order harmonic generation from grating-structured solid-surface by femtosecond laser pulse

    Wang, Yang; Song, Hai-Ying; Liu, H. Y.; Liu, Shi-Bing

    2017-07-01

    We theoretically study high-order harmonic generation (HHG) from relativistically driven overdense plasma targets with rectangularly grating-structured surfaces by femtosecond laser pulses. Our particle-in-cell (PIC) simulations show that, under the conditions of low laser intensity and plasma density, the harmonics emit principally along small angles deviating from the target surface. Further investigation of the surface electron dynamics reveals that the electron bunches are formed by the interaction between the laser field and the target surface, giving rise to the oscillation of equivalent electric-dipole (OEED), which enhances specific harmonic orders. Our work helps understand the mechanism of harmonic emissions from grating targets and the distinction from the planar harmonic scheme.

  14. Collection and spectral control of high-order harmonics generated with a 50 W high-repetition rate Ytterbium femtosecond laser system

    Cabasse, A; Hazera, Ch; Quintard, L; Cormier, E; Petit, S; Constant, E

    2016-01-01

    We generate high-order harmonics with a 50 W, Yb femtosecond fiber laser system operating at 100 kHz in a tight focusing configuration. We achieve a high photon flux even with pulses longer than 500 fs. We collect the diverging extreme ultraviolet (XUV) harmonic beam in a 35 mrad wide solid angle by using a spectrometer designed to handle the high thermal load under vacuum and refocus the XUV beam onto a detector where the beam is characterised or can alternatively be used for experiments. This setup is designed for a 50 eV XUV bandwidth and offers the possibility to perform XUV-IR pump probe experiments with both temporal and spectral resolution. The high-order harmonics were generated and optimized at 100 kHz by using several gas target geometries (a gas jet and a semi-infinite gas cell) and several gases (argon, krypton, xenon) that provide XUV beams with different characteristics. After the spectrometer and for high-order harmonic generation (HHG) in xenon, we detect more than 4 × 10 10 photons per second over four harmonics, that is a useful XUV power on target of 0.1 μW. This corresponds to the emission of more than 1 μW per harmonic at the source and we achieved a similar flux with both the semi-infinite cell and the jet. In addition, we observe a strong spectral selectivity when generating harmonics in a semi-infinite gas cell as few harmonics clearly dominate the neighbouring harmonics. We attribute this spectral selectivity to phase matching effects. (paper)

  15. Second harmonic generation microscopy

    Brüggemann, Dagmar Adeline; Brewer, Jonathan R.; Risbo, Jens

    2010-01-01

    Myofibers and collagen show non-linear optical properties enabling imaging using second harmonic generation (SHG) microscopy. The technique is evaluated for use as a tool for real-time studies of thermally induced changes in thin samples of unfixed and unstained pork. The forward and the backward...... scattered SHG light reveal complementary features of the structures of myofibers and collagen fibers. Upon heating the myofibers show no structural changes before reaching a temperature of 53 °C. At this temperature the SHG signal becomes extinct. The extinction of the SHG at 53 °C coincides with a low......-temperature endotherm peak observable in the differential scanning calorimetry (DSC) thermograms. DSC analysis of epimysium, the connective tissue layer that enfold skeletal muscles, produces one large endotherm starting at 57 °C and peaking at 59.5 °C. SHG microscopy of collagen fibers reveals a variability of thermal...

  16. Mechanism of equivalent electric dipole oscillation for high-order harmonic generation from grating-structured solid-surface by femtosecond laser pulse

    Wang, Yang; Song, Hai-Ying; Liu, H.Y.; Liu, Shi-Bing, E-mail: sbliu@bjut.edu.cn

    2017-07-12

    Highlights: • Proposed a valid mechanism of high harmonic generation by laser grating target interaction: oscillation of equivalent electric dipole (OEED). • Found that there also exist harmonic emission at large emission angle but not just near-surface direction as the former researches had pointed out. • Show the process of the formation and motion of electron bunches at the grating-target surface irradiating with femtosecond laser pulse. - Abstract: We theoretically study high-order harmonic generation (HHG) from relativistically driven overdense plasma targets with rectangularly grating-structured surfaces by femtosecond laser pulses. Our particle-in-cell (PIC) simulations show that, under the conditions of low laser intensity and plasma density, the harmonics emit principally along small angles deviating from the target surface. Further investigation of the surface electron dynamics reveals that the electron bunches are formed by the interaction between the laser field and the target surface, giving rise to the oscillation of equivalent electric-dipole (OEED), which enhances specific harmonic orders. Our work helps understand the mechanism of harmonic emissions from grating targets and the distinction from the planar harmonic scheme.

  17. Effect of the dynamic core-electron polarization of CO molecules on high-order harmonic generation

    Le, Cam-Tu; Hoang, Van-Hung; Tran, Lan-Phuong; Le, Van-Hoang

    2018-04-01

    We theoretically investigate the influence of dynamic core-electron polarization (DCeP) of CO molecules on high-order harmonic generation (HHG) by solving the time-dependent Schrödinger equation (TDSE) within the single-active-electron (SAE) approximation. The effect of DCeP is shown to depend strongly on the molecular orientation angle θ . Particularly, compared to the calculations without DCeP, the inclusion of this effect gives rise to an enhancement of harmonic intensity at θ =0° when the electric field aligns along the O-C direction and to a suppression at θ =180° when the field heads in the opposite direction. Meanwhile, when the electric field is perpendicular to the molecular axis, the effect is almost insignificant. The phenomenon is thought to be linked to the ionization process. However, this picture is not completed yet. By solving the TDSE within the SAE approximation and conducting a classical simulation, we are able to obtain the ionization probability as well as the ionization rate and prove that HHG, in fact, receives a major contribution from electrons ionized at only a certain time interval, rather than throughout the whole pulse propagation. Including DCeP, the variation of the ionization rate in this interval highly correlates to that of the HHG intensity. To better demonstrate the origin of this manifestation, we also show the alternation DCeP makes on the effective potential that corresponds to the observed change in the ionization rate and consequently the HHG intensity. Our results confirm previous studies' observations and, more importantly, provide the missing physical explanation. With the role of DCeP now better understood for the entire range of the orientation angle, this effect can be handled more conveniently for calculating the HHG of other targets.

  18. High-order harmonic generation driven by inhomogeneous plasmonics fields spatially bounded: influence on the cut-off law

    Neyra, E.; Videla, F.; Ciappina, M. F.; Pérez-Hernández, J. A.; Roso, L.; Lewenstein, M.; Torchia, G. A.

    2018-03-01

    We study high-order harmonic generation (HHG) in model atoms driven by plasmonic-enhanced fields. These fields result from the illumination of plasmonic nanostructures by few-cycle laser pulses. We demonstrate that the spatial inhomogeneous character of the laser electric field, in a form of Gaussian-shaped functions, leads to an unexpected relationship between the HHG cutoff and the laser wavelength. Precise description of the spatial form of the plasmonic-enhanced field allows us to predict this relationship. We combine the numerical solutions of the time-dependent Schrödinger equation (TDSE) with the plasmonic-enhanced electric fields obtained from 3D finite element simulations. We additionally employ classical simulations to supplement the TDSE outcomes and characterize the extended HHG spectra by means of their associated electron trajectories. A proper definition of the spatially inhomogeneous laser electric field is instrumental to accurately describe the underlying physics of HHG driven by plasmonic-enhanced fields. This characterization opens up new perspectives for HHG control with various experimental nano-setups.

  19. Spin-resolved photoelectron spectroscopy using femtosecond extreme ultraviolet light pulses from high-order harmonic generation

    Plötzing, M.; Adam, R., E-mail: r.adam@fz-juelich.de; Weier, C.; Plucinski, L.; Schneider, C. M. [Forschungszentrum Jülich GmbH, Peter Grünberg Institut (PGI-6), 52425 Jülich (Germany); Eich, S.; Emmerich, S.; Rollinger, M.; Aeschlimann, M. [University of Kaiserslautern and Research Center OPTIMAS, 67663 Kaiserslautern (Germany); Mathias, S. [Georg-August-Universität Göttingen, I. Physikalisches Institut, 37077 Göttingen (Germany)

    2016-04-15

    The fundamental mechanism responsible for optically induced magnetization dynamics in ferromagnetic thin films has been under intense debate since almost two decades. Currently, numerous competing theoretical models are in strong need for a decisive experimental confirmation such as monitoring the triggered changes in the spin-dependent band structure on ultrashort time scales. Our approach explores the possibility of observing femtosecond band structure dynamics by giving access to extended parts of the Brillouin zone in a simultaneously time-, energy- and spin-resolved photoemission experiment. For this purpose, our setup uses a state-of-the-art, highly efficient spin detector and ultrashort, extreme ultraviolet light pulses created by laser-based high-order harmonic generation. In this paper, we present the setup and first spin-resolved spectra obtained with our experiment within an acquisition time short enough to allow pump-probe studies. Further, we characterize the influence of the excitation with femtosecond extreme ultraviolet pulses by comparing the results with data acquired using a continuous wave light source with similar photon energy. In addition, changes in the spectra induced by vacuum space-charge effects due to both the extreme ultraviolet probe- and near-infrared pump-pulses are studied by analyzing the resulting spectral distortions. The combination of energy resolution and electron count rate achieved in our setup confirms its suitability for spin-resolved studies of the band structure on ultrashort time scales.

  20. Phase matching of high order harmonic generation using dynamic phase modulation caused by a non-collinear modulation pulse

    Cohen, Oren; Kapteyn, Henry C.; Mumane, Margaret M.

    2010-02-16

    Phase matching high harmonic generation (HHG) uses a single, long duration non-collinear modulating pulse intersecting the driving pulse. A femtosecond driving pulse is focused into an HHG medium (such as a noble gas) to cause high-harmonic generation (HHG), for example in the X-ray region of the spectrum, via electrons separating from and recombining with gas atoms. A non-collinear pulse intersects the driving pulse within the gas, and modulates the field seen by the electrons while separated from their atoms. The modulating pulse is low power and long duration, and its frequency and amplitude is chosen to improve HHG phase matching by increasing the areas of constructive interference between the driving pulse and the HHG, relative to the areas of destructive interference.

  1. Higher order harmonics of reactor neutron equation

    Li Fu; Hu Yongming; Luo Zhengpei

    1996-01-01

    The flux mapping method using the higher order harmonics of the neutron equation is proposed. Based on the bi-orthogonality of the higher order harmonics, the process and formulas for higher order harmonics calculation are derived via the source iteration method with source correction. For the first time, not only any order harmonics for up-to-3-dimensional geometry are achieved, but also the preliminary verification to the capability for flux mapping have been carried out

  2. The control of electron quantum trajectories on the high-order harmonic generation of CO and N2 molecules in the presence of a low frequency field.

    Koushki, A M; Sadighi-Bonabi, R; Mohsen-Nia, M; Irani, E

    2018-04-14

    In the present work, an efficient method is theoretically investigated for extending high-order harmonics and ultrashort attosecond pulse generation in N 2 and CO molecules by using the time-dependent density functional theory approach. Our results show that by utilizing chirped laser field in the presence of a low frequency field, not only is the harmonic cutoff extended remarkably but also the single short quantum trajectory is selected to contribute to the harmonic spectra. When a low frequency field is added to the two-color chirped laser field, the long quantum trajectories are suppressed and only the short quantum trajectories contribute to the higher harmonic emission mechanism. As a result, the spectral modulation is significantly decreased and an intense ultrashort pulse can be generated from the supercontinuum region of high harmonics. With such a scheme, the isolated ultrashort attosecond pulses can be generated in length, velocity, and acceleration gauges. Furthermore, these results are explained by using the classical and quantum time-frequency analyses.

  3. Second harmonic generation in a bounded magnetoplasma

    Thomas, D.G.

    1975-01-01

    An experimental study of second harmonic generation in a magnetized plasma contained in a cylindrical cavity resonator shows how the harmonic power varies with fundamental power, background gas pressure, and magnetization. Two cavities were designed. For each the TM010 resonance was in the S-band and the TM011 resonance in the C-band. Both frequencies were harmonically related when the d.c. discharge sustaining the plasma was adjusted to give plasma frequencies of approximately 0.7 GHz and 1.53 GHz. The experimental results show the harmonic power approximately proportional to the square of the fundamental power from 5 to 100 mw, and a decreasing function of pressure from 10 to 150 millitorr. Experiments at constant plasma frequency and varying magnetic field from 0 to 3000 Gauss show a sharp drop in harmonic power to undetectable levels when the electron cyclotron frequency approximates either the fundamental or second harmonic frequencies. These effects are attributed, respectively, to the coupling of fundamental power to other modes and to cavity detuning away from the harmonic. With the plasma frequency adjusted to maintain simultaneous resonance of fundamental and harmonic, a harmonic signal maximum occurred when the upper hybrid frequency approximated the harmonic frequency. Several anomalies, apparently related to the magnetization, background gas, and electron density distribution were observed. Otherwise, the results are qualitatively consistent with the first order theory for a cold, collisional plasma

  4. Intense harmonic generation from various ablation media

    Ozaki, T.; Elouga, L.; Suzuki, M.; Kuroda, H.; Ganeev, R.A.

    2006-01-01

    Complete test of publication follows. High-order harmonic generation (HHG) is a unique source of coherent extreme ultraviolet (XUV) radiation, which can produce soft x-rays within the spectral 'water-window' (between 2.3 and 4.4 nm), and ultimately short pulses with attosecond duration. However, the intensity of present-day harmonics is still low, and serious applications will need an increase of the conversion efficiency. Instead of using gas media, one can also use ablation material, produced on solid targets using a low-intensity prepulse, as the nonlinear medium to generate high-order harmonics. Recently, we have successfully demonstrated the generation of up to the 63 rd harmonic (λ = 12.6 nm) of a Ti:sapphire laser radiation using boron ablation, and a strong enhancement in the intensity of the 13 th harmonic from indium ablation. These harmonics were generated with a modest laser (10 mJ, 150 fs) and with the pre-pulse to main pulse energy ratio constant. In this paper, we perform systematic investigations of ablation harmonics, using the 200 mJ, 30 fs Ti:sapphire beam line of the Canadian Advanced Laser Light Source (ALLS) facility. ALLS allows studying ablation harmonics over wider experimental parameters, and with independent control over the pre-pulse and main pulse energies. The 10 Hz, 200 mJ Ti:sapphire beam line of ALLS is divided into two beams. Each beam has its own energy control system, which allows independent control over the energy of each beam. One of the beams is used as a pre-pulse for creating ablation, which is focused onto the solid target without pulse compression, with pulse duration of 200 ps. The second beam is used as the main pulse for harmonic generation. The main pulse is delayed in time relative to the pre-pulse by propagating through an optical delay line, and then sent through a pulse compressor. The compressed pulse duration have typical pulse duration of 30 fs FWHM, which is then focused onto the ablation medium using MgF 2

  5. Higher-order quasi-phase matched second harmonic generation in periodically poled MgO-doped stoichiometric LiTaO3

    Yu, Nan Ei; Kurimura, Sunao; Kitamura, Kenji

    2005-01-01

    A periodically poled device was investigated by using fourth-order quasi-phase-matched (QPM) second harmonic generation (SHG) in MgO-doped stoichiometric lithium tantalate (LiTaO 3 ). The effective nonlinear coefficient was found be 2.4 pm/V by using fourth-order QPM SHG at the fundamental wavelength of 1064 nm. For first-order QPM SHG, the effective value of d 33 could be 9.2 pm/V. Using the sensitive higher-order QPM SHG method, we investigated the relationship between the domain duty ratio and the conversion efficiency.

  6. Quantum optical signatures in strong-field laser physics: Infrared photon counting in high-order-harmonic generation.

    Gonoskov, I A; Tsatrafyllis, N; Kominis, I K; Tzallas, P

    2016-09-07

    We analytically describe the strong-field light-electron interaction using a quantized coherent laser state with arbitrary photon number. We obtain a light-electron wave function which is a closed-form solution of the time-dependent Schrödinger equation (TDSE). This wave function provides information about the quantum optical features of the interaction not accessible by semi-classical theories. With this approach we can reveal the quantum optical properties of high harmonic generation (HHG) process in gases by measuring the photon statistics of the transmitted infrared (IR) laser radiation. This work can lead to novel experiments in high-resolution spectroscopy in extreme-ultraviolet (XUV) and attosecond science without the need to measure the XUV light, while it can pave the way for the development of intense non-classical light sources.

  7. Spatial mode discrimination using second harmonic generation

    Delaubert, Vincent; Lassen, Mikael Østergaard; Pulford, David

    2007-01-01

    Second harmonic generation can be used as a technique for controlling the spatial mode structure of optical beams. We demonstrate experimentally the generation of higher order spatial modes, and that it is possible to use nonlinear phase matching as a predictable and robust technique for the conv...

  8. Comparison of high-order-harmonic generation on single-layer graphene flakes with armchair and zigzag types in an intense laser field

    Guo, Jing; Zhong, Huiying; Yan, Bing; Chen, Yi; Jiang, Yuanfei; Wang, Ting-feng; Shao, Jun-feng; Zheng, Chang-bin; Liu, Xue-Shen

    2016-03-01

    The high-order-harmonic generation (HHG) of graphene in an intense laser field is investigated using the strong-field approximation method. The initial wave function is presented by gaussian and gamess software. The molecular structure along the x and y axes represents different types of graphene: armchair and zigzag, respectively. The results show that the HHG intensity of the armchair type of graphene is two magnitudes higher than that of the zigzag type in the plateau area. The ionization yield and electron density distribution are also presented to further explain this difference. Finally, by superposing a properly selected range of harmonics, a main pulse with the duration of 91 and 99 attoseconds accompanied by weak satellite pulses will be generated for the case of armchair and zigzag graphene, respectively, and the corresponding intensity from armchair graphene is much higher than that from zigzag graphene.

  9. High-order-harmonic generation from solids: The contributions of the Bloch wave packets moving at the group and phase velocities

    Du, Tao-Yuan; Huang, Xiao-Huan; Bian, Xue-Bin

    2018-01-01

    We study numerically the Bloch electron wave-packet dynamics in periodic potentials to simulate laser-solid interactions. We introduce an alternative perspective in the coordinate space combined with the motion of the Bloch electron wave packets moving at group and phase velocities under the laser fields. This model interprets the origins of the two contributions (intra- and interband transitions) in the high-order harmonic generation (HHG) processes by investigating the local and global behaviours of the wave packets. It also elucidates the underlying physical picture of the HHG intensity enhancement by means of carrier-envelope phase, chirp, and inhomogeneous fields. It provides a deep insight into the emission of high-order harmonics from solids. This model is instructive for experimental measurements and provides an alternative avenue to distinguish mechanisms of the HHG from solids in different laser fields.

  10. Controlling electron quantum paths for generation of circularly polarized high-order harmonics by H2+ subject to tailored (ω , 2 ω ) counter-rotating laser fields

    Heslar, John; Telnov, Dmitry A.; Chu, Shih-I.

    2018-04-01

    Recently, studies of high-order harmonics (HHG) from atoms driven by bichromatic counter-rotating circularly polarized laser fields as a source of coherent circularly polarized extreme ultraviolet (XUV) and soft-x-ray beams in a tabletop-scale setup have received considerable attention. Here, we demonstrate the ability to control the electron recollisions giving three returns per one cycle of the fundamental frequency ω by using tailored bichromatic (ω , 2 ω ) counter-rotating circularly polarized laser fields with a molecular target. The full control of the electronic pathway is first analyzed by a classical trajectory analysis and then extended to a detailed quantum study of H2+ molecules in bichromatic (ω , 2 ω ) counter-rotating circularly polarized laser fields. The radiation spectrum contains doublets of left- and right-circularly polarized harmonics in the XUV ranges. We study in detail the below-, near-, and above-threshold harmonic regions and describe how excited-state resonances alter the ellipticity and phase of the generated harmonic peaks.

  11. Higher-order harmonics of general limited diffraction Bessel beams

    Ding De-Sheng; Huang Jin-Huang

    2016-01-01

    In this paper, we extensively study the higher-order harmonic generation of the general limited diffraction m -th-order Bessel beam. The analysis is based on successive approximations of the Khokhlov–Zabolotskaya–Kuznetsov (KZK) equation. Asymptotic expansions are presented for higher-order harmonic Bessel beams in near and far fields. The validity of asymptotic approximation is also analyzed. The higher-order harmonic of the Bessel beam with the lowest zero-order is taken as a special example. (special topic)

  12. Higher-order harmonics of general limited diffraction Bessel beams

    Ding, De-Sheng; Huang, Jin-Huang

    2016-12-01

    In this paper, we extensively study the higher-order harmonic generation of the general limited diffraction m-th-order Bessel beam. The analysis is based on successive approximations of the Khokhlov-Zabolotskaya-Kuznetsov (KZK) equation. Asymptotic expansions are presented for higher-order harmonic Bessel beams in near and far fields. The validity of asymptotic approximation is also analyzed. The higher-order harmonic of the Bessel beam with the lowest zero-order is taken as a special example. Project supported by the National Natural Science Foundation of China (Grant Nos. 11074038 and 11374051).

  13. Quantum-mechanical elaboration for the description of low- and high-order harmonics generated by extended gas media: prospects to the efficiency enhancement in spatially modulated media

    Stremoukhov, Sergey Yu; Andreev, Anatoly V.

    2018-03-01

    A simple model fully matching the description of the low- and high-order harmonic generation in extended media interacting with multicolor laser fields is proposed. The extended atomic media is modeled by a 1D chain of atoms, the number of atoms and the distance between them depend on the pressure of the gas and the length of the gas cell. The response of the individual atoms is calculated accurately in the frame of the non-perturbative theory where the driving field for each atom is calculated with account of dispersion properties of any multicolor field component. In spite of the simplicity of the proposed model it provides the detailed description of behaviour of harmonic spectra under variation of the gas pressure and medium length, it also predicts a scaling law for harmonic generation (an invariant). To demonstrate the wide range of applications of the model we have simulated the results of recent experiments dealing with spatially modulated media and obtained good coincidence between the numerical results and the experimental ones.

  14. Optical High Harmonic Generation in C60

    Zhang, Guoping

    2005-03-01

    C60 et al. Physical Review Letters Physical Review B High harmonic generation (HHG) requires a strong laser field, but in a relatively weak laser field is sufficient. Numerical results presented here show while its low order harmonics result from the laser field, its high order ones are mainly from the multiple excitations. Since high order harmonics directly correlate electronic transitions, the HHG spectrum accurately measures transition energies. Therefore, is not only a promising material for HHG, but may also present an opportunity to develop HHG into an electronic structure probing tool. References: G. P. Zhang, 91, 176801 (2003); G. P. Zhang and T. F. George, 68, 165410 (2003); P. B. Corkum, 71, 1994 (1993); G. P. Zhang and Thomas F. George, 93, 147401 (2004); H. Niikura ,ature 417, 917 (2002); ibid. 421, 826 (2003); Y. Mairesse ,cience 302, 1540 (2003); A. Baltuska ,ature 421, 611 (2003).

  15. The role of the electron recoiling mechanism in coherent light high-order harmonics generation: from the source to the applications

    Simoncig, Alberto

    2010-01-01

    2008/2009 I processi di generazione di armoniche di ordine superiore (High-order Harmonic Generation o HHG) in gas inerti rappresentano, attualmente, la tecnica piu` promettente per la creazione di impulsi di luce coerente nell'estremo ultra-violetto (EUV) in una configurazione table-top. I processi HHG si basano sull'interazione non-lineare, tra impulsi laser ultra-corti, tipicamente dell'ordine della decina di femtosecondi, e atomi di gas inerti. Le caratteristiche che distinguono i...

  16. Optical Third-Harmonic Generation in Graphene

    Sung-Young Hong

    2013-06-01

    Full Text Available We report strong third-harmonic generation in monolayer graphene grown by chemical vapor deposition and transferred to an amorphous silica (glass substrate; the photon energy is in three-photon resonance with the exciton-shifted van Hove singularity at the M point of graphene. The polarization selection rules are derived and experimentally verified. In addition, our polarization- and azimuthal-rotation-dependent third-harmonic-generation measurements reveal in-plane isotropy as well as anisotropy between the in-plane and out-of-plane nonlinear optical responses of graphene. Since the third-harmonic signal exceeds that from bulk glass by more than 2 orders of magnitude, the signal contrast permits background-free scanning of graphene and provides insight into the structural properties of graphene.

  17. Second harmonic generation and sum frequency generation

    Pellin, M.J.; Biwer, B.M.; Schauer, M.W.; Frye, J.M.; Gruen, D.M.

    1990-01-01

    Second harmonic generation and sum frequency generation are increasingly being used as in situ surface probes. These techniques are coherent and inherently surface sensitive by the nature of the mediums response to intense laser light. Here we will review these two techniques using aqueous corrosion as an example problem. Aqueous corrosion of technologically important materials such as Fe, Ni and Cr proceeds from a reduced metal surface with layer by layer growth of oxide films mitigated by compositional changes in the chemical makeup of the growing film. Passivation of the metal surface is achieved after growth of only a few tens of atomic layers of metal oxide. Surface Second Harmonic Generation and a related nonlinear laser technique, Sum Frequency Generation have demonstrated an ability to probe the surface composition of growing films even in the presence of aqueous solutions. 96 refs., 4 figs

  18. Coherent harmonics generated by a super-short electron pulse

    Ding Wu

    1996-01-01

    A novel mechanism generating superradiance harmonics is found. In this superradiance harmonics, the temporal width of harmonics is extremely short, the ratio of high harmonic fundamental wave is much higher than the known superradiance harmonics

  19. Broadband dynamic phase matching of high-order harmonic generation by a high-peak-power soliton pump field in a gas-filled hollow photonic-crystal fiber.

    Serebryannikov, Evgenii E; von der Linde, Dietrich; Zheltikov, Aleksei M

    2008-05-01

    Hollow-core photonic-crystal fibers are shown to enable dynamically phase-matched high-order harmonic generation by a gigawatt soliton pump field. With a careful design of the waveguide structure and an appropriate choice of input-pulse and gas parameters, a remarkably broadband phase matching can be achieved for a soliton pump field and a large group of optical harmonics in the soft-x-ray-extreme-ultraviolet spectral range.

  20. Tunneling ionization and harmonic generation in two-color fields

    Kondo, K.; Kobayashi, Y.; Sagisaka, A.; Nabekawa, Y.; Watanabe, S.

    1996-01-01

    Tunneling ionization and harmonic generation in two-color fields were studied with a fundamental beam (ω) and its harmonics (2ω,3ω), which were generated by a 100-fs Ti:sapphire laser. Ion yields of atoms and molecules were successfully controlled by means of a change in the relative phase between ω and 3ω pulses. Two-color interference was clearly observed in photoelectron spectra and harmonic spectra. In the ω endash 2ω field even-order harmonics were observed in which the intensity was almost equal to that of the odd harmonics because of an asymmetric optical field. These results were compared with the quasi-static model for ionization and with the quantum theory for harmonic generation. copyright 1996 Optical Society of America

  1. Harmonic operation of high gain harmonic generation free electron laser

    Deng Haixiao; Chinese Academy of Sciences, Beijing; Dai Zhimin

    2008-01-01

    In high gain harmonic generation (HGHG) free electron laser (FEL), with the right choice of parameters of the modulator undulator, the dispersive section and the seed laser, one may make the spatial bunching of the electron beam density distribution correspond to one of the harmonic frequencies of the radiator radiation, instead of the fundamental frequency of the radiator radiation in conventional HGHG, thus the radiator undulator is in harmonic operation (HO) mode. In this paper, we investigate HO of HGHG FEL. Theoretical analyses with universal method are derived and numerical simulations in ultraviolet and deep ultraviolet spectral regions are given. It shows that the power of the 3rd harmonic radiation in the HO of HGHG may be as high as 18.5% of the fundamental power level. Thus HO of HGHG FEL may obtain short wavelength by using lower beam energy. (authors)

  2. Phase-matched third harmonic generation in a plasma

    Rax, J.M.; Fisch, N.J.

    1993-01-01

    Relativistic third harmonic generation in a plasma is investigated. The growth of a third harmonic wave is limited by the difference between the phase velocity of the pump and driven waves. This phase velocity mismatch results in a third harmonic amplitude saturation and oscillation. In order to overcome this saturation, the authors describe a phase-matching scheme based on a resonant density modulation. The limitations of this scheme are analyzed

  3. Second harmonic generation in resonant optical structures

    Eichenfield, Matt; Moore, Jeremy; Friedmann, Thomas A.; Olsson, Roy H.; Wiwi, Michael; Padilla, Camille; Douglas, James Kenneth; Hattar, Khalid Mikhiel

    2018-01-09

    An optical second-harmonic generator (or spontaneous parametric down-converter) includes a microresonator formed of a nonlinear optical medium. The microresonator supports at least two modes that can be phase matched at different frequencies so that light can be converted between them: A first resonant mode having substantially radial polarization and a second resonant mode having substantially vertical polarization. The first and second modes have the same radial order. The thickness of the nonlinear medium is less than one-half the pump wavelength within the medium.

  4. Second Harmonic Generation, Electrooptical Pockels Effect, and Static First-Order Hyperpolarizabilities of 2,2′-Bithiophene Conformers: An HF, MP2, and DFT Theoretical Investigation

    Andrea Alparone

    2013-01-01

    Full Text Available The static and dynamic electronic (hyperpolarizabilities of the equilibrium conformations of 2,2′-bithiophene (anti-gauche and syn-gauche were computed in the gas phase. The calculations were carried out using Hartree-Fock (HF, Møller-Plesset second-order perturbation theory (MP2, and density functional theory methods. The properties were evaluated for the second harmonic generation (SHG, and electrooptical Pockels effect (EOPE nonlinear optical processes at the typical λ=1064 nm of the Nd:YAG laser. The anti-gauche form characterized by the S–C2–C2′–S dihedral angle of 137° (MP2/6-311G** is the global minimum on the potential energy surface, whereas the syn-gauche rotamer (S–C2–C2′–S = 48°, MP2/6-311G** lies ca. 0.5 kcal/mol above the anti-gauche form. The structural properties of the gauche structures are rather similar to each other. The MP2 electron correlation effects are dramatic for the first-order hyperpolarizabilities of the 2,2′-bithiophenes, decreasing the HF values by ca. a factor of three. When passing from the anti-gauche to the syn-gauche conformer, the static and frequency-dependent first-order hyperpolarizabilities increase by ca. a factor of two. Differently, the electronic polarizabilities and second-order hyperpolarizabilities of these rotamers are rather close to each other. The syn-gauche structure could be discriminated from the anti-gauche one through its much more intense SHG and EOPE signals.

  5. High-order harmonic conversion efficiency in helium

    Crane, J.K.

    1992-01-01

    Calculated results are presented for the energy, number of photons, and conversion efficiency for high-order harmonic generation in helium. The results show the maximum values that we should expect to achieve experimentally with our current apparatus and the important parameters for scaling this source to higher output. In the desired operating regime where the coherence length, given by L coh =πb/(q-1), is greater than the gas column length, l, the harmonic output can be summarized by a single equation: N q =[(π z n z b 3 τ q |d q | z )/4h]{(p/q)(2l/b) z }. N q - numbers of photons of q-th harmonic; n - atom density; b - laser confocal parameter; τ q - pulse width of harmonic radiation; q - harmonic order; p - effective order of nonlinearity. (Note the term in brackets, the phase-matching function, has been separated from the rest of the expression in order to be consistent with the relevant literature)

  6. Understanding fifth-harmonic generation in CLBO

    Patankar, S.; Yang, S. T.; Moody, J. D.; Bayramian, A. J.; Swadling, G. F.; Barker, D.; Datte, P.; Mennerat, G.; Norton, M.; Carr, C. W.; Begishev, I. A.; Bromage, J.; Ross, J. S.

    2018-02-01

    We report on results of fifth harmonic generation in Cesium Lithium Borate (CLBO) using a three-crystal cascaded frequency conversion scheme designed to study the energy balance of the final sum frequency generation stage. The experimental setup independently combines the first and fourth harmonic of a Nd:Glass laser in a 5mm thick CLBO crystal. Energy balance between the incoming and output energy is close to unity when the CLBO is out of phase matching and approximately 80% when the crystal is in phase matching. A detailed analysis of the residual fundamental and fourth harmonic energy indicates 5th harmonic light is being generated but only 26% is unaccounted for. We attribute the missing light to linear transmission loss in the CLBO oven. The ratio of the output to input energy is unity when the missing 5th harmonic is incorporated into the calculations. Two-dimensional plane wave mixing simulations show agreement with the results at lower intensities.

  7. Muonic molecular ions p p μ and p d μ driven by superintense VUV laser pulses: Postexcitation muonic and nuclear oscillations and high-order harmonic generation

    Paramonov, Guennaddi K.; Saalfrank, Peter

    2018-05-01

    The non-Born-Oppenheimer quantum dynamics of p p μ and p d μ molecular ions excited by ultrashort, superintense VUV laser pulses polarized along the molecular axis (z ) is studied by the numerical solution of the time-dependent Schrödinger equation within a three-dimensional (3D) model, including the internuclear distance R and muon coordinates z and ρ , a transversal degree of freedom. It is shown that in both p p μ and p d μ , muons approximately follow the applied laser field out of phase. After the end of the laser pulse, expectation values , , and demonstrate "post-laser-pulse" oscillations in both p p μ and p d μ . In the case of p d μ , the post-laser-pulse oscillations of and appear as shaped "echo pulses." Power spectra, which are related to high-order harmonic generation (HHG), generated due to muonic and nuclear motion are calculated in the acceleration form. For p d μ it is found that there exists a unique characteristic frequency ωoscp d μ representing both frequencies of post-laser-pulse muonic oscillations and the frequency of nuclear vibrations, which manifest themselves by very sharp maxima in the corresponding power spectra of p d μ . The homonuclear p p μ ion does not possess such a unique characteristic frequency. The "exact" dynamics and power, and HHG spectra of the 3D model are compared with a Born-Oppenheimer, fixed-nuclei model featuring interesting differences: postpulse oscillations are absent and HHG spectra are affected indirectly or directly by nuclear motion.

  8. Synthesis of variable harmonic impedance in inverter-interfaced distributed generation unit for harmonic damping throughout a distribution network

    Wang, Xiongfei; Blaabjerg, Frede; Chen, Zhe

    2012-01-01

    This paper proposes a harmonic impedance synthesis technique for voltage-controlled distributed generation inverter in order to damp harmonic voltage distortion on a distribution network. The approach employs a multiloop control scheme, where a selective load harmonic current feedforward loop bas...

  9. Harmonic generation with a dual frequency pulse.

    Keravnou, Christina P; Averkiou, Michalakis A

    2014-05-01

    Nonlinear imaging was implemented in commercial ultrasound systems over the last 15 years offering major advantages in many clinical applications. In this work, pulsing schemes coupled with a dual frequency pulse are presented. The pulsing schemes considered were pulse inversion, power modulation, and power modulated pulse inversion. The pulse contains a fundamental frequency f and a specified amount of its second harmonic 2f. The advantages and limitations of this method were evaluated with both acoustic measurements of harmonic generation and theoretical simulations based on the KZK equation. The use of two frequencies in a pulse results in the generation of the sum and difference frequency components in addition to the other harmonic components. While with single frequency pulses, only power modulation and power modulated pulse inversion contained odd harmonic components, with the dual frequency pulse, pulse inversion now also contains odd harmonic components.

  10. Synthesis of Variable Harmonic Impedance in Inverter-Interfaced Distributed Generation Unit for Harmonic Damping Throughout a Distribution Network

    Wang, Xiongfei; Blaabjerg, Frede; Chen, Zhe

    2012-01-01

    This paper proposes a harmonic impedance synthesis technique for voltage-controlled distributed generation inverters in order to damp harmonic voltage distortion on a distribution network. The approach employs a multiloop control scheme, where a selective harmonic load current feedforward loop...... at the dominant harmonic frequencies. Thus, the harmonic voltage drop on the grid-side inductance and the harmonic resonances throughout a distribution feeder with multiple shunt-connected capacitors can be effectively attenuated. Simulation and laboratory test results validate the performance of the proposed...

  11. Importance of length and sequence order on magnesium binding to surface-bound oligonucleotides studied by second harmonic generation and atomic force microscopy.

    Holland, Joseph G; Geiger, Franz M

    2012-06-07

    The binding of magnesium ions to surface-bound single-stranded oligonucleotides was studied under aqueous conditions using second harmonic generation (SHG) and atomic force microscopy (AFM). The effect of strand length on the number of Mg(II) ions bound and their free binding energy was examined for 5-, 10-, 15-, and 20-mers of adenine and guanine at pH 7, 298 K, and 10 mM NaCl. The binding free energies for adenine and guanine sequences were calculated to be -32.1(4) and -35.6(2) kJ/mol, respectively, and invariant with strand length. Furthermore, the ion density for adenine oligonucleotides did not change as strand length increased, with an average value of 2(1) ions/strand. In sharp contrast, guanine oligonucleotides displayed a linear relationship between strand length and ion density, suggesting that cooperativity is important. This data gives predictive capabilities for mixed strands of various lengths, which we exploit for 20-mers of adenines and guanines. In addition, the role sequence order plays in strands of hetero-oligonucleotides was examined for 5'-A(10)G(10)-3', 5'-(AG)(10)-3', and 5'-G(10)A(10)-3' (here the -3' end is chemically modified to bind to the surface). Although the free energy of binding is the same for these three strands (averaged to be -33.3(4) kJ/mol), the total ion density increases when several guanine residues are close to the 3' end (and thus close to the solid support substrate). To further understand these results, we analyzed the height profiles of the functionalized surfaces with tapping-mode atomic force microscopy (AFM). When comparing the average surface height profiles of the oligonucleotide surfaces pre- and post- Mg(II) binding, a positive correlation was found between ion density and the subsequent height decrease following Mg(II) binding, which we attribute to reductions in Coulomb repulsion and strand collapse once a critical number of Mg(II) ions are bound to the strand.

  12. Quasi-phase-matching of only even-order high harmonics.

    Diskin, Tzvi; Cohen, Oren

    2014-03-24

    High harmonic spectrum of a quasi-monochromatic pump that interacts with isotropic media consists of only odd-order harmonics. Addition of a secondary pump, e.g. a static field or the second harmonic of the primary pump, can results with generation of both odd and even harmonics of the primary pump. We propose a method for quasi-phase matching of only the even-order harmonics of the primary pump. We formulate a theory for this process and demonstrate it numerically. We also show that it leads to attosecond pulse trains with constant carrier envelop phase and high repetition rate.

  13. Harmonic sums and polylogarithms generated by cyclotomic polynomials

    Ablinger, Jakob; Schneider, Carsten [Johannes Kepler Univ., Linz (Austria). Research Inst. for Symbolic Computation; Bluemlein, Johannes [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany)

    2011-05-15

    The computation of Feynman integrals in massive higher order perturbative calculations in renormalizable Quantum Field Theories requires extensions of multiply nested harmonic sums, which can be generated as real representations by Mellin transforms of Poincare-iterated integrals including denominators of higher cyclotomic polynomials. We derive the cyclotomic harmonic polylogarithms and harmonic sums and study their algebraic and structural relations. The analytic continuation of cyclotomic harmonic sums to complex values of N is performed using analytic representations. We also consider special values of the cyclotomic harmonic polylogarithms at argument x=1, resp., for the cyclotomic harmonic sums at N{yields}{infinity}, which are related to colored multiple zeta values, deriving various of their relations, based on the stuffle and shuffle algebras and three multiple argument relations. We also consider infinite generalized nested harmonic sums at roots of unity which are related to the infinite cyclotomic harmonic sums. Basis representations are derived for weight w=1,2 sums up to cyclotomy l=20. (orig.)

  14. Directional enhancement of selected high-order-harmonics from intense laser irradiated blazed grating targets.

    Zhang, Guobo; Chen, Min; Liu, Feng; Yuan, Xiaohui; Weng, Suming; Zheng, Jun; Ma, Yanyun; Shao, Fuqiu; Sheng, Zhengming; Zhang, Jie

    2017-10-02

    Relativistically intense laser solid target interaction has been proved to be a promising way to generate high-order harmonics, which can be used to diagnose ultrafast phenomena. However, their emission direction and spectra still lack tunability. Based upon two-dimensional particle-in-cell simulations, we show that directional enhancement of selected high-order-harmonics can be realized using blazed grating targets. Such targets can select harmonics with frequencies being integer times of the grating frequency. Meanwhile, the radiation intensity and emission area of the harmonics are increased. The emission direction is controlled by tailoring the local blazed structure. Theoretical and electron dynamics analysis for harmonics generation, selection and directional enhancement from the interaction between multi-cycle laser and grating target are carried out. These studies will benefit the generation and application of laser plasma-based high order harmonics.

  15. High-harmonic generation in a dense medium

    Strelkov, V.V.; Platonenko, V.T.; Becker, A.

    2005-01-01

    The high-harmonic generation in a plasma or gas under conditions when the single-atom response is affected by neighboring ions or atoms of the medium is studied theoretically. We solve numerically the three-dimensional Schroedinger equation for a single-electron atom in the combined fields of the neighboring particles and the laser, and average the results over different random positions of the particles using the Monte Carlo method. Harmonic spectra are calculated for different medium densities and laser intensities. We observe a change of the harmonic properties due to a random variation of the harmonic phase induced by the field of the medium, when the medium density exceeds a certain transition density. The transition density is found to depend on the harmonic order, but it is almost independent of the fundamental intensity. It also differs for the two (shorter and longer) quantum paths. The latter effect leads for ionic densities in the transition regime to a narrowing of the harmonic lines and a shortening of the attosecond pulses generated using a group of harmonics

  16. Resonant second harmonic generation in potassium vapor

    Kim, D.; Mullin, C.S.; Shen, Y.R.; Lawrence Berkeley Lab., CA

    1995-06-01

    Picosecond pulses are used to study resonant second harmonic generation in potassium vapor. Although the process is both microscopically and macroscopically forbidden, it can readily be observed. The results can be quantitatively understood by a multiphoton-ionization-initiated, dc-field-induced, coherent transient model

  17. Harmonic generation with multiple wiggler schemes

    Bonifacio, R.; De Salvo, L.; Pierini, P. [Universita degli Studi, Milano (Italy)

    1995-02-01

    In this paper the authors give a simple theoretical description of the basic physics of the single pass high gain free electron laser (FEL), describing in some detail the FEL bunching properties and the harmonic generation technique with a multiple-wiggler scheme or a high gain optical klystron configuration.

  18. Coherence properties of the harmonic generation in intense laser field

    Salieres, P.

    1995-01-01

    In this thesis is presented an experimental and theoretical study of the harmonic generation in intense field and coherence properties of this radiation. The first part reminds the main harmonic specter characteristics. Follow then experimental studies of the tray extension with the laser lighting, the harmonic generation by ions, and the influence of the laser field on the efficiency of generation. The second part presents the quantum model of the harmonic generation in tunnel regime that we have used for the calculation of the dipoles. We compare dependence in lighting of some harmonic, by insisting on the characteristic behavior of the atomic phase. The theory of the propagation is presented in third part. After the reminder of the case of a perturbative polarization, we develop the case of the polarization in tunnel regime. With the help of numerical simulations, we show the influence of the atomic phase on the agreement of phase, and therefore on the efficiency of conversion and profiles of generation in the medium. The importance of the geometry of the interaction is underlined. The part IV presents the study of the spatial coherence of the harmonic radiation. We develop first consequences of the theory of the agreement of phase for profiles of emission. Then the comparison with experimental profiles is detailed in function of the different parameters( order of non linearity, laser lighting, position of the focus by report in the gaseous medium). The study of the spectral and temporal coherence of the part V begins with the experimental effect investigation of the ionization on specters of the harmonic of weak order. We present then theoretical predictions of the preceding model for spectral and temporal profiles of the harmonic of highest order, generated in tunnel regime. The part VI is devoted to the UVX source aspect of the harmonic radiation. General characteristics (number of photons, agreement) are first detailed, then we present the first experiences

  19. Recent progress of below-threshold harmonic generation

    Xiong, Wei-Hao; Peng, Liang-You; Gong, Qihuang

    2017-01-01

    The harmonics generated from the interaction of a strong laser field with atoms and molecules in the gas phase can be applied as coherent light sources and detecting techniques for structures and dynamics in matter. In the last three decades, the most prevailing experimental and theoretical studies have been focused on the high-order harmonic generation due to its applications in attosecond science. However, low-order harmonics near the ionization threshold of the target have been less explored, partially because the spectrum in this region is more complicated from both the theoretical and experimental point of view. After several pioneering investigations in the mid 1990s, near threshold harmonics (NTHs) begun to draw a great attention again because of the development of high repetition rate cavity enhanced harmonics about 10 years ago. Very recently, NTHs have attracted a lot of experimental and theoretical studies due to their potential applications as light sources and complicated mechanisms. In this topical review, we will summarize the progress of NTHs, including the early and recent experimental measurements in atoms and molecules, as well as the relevant theoretical explorations of these harmonics. (topical review)

  20. Optimization of high harmonic generation by genetic algorithm

    Constance Valentin; Olga Boyko; Gilles Rey; Brigitte Mercier; Evaggelos Papalazarou; Laure Antonucci; Philippe Balcou

    2006-01-01

    Complete test of publication follows. High Harmonic Generation (HHG) is very sensitive to pulse shape of the fundamental laser. We have first used an Acousto-Optic Programmable Dispersive Filter (AOPDF) in order to modify the spectral phase and second, a deformable mirror in order to modify the wavefront. We have optimized harmonic signal using a genetic algorithm coupled with both setups. We show the influence of macroscopic parameters for optimization process. Genetic algorithms have been already used to modify pulse shapes of the fundamental laser in order to optimize high harmonic signals, in order to change the emission wavelength of one harmonic or to modify the fundamental wavefront to optimize harmonic signals. For the first time, we present a systematic study of the optimization of harmonic signals using the AOPDF. Signal optimizations by a factor 2 to 10 have been measured depending of parameters of generation. For instance, one of the interesting result concerns the effect of macroscopic parameters as position of the entrance of the cell with respect to the focus of the IR laser when we change the pulse shapes. For instance, the optimization is higher when the cell entrance is above the focus where the intensity gradients are higher. Although the spectral phase of the IR laser is important for the response of one atom, the optimization depends also of phase-matching and especially of the effect intensity gradients. Other systematic studies have been performed as well as measurements of temporal profiles and wavefronts of the IR beam. These studies allow bringing out the behaviour of high harmonic generation with respect to the optimization process.

  1. Plasma wave and second harmonic generation

    Sodha, M.S.; Sharma, J.K.; Tewari, D.P.; Sharma, R.P.; Kaushik, S.C.

    1978-01-01

    An investigation is made of a plasma wave at pump wave frequency and second harmonic generation caused by a self induced transverse inhomogeneity introduced by a Gaussian electromagnetic beam in a hot collisionless plasma. In the presence of a Gaussian beam the carriers get redistributed from the high field region to the low field region by ponderomative force and a transverse density gradient is established in the plasma. When the electric vector of the main beam is parallel to this density gradient, a plasma wave at the pump wave frequency is generated. In addition to this the transverse intensity gradient of the electromagnetic wave also contributes significantly to the plasma wave generation. The power of the plasma wave exhibits a maximum and minimum with the power of the pump wave (at z = 0). The generated plasma wave interacts with the electromagnetic wave and leads to the generation of a second harmonic. Furthermore, if the initial power of the pump wave is more than the critical power for self-focusing, the beam gets self-focused and hence the generated plasma wave and second harmonic which depend upon the background electron concentration and power of the main beam also get accordingly modified. (author)

  2. Dependence of high order harmonics intensity on laser focal spot position in preformed plasma plumes

    Singhal, H.; Ganeev, R.; Naik, P. A.; Arora, V.; Chakravarty, U.; Gupta, P. D.

    2008-01-01

    The dependence of the high-order harmonic intensity on the laser focal spot position in laser produced plasma plumes is experimentally studied. High order harmonics up to the 59th order (λ∼13.5 nm) were generated by focusing 48 fs laser pulses from a Ti:sapphire laser system in silver plasma plume produced using 300 ps uncompressed laser radiation as the prepulse. The intensity of harmonics nearly vanished when the best focus was located in the plume center, whereas it peaked on either side with unequal intensity. The focal spot position corresponding to the peak harmonic intensity moved away from the plume center for higher order harmonics. The results are explained in terms of the variation of phase mismatch between the driving laser beam and harmonics radiation produced, relativistic drift of electrons, and defocusing effect due to radial ionization gradient in the plasma for different focal spot positions

  3. Harmonic generation and flux quantization in granular superconductors

    Lam, Q.H.; Jeffries, C.D.

    1989-01-01

    Simple dynamical models of granular superconductors are used to compute the generation of harmonic power in ac and dc magnetic fields. In zero order, the model is a single superconducting loop, with or without a weak link. The sample-average power is predicted by averaging over suitable distribution functions for loop areas and orientations in a dc magnetic field. In a first-order model, inductance and resistance are also included. In all models the power at high harmonics shows strikingly sharp dips periodic in the dc field, revealing flux quantization in the prototype loops

  4. Higher-order harmonics of limited diffraction Bessel beams

    Ding; Lu

    2000-03-01

    We investigate theoretically the nonlinear propagation of the limited diffraction Bessel beam in nonlinear media, under the successive approximation of the KZK equation. The result shows that the nth-order harmonic of the Bessel beam, like its fundamental component, is radially limited diffracting, and that the main beamwidth of the nth-order harmonic is exactly 1/n times that of the fundamental.

  5. Efficient and tunable high-order harmonic light sources for photoelectron spectroscopy at surfaces

    Chiang, Cheng-Tien; Huth, Michael; Trützschler, Andreas; Schumann, Frank O.; Kirschner, Jürgen; Widdra, Wolf

    2015-01-01

    Highlights: • An overview of photoelectron spectroscopy using high-order harmonics is presented. • Photoemission spectra on Ag(0 0 1) using megahertz harmonics are shown. • A gas recycling system for harmonic generation is presented. • Non-stop operation of megahertz harmonics up to 76 h is demonstrated. • The bandwidth and pulse duration of the harmonics are discussed. - Abstract: With the recent progress in high-order harmonic generation (HHG) using femtosecond lasers, laboratory photoelectron spectroscopy with an ultrafast, widely tunable vacuum-ultraviolet light source has become available. Despite the well-established technique of HHG-based photoemission experiments at kilohertz repetition rates, the efficiency of these setups can be intrinsically limited by the space-charge effects. Here we present recent developments of compact HHG light sources for photoelectron spectroscopy at high repetition rates up to megahertz, and examples for angle-resolved photoemission experiments are demonstrated.

  6. Selective suppression of high-order harmonics within phase-matched spectral regions.

    Lerner, Gavriel; Diskin, Tzvi; Neufeld, Ofer; Kfir, Ofer; Cohen, Oren

    2017-04-01

    Phase matching in high-harmonic generation leads to enhancement of multiple harmonics. It is sometimes desired to control the spectral structure within the phase-matched spectral region. We propose a scheme for selective suppression of high-order harmonics within the phase-matched spectral region while weakly influencing the other harmonics. The method is based on addition of phase-mismatched segments within a phase-matched medium. We demonstrate the method numerically in two examples. First, we show that one phase-mismatched segment can significantly suppress harmonic orders 9, 15, and 21. Second, we show that two phase-mismatched segments can efficiently suppress circularly polarized harmonics with one helicity over the other when driven by a bi-circular field. The new method may be useful for various applications, including the generation of highly helical bright attosecond pulses.

  7. Polarization control of high order harmonics in the EUV photon energy range.

    Vodungbo, Boris; Barszczak Sardinha, Anna; Gautier, Julien; Lambert, Guillaume; Valentin, Constance; Lozano, Magali; Iaquaniello, Grégory; Delmotte, Franck; Sebban, Stéphane; Lüning, Jan; Zeitoun, Philippe

    2011-02-28

    We report the generation of circularly polarized high order harmonics in the extreme ultraviolet range (18-27 nm) from a linearly polarized infrared laser (40 fs, 0.25 TW) focused into a neon filled gas cell. To circularly polarize the initially linearly polarized harmonics we have implemented a four-reflector phase-shifter. Fully circularly polarized radiation has been obtained with an efficiency of a few percents, thus being significantly more efficient than currently demonstrated direct generation of elliptically polarized harmonics. This demonstration opens up new experimental capabilities based on high order harmonics, for example, in biology and materials science. The inherent femtosecond time resolution of high order harmonic generating table top laser sources renders these an ideal tool for the investigation of ultrafast magnetization dynamics now that the magnetic circular dichroism at the absorption M-edges of transition metals can be exploited.

  8. Feasibility study of generating ultra-high harmonic radiation with a single stage echo-enabled harmonic generation scheme

    Zhou, Kaishang, E-mail: zhoukaishang@sinap.ac.cn; Feng, Chao, E-mail: fengchao@sinap.ac.cn; Wang, Dong, E-mail: wangdong@sinap.ac.cn

    2016-10-21

    The echo enabled harmonic generation (EEHG) scheme holds the ability for the generation of fully coherent soft x-ray free-electron laser (FEL) pulses directly from external UV seeding sources. In this paper, we study the feasibility of using a single stage EEHG to generate coherent radiation in the “water window” and beyond. Using the high-order operating modes of the EEHG scheme, intensive numerical simulations have been performed considering various three-dimensional effects. The simulation results demonstrated that coherent soft x-ray radiation at 150th harmonic (1.77 nm) of the seed can be produced by a single stage EEHG. The decreasing of the final bunching factor at the desired harmonic caused by intra beam scattering (IBS) effect has also been analyzed.

  9. Prediction of Metastasis Using Second Harmonic Generation

    2016-07-01

    small but statistically significant difference in average F/B of treated US patients versus untreated Dutch patients. Fig. 1. Display of all...predictive ability of models incorporating F/B using a multivariate linear model, but this time applying the analysis to the entire ER+ and ER- cohort. As...AWARD NUMBER: W81XWH-15-1-0040 TITLE: Prediction of Metastasis Using Second Harmonic Generation PRINCIPAL INVESTIGATOR: Edward Brown

  10. Dynamics of harmonic generation in atoms and molecules

    Boutu, W.

    2007-09-01

    Harmonics are generated when an ultra-short laser impulse with an energy of 10 14 W/cm 2 is focused on a gas jet. A radiation in the UV X range is then emitted in the direction of the incident laser beam. This radiation has a periodical spectral structure composed of odd harmonics of the fundamental frequency. The first part of this work is dedicated to the optimization of the harmonic radiation. We have studied an alternative and cheaper solution to the flexible mirror, we have used a set of concentric phase plates in order to control the spatial phase of the beam and create an enlarged square profile near the focusing spot. We show how different parameters like phase shift or luminous-flux density or jet position have an impact on the harmonic signal. This second part of this work deals with the generation of high order harmonics in N 2 and CO 2 molecules. The experimental setting is based on the RABITT method (reconstruction of the atto-second burst by interference of 2-photon transitions). We have observed the presence of a spectral minimum linked to a phenomena of quantum interferences between the molecule and the electron wave packet. Moreover, a shift in the spectral phase appears at the place of the interference. (A.C.)

  11. Generating transverse response explicitly from harmonic oscillators

    Yao, Yuan; Tang, Ying; Ao, Ping

    2017-10-01

    We obtain stochastic dynamics from a system-plus-bath mechanism as an extension of the Caldeira-Leggett (CL) model in the classical regime. An effective magnetic field and response functions with both longitudinal and transverse parts are exactly generated from the bath of harmonic oscillators. The effective magnetic field and transverse response are antisymmetric matrices: the former is explicitly time-independent corresponding to the geometric magnetism, while the latter can have memory. The present model can be reduced to previous representative examples of stochastic dynamics describing nonequilibrium processes. Our results demonstrate that a system coupled with a bath of harmonic oscillators is a general approach to studying stochastic dynamics, and provides a method to experimentally implement an effective magnetic field from coupling to the environment.

  12. Coherent bremsstrahlung generation of harmonics in a laser-produced plasma

    Silin, Viktor P

    1999-01-01

    Foundations of a theory of generation of the harmonics of a laser pump in a fully ionised plasma are proposed. This theory makes it possible to describe the relationships governing harmonic generation in an analytical form. For an elliptically polarised pump field with a low degree of circular polarisation A, the range of plasma parameters is established in which the number of harmonics is found to be of the order of A -1 . Anomalous polarisation properties of the harmonics are predicted. In this case, their polarisation is seen to be nearly perpendicular to the pump polarisation and the degree of circular polarisation increases with the harmonic order number. The harmonic-order-dependent intensity of the pump field which results in circular polarisation of a harmonic is determined making allowance for thermal plasma motion. The conditions under which increasing the low degree of circular pump polarisation increases the efficiency of harmonic generation are established. The nonlinear dependence of the pump polarisation on its intensity under the conditions of collisional absorption in a plasma are identified and an instability of the circular polarisation is revealed. For a plane-polarised pump, it is shown how the maximum power of a harmonic and the pump power corresponding to this maximum scale up with the harmonic order number. The conditions under which the number of harmonics generated is limited owing to the relativistic nature of electron motion in the pump field are established. This effect appears for an unexpectedly weak relativity. (invited paper)

  13. Analysis of Even Harmonics Generation in an Isolated Electric Power System

    Kanao, Norikazu; Hayashi, Yasuhiro; Matsuki, Junya

    Harmonics bred from loads are mainly odd order because the current waveform has half-wave symmetry. Since the even harmonics are negligibly small, those are not generally measured in electric power systems. However, even harmonics were measured at a 500/275/154kV substation in Hokuriku Electric Power Company after removal of a transmission line fault. The even harmonics caused malfunctions of protective digital relays because the relays used 4th harmonics at the input filter as automatic supervisory signal. This paper describes the mechanism of generation of the even harmonics by comparing measured waveforms with ATP-EMTP simulation results. As a result of analysis, it is cleared that even harmonics are generated by three causes. The first cause is a magnetizing current of transformers due to flux deviation by DC component of a fault current. The second one is due to harmonic conversion of a synchronous machine which generates even harmonics when direct current component or even harmonic current flow into the machine. The third one is that increase of harmonic impedance due to an isolated power system produces harmonic voltages. The design of the input filter of protective digital relays should consider even harmonics generation in an isolated power system.

  14. Probing two-centre interference in molecular high harmonic generation

    Vozzi, C; Calegari, F; Benedetti, E; Berlasso, R; Sansone, G; Stagira, S; Nisoli, M; Altucci, C; Velotta, R; Torres, R; Heesel, E; Kajumba, N; Marangos, J P

    2006-01-01

    Two-centre interference in the recombination step of molecular high harmonic generation (HHG) has been probed in CO 2 and O 2 . We report the order dependence of characteristic enhancements or suppressions of high harmonic production in aligned samples of both molecules. In CO 2 , a robust destructive interference was seen consistent with the known separation of the oxygen atoms that are active in HHG. In O 2 , a harmonic enhancement was found indicating constructive interference. A good agreement was found with a simple two-centre interference model that includes the angular distribution function of the sample. The effective momentum of the electron wave was determined from the spectral position of these interferences. Ellipticity-dependent studies in CO 2 clearly show how the destructive interference can be 'switched off' by increasing the degree of ellipticity and thus shifting the effective resonance condition

  15. Promoting Spontaneous Second Harmonic Generation through Organogelation.

    Marco, A Belén; Aparicio, Fátima; Faour, Lara; Iliopoulos, Konstantinos; Morille, Yohann; Allain, Magali; Franco, Santiago; Andreu, Raquel; Sahraoui, Bouchta; Gindre, Denis; Canevet, David; Sallé, Marc

    2016-07-27

    An organogelator based on the Disperse Red nonlinear optical chromophore was synthesized according to a simple and efficient three-step procedure. The supramolecular gel organization leads to xerogels which display a spontaneous second harmonic generation (SHG) response without any need for preprocessing, and this SHG activity appears to be stable over several months. These findings, based on an intrinsic structural approach, are supported by favorable intermolecular supramolecular interactions, which promote a locally non-centrosymmetric NLO-active organization. This is in sharp contrast with most materials designed for SHG purposes, which generally require the use of expensive or heavy-to-handle external techniques for managing the dipoles' alignment.

  16. The analysis of harmonic generation coefficients in the ablative Rayleigh-Taylor instability

    Lu, Yan; Fan, Zhengfeng; Lu, Xinpei; Ye, Wenhua; Zou, Changlin; Zhang, Ziyun; Zhang, Wen

    2017-10-01

    In this research, we use the numerical simulation method to investigate the generation coefficients of the first three harmonics and the zeroth harmonic in the Ablative Rayleigh-Taylor Instability. It is shown that the interface shifts to the low temperature side during the ablation process. In consideration of the third-order perturbation theory, the first three harmonic amplitudes of the weakly nonlinear regime are calculated and then the harmonic generation coefficients are obtained by curve fitting. The simulation results show that the harmonic generation coefficients changed with time and wavelength. Using the higher-order perturbation theory, we find that more and more harmonics are generated in the later weakly nonlinear stage, which is caused by the negative feedback of the later higher harmonics. Furthermore, extending the third-order theory to the fifth-order theory, we find that the second and the third harmonics coefficients linearly depend on the wavelength, while the feedback coefficients are almost constant. Further analysis also shows that when the fifth-order theory is considered, the normalized effective amplitudes of second and third harmonics can reach about 25%-40%, which are only 15%-25% in the frame of the previous third-order theory. Therefore, the third order perturbation theory is needed to be modified by the higher-order theory when ηL reaches about 20% of the perturbation wavelength.

  17. Limitations and improvements for harmonic generation measurements

    Best, Steven; Croxford, Anthony; Neild, Simon

    2014-01-01

    A typical acoustic harmonic generation measurement comes with certain limitations. Firstly, the use of the plane wave-based analysis used to extract the nonlinear parameter, β, ignores the effects of diffraction, attenuation and receiver averaging which are common to most experiments, and may therefore limit the accuracy of a measurement. Secondly, the method usually requires data obtained from a through-transmission type setup, which may not be practical in a field measurement scenario where access to the component is limited. Thirdly, the technique lacks a means of pinpointing areas of damage in a component, as the measured nonlinearity represents an average over the length of signal propagation. Here we describe a three-dimensional model of harmonic generation in a sound beam, which is intended to provide a more realistic representation of a typical experiment. The presence of a reflecting boundary is then incorporated into the model to assess the feasibility of performing single-sided measurements. Experimental validation is provided where possible. Finally, a focusing acoustic source is modelled to provide a theoretical indication of the afforded advantages when the nonlinearity is localized

  18. Third-harmonic generation for photoionization studies

    Compton, R.N.; Miller, J.C.

    1982-01-01

    Our group at Oak Ridge National Laboratory (ORNL) has studied resonantly enhanced multiphoton ionization (MPI) of alkali atoms, rare gases, and small molecules using tightly focused dye laser beams (power densities of 10 9 to 10 11 W/cm 2 ). In the case of alkali atoms, some ionization signals appear as a result of gas density effects (dimers or quasi-collisions) as previously discovered by Collins and his collaborators. These have been termed hybrid-resonances. By contrast, in the case of the rare gases, certain resonance ionization signals disappear with increasing gas density. The disappearance of the ionization signals in the rare gases is due to the interference of excitation of the third-harmonic and fundamental laser beam. At low pressure (10 -7 to 10 -5 torr) we have studied (1) mass spectra, (2) kinetic energy released in ionic fragmentation, and (3) photoelectron kinetic energy spectra using time-of-flight mass analysis and a 160 0 spherical sector electrostatic energy analyzer. These experiments, combined with two-color dye laser experiments, can often offer an unambiguous and detailed description of the MPI and subsequent fragmentation events. The major part of this talk will be devoted to the production and the use of vacuum ultraviolet (VUV) light from third-harmonic generation (THG) in the rare gases

  19. Transient regime in second harmonic generation

    Szeftel, Jacob; Sandeau, Laure; Sandeau, Nicolas; Delezoide, Camille; Khater, Antoine

    2013-09-01

    The time growth of the electromagnetic field at the fundamental and double frequencies is studied from the very onset of the second harmonic generation (SHG) process for a set of dipoles lacking a symmetry centre and exhibiting a nonresonant coupling with a classical electromagnetic field. This approach consists first of solving the Schrödinger equation by applying a generalised Rabi rotation to the Hamiltonian describing the light-dipole interaction. This rotation has been devised for the resulting Hamiltonian to show up time-independent for both components of the electromagnetic field at the fundamental frequency and the second harmonic one. Then an energy conservation argument, derived from the Poynting theorem, is introduced to work out an additional relationship between the electromagnetic field and its associated electric polarisation. Finally this analysis yields the full time behaviour of all physical quantities of interest. The calculated results reproduce accurately both the observed spatial oscillations of the SHG intensity (Maker's fringes) and its power law dependence on the intensity of the incoming light at the fundamental frequency.

  20. Phase matching of high-order harmonics in a semi-infinite gas cell

    Steingrube, Daniel S.; Vockerodt, Tobias; Schulz, Emilia; Morgner, Uwe; Kovacev, Milutin

    2009-01-01

    Phase matching of high-order harmonic generation is investigated experimentally for various parameters in a semi-infinite gas-cell (SIGC) geometry. The optimized harmonic yield is identified using two different noble gases (Xe and He) and its parameter dependence is studied in a systematic way. Beside the straightforward setup of the SIGC, this geometry promises a high photon flux due to a large interaction region. Moreover, since the experimental parameters within this cell are known accurately, direct comparison to simulations is performed. Spectral splitting and blueshift of high-order harmonics are observed.

  1. Electroencephalography in ellipsoidal geometry with fourth-order harmonics.

    Alcocer-Sosa, M; Gutierrez, D

    2016-08-01

    We present a solution to the electroencephalographs (EEG) forward problem of computing the scalp electric potentials for the case when the head's geometry is modeled using a four-shell ellipsoidal geometry and the brain sources with an equivalent current dipole (ECD). The proposed solution includes terms up to the fourth-order ellipsoidal harmonics and we compare this new approximation against those that only considered up to second- and third-order harmonics. Our comparisons use as reference a solution in which a tessellated volume approximates the head and the forward problem is solved through the boundary element method (BEM). We also assess the solution to the inverse problem of estimating the magnitude of an ECD through different harmonic approximations. Our results show that the fourth-order solution provides a better estimate of the ECD in comparison to lesser order ones.

  2. Analysis of higher order harmonics with holographic reflection gratings

    Mas-Abellan, P.; Madrigal, R.; Fimia, A.

    2017-05-01

    Silver halide emulsions have been considered one of the most energetic sensitive materials for holographic applications. Nonlinear recording effects on holographic reflection gratings recorded on silver halide emulsions have been studied by different authors obtaining excellent experimental results. In this communication specifically we focused our investigation on the effects of refractive index modulation, trying to get high levels of overmodulation that will produce high order harmonics. We studied the influence of the overmodulation and its effects on the transmission spectra for a wide exposure range by use of 9 μm thickness films of ultrafine grain emulsion BB640, exposed to single collimated beams using a red He-Ne laser (wavelength 632.8 nm) with Denisyuk configuration obtaining a spatial frequency of 4990 l/mm recorded on the emulsion. The experimental results show that high overmodulation levels of refractive index produce second order harmonics with high diffraction efficiency (higher than 75%) and a narrow grating bandwidth (12.5 nm). Results also show that overmodulation produce diffraction spectra deformation of the second order harmonic, transforming the spectrum from sinusoidal to approximation of square shape due to very high overmodulation. Increasing the levels of overmodulation of refractive index, we have obtained higher order harmonics, obtaining third order harmonic with diffraction efficiency (up to 23%) and narrowing grating bandwidth (5 nm). This study is the first step to develop a new easy technique to obtain narrow spectral filters based on the use of high index modulation reflection gratings.

  3. Second Harmonic Generation of Unpolarized Light

    Ding, Changqin; Ulcickas, James R. W.; Deng, Fengyuan; Simpson, Garth J.

    2017-11-01

    A Mueller tensor mathematical framework was applied for predicting and interpreting the second harmonic generation (SHG) produced with an unpolarized fundamental beam. In deep tissue imaging through SHG and multiphoton fluorescence, partial or complete depolarization of the incident light complicates polarization analysis. The proposed framework has the distinct advantage of seamlessly merging the purely polarized theory based on the Jones or Cartesian susceptibility tensors with a more general Mueller tensor framework capable of handling partial depolarized fundamental and/or SHG produced. The predictions of the model are in excellent agreement with experimental measurements of z -cut quartz and mouse tail tendon obtained with polarized and depolarized incident light. The polarization-dependent SHG produced with unpolarized fundamental allowed determination of collagen fiber orientation in agreement with orthogonal methods based on image analysis. This method has the distinct advantage of being immune to birefringence or depolarization of the fundamental beam for structural analysis of tissues.

  4. Numerical studies of third-harmonic generation in laser filament in air perturbed by plasma spot

    Feng Liubin; Lu Xin; Liu Xiaolong; Li Yutong; Chen Liming; Ma Jinglong; Dong Quanli; Wang Weimin; Xi Tingting; Sheng Zhengming; Zhang Jie; He Duanwei

    2012-01-01

    Third-harmonic emission from laser filament intercepted by plasma spot is studied by numerical simulations. Significant enhancement of the third-harmonic generation is obtained due to the disturbance of the additional plasma. The contribution of the pure plasma effect and the possible plasma-enhanced third-order susceptibility on the third-harmonic generation enhancement are compared. It is shown that the plasma induced cancellation of destructive interference [Y. Liu et al., Opt. Commun. 284, 4706 (2011)] of two-colored filament is the dominant mechanism of the enhancement of third-harmonic generation.

  5. Control and metrology of high harmonic generation on plasma mirrors

    Monchoce, Sylvain

    2014-01-01

    When an ultra intense femtosecond laser with high contrast is focused on a solid target, the laser field at focus is sufficient enough to completely ionize the target surface during the rising edge of the laser pulse and form a plasma. This dense plasma entirely reflects the incident beam in the specular direction: this is a so-called plasma mirror. As the interaction between the laser and the plasma mirror is highly non-linear, it thus leads to the high harmonic generation (HHG) in the reflected beam. In the temporal domain, this harmonic spectrum is associated to a train of atto-second pulses. The aim of my PhD were to experimentally control this HHG and to measure the properties of the harmonics. We first studied the optimization of the harmonic signal, and then the spatial characterization of the harmonic beam in the far-field (harmonic divergence). These characterizations are not only important to develop an intense XUV/atto-second light source, but also to get a better understanding of the laser-matter interaction at very high intensity. We have thus been able to get crucial information of the electrons and ions dynamics of the plasma, showing that the harmonics can also be used as a diagnostic of the laser-plasma interaction. We then developed a new general approach for optically-controlled spatial structuring of overdense plasmas generated at the surface of initially plain solid targets. We demonstrate it experimentally by creating sinusoidal plasma gratings of adjustable spatial periodicity and depth, and study the interaction of these transient structures with an ultra-intense laser pulse to establish their usability at relativistically high intensities. We then show how these gratings can be used as a 'spatial ruler' to determine the source size of the high-order harmonic beams produced at the surface of an overdense plasma. These results open new directions both for the metrology of laser-plasma interactions and the emerging field of ultrahigh

  6. Effects of multiple electronic shells on strong-field multiphoton ionization and high-order harmonic generation of diatomic molecules with arbitrary orientation: An all-electron time-dependent density-functional approach

    Telnov, Dmitry A.; Chu, S.-I

    2009-01-01

    We present a time-dependent density-functional theory approach with proper long-range potential for an ab initio study of the effect of correlated multielectron responses on the multiphoton ionization (MPI) and high-order harmonic generation (HHG) of diatomic molecules N 2 and F 2 in intense short laser pulse fields with arbitrary molecular orientation. We show that the contributions of inner molecular orbitals to the total MPI probability can be sufficiently large or even dominant over the highest-occupied molecular orbital, depending on detailed electronic structure and symmetry, laser field intensity, and orientation angle. The multielectron effects in HHG are also very important. They are responsible for enhanced HHG at some orientations of the molecular axis. Even strongly bound electrons may have a significant influence on the HHG process.

  7. Retrieval of interatomic separations of molecules from laser-induced high-order harmonic spectra

    Le, Van-Hoang; Nguyen, Ngoc-Ty; Jin, C; Le, Anh-Thu; Lin, C D

    2008-01-01

    We illustrate an iterative method for retrieving the internuclear separations of N 2 , O 2 and CO 2 molecules using the high-order harmonics generated from these molecules by intense infrared laser pulses. We show that accurate results can be retrieved with a small set of harmonics and with one or few alignment angles of the molecules. For linear molecules the internuclear separations can also be retrieved from harmonics generated using isotropically distributed molecules. By extracting the transition dipole moment from the high-order harmonic spectra, we further demonstrated that it is preferable to retrieve the interatomic separation iteratively by fitting the extracted dipole moment. Our results show that time-resolved chemical imaging of molecules using infrared laser pulses with femtosecond temporal resolutions is possible

  8. Retrieval of interatomic separations of molecules from laser-induced high-order harmonic spectra

    Le, Van-Hoang; Nguyen, Ngoc-Ty [Department of Physics, University of Pedagogy, 280 An Duong Vuong, Ward 5, Ho Chi Minh City (Viet Nam); Jin, C; Le, Anh-Thu; Lin, C D [J. R. Macdonald Laboratory, Department of Physics, Kansas State University, Manhattan, KS 66506 (United States)

    2008-04-28

    We illustrate an iterative method for retrieving the internuclear separations of N{sub 2}, O{sub 2} and CO{sub 2} molecules using the high-order harmonics generated from these molecules by intense infrared laser pulses. We show that accurate results can be retrieved with a small set of harmonics and with one or few alignment angles of the molecules. For linear molecules the internuclear separations can also be retrieved from harmonics generated using isotropically distributed molecules. By extracting the transition dipole moment from the high-order harmonic spectra, we further demonstrated that it is preferable to retrieve the interatomic separation iteratively by fitting the extracted dipole moment. Our results show that time-resolved chemical imaging of molecules using infrared laser pulses with femtosecond temporal resolutions is possible.

  9. Phase-dependent quantum interference between different pathways in bichromatic harmonic generation

    Jun, Cai; Li-Ming, Wang; Hao-Xue, Qiao

    2009-01-01

    This paper studies the harmonic generation of the hydrogen atom subjected to a collinear bichromatic laser field by numerically solving the time-dependent Schrödinger equation using the split-operator pseudo-spectral method. By adding a frequency variation to the additional field, the contributions of different pathways to particular order harmonic generation can be isolated. The quantum interference pattern between harmonic pathways, which influences the harmonic intensity, is found to be either constructive or destructive with respect to different relative phase of the two field components. Detailed description of up to the 35th-order harmonics and the harmonic pathways for a wide range of field parameters is presented. (atomic and molecular physics)

  10. Temporally coherent x-ray laser with the high order harmonic light

    Hasegawa, Noboru; Kawachi, Tetsuya; Kishimoto, Maki; Sukegawa, Kouta; Tanaka, Momoko; Ochi, Yoshihiro; Nishikino, Masaharu; Kawazome, Hayato; Nagashima, Keisuke

    2005-01-01

    We obtained the neon-like manganese x-ray laser with the injection of the high order harmonic light as the seed x-ray at the wavelength of 26.9 nm for the purpose of generation of the temporally coherent x-ray laser. The x-ray amplifier, which has quite narrow spectral width, selected and amplified the temporally coherent mode of the harmonic light. The temporal coherence of the mode selected harmonic light was nearly transform limited pulse, and the obtained x-ray laser with the seed x-ray expected to be nearly temporally coherent x-ray. (author)

  11. Non-critically phase-matched second harmonic generation and third order nonlinearity in organic crystal glucuronic acid γ-lactone

    Saripalli, Ravi Kiran; Katturi, Naga Krishnakanth; Soma, Venugopal Rao; Bhat, H. L.; Elizabeth, Suja

    2017-12-01

    The linear, second order, and third order nonlinear optical properties of glucuronic acid γ-lactone single crystals were investigated. The optic axes and principal dielectric axes were identified through optical conoscopy and the principal refractive indices were obtained using the Brewster's angle method. Conic sections were observed which is perceived to be due to spontaneous non-collinear phase matching. The direction of collinear phase matching was determined and the deff evaluated in this direction was 0.71 pm/V. Open and closed aperture Z-scan measurements with femtosecond pulses revealed high third order nonlinearity in the form of self-defocusing, two-photon absorption, as well as saturable absorption.

  12. Accurate calculation of high harmonics generated by relativistic Thomson scattering

    Popa, Alexandru

    2008-01-01

    The recent emergence of the field of ultraintense laser pulses, corresponding to beam intensities higher than 10 18 W cm -2 , brings about the problem of the high harmonic generation (HHG) by the relativistic Thomson scattering of the electromagnetic radiation by free electrons. Starting from the equations of the relativistic motion of the electron in the electromagnetic field, we give an exact solution of this problem. Taking into account the Lienard-Wiechert equations, we obtain a periodic scattered electromagnetic field. Without loss of generality, the solution is strongly simplified by observing that the electromagnetic field is always normal to the direction electron-detector. The Fourier series expansion of this field leads to accurate expressions of the high harmonics generated by the Thomson scattering. Our calculations lead to a discrete HHG spectrum, whose shape and angular distribution are in agreement with the experimental data from the literature. Since no approximations were made, our approach is also valid in the ultrarelativistic regime, corresponding to intensities higher than 10 23 W cm -2 , where it predicts a strong increase of the HHG intensities and of the order of harmonics. In this domain, the nonlinear Thomson scattering could be an efficient source of hard x-rays

  13. Nonlinear harmonic generation and proposed experimental verification in SASE FELs

    Freund, H P; Milton, S V

    2000-01-01

    Recently, a 3D, polychromatic, nonlinear simulation code was developed to study the growth of nonlinear harmonics in self-amplified spontaneous emission (SASE) free-electron lasers (FELs). The simulation was applied to the parameters for each stage of the Advanced Photon Source (APS) SASE FEL, intended for operation in the visible, UV, and short UV wavelength regimes, respectively, to study the presence of nonlinear harmonic generation. Significant nonlinear harmonic growth is seen. Here, a discussion of the code development, the APS SASE FEL, the simulations and results, and, finally, the proposed experimental procedure for verification of such nonlinear harmonic generation at the APS SASE FEL will be given.

  14. Second-harmonic generation in substoichiometric silicon nitride layers

    Pecora, Emanuele; Capretti, Antonio; Miano, Giovanni; Dal Negro, Luca

    2013-03-01

    Harmonic generation in optical circuits offers the possibility to integrate wavelength converters, light amplifiers, lasers, and multiple optical signal processing devices with electronic components. Bulk silicon has a negligible second-order nonlinear optical susceptibility owing to its crystal centrosymmetry. Silicon nitride has its place in the microelectronic industry as an insulator and chemical barrier. In this work, we propose to take advantage of silicon excess in silicon nitride to increase the Second Harmonic Generation (SHG) efficiency. Thin films have been grown by reactive magnetron sputtering and their nonlinear optical properties have been studied by femtosecond pumping over a wide range of excitation wavelengths, silicon nitride stoichiometry and thermal processes. We demonstrate SHG in the visible range (375 - 450 nm) using a tunable 150 fs Ti:sapphire laser, and we optimize the SH emission at a silicon excess of 46 at.% demonstrating a maximum SHG efficiency of 4x10-6 in optimized films. Polarization properties, generation efficiency, and the second order nonlinear optical susceptibility are measured for all the investigated samples and discussed in terms of an effective theoretical model. Our findings show that the large nonlinear optical response demonstrated in optimized Si-rich silicon nitride materials can be utilized for the engineering of nonlinear optical functions and devices on a Si chip.

  15. Effects of external magnetic field on harmonics generated in laser interaction with underdense plasma

    Faghihi-Nik, M.; Ghorbanalilu, M.; Shokri, B.

    2010-01-01

    Complete text of publication follows. Generation of harmonic radiation is an important subject of laser plasma interaction and attracts great attention due to a wide range of applications. It has been seen that intense electromagnetic and quasi-static transverse magnetic fields are generated in laser plasma interaction. An extremely intense magnetic field (up to hundreds of MG) has been observed by experimental measurements in interaction of short laser pulses with plasma. These self-generated or applied magnetic fields affect the propagation of the laser pulses. In most laser interactions with homogeneous plasma, odd harmonics of laser frequency are generated. In this paper, we point out the possibility of even harmonics generation when a linearly polarized laser beam propagates in homogeneous plasma in the presence of a transverse magnetic field. It is shown that applying external field induces a transverse current density oscillating twice of the laser field which leds to generation of second harmonic radiation. This current density is derived using the perturbation method, and the steady state amplitude of the second harmonic obtained by solution of the wave equation. By the same procedure the current density and then the steady state amplitude of higher order harmonics are calculated. The efficiency of harmonic generation (the ratio of harmonic power to incident power) is a drastically function of the strength of external magnetic field. It is found that the efficiency of even harmonics is zero in the absence of magnetic field and increases as the magnetic field is increased. For odd harmonics, applying the external magnetic field enhances the generated harmonics as well. The conversion efficiency also increases with increase in plasma density and intensity of the laser beam.

  16. Harmonic development of tide-generating potential of terrestrial planets

    Kudryavtsev, Sergey M.

    2008-08-01

    The aim of this study is to obtain high-accurate harmonic developments of the tide-generating potential (TGP) of Mercury, Venus and Mars. The planets’ TGP values have been first calculated on the base of DE/LE-406 numerical planetary/lunar ephemerides over a long period of time and then processed by a new spectral analysis method. According to this method the development is directly made to Poisson series where both amplitudes and arguments of the series’ terms are high-degree polynomials of time. A new harmonic development of Mars TGP is made over the time period 1900 AD 2100 AD and includes 767 second-order Poisson series’ terms of minimum amplitude equal to 10-7 m2 s-2. Analogous series composing both Mercury and Venus TGP harmonic models are built over the time period 1000 AD 3000 AD and include 1,061 and 693 terms, respectively. A modification of the standard HW95 format for representation of the terrestrial planets’ TGP is proposed. The number of terms in the planets’ TGP models transformed to the modified HW95 format is 650 for Mercury, 422 for Venus, and 480 for Mars. The quality of the new developments of the terrestrial planets’ TGP is better than that of the similar developments obtained earlier.

  17. High-Harmonic Generation in Solids with and without Topological Edge States

    Bauer, Dieter; Hansen, Kenneth Christian Klochmann

    2018-01-01

    High-harmonic generation in the two topological phases of a finite, one-dimensional, periodic structure is investigated using a self-consistent time-dependent density functional theory approach. For harmonic photon energies smaller than the band gap, the harmonic yield is found to differ by up...... to 14 orders of magnitude for the two topological phases. This giant topological effect is explained by the degree of destructive interference in the harmonic emission of all valence-band (and edge-state) electrons, which strongly depends on whether or not topological edge states are present...

  18. Harmonics: Generation and Suppression in AC System Networks ...

    However, reactive power flow in electrical networks has adverse effects depending on their magnitude and the nature of the supply network. How these harmonics are generated by nonlinear loads and the means by which they can be kept low are the focus of this paper. Keywords: non-linear loads, harmonics, reactive ...

  19. Single-shot fluctuations in waveguided high-harmonic generation

    Goh, S.J.; Tao, Y.; van der Slot, Petrus J.M.; Bastiaens, Hubertus M.J.; Herek, Jennifer Lynn; Biedron, S.G.; Danailov, M.B.; Milton, S.V.; Boller, Klaus J.

    2015-01-01

    For exploring the application potential of coherent soft x-ray (SXR) and extreme ultraviolet radiation (XUV) provided by high-harmonic generation, it is important to characterize the central output parameters. Of specific importance are pulse-to-pulse (shot-to-shot) fluctuations of the high-harmonic

  20. Symmetry properties of second harmonics generated by antisymmetric Lamb waves

    Zhu, Wujun; Xiang, Yanxun; Liu, Chang-Jun; Deng, Mingxi; Xuan, Fu-Zhen

    2018-03-01

    Symmetry properties of second harmonics generated by antisymmetric primary Lamb waves are systematically studied in this work. In theory, the acoustic field of second harmonic Lamb waves is obtained by using the perturbation approximation and normal modal method, and the energy flux transfer from the primary Lamb waves to second harmonics is mainly explored. Symmetry analyses indicate that either the symmetric or antisymmetric Lamb waves can merely generate the symmetric second harmonics. Finite element simulations are performed on the nonlinear Lamb wave propagation of the antisymmetric A0 mode in the low frequency region. The signals of the second harmonics and the symmetric second harmonic s0 mode are found to be exactly equivalent in the time domain. The relative acoustic nonlinearity parameter A2/A12 oscillates with the propagation distance, and the oscillation amplitude and spatial period are well consistent with the theoretical prediction of the A0-s0 mode pair, which means that only the second harmonic s0 mode is generated by the antisymmetric primary A0 mode. Experiments are further conducted to examine the cumulative generation of symmetric second harmonics for the antisymmetric-symmetric mode pair A3-s6. Results show that A2/A12 increases linearly with the propagation distance, which means that the symmetric second harmonic s6 mode is generated cumulatively by the antisymmetric primary A3 mode. The present investigation systematically corroborates the proposed theory that only symmetric second harmonics can be generated accompanying the propagation of antisymmetric primary Lamb waves in a plate.

  1. Harmonics Generation by Surface Plasmon Polaritons on Single Nanowires.

    de Hoogh, Anouk; Opheij, Aron; Wulf, Matthias; Rotenberg, Nir; Kuipers, L

    2016-08-17

    We present experimental observations of visible wavelength second- and third-harmonic generation on single plasmonic nanowires of variable widths. We identify that near-infrared surface plasmon polaritons, which are guided along the nanowire, act as the source of the harmonics generation. We discuss the underlying mechanism of this nonlinear process, using a combination of spatially resolved measurements and numerical simulations to show that the visible harmonics are generated via a combination of both local and propagating plasmonic modes. Our results provide the first demonstration of nanoscale nonlinear optics with guided, propagating plasmonic modes on a lithographically defined chip, opening up new routes toward integrated optical circuits for information processing.

  2. 乙烯分子在激光场中的多光子电离及高次谐波的产生%High-order harmonic generation and multi-photon ionization of ethylene in laser fields

    王志萍; 张丰收; 王菁

    2012-01-01

    Applying the time dependent local density approximation(TDLDA),the high-order harmonic generation(HHG)spectra and the ionization probabilities of ethylene subject to the one-colour and two-colour laser field are explored.It is found that HHG spectra of ethylent exhibits the plateau obviously from the fifth order to the ninth order harmonic and the odd harmonics are strengthed in the one-colour laser field.Furthermore,the ionization of ethylene is enhanced in the two-colour laser field resulting the appearance of the high charge state and the even harmonics.%本文运用含时密度泛函理论和局域密度近似方法,分别研究了乙烯分子在单色激光场、双色激光场中电离和高次谐波的产生。计算结果表明,在单色激光场中,乙烯分子的高次谐波谱呈现出明显的平台区和奇次谐波加强的特征:在双色激光场中,乙烯分子的电离增强而出现高电荷态几率,并伴有偶次谐波的出现。

  3. Elliptically polarized high-order harmonics from aligned molecules within the strong-field approximation

    Etches, Adam; Madsen, Christian Bruun; Madsen, Lars Bojer

    A correction term is introduced in the stationary-point analysis on high-order harmonic generation (HHG) from aligned molecules. Arising from a multi-centre expansion of the electron wave function, this term brings our numerical calculations of the Lewenstein model into qualitative agreement...

  4. Optical klystron and harmonic generation free electron laser

    Qika Jia

    2005-06-01

    Full Text Available The optical field evolution of an optical klystron free electron laser is analytically described for both low gain and high gain cases. The harmonic optical klystron (HOK in which the second undulator is resonant on the higher harmonic of the first undulator is analyzed as a harmonic amplifier. The optical field evolution equation of the HOK is derived analytically for both the CHG mode (coherent harmonic generation, the quadratic gain regime and the HGHG mode (high gain harmonic generation, the exponential gain regime, the effects of energy spread, energy modulation, and dispersion in the whole process are taken into account. The linear theory is given and discussed for the HGHG mode. The analytical formula is given for the CHG mode.

  5. High-order harmonic propagation in gases within the discrete dipole approximation

    Hernandez-Garcia, C.; Perez-Hernandez, J. A.; Ramos, J.; Jarque, E. Conejero; Plaja, L.; Roso, L.

    2010-01-01

    We present an efficient approach for computing high-order harmonic propagation based on the discrete dipole approximation. In contrast with other approaches, our strategy is based on computing the total field as the superposition of the driving field with the field radiated by the elemental emitters of the sample. In this way we avoid the numerical integration of the wave equation, as Maxwell's equations have an analytical solution for an elementary (pointlike) emitter. The present strategy is valid for low-pressure gases interacting with strong fields near the saturation threshold (i.e., partially ionized), which is a common situation in the experiments of high-order harmonic generation. We use this tool to study the dependence of phase matching of high-order harmonics with the relative position between the beam focus and the gas jet.

  6. Surface structure enhanced second harmonic generation in organic nanofibers

    Fiutowski, Jacek; Maibohm, Christian; Kostiučenko, Oksana

    Second-harmonic generation upon femto-second laser irradiation of nonlinearly optically active nanofibers grown from nonsymmetrically functionalized para-quarterphenylene (CNHP4) molecules is investigated. Following growth on mica templates, the nanofibers have been transferred onto lithography...

  7. Enhancement of harmonic generation using a two section undulator

    Prazeres, R.; Glotin, F.; Jaroszynski, D.A.; Ortega, J.M.; Rippon, C.

    1999-01-01

    Enhancement of the 2nd and 3rd harmonic of the wavelength of a Free-Electron Laser (FEL) has been measured when a single electron beam is crossing a two-section undulator. To produce the harmonic radiation enhancement, the undulator is arranged so that the resonance wavelength of the 2nd undulator (downstream) matches a harmonic of the 1st undulator (upstream). Both the fundamental and the harmonic optical fields evolve in the same optical cavity and are coupled out with different extraction efficiency, through a hole in one of the cavity mirrors. We present measurements that show that the optical power at the 2nd and 3rd harmonic can be enhanced, by about one order of magnitude, in two configurations: when the resonance wavelength of the 2nd undulator matches the harmonic of 1st one (harmonic configuration), or when the gap of the 2nd undulator is slightly larger than first one (step-tapered configuration). We examine the dependence of the harmonic power on the gap of the 2nd undulator. This fundamental/harmonic mode of operation of the FEL may have useful applications in the production of coherent X-ray and VUV radiation, a spectral range where high reflectivity optical cavity mirrors are difficult or impossible to manufacture

  8. Second harmonic generation in Te crystal using free electron laser

    Yamauchi, T; Minehara, E J

    2002-01-01

    The second harmonic generation signal converted from the fundamental wavelength of 22 mu m of a free electron laser was observed for the first time using a birefringent Te crystal. The experimental conversion efficiency of Te crystal for second harmonic generation is 0.53%, which is equivalent to the theoretical value within a factor of 2. The Te crystal has been incorporated into an autocorrelator system to measure the micro-pulse width of infrared free electron laser successfully. (author)

  9. Harmonic generation by atomic and nanoparticle precursors in a ZnS laser ablation plasma

    Oujja, M.; Lopez-Quintas, I.; Benítez-Cañete, A.; Nalda, R. de; Castillejo, M.

    2017-01-01

    Highlights: • Plume species in infrared ns laser ablation of ZnS studied by low-order harmonic generation. • Different spatiotemporal properties of harmonics from atoms and nanoparticles. • Results compared with calculations of optical frequency up-conversion in perturbative regime. - Abstract: Harmonic generation of a driving laser propagating across a laser ablation plasma serves for the diagnosis of multicomponent plumes. Here we study the contribution of atomic and nanoparticle precursors to the generation of coherent ultraviolet and vacuum ultraviolet light as low-order harmonics of the fundamental emission (1064 nm) of a Q-switched Nd:YAG laser in a nanosecond infrared ZnS laser ablation plasma. Odd harmonics from the 3rd up to the 9th order (118.2 nm) have been observed with distinct temporal and spatial characteristics which were determined by varying the delay between the ablation and driving nanosecond pulses and by spatially scanning the plasma with the focused driving beam propagating parallel to the target. At short distances from the target surface (≤1 mm), the harmonic intensity displays two temporal components peaked at around 250 ns and 10 μs. While the early component dies off quickly with increasing harmonic order and vanishes for the 9th order, the late component is notably intense for the 7th harmonic and is still clearly visible for the 9th. Spectral analysis of spontaneous plume emissions help to assign the origin of the two components. While the early plasma component is mainly constituted by neutral Zn atoms, the late component is mostly due to nanoparticles, which upon interaction with the driving laser are subject to breakup and ionization. With the aid of calculations of the phase matching integrals within the perturbative model of optical harmonic generation, these results illustrate how atom and nanoparticle populations, with differing temporal and spatial distributions within the ablation plasma, contribute to the nonlinear

  10. Waveforms for optimal sub-keV high-order harmonics with synthesized two- or three-colour laser fields.

    Jin, Cheng; Wang, Guoli; Wei, Hui; Le, Anh-Thu; Lin, C D

    2014-05-30

    High-order harmonics extending to the X-ray region generated in a gas medium by intense lasers offer the potential for providing tabletop broadband light sources but so far are limited by their low conversion efficiency. Here we show that harmonics can be enhanced by one to two orders of magnitude without an increase in the total laser power if the laser's waveform is optimized by synthesizing two- or three-colour fields. The harmonics thus generated are also favourably phase-matched so that radiation is efficiently built up in the gas medium. Our results, combined with the emerging intense high-repetition MHz lasers, promise to increase harmonic yields by several orders to make harmonics feasible in the near future as general bright tabletop light sources, including intense attosecond pulses.

  11. Pump-probe study of atoms and small molecules with laser driven high order harmonics

    Cao, Wei

    A commercially available modern laser can emit over 1015 photons within a time window of a few tens of femtoseconds (10-15second), which can be focused into a spot size of about 10 mum, resulting in a peak intensity above 1014W/cm2. This paves the way for table-top strong field physics studies such as above threshold ionization (ATI), non-sequential double ionization (NSDI), high order harmonic generation (HHG), etc.. Among these strong laser-matter interactions, high order harmonic generation, which combines many photons of the fundamental laser field into a single photon, offers a unique way to generate light sources in the vacuum ultraviolet (VUV) or extreme ultraviolet (EUV) region. High order harmonic photons are emitted within a short time window from a few tens of femtoseconds down to a few hundreds of attoseconds (10 -18second). This highly coherent nature of HHG allows it to be synchronized with an infrared (IR) laser pulse, and the pump-probe technique can be adopted to study ultrafast dynamic processes in a quantum system. The major work of this thesis is to develop a table-top VUV(EUV) light source based on HHG, and use it to study dynamic processes in atoms and small molecules with the VUV(EUV)-pump IR-probe method. A Cold Target Recoil Ion Momentum Spectroscopy (COLTRIMS) apparatus is used for momentum imaging of the interaction products. Two types of high harmonic pump pulses are generated and applied for pump-probe studies. The first one consists of several harmonics forming a short attosecond pulse train (APT) in the EUV regime (around 40 eV). We demonstrate that, (1) the auto-ionization process triggered by the EUV in cation carbon-monoxide and oxygen molecules can be modified by scanning the EUV-IR delay, (2) the phase information of quantum trajectories in bifurcated high harmonics can be extracted by performing an EUV-IR cross-correlation experiment, thus disclosing the macroscopic quantum control in HHG. The second type of high harmonic source

  12. Cumulative second-harmonic generation of Lamb waves propagating in a two-layered solid plate

    Xiang Yanxun; Deng Mingxi

    2008-01-01

    The physical process of cumulative second-harmonic generation of Lamb waves propagating in a two-layered solid plate is presented by using the second-order perturbation and the technique of nonlinear reflection of acoustic waves at an interface. In general, the cumulative second-harmonic generation of a dispersive guided wave propagation does not occur. However, the present paper shows that the second-harmonic of Lamb wave propagation arising from the nonlinear interaction of the partial bulk acoustic waves and the restriction of the three boundaries of the solid plates does have a cumulative growth effect if some conditions are satisfied. Through boundary condition and initial condition of excitation, the analytical expression of cumulative second-harmonic of Lamb waves propagation is determined. Numerical results show the cumulative effect of Lamb waves on second-harmonic field patterns. (classical areas of phenomenology)

  13. Second-harmonic generation in second-harmonic fiber Bragg gratings.

    Steel, M J; de Sterke, C M

    1996-06-20

    We consider the production of second-harmonic light in gratings resonant with the generated field, through a Green's function approach. We recover some standard results and obtain new limits for the uniform grating case. With the extension to nonuniform gratings, we find the Green's function for the second harmonic in a grating with an arbitrary phase shift at some point. We then obtain closed form approximate expressions for the generated light for phase shifts close to π/2 and at the center of the grating. Finally, comparing the uniform and phase-shifted gratings with homogeneous materials, we discuss the enhancement in generated light and the bandwidth over which it occurs, and the consequences for second-harmonic generation in optical fiber Bragg gratings.

  14. High Harmonic Radiation Generation and Attosecond pulse generation from Intense Laser-Solid Interactions

    Thomas, Alexander Roy [Univ. of Michigan, Ann Arbor, MI (United States); Krushelnick, Karl [Univ. of Michigan, Ann Arbor, MI (United States)

    2016-09-08

    We have studied ion motion effects in high harmonic generation, including shifts to the harmonics which result in degradation of the attosecond pulse train, and how to mitigate them. We have examined the scaling with intensity of harmonic emission. We have also switched the geometry of the interaction to measure, for the first time, harmonics from a normal incidence interaction. This was performed by using a special parabolic reflector with an on axis hole and is to allow measurements of the attosecond pulses using standard techniques. Here is a summary of the findings: First high harmonic generation in laser-solid interactions at 1021 Wcm-2, demonstration of harmonic focusing, study of ion motion effects in high harmonic generation in laser-solid interactions, and demonstration of harmonic amplification.

  15. On-the-Fly Control of High-Harmonic Generation Using a Structured Pump Beam

    Hareli, Liran; Lobachinsky, Lilya; Shoulga, Georgiy; Eliezer, Yaniv; Michaeli, Linor; Bahabad, Alon

    2018-05-01

    We demonstrate experimentally a relatively simple yet powerful all-optical enhancement and control technique for high harmonic generation. This is achieved by using as a pump beam two different spatial optical modes interfering together to realize tunable periodic quasi-phase matching of the interaction. With this technique, we demonstrate on-the-fly quasi-phase matching of harmonic orders 29-41 at ambient gas pressure levels of 50 and 100 Torr, where an up to 100-fold enhancement of the emission is observed. The technique is scalable to different harmonic orders and ambient pressure conditions.

  16. Enhancement of high-order harmonics in a plasma waveguide formed in clustered Ar gas.

    Geng, Xiaotao; Zhong, Shiyang; Chen, Guanglong; Ling, Weijun; He, Xinkui; Wei, Zhiyi; Kim, Dong Eon

    2018-02-05

    Generation of high-order harmonics (HHs) is intensified by using a plasma waveguide created by a laser in a clustered gas jet. The formation of a plasma waveguide and the guiding of a laser beam are also demonstrated. Compared to the case without a waveguide, harmonics were strengthened up to nine times, and blue-shifted. Numerical simulation by solving the time-dependent Schrödinger equation in strong field approximation agreed well with experimental results. This result reveals that the strengthening is the result of improved phase matching and that the blue shift is a result of change in fundamental laser frequency due to self-phase modulation (SPM).

  17. High-order harmonics from bow wave caustics driven by a high-intensity laser

    Pirozhkov, A.S.; Kando, M.; Esirkepov, T.Zh.

    2012-01-01

    We propose a new mechanism of high-order harmonic generation during an interaction of a high-intensity laser pulse with underdense plasma. A tightly focused laser pulse creates a cavity in plasma pushing electrons aside and exciting the wake wave and the bow wave. At the joint of the cavity wall and the bow wave boundary, an annular spike of electron density is formed. This spike surrounds the cavity and moves together with the laser pulse. Collective motion of electrons in the spike driven by the laser field generates high-order harmonics. A strong localization of the electron spike, its robustness to oscillations imposed by the laser field and, consequently, its ability to produce high-order harmonics is explained by catastrophe theory. The proposed mechanism explains the experimental observations of high-order harmonics with the 9 TW J-KAREN laser (JAEA, Japan) and the 120 TW Astra Gemini laser (CLF RAL, UK) [A. S. Pirozhkov, et al., arXiv:1004.4514 (2010); A. S. Pirozhkov et al, AIP Proceedings, this volume]. The theory is corroborated by high-resolution two-and three-dimensional particle-in-cell simulations.

  18. Harmonic generation effect in high-Tc films

    Khare, Neeraj; Shrivastava, S.K.; Padmanabhan, V.P.N.; Khare, Sangeeta; Gupta, A.K.

    1997-01-01

    Harmonic generation in thick BPSCCO and thin YBCO films are reported. The application of an ac field (H ac > H c1 ) of frequency f causes the generation of odd harmonics of frequency (2n+1)f. The application of dc field in addition to the ac field causes the appearance of even harmonics also in the BPSCCO film. However, the appearance of even harmonics is not observed in YBCO film with high J c ∼ 1.6x10 6 A/cm 2 and appearance of second harmonic with small magnitude is observed in YBCO film with low J c ∼ 2x10 3 A/cm 2 . The variation of amplitudes of these harmonics are studied as a function of magnitude of ac and dc field and the results are explained in the framework of critical state model. A high-T c film magnetometer based on the measurement of the amplitude of second harmonic has been developed whose field sensitivity is ∼ 1.5x10 -8 T. (author)

  19. Second-harmonic generation of practical Bessel beams

    Huang, Jin H.; Ding, Desheng; Hsu, Yin-Sung

    2009-11-01

    A fast Gaussian expansion approach is used to investigate fundamental and second-harmonic generation in practical Bessel beams of finite aperture. The analysis is based on the integral solutions of the KZK equation under the quasilinear approximation. The influence of the medium's attenuation on the beam profile is considered. Analysis results show that the absorption parameter has a significant effect on the far-field beam profile of the second harmonic. Under certain circumstances, the second harmonic of a practical Bessel beam still has the main properties of an ideal Bessel beam of infinite aperture when it propagates within its depth of field.

  20. Optical third-harmonic generation using ultrashort laser pulses

    Stoker, D.; Keto, J.W.; Becker, M.F.

    2005-01-01

    To better predict optical third-harmonic generation (THG) in transparent dielectrics, we model a typical ultrashort pulsed Gaussian beam, including both group velocity mismatch and phase mismatch of the fundamental and harmonic fields. We find that competition between the group velocity mismatch and phase mismatch leads to third-harmonic generation that is sensitive only to interfaces. In this case, the spatial resolution is determined by the group velocity walk-off length. THG of modern femtosecond lasers in optical solids is a bulk process, without a surface susceptibility, but bears the signature of a surface enhancement effect in z-scan measurements. We demonstrate the accuracy of the model, by showing the agreement between the predicted spectral intensity and the measured third-harmonic spectrum from a thin sapphire crystal

  1. Second harmonic generation in a molecular magnetic chain

    Cavigli, L.; Sessoli, R.; Gurioli, M.; Bogani, L.

    2006-05-01

    A setup for the determination of all the components of the second harmonic generation tensor in molecular materials is presented. It allows overcoming depletion problems, which one can expect to be common in molecular systems. A preliminary characterization of the nonlinear properties of the single chain magnet CoPhOMe is carried out. We observe a high second harmonic signal, comparable to that of urea, and show that the bulk contributions are dominant over the surface ones.

  2. Using self-generated harmonics as a diagnostic of high intensity laser-produced plasmas

    Krushelnick, K; Watts, I; Tatarakis, M; Gopal, A; Wagner, U; Beg, F N; Clark, E L; Clarke, R J; Dangor, A E; Norreys, P A; Wei, M S; Zepf, M

    2002-01-01

    The interaction of high intensity laser pulses (up to I∼10 20 W cm -2 ) with plasmas can generate very high order harmonics of the laser frequency (up to the 75th order have been observed). Measurements of the properties of these harmonics can provide important insights into the plasma conditions which exist during such interactions. For example, observations of the spectrum of the harmonic emission can provide information of the dynamics of the critical surface as well as information on relativistic non-linear optical effects in the plasma. However, most importantly, observations of the polarization properties of the harmonics can provide a method to measure the ultra-strong magnetic fields (greater than 350 MG) which can be generated during these interactions. It is likely that such techniques can be scaled to provide a significant amount of information from experiments at even higher intensities

  3. Wiggler magnetic field assisted third harmonic generation in expanding clusters

    Vij, Shivani

    2018-04-01

    A simple theoretical model is constructed to study the wiggler magnetic field assisted third harmonic generation of intense short pulse laser in a cluster in its expanding phase. The ponderomotive force of laser causes density perturbations in cluster electron density which couples with wiggler magnetic field to produce a nonlinear current that generates transverse third harmonic. An intense short pulse laser propagating through a gas embedded with atomic clusters, converts it into hot plasma balls via tunnel ionization. Initially, the electron plasma frequency inside the clusters ω pe > \\sqrt{3}{ω }1 (with ω 1 being the frequency of the laser). As the cluster expands under Coulomb force and hydrodynamic pressure, ω pe decreases to \\sqrt{3}{ω }1. At this time, there is resonant enhancement in the efficiency of the third harmonic generation. The efficiency of third harmonic generation is enhanced due to cluster plasmon resonance and by phase matching due to wiggler magnetic field. The effect of cluster size on the expansion rate is studied to observe that the clusters of different radii would expand differently. The impact of laser intensity and wiggler magnetic field on the efficiency of third harmonic generation is also explored.

  4. High harmonic generation in H and HD by intense femtosecond ...

    2013-04-24

    Apr 24, 2013 ... We have argued that for these conditions the harmonic generation due to the transitions in the electronic ... (XUV) or soft X-ray range and generation of very high-energy attosecond (as) pulses have been widely ..... [3] Y Liang, S Augst, S L Chin, Y Beaudoin and M Chaker, J. Phys. B 27, 5119 (1994).

  5. High level harmonic radiation: atto-second impulse generation, application to coherent radiation

    Kovacev, Milutin

    2003-01-01

    The work presented in this thesis is dedicated to the characterization and optimization of the unique properties of high order harmonic generation in a rare gas: high brilliance, short pulse duration (femtosecond to atto-second, 1 as = 10"-"1"8 s and good mutual coherence. In the first part of this work, we concentrate on the exploitation of a scaling law using a high-energy laser loosely focused inside an extended gaseous medium. For the first time, the generated harmonic energy exceeds the 1 μJ level per laser pulse using the fifteenth harmonic order at a wavelength of 53 nm. The conversion efficiency reaches 4.10"-"5, which results from the combination of a strong dipolar response and a good phase matching within a generating volume that is extended by self guiding of the generating laser pulse. In the second part, our interest is devoted to the temporal profile of the harmonic emission and its atto-second structure. We first demonstrate the feasibility of a spatial/spectral selection of the contributions associated to the two main electronic trajectories, allowing thereby the generation of regular atto-second pulse trains. We then characterize such a pulse train by the measurement of the relative phases of consecutive harmonics. Finally, we describe an original technique for the temporal confinement of the harmonic emission by manipulating the ellipticity of the generating laser beam. In the third part, our interest is dedicated to the mutual coherence properties of the harmonic emission. We first demonstrate the precise control of the relative phase of the harmonic pulses by multiple beam interference in the XUV. This frequency-domain interferometry using four phase-locked temporally separated pulses shows an extreme sensitivity to the relative phase of the pulses on an atto-second time scale. We then measure the first order autocorrelation trace of the harmonic beam thanks to the generation of two harmonic sources mutually coherent and spatially separated

  6. Efficient second harmonic generation by para-nitroaniline embedded in electro-spun polymeric nanofibres

    Gonçalves, Hugo; Saavedra, Inês; Ferreira, Rute AS; Lopes, PE; de Matos Gomes, Etelvina; Belsley, Michael

    2018-03-01

    Intense well polarized second harmonic light was generated by poly(methyl methacrylate) nanofibres with embedded para-nitroaniline nanocrystals. Subwavelength diameter fibres were electro-spun using a 1:2 weight ratio of chromophore to polymer. Analysis of the generated second harmonic light indicates that the para-nitroaniline molecules, which nominally crystalize in the centrosymmetric space group, were organized into noncentrosymmetric structures leading to a second order susceptibility dominated by a single tensor element. Under the best deposition conditions, the nanofibrers display an effective nonlinear optical susceptibility approximately two orders of magnitude greater than that of potassium dihydrogen phosphate. Generalizing this approach to a broad range of organic molecules with strong individual molecular second order nonlinear responses, but which nominally form centrosymmetric organic crystals, could open a new pathway for the fabrication of efficient sub-micron sized second harmonic light generators.

  7. Seeding High Gain Harmonic Generation with Laser Harmonics produced in Gases

    Lambert, Guillaume; Couprie, Marie Emmanuelle; Garzella, David; Doria, Andrea; Giannessi, Luca; Hara, Toru; Kitamura, Hideo; Shintake, Tsumoru

    2004-01-01

    Free electron Lasers employing High Gain Harmonic generation (HGHG) schemes are very promising coherent ligth sources for the soft X-ray regime. They offer both transverse and longitudinal coherence, while Self Amplified Spontaneous Emission schemes have a longitudinal coherence limited. We propose here to seed HGHG with high harmonics produced by a Ti:Sa femtosecond laser focused on a gas jet, tuneable in the 100-10 nm spectral region. Specifities concerning the implementation of this particular laser source as a seed for HGHG are investigated. Semi analytical , numerical 1D and 3D calculations are given, for the cases of the SCSS, SPARC and ARC-EN-CIEL projects.

  8. Orientation dependence of temporal and spectral properties of high-order harmonics in solids

    Wu, Mengxi; You, Yongsing; Ghimire, Shambhu; Reis, David A.; Browne, Dana A.; Schafer, Kenneth J.; Gaarde, Mette B.

    2017-12-01

    We investigate the connection between crystal symmetry and temporal and spectral properties of high-order harmonics in solids. We calculate the orientation-dependent harmonic spectrum driven by an intense, linearly polarized infrared laser field, using a momentum-space description of the generation process in terms of strong-field-driven electron dynamics on the band structure. We show that the orientation dependence of both the spectral yield and the subcycle time profile of the harmonic radiation can be understood in terms of the coupling strengths and relative curvatures of the valence band and the low-lying conduction bands. In particular, we show that in some systems this gives rise to a rapid shift of a quarter optical cycle in the timing of harmonics in the secondary plateau as the crystal is rotated relative to the laser polarization. We address recent experimental results in MgO [Y. S. You et al., Nat. Phys. 13, 345 (2017)., 10.1038/nphys3955] and show that the observed change in orientation dependence for the highest harmonics can be interpreted in the momentum space picture in terms of the contributions of several different conduction bands.

  9. Studies of harmonic generation in free electron lasers

    Goldammer, K.

    2007-01-01

    Nonlinear harmonic generation is one of the most interesting aspects of Free Electron Lasers under study today. It provides for coherent, high intensity radiation at higher harmonics of the FEL resonant frequency. The sources, numerical simulation and applications of harmonic radiation in cascaded High Gain Harmonic Generation FELs were the subject of this thesis. Harmonic emission in FELs originates from harmonic microbunching of the particles and the particular electron trajectory during FEL interaction. Numerical FEL simulation codes model these analytical equations and predict the performance of Free Electron Lasers with good accuracy. This thesis has relied heavily upon the FEL simulation code Genesis 1.3 which has been upgraded in the framework of this thesis to compute harmonic generation in a self-consistent manner. Tests against analytical predictions suggest that the harmonic power levels as well as harmonic gain lengths are simulated correctly. A benchmark with the FEL simulation code GINGER yields excellent agreement of the harmonic saturation length and saturation power. The new version of the simulation code Genesis was also tested against measurements from the VUV-FEL FLASH at DESY. The spectral power distributions of fundamental and third harmonic radiation were recorded at 25.9 nm and 8.6 nm, respectively. The relative bandwidths (FWHM) were in the range of 2 % for both the fundamental as well as the third harmonic, which was accurately reproduced by time-dependent simulations with Genesis. The new code was also used to propose and evaluate a new design for the BESSY Soft X-Ray FEL, a cascaded High Gain Harmonic Generation FEL proposed by BESSY in Berlin. The original design for the BESSY High Energy FEL line requires four HGHG stages to convert the initial seed laser wavelength of 297.5 nm down to 1.24 nm. A new scheme is proposed that makes use of fifth harmonic radiation from the first stage and reduces the number of HGHG stages to three. It

  10. Studies of harmonic generation in free electron lasers

    Goldammer, K.

    2007-11-12

    Nonlinear harmonic generation is one of the most interesting aspects of Free Electron Lasers under study today. It provides for coherent, high intensity radiation at higher harmonics of the FEL resonant frequency. The sources, numerical simulation and applications of harmonic radiation in cascaded High Gain Harmonic Generation FELs were the subject of this thesis. Harmonic emission in FELs originates from harmonic microbunching of the particles and the particular electron trajectory during FEL interaction. Numerical FEL simulation codes model these analytical equations and predict the performance of Free Electron Lasers with good accuracy. This thesis has relied heavily upon the FEL simulation code Genesis 1.3 which has been upgraded in the framework of this thesis to compute harmonic generation in a self-consistent manner. Tests against analytical predictions suggest that the harmonic power levels as well as harmonic gain lengths are simulated correctly. A benchmark with the FEL simulation code GINGER yields excellent agreement of the harmonic saturation length and saturation power. The new version of the simulation code Genesis was also tested against measurements from the VUV-FEL FLASH at DESY. The spectral power distributions of fundamental and third harmonic radiation were recorded at 25.9 nm and 8.6 nm, respectively. The relative bandwidths (FWHM) were in the range of 2 % for both the fundamental as well as the third harmonic, which was accurately reproduced by time-dependent simulations with Genesis. The new code was also used to propose and evaluate a new design for the BESSY Soft X-Ray FEL, a cascaded High Gain Harmonic Generation FEL proposed by BESSY in Berlin. The original design for the BESSY High Energy FEL line requires four HGHG stages to convert the initial seed laser wavelength of 297.5 nm down to 1.24 nm. A new scheme is proposed that makes use of fifth harmonic radiation from the first stage and reduces the number of HGHG stages to three. It

  11. Modulated phase matching and high-order harmonic enhancement mediated by the carrier-envelope phase

    Faccio, Daniele; Serrat, Carles; Cela, Jose M.; Farres, Albert; Di Trapani, Paolo; Biegert, Jens

    2010-01-01

    The process of high-order harmonic generation in gases is numerically investigated in the presence of a few-cycle pulsed-Bessel-beam pump, featuring a periodic modulation in the peak intensity due to large carrier-envelope-phase mismatch. A two-decade enhancement in the conversion efficiency is observed and interpreted as the consequence of a mechanism known as a nonlinearly induced modulation in the phase mismatch.

  12. Venus spherical harmonic gravity model to degree and order 60

    Konopliv, Alex S.; Sjogren, William L.

    1994-01-01

    The Magellan and Pioneer Venus Orbiter radiometric tracking data sets have been combined to produce a 60th degree and order spherical harmonic gravity field. The Magellan data include the high-precision X-band gravity tracking from September 1992 to May 1993 and post-aerobraking data up to January 5, 1994. Gravity models are presented from the application of Kaula's power rule for Venus and an alternative a priori method using surface accelerations. Results are given as vertical gravity acceleration at the reference surface, geoid, vertical Bouguer, and vertical isostatic maps with errors for the vertical gravity and geoid maps included. Correlation of the gravity with topography for the different models is also discussed.

  13. Optical Chirality in Nonlinear Optics: Application to High Harmonic Generation.

    Neufeld, Ofer; Cohen, Oren

    2018-03-30

    Optical chirality (OC)-one of the fundamental quantities of electromagnetic fields-corresponds to the instantaneous chirality of light. It has been utilized for exploring chiral light-matter interactions in linear optics, but has not yet been applied to nonlinear processes. Motivated to explore the role of OC in the generation of helically polarized high-order harmonics and attosecond pulses, we first separate the OC of transversal and paraxial beams to polarization and orbital terms. We find that the polarization-associated OC of attosecond pulses corresponds approximately to that of the pump in the quasimonochromatic case, but not in the multichromatic pump cases. We associate this discrepancy with the fact that the polarization OC of multichromatic pumps vary rapidly in time along the optical cycle. Thus, we propose new quantities, noninstantaneous polarization-associated OC, and time-scale-weighted polarization-associated OC, and show that these quantities link the chirality of multichromatic pumps and their generated attosecond pulses. The presented extension to OC theory should be useful for exploring various nonlinear chiral light-matter interactions. For example, it stimulates us to propose a tricircular pump for generation of highly elliptical attosecond pulses with a tunable ellipticity.

  14. Optical Chirality in Nonlinear Optics: Application to High Harmonic Generation

    Neufeld, Ofer; Cohen, Oren

    2018-03-01

    Optical chirality (OC)—one of the fundamental quantities of electromagnetic fields—corresponds to the instantaneous chirality of light. It has been utilized for exploring chiral light-matter interactions in linear optics, but has not yet been applied to nonlinear processes. Motivated to explore the role of OC in the generation of helically polarized high-order harmonics and attosecond pulses, we first separate the OC of transversal and paraxial beams to polarization and orbital terms. We find that the polarization-associated OC of attosecond pulses corresponds approximately to that of the pump in the quasimonochromatic case, but not in the multichromatic pump cases. We associate this discrepancy with the fact that the polarization OC of multichromatic pumps vary rapidly in time along the optical cycle. Thus, we propose new quantities, noninstantaneous polarization-associated OC, and time-scale-weighted polarization-associated OC, and show that these quantities link the chirality of multichromatic pumps and their generated attosecond pulses. The presented extension to OC theory should be useful for exploring various nonlinear chiral light-matter interactions. For example, it stimulates us to propose a tricircular pump for generation of highly elliptical attosecond pulses with a tunable ellipticity.

  15. Third-harmonic generation by a Gaussian electromagnetic beam in a magnetoplasma

    Sodha, M.S.; Umesh, G.

    1978-01-01

    This paper presents an investigation of nonlinear third-harmonic generation in a weakly collisional magnetoplasma due to simultaneous propagation of both the right and left circularly polarized modes, having a Gaussian intensity distribution; self-focusing has been taken into account. At moderate powers, the self-focusing is seen to enhance the harmonic output by two orders of magnitude; at high powers, propagation occurs in an almost uniform waveguide devoid of plasma, and the harmonic output is, consequently, decreased. In the vicinity (ω/sub c//ω=0.7) of the electron cyclotron resonance, the harmonic output of the extraordinary mode is enhanced by an order of magnitude; the present theory is not applicable at resonance

  16. High-order harmonics measured by the photon statistics of the infrared driving-field exiting the atomic medium.

    Tsatrafyllis, N; Kominis, I K; Gonoskov, I A; Tzallas, P

    2017-04-27

    High-order harmonics in the extreme-ultraviolet spectral range, resulting from the strong-field laser-atom interaction, have been used in a broad range of fascinating applications in all states of matter. In the majority of these studies the harmonic generation process is described using semi-classical theories which treat the electromagnetic field of the driving laser pulse classically without taking into account its quantum nature. In addition, for the measurement of the generated harmonics, all the experiments require diagnostics in the extreme-ultraviolet spectral region. Here by treating the driving laser field quantum mechanically we reveal the quantum-optical nature of the high-order harmonic generation process by measuring the photon number distribution of the infrared light exiting the harmonic generation medium. It is found that the high-order harmonics are imprinted in the photon number distribution of the infrared light and can be recorded without the need of a spectrometer in the extreme-ultraviolet.

  17. Second harmonic generation from corona-poled polymer thin films ...

    2014-02-09

    Feb 9, 2014 ... We characterize thermal stability of second harmonic generation (SHG) properties of four different Y-type polymers poled using corona poling method. These polymers are based on donor–acceptor–donor-type repeating unit with different aromatic moieties acting as donors and dicyanomethylene acting as ...

  18. Second harmonic generation from photonic structured GaN nanowalls

    Soya, Takahiro; Inose, Yuta; Kunugita, Hideyuki; Ema, Kazuhiro; Yamano, Kouji; Kikuchi, Akihiko; Kishino, Katsumi, E-mail: t-soya@sophia.ac.j [Department of Engineering and Applied Sciences, Sophia University 7-1, Kioi-cho, Chiyoda-ku, Tokyo 102-8554 (Japan)

    2009-11-15

    We observed large enhancement of reflected second harmonic generation (SHG) using the one-dimensional photonic effect in regularly arranged InGaN/GaN single-quantum-well nanowalls. Using the effect when both fundamental and SH resonate with the photonic mode, we obtained enhancement of about 40 times compared with conditions far from resonance.

  19. Generation of high harmonics and attosecond pulses with ultrashort ...

    2014-07-11

    Jul 11, 2014 ... Two aspects of ultrashort pulse filaments are specifically discussed: (i) numerical simulation results on pulse self-compression by filamentation in a gas cell filled with noble gas. Measurements of high harmonics generated by the pulse extracted from the filament allows for the detection of intensity spikes ...

  20. Theory of second-harmonic generation in silica nanowires

    Lægsgaard, Jesper

    2010-01-01

    , while generating the second harmonic in one of the modes of the LP11 multiplet. This is shown to work in both circular and microstructured nanowires, although only one of the LP11 modes can be phase-matched in the microstructure. The prospect of obtaining large conversion efficiencies in silica...

  1. Theory of surface second-harmonic generation in silica nanowires

    Lægsgaard, Jesper

    2010-01-01

    , while generating the second harmonic in one of the modes of the LP11 multiplet. This is shown to work in both circular and microstructured nanowires, although only one of the LP11 modes can be phase-matched in the microstructure. The prospect of obtaining large conversion efficiencies in silica...

  2. Imaging theory of nonlinear second harmonic and third harmonic generations in confocal microscopy

    TANG Zhilie; XING Da; LIU Songhao

    2004-01-01

    The imaging theory of nonlinear second harmonic generation (SHG) and third harmonic generation (THG) in confocal microscopy is presented in this paper. The nonlinear effect of SHG and THG on the imaging properties of confocal microscopy has been analyzed in detail by the imaging theory. It is proved that the imaging process of SHG and THG in confocal microscopy, which is different from conventional coherent imaging or incoherent imaging, can be divided into two different processes of coherent imaging. The three-dimensional point spread functions (3D-PSF) of SHG and THG confocal microscopy are derived based on the nonlinear principles of SHG and THG. The imaging properties of SHG and THG confocal microscopy are discussed in detail according to its 3D-PSF. It is shown that the resolution of SHG and THG confocal microscopy is higher than that of single-and two-photon confocal microscopy.

  3. Near-field second-harmonic generation from gold nanoellipsoids

    Celebrano, M; Zavelani-Rossi, M; Polli, D; Cerullo, G [Istituto di Fotonica e Nanotecnologie, CNR, Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo Da Vinci 32, 20133 Milano (Italy); Biagioni, P; Finazzi, M; Duo, L [LNESS - Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo Da Vinci 32, 20133 Milano (Italy); Labardi, M; Allegrini, M [CNR-INFM, polyLab, Dipartimento di Fisica ' Enrico Fermi' , Universita di Pisa, Largo Pontecorvo 3, 56127 Pisa (Italy); Grand, J; Adam, P M; Royer, P [Laboratoire de Nanotechnologie et d' Instrumentation Optique, Universite de Technologie de Troyes, 12 rue Marie Curie, BP 2060 10010 Troyes cedex (France)

    2008-07-01

    Second-harmonic generation from single gold nanofabricated particles is experimentally investigated by a nonlinear scanning near-field optical microscope (SNOM). High peak power femtosecond polarized light pulses at the output of a hollow pyramid aperture allow for efficient second-harmonic imaging, with sub-100-nm spatial resolution and high contrast. The near-field nonlinear response is found to be directly related to both local surface plasmon resonances and particle morphology. The combined analysis of linear and second-harmonic SNOM images allows one to discriminate among near-field scattering, absorption and re-emission processes, which would not be possible with linear techniques alone. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  4. Ellipticity and the offset angle of high harmonics generated by homonuclear diatomic molecules

    Odzak, S; Milosevic, D B

    2011-01-01

    In our recent paper (2010 Phys. Rev. A 82 023412) we introduced a theory of high-order harmonic generation by diatomic molecules exposed to an elliptically polarized laser field and have shown that the nth harmonic emission rate has contributions of the components of the T-matrix element in the direction of the laser-field polarization and in the direction perpendicular to it. Using both components of the T-matrix element we now develop a theoretical approach for calculating ellipticity and the offset angle of high harmonics. We show that the emitted harmonics generated by aligned molecules are elliptically polarized even if the applied field is linearly polarized. Using examples of N 2 , O 2 and Ar 2 molecules we show the existence of extrema and sudden changes of the harmonic ellipticity and the offset angle for particular molecular alignment and explain them by the destructive two-centre interference. Taking into account that the aligned molecules are an anisotropic medium for high harmonic generation, we introduce elliptic dichroism as a measure of this anisotropy, for both components of the T-matrix element. We propose that the measurement of the elliptic dichroism may reveal further information about the molecular structure.

  5. Transmit beamforming for optimal second-harmonic generation.

    Hoilund-Kaupang, Halvard; Masoy, Svein-Erik

    2011-08-01

    A simulation study of transmit ultrasound beams from several transducer configurations is conducted to compare second-harmonic imaging at 3.5 MHz and 11 MHz. Second- harmonic generation and the ability to suppress near field echoes are compared. Each transducer configuration is defined by a chosen f-number and focal depth, and the transmit pressure is estimated to not exceed a mechanical index of 1.2. The medium resembles homogeneous muscle tissue with nonlinear elasticity and power-law attenuation. To improve computational efficiency, the KZK equation is utilized, and all transducers are circular-symmetric. Previous literature shows that second-harmonic generation is proportional to the square of the transmit pressure, and that transducer configurations with different transmit frequencies, but equal aperture and focal depth in terms of wavelengths, generate identical second-harmonic fields in terms of shape. Results verify this for a medium with attenuation f1. For attenuation f1.1, deviations are found, and the high frequency subsequently performs worse than the low frequency. The results suggest that high frequencies are less able to suppress near-field echoes in the presence of a heterogeneous body wall than low frequencies.

  6. High-Harmonic Generation in Solids with and without Topological Edge States

    Bauer, Dieter; Hansen, Kenneth K.

    2018-04-01

    High-harmonic generation in the two topological phases of a finite, one-dimensional, periodic structure is investigated using a self-consistent time-dependent density functional theory approach. For harmonic photon energies smaller than the band gap, the harmonic yield is found to differ by up to 14 orders of magnitude for the two topological phases. This giant topological effect is explained by the degree of destructive interference in the harmonic emission of all valence-band (and edge-state) electrons, which strongly depends on whether or not topological edge states are present. The combination of strong-field laser physics with topological condensed matter opens up new possibilities to electronically control strong-field-based light or particle sources or—conversely—to steer by all optical means topological electronics.

  7. Polymer poling characterization using second harmonic generation (SHG)

    Tellier, Gildas; Averty, Dominique; Blart, Errol; Boisrobert, Christian; Gundel, Hartmut; Le Tacon, Sylvain; Monnereau, Cyrille; Odobel, Fabrice; Seveno, Raynald

    2006-04-01

    Several polymer molecules have structures which are suitable for the non-linear optic applications. We report on the design and fabrication of a high performance electro-optic modulator made of polymer thin films. The polymer we study contains a chromophore based on Disperse Red One covalently grafted to a host-matrix. The polymer materials are deposited in thin layers on a glass substrate by chemical solution deposition, either by spin-coating or by dip-coating. The thickness of the films is ranging from a hundred nanometers to several micrometers. Initially, the polymer molecules are randomly oriented and the films are isotropic, hence no electro-optic effect can be observed. In order to break the symmetry and align the chromophores, the films are submitted to the so-called corona poling process. As a result, their structure become non-centrosymmetric and the second-order susceptibility is no longer zero. The corona poling method consists of applying a high electric field to the polymer by means of a needle electrode, placed above the polymer film which is posed on a grounded sample support electrode. Thermal regulation of the support electrode allows to control the temperature during the poling of the films. Once the poling process has been established, a chemical cross-linking function is thermally activated in order to fix the orientation of the chromophores in the polymer matrix. The orientation and its stability in time is evaluated with a Second Harmonic Generation measurement set-up using the Makers Fringes configuration. We studied the influence of the poling temperature, the distance between the corona needle electrode and the sample, the high voltage applied, and the duration of the poling process on the efficiency of chromophore orientation in order to optimize the poling procedure. Finally, aging of poled polymer samples has been investigated at elevated temperatures, confirming the stability of the cross-linking process.

  8. Higher-order harmonics coupling in different free-electron laser codes

    Giannessi, L.; Freund, H. P.; Musumeci, P.; Reiche, S.

    2008-08-01

    The capability for simulation of the dynamics of a free-electron laser including the higher-order harmonics in linear undulators exists in several existing codes as MEDUSA [H.P. Freund, S.G. Biedron, and S.V. Milton, IEEE J. Quantum Electron. 27 (2000) 243; H.P. Freund, Phys. Rev. ST-AB 8 (2005) 110701] and PERSEO [L. Giannessi, Overview of Perseo, a system for simulating FEL dynamics in Mathcad, , in: Proceedings of FEL 2006 Conference, BESSY, Berlin, Germany, 2006, p. 91], and has been recently implemented in GENESIS 1.3 [See ]. MEDUSA and GENESIS also include the dynamics of even harmonics induced by the coupling through the betatron motion. In addition MEDUSA, which is based on a non-wiggler averaged model, is capable of simulating the generation of even harmonics in the transversally cold beam regime, i.e. when the even harmonic coupling arises from non-linear effects associated with longitudinal particle dynamics and not to a finite beam emittance. In this paper a comparison between the predictions of the codes in different conditions is given.

  9. Evidence of the 2s2p(1P) doubly excited state in the harmonic generation spectrum of helium

    Ngoko Djiokap, J. M.; Starace, Anthony F.

    2011-01-01

    By solving the two-active-electron time-dependent Schroedinger equation in an intense, ultrashort laser field, we investigate evidence of electron correlations in the high-order harmonic generation spectrum of helium. As the frequency of the driving laser pulse varies from 4.6 to 6.6 eV, the 13th, 11th, and 9th harmonics sequentially become resonant with the transition between the ground state and the isolated 2s2p( 1 P) autoionizing state of helium, which dramatically enhances these harmonics and changes their profiles. When each of the 9th and 13th harmonics are in resonance with this autoionizing state, there is also a low-order multiphoton resonance with a Rydberg state, resulting in a particularly large enhancement of these harmonics relative to neighboring harmonics. When the 11th harmonic is in resonance with the 2s2p( 1 P) autoionizing state, the 13th harmonic is simultaneously in resonance with numerous higher-energy autoionizing states, resulting in a competition between these two harmonics for intensity. These results demonstrate that even electron correlations occurring over a narrow energy interval can have a significant effect on strong-field processes such as harmonic generation.

  10. Generation of Bright Phase-matched Circularly-polarized Extreme Ultraviolet High Harmonics

    2014-12-08

    1995). 42. Eichmann , H. et al. Polarization-dependent high-order two-color mixing. Phys. Rev. A 51, R3414–R3417 (1995). 43. Fleischer, A., Kfir, O...calculations of polarization-dependent two- color high-harmonic generation. Phys. Rev. A 52, 2262–2278 (1995). 10. Eichmann , H. et al. polarization

  11. Theory of third-harmonic generation using Bessel beams, and self-phase-matching

    Tewari, S.P.; Huang, H.; Boyd, R.W.

    1996-01-01

    Taking Bessel beams (J 0 beam) as a representation of a conical beam, and a slowly varying envelope approximation (SVEA) we obtain the results for the theory of third-harmonic generation from an atomic medium. We demonstrate how the phenomenon of self-phase-matching is contained in the transverse-phase-matching integral of the theory. A method to calculate the transverse-phase-matching integral containing four Bessel functions is described which avoids the computer calculations of the Bessel functions. In order to consolidate the SVEA result an alternate method is used to obtain the exact result for the third-harmonic generation. The conditions are identified in which the exact result goes over to the result of the SVEA. The theory for multiple Bessel beams is also discussed which has been shown to be the source of the wide width of the efficiency curve of the third-harmonic generation observed in experiments. copyright 1996 The American Physical Society

  12. Single-order laser high harmonics in XUV for ultrafast photoelectron spectroscopy of molecular wavepacket dynamics

    Mizuho Fushitani

    2016-11-01

    Full Text Available We present applications of extreme ultraviolet (XUV single-order laser harmonics to gas-phase ultrafast photoelectron spectroscopy. Ultrashort XUV pulses at 80 nm are obtained as the 5th order harmonics of the fundamental laser at 400 nm by using Xe or Kr as the nonlinear medium and separated from other harmonic orders by using an indium foil. The single-order laser harmonics is applied for real-time probing of vibrational wavepacket dynamics of I2 molecules in the bound and dissociating low-lying electronic states and electronic-vibrational wavepacket dynamics of highly excited Rydberg N2 molecules.

  13. Single-order laser high harmonics in XUV for ultrafast photoelectron spectroscopy of molecular wavepacket dynamics.

    Fushitani, Mizuho; Hishikawa, Akiyoshi

    2016-11-01

    We present applications of extreme ultraviolet (XUV) single-order laser harmonics to gas-phase ultrafast photoelectron spectroscopy. Ultrashort XUV pulses at 80 nm are obtained as the 5th order harmonics of the fundamental laser at 400 nm by using Xe or Kr as the nonlinear medium and separated from other harmonic orders by using an indium foil. The single-order laser harmonics is applied for real-time probing of vibrational wavepacket dynamics of I 2 molecules in the bound and dissociating low-lying electronic states and electronic-vibrational wavepacket dynamics of highly excited Rydberg N 2 molecules.

  14. Second harmonic generation reveals matrix alterations during breast tumor progression

    Burke, Kathleen; Tang, Ping; Brown, Edward

    2013-03-01

    Alteration of the extracellular matrix in tumor stroma influences efficiency of cell locomotion away from the primary tumor into surrounding tissues and vasculature, thereby affecting metastatic potential. We study matrix changes in breast cancer through the use of second harmonic generation (SHG) of collagen in order to improve the current understanding of breast tumor stromal development. Specifically, we utilize a quantitative analysis of the ratio of forward to backward propagating SHG signal (F/B ratio) to monitor collagen throughout ductal and lobular carcinoma development. After detection of a significant decrease in the F/B ratio of invasive but not in situ ductal carcinoma compared with healthy tissue, the collagen F/B ratio is investigated to determine the evolution of fibrillar collagen changes throughout tumor progression. Results are compared with the progression of lobular carcinoma, whose F/B signature also underwent significant evolution during progression, albeit in a different manner, which offers insight into varying methods of tissue penetration and collagen manipulation between the carcinomas. This research provides insights into trends of stromal reorganization throughout breast tumor development.

  15. Chirp analysis of high-order harmonics from atoms driven by intense femtosecond laser pulses

    Kim, Hyung Taek; Kim, I Jong; Hong, Kyung-Han; Lee, Dong Gun; Kim, Jung-Hoon; Nam, Chang Hee

    2004-01-01

    The spectral structure of harmonics was experimentally controlled by changing the chirp of femtosecond laser pulses, and the dependence of harmonic chirp on atomic species was analysed using harmonics from neon and helium. Experimental results and theoretical analysis based on the Wigner distribution function showed that the spectral structure varied sensitively to laser chirp and the harmonic chirp was determined by the competition between dynamically induced negative chirp and self-phase modulation induced positive chirp. The generation of sharp and bright harmonics was achieved with appropriately chirped laser pulses under given experimental conditions, especially negatively chirped pulses in the case of laser intensity above the saturation intensity for optical-field ionization

  16. Second-harmonic generation in shear wave beams with different polarizations

    Spratt, Kyle S.; Ilinskii, Yurii A.; Zabolotskaya, Evgenia A.; Hamilton, Mark F.

    2015-10-01

    A coupled pair of nonlinear parabolic equations was derived by Zabolotskaya [1] that model the transverse components of the particle motion in a collimated shear wave beam propagating in an isotropic elastic solid. Like the KZK equation, the parabolic equation for shear wave beams accounts consistently for the leading order effects of diffraction, viscosity and nonlinearity. The nonlinearity includes a cubic nonlinear term that is equivalent to that present in plane shear waves, as well as a quadratic nonlinear term that is unique to diffracting beams. The work by Wochner et al. [2] considered shear wave beams with translational polarizations (linear, circular and elliptical), wherein second-order nonlinear effects vanish and the leading order nonlinear effect is third-harmonic generation by the cubic nonlinearity. The purpose of the current work is to investigate the quadratic nonlinear term present in the parabolic equation for shear wave beams by considering second-harmonic generation in Gaussian beams as a second-order nonlinear effect using standard perturbation theory. In order for second-order nonlinear effects to be present, a broader class of source polarizations must be considered that includes not only the familiar translational polarizations, but also polarizations accounting for stretching, shearing and rotation of the source plane. It is found that the polarization of the second harmonic generated by the quadratic nonlinearity is not necessarily the same as the polarization of the source-frequency beam, and we are able to derive a general analytic solution for second-harmonic generation from a Gaussian source condition that gives explicitly the relationship between the polarization of the source-frequency beam and the polarization of the second harmonic.

  17. Second-harmonic generation in shear wave beams with different polarizations

    Spratt, Kyle S., E-mail: sprattkyle@gmail.com; Ilinskii, Yurii A.; Zabolotskaya, Evgenia A.; Hamilton, Mark F. [Applied Research Laboratories, The University of Texas at Austin, P. O. Box 8029, Austin, Texas 78713–8029, US (United States)

    2015-10-28

    A coupled pair of nonlinear parabolic equations was derived by Zabolotskaya [1] that model the transverse components of the particle motion in a collimated shear wave beam propagating in an isotropic elastic solid. Like the KZK equation, the parabolic equation for shear wave beams accounts consistently for the leading order effects of diffraction, viscosity and nonlinearity. The nonlinearity includes a cubic nonlinear term that is equivalent to that present in plane shear waves, as well as a quadratic nonlinear term that is unique to diffracting beams. The work by Wochner et al. [2] considered shear wave beams with translational polarizations (linear, circular and elliptical), wherein second-order nonlinear effects vanish and the leading order nonlinear effect is third-harmonic generation by the cubic nonlinearity. The purpose of the current work is to investigate the quadratic nonlinear term present in the parabolic equation for shear wave beams by considering second-harmonic generation in Gaussian beams as a second-order nonlinear effect using standard perturbation theory. In order for second-order nonlinear effects to be present, a broader class of source polarizations must be considered that includes not only the familiar translational polarizations, but also polarizations accounting for stretching, shearing and rotation of the source plane. It is found that the polarization of the second harmonic generated by the quadratic nonlinearity is not necessarily the same as the polarization of the source-frequency beam, and we are able to derive a general analytic solution for second-harmonic generation from a Gaussian source condition that gives explicitly the relationship between the polarization of the source-frequency beam and the polarization of the second harmonic.

  18. Second-harmonic generation in shear wave beams with different polarizations

    Spratt, Kyle S.; Ilinskii, Yurii A.; Zabolotskaya, Evgenia A.; Hamilton, Mark F.

    2015-01-01

    A coupled pair of nonlinear parabolic equations was derived by Zabolotskaya [1] that model the transverse components of the particle motion in a collimated shear wave beam propagating in an isotropic elastic solid. Like the KZK equation, the parabolic equation for shear wave beams accounts consistently for the leading order effects of diffraction, viscosity and nonlinearity. The nonlinearity includes a cubic nonlinear term that is equivalent to that present in plane shear waves, as well as a quadratic nonlinear term that is unique to diffracting beams. The work by Wochner et al. [2] considered shear wave beams with translational polarizations (linear, circular and elliptical), wherein second-order nonlinear effects vanish and the leading order nonlinear effect is third-harmonic generation by the cubic nonlinearity. The purpose of the current work is to investigate the quadratic nonlinear term present in the parabolic equation for shear wave beams by considering second-harmonic generation in Gaussian beams as a second-order nonlinear effect using standard perturbation theory. In order for second-order nonlinear effects to be present, a broader class of source polarizations must be considered that includes not only the familiar translational polarizations, but also polarizations accounting for stretching, shearing and rotation of the source plane. It is found that the polarization of the second harmonic generated by the quadratic nonlinearity is not necessarily the same as the polarization of the source-frequency beam, and we are able to derive a general analytic solution for second-harmonic generation from a Gaussian source condition that gives explicitly the relationship between the polarization of the source-frequency beam and the polarization of the second harmonic

  19. Strong nonlinear harmonic generation in a PZT/Aluminum resonator

    Parenthoine, D; Haumesser, L; Meulen, F Vander; Tran-Huu-Hue, L-P, E-mail: parenthoine@univ-tours.f [University Francois Rabelais of Tours, U 930 Imagerie et Cerveau, CNRS 2448, ENIVL, rue de la Chocolaterie, BP 3410, 41034 Blois (France)

    2009-11-01

    In this work, the extentional vibration mode of a coupled PZT/ Aluminum rod resonator is studied experimentally. Geometrical characteristics of the PZT are its 27 mm length and its 4x4 mm{sup 2} cross section area. The excitation voltage consists in sinusoidal bursts in the frequency range (20-80 kHz). Velocity measurements are performed at both ends of this system, using a laser probe. Strong harmonic distortions in the mechanical response (up to -20 dB with respect to the primary wave amplitude) have been observed. The corresponding input levels are far lower than those which are necessary to observe quadratic second harmonic generation in a free PZT resonator. The strong nonlinear effect can be explained as a super-harmonic resonance of the system due to a specific ratio between the eigen frequencies of the two parts of the resonator. Evolution of fundamental and harmonic responses are observed as a function of input levels, highlighting hysteretic behavior.

  20. J.F. Schouten revisited : pitch of complex tones having many high-order harmonics

    Smurzynski, J.; Houtsma, A.J.M.

    1988-01-01

    Four experiments are reported which deal with pitch perception of harmonic complex tones containing many high-order, aurally unresolvable partials. Melodic-interval identilication performance ill the case of sounds with increasing harmonic order remains significantly above chalice level, even if the

  1. Higher-Order Program Generation

    Rhiger, Morten

    for OCaml, a dialect of ML, that provides run-time code generation for OCaml programs. We apply these byte-code combinators in semantics-directed compilation for an imperative language and in run-time specialization using type-directed partial evaluation. Finally, we present an approach to compiling goal......This dissertation addresses the challenges of embedding programming languages, specializing generic programs to specific parameters, and generating specialized instances of programs directly as executable code. Our main tools are higher-order programming techniques and automatic program generation....... It is our thesis that they synergize well in the development of customizable software. Recent research on domain-specific languages propose to embed them into existing general-purpose languages. Typed higher-order languages have proven especially useful as meta languages because they provide a rich...

  2. Gas jet structure influence on high harmonic generation

    Grant-Jacob, James; Mills, Benjamin; Butcher, Thomas J.; Chapman, Richard T.; Brocklesby, William S.; Frey, Jeremy G.

    2011-01-01

    Gas jets used as sources for high harmonic generation (HHG) have a complex three-dimensional density and velocity profile. This paper describes how the profile influences the generation of extreme-UV light. As the position of the laser focus is varied along the jet flow axis, we show that the intensity of the output radiation varies by approximately three times, with the highest flux being observed when the laser is focused into the Mach disc. The work demonstrated here will aid in the optimi...

  3. Bunching phase and constraints on echo enabled harmonic generation

    Hemsing, E.

    2018-05-01

    A simple mathematical description is developed for the bunching spectrum in echo enabled harmonic generation (EEHG) that incorporates the effect of additional electron beam energy modulations. Under common assumptions, they are shown to contribute purely through the phase of the longitudinal bunching factor, which allows the spectral moments of the bunching to be calculated directly from the known energy modulations. In particular, the second moment (spectral bandwidth) serves as simple constraint on the amplitude of the energy modulations to maintain a transform-limited seed. We show that, in general, the impact on the spectrum of energy distortions that develop between the EEHG chicanes scales like the harmonic number compared to distortions that occur upstream. This may limit the parameters that will allow EEHG to reach short wavelengths in high brightness FELs.

  4. Third-harmonic generation in isotropic media by focused pulses

    Tasgal, Richard S.; Band, Y.B.

    2004-01-01

    For focused pulses of light in isotropic nonlinear media, third-harmonic generation can be strongly affected by group-velocity mismatch between the fundamental and third-harmonic. There is a characteristic time determined by the group-velocity mismatch and the Rayleigh range of the focused pulse. The dynamics depend on two dimensionless quantities, namely the ratio of the characteristic time to the pulse duration and the phase-velocity mismatch times the Rayleigh range. Pulses shorter than the characteristic time have physics described by simple analytic formulas. Pulses near the characteristic time have an intermediate behavior given by an explicit but more complicated formula. Pulses longer than the characteristic time tend to the continuous-wave case

  5. Higher harmonics generation in relativistic electron beam with virtual cathode

    Kurkin, S. A., E-mail: KurkinSA@gmail.com; Badarin, A. A.; Koronovskii, A. A.; Hramov, A. E. [Saratov State Technical University, Politechnicheskaja 77, Saratov 410028, Russia and Saratov State University, Astrakhanskaja 83, Saratov 410012 (Russian Federation)

    2014-09-15

    The study of the microwave generation regimes with intense higher harmonics taking place in a high-power vircator consisting of a relativistic electron beam with a virtual cathode has been made. The characteristics of these regimes, in particular, the typical spectra and their variations with the change of the system parameters (beam current, the induction of external magnetic field) as well as physical processes occurring in the system have been analyzed by means of 3D electromagnetic simulation. It has been shown that the system under study demonstrates the tendency to the sufficient growth of the amplitudes of higher harmonics in the spectrum of current oscillations in the VC region with the increase of beam current. The obtained results allow us to consider virtual cathode oscillators as promising high power mmw-to-THz sources.

  6. Probing temporal aspects of high-order harmonic pulses via multi-colour, multi-photon ionization processes

    Mauritsson, J [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803-4001 (United States); Johnsson, P [Department of Physics, Lund Institute of Technology, PO Box 118, SE-22100 Lund (Sweden); Lopez-Martens, R [Department of Physics, Lund Institute of Technology, PO Box 118, SE-22100 Lund (Sweden); Varju, K [Department of Physics, Lund Institute of Technology, PO Box 118, SE-22100 Lund (Sweden); L' Huillier, A [Department of Physics, Lund Institute of Technology, PO Box 118, SE-22100 Lund (Sweden); Gaarde, M B [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803-4001 (United States); Schafer, K J [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803-4001 (United States)

    2005-07-14

    High-order harmonics generated through the interaction of atoms and strong laser fields are a versatile, laboratory-scale source of extreme ultraviolet (XUV) radiation on a femtosecond or even attosecond time-scale. In order to be a useful experimental tool, however, this radiation has to be well characterized, both temporally and spectrally. In this paper we discuss how multi-photon, multi-colour ionization processes can be used to completely characterize either individual harmonics or attosecond pulse trains. In particular, we discuss the influence of the intensity and duration of the probe laser, and how these parameters effect the accuracy of the XUV characterization.

  7. Probing temporal aspects of high-order harmonic pulses via multi-colour, multi-photon ionization processes

    Mauritsson, J; Johnsson, P; Lopez-Martens, R; Varju, K; L'Huillier, A; Gaarde, M B; Schafer, K J

    2005-01-01

    High-order harmonics generated through the interaction of atoms and strong laser fields are a versatile, laboratory-scale source of extreme ultraviolet (XUV) radiation on a femtosecond or even attosecond time-scale. In order to be a useful experimental tool, however, this radiation has to be well characterized, both temporally and spectrally. In this paper we discuss how multi-photon, multi-colour ionization processes can be used to completely characterize either individual harmonics or attosecond pulse trains. In particular, we discuss the influence of the intensity and duration of the probe laser, and how these parameters effect the accuracy of the XUV characterization

  8. Characterization of muscle contraction with second harmonic generation microscopy

    Prent, Nicole

    Muscle cells have the ability to change length and generate force due to orchestrated action of myosin nanomotors that cause sliding of actin filaments along myosin filaments in the sarcomeres, the fundamental contractile units, of myocytes. The correlated action of hundreds of sarcomeres is needed to produce the myocyte contractions. This study probes the molecular structure of the myofilaments and investigates the movement correlations between sarcomeres during contraction. In this study, second harmonic generation (SHG) microscopy is employed for imaging striated myocytes. Myosin filaments in striated myocytes inherently have a nonzero second-order susceptibility, [special characters omitted] and therefore generate efficient SHG. Employing polarization-in polarization-out (PIPO) SHG microscopy allows for the accurate determination of the characteristic ratio, [special characters omitted] in birefringent myocytes, which describes the structure of the myosin filament. Analysis shows that the b value at the centre of the myosin filament, where the nonlinear dipoles are better aligned, is slightly lower than the value at the edges of the filament, where there is more disorder in orientation of the nonlinear dipoles from the myosin heads. Forced stretching of myocytes resulted in an SHG intensity increase with the elongation of the sarcomere. SHG microscopy captured individual sarcomeres during contraction, allowing for the measurement of sarcomere length (SL) and SHG intensity (SI) fluctuations. The fluctuations also revealed higher SHG intensity in elongated sarcomeres. The sarcomere synchronization model (SSM) for contracting and quiescent myocytes was developed, and experimentally verified for three cases (isolated cardiomyocyte, embryonic chicken cardiomyocyte, and larva myocyte). During contraction, the action of SLs and SIs between neighbouring sarcomeres partially correlated, whereas in quiescent myocytes the SLs show an anti-correlation and the SIs have no

  9. Influence of temperature rise distribution in second harmonic generation crystal on intensity distributions of output second harmonic wave

    Li Wei; Feng Guoying; Li Gang; Huang Yu; Zhang Qiuhui

    2009-01-01

    Second-harmonic generation (SHG) of high-intensity laser with an SHG crystal for type I angle phase matching has been studied by the use of a split-step algorithm based on the fast Fourier transform and a fourth-order Runge-Kutta (R-K) integrator. The transverse walk-off effect, diffraction, the second-order and the third-order nonlinear effects have been taken into consideration. Influences of a temperature rise distribution of the SHG crystal on the refractive indices of ordinary wave and extraordinary wave have been discussed. The rules of phase mismatching quantity, intensity distribution of output beam and frequency conversion efficiency varying with the temperature rise distribution of the SHG crystal have been analyzed quantitatively. The calculated results indicate that in a high power frequency conversion system, the temperature rise distribution of SHG crystal would result in the phase mismatching of fundamental and harmonic waves, leading to the variation of intensity distribution of the output beam and the decrease of the conversion efficiency. (authors)

  10. Ellipticity dependence of high harmonics generated using 400 nm driving lasers

    Cheng, Yan; Khan, Sabih; Zhao, Kun; Zhao, Baozhen; Chini, Michael; Chang, Zenghu

    2011-05-01

    High order harmonics generated from 400 nm driving pulses hold promise of scaling photon flux of single attosecond pulses by one to two orders of magnitude. We report ellipticity dependence and phase matching of high order harmonics generated from such pulses in Neon gas target and compared them with similar measurements using 800 nm driving pulses. Based on measured ellipticity dependence, we predict that double optical gating (DOG) and generalized double optical gating (GDOG) can be employed to extract intense single attosecond pulses from pulse train, while polarization gating (PG) may not work for this purpose. This material is supported by the U.S. Army Research Office under grant number W911NF-07-1-0475, and by the Chemical Sciences, Geosciences and Biosciences Division, Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy.

  11. Optical Cherenkov radiation in ultrafast cascaded second-harmonic generation

    Bache, Morten; Bang, Ole; Zhou, Binbin

    2010-01-01

    -matching point is located in the absorption region of the crystal, effectively absorbing the generated dispersive wave. By calculating the phase-matching curves for typically used frequency conversion crystals, we point out that the mid-IR absorption in the crystal in many cases automatically will filter away....... The beating between the dispersive wave and the soliton generates trailing temporal oscillations on the compressed soliton. Insertion of a simple short-wave pass filter after the crystal can restore a clean soliton. On the other hand, bandpass filtering around the dispersive wave peak results in near......We show through theory and numerics that when few-cycle femtosecond solitons are generated through cascaded (phase-mismatched) second-harmonic generation, these broadband solitons can emit optical Cherenkov radiation in the form of linear dispersive waves located in the red part of the spectrum...

  12. Kerr-like behaviour of second harmonic generation in the far-off resonant regime

    Peřinová, Vlasta; Lukš, Antonín; Křepelka, Jaromír; Leoński, Wiesław; Peřina, Jan

    2018-05-01

    We separate the Kerr-like behaviour of the second-harmonic generation in the far-off resonant regime from the oscillations caused by the time-dependence of the interaction energy. To this purpose, we consider the approximation obtained from the exact dynamics by the method of small rotations. The Floquet-type decomposition of the approximate dynamics comprises the Kerr-like dynamics and oscillations of the same order of magnitude as those assumed for the exact dynamics of the second-harmonic generation. We have found that a superposition of two states of concentrated quantum phase arises in the fundamental mode in the second-harmonic generation in the far-off resonant limit at a later time than a superposition of two coherent states in the corresponding Kerr medium and the difference is larger for higher initial coherent amplitudes. The quantum phase fluctuation is higher for the same initial coherent amplitudes in the fundamental mode in the second-harmonic generation in the far-off resonant limit than in the corresponding Kerr medium and the difference is larger for higher initial coherent amplitudes.

  13. The diffraction and walk off in the second harmonic generation

    He Yujuan; Cai Bangwei; Zhang Bin

    2000-01-01

    Taking the second harmonic generation of Gaussian beam in a KDP crystal of type I matching for example, the effects of diffraction and walk off on doubling conversion efficiency have been worked out. The result indicates that the effect of diffraction is very small and can even by neglected. When the input Gaussian beam size is very small, the effect of walk off is very deleterious on doubling conversion. Along with the enlarging of beam size, the effect of walk off is much smaller and can even be neglected

  14. The echo-enabled harmonic generation options for FLASH II

    Deng, Haixiao; Decking, Winfried; Faatz, Bart

    2011-03-01

    FLASH II is an upgrade to the existing free electron laser (FEL) FLASH. The echo-enabled harmonic generation (EEHG) scheme is proposed to be a potential seeding option of FLASH II. In this paper, the possibility of EEHG operation of FLASH II is investigated for the first time. With a combination of existing numerical codes, i.e. a laser-beam interaction code in an undulator (LBICU), a beam tracking code in a chicane (ELEGANT) and an universal FEL simulating code (GENESIS), the effects of beam energy chirp and coherent synchrotron radiation (CSR) on EEHG operation are studied as well. In addition, several interesting issues concerning EEHG simulation are discussed. (orig.)

  15. Second harmonic generation spectroscopy on Si surfaces and interfaces

    Pedersen, Kjeld

    2010-01-01

    Optical second harmonic generation (SHG) spectroscopy studies of Si(111) surfaces and interfaces are reviewed for two types of systems: (1) clean 7 x 7 and root 3 x root 3-Ag reconstructed surfaces prepared under ultra-high vacuum conditions where surface states are excited and (2) interfaces...... in silicon-on-insulator (SOI) structures and thin metal films on Si surfaces where several interfaces contribute to the SHG. In all the systems resonances are seen at interband transitions near the bulk critical points E-1 and E-2. On the clean surfaces a number of resonances appear below the onset of bulk...

  16. Geometric effect on second harmonic generation from gold grating

    Lu, Jiao; Ding, Baoyong; Huo, Yanyan; Ning, Tingyin

    2018-05-01

    We numerically investigate second harmonic generation from gold gratings of an ideal rectangular and ladder-shaped cross-section. The SHG efficiency from the gold gratings of the ladder-shaped cross-section is significantly enhanced compared with that from the ideal rectangular cross-section with a maximum enhancement factor of around two. The enhancement is ascribe to the nanostructure dependent local fundamental electric field, the nonlinear sources and thus the far field radiation. Our results have a practical meaning in the explanation of experimental SHG measurement, and the modulation of SHG response in the metallic nanostructure.

  17. How classical gluon fields generate odd azimuthal harmonics for the two-gluon correlation function in high-energy collisions

    Kovchegov, Yuri V.; Skokov, Vladimir V.

    2018-05-01

    We show that, in the saturation/color glass condensate framework, odd azimuthal harmonics of the two-gluon correlation function with a long-range separation in rapidity are generated by the higher-order saturation corrections in the interactions with the projectile and the target. At the very least, the odd harmonics require three scatterings in the projectile and three scatterings in the target. We derive the leading-order expression for the two-gluon production cross section which generates odd harmonics: the expression includes all-order interactions with the target and three interactions with the projectile. We evaluate the obtained expression both analytically and numerically, confirming that the odd-harmonics contribution to the two-gluon production in the saturation framework is nonzero.

  18. Harmonizing the prototypes concerning the fast reactors of 4. generation

    Anon.

    2008-01-01

    In january 2008, an agreement was signed between the Japan Atomic Energy Agency (JAEA), the American Department of Energy (DOE) and the French Atomic Energy Commission, in order to harmonize the projects of the 3 countries for the development of prototypes of sodium-cooled fast reactors. This cooperation concerns the following issues: -) the purpose of the prototypes, -) common set of safety rules, -) technical innovations for reducing construction, operating and maintenance costs, and -) information exchange about the level of power, the type of nuclear fuels and the time schedule of these prototypes. (A.C.)

  19. Stator Current Harmonic Control with Resonant Controller for Doubly Fed Induction Generator

    Liu, Changjin; Blaabjerg, Frede; Chen, Wenjie

    2012-01-01

    rotor current control loop for harmonic suppression. The overall control scheme is implemented in dq frame. Based on a mathematical model of the DFIG control system, the effects on system stability using the resonant controller, an analysis of the steady-state error, and the dynamic performance......, are discussed in this paper. Taking these effects into account, the parameters of the resonant controller can be designed and effectively damp the influence from the grid voltage harmonics. As a result, the impacts of the negative sequence fifth- and positive sequence seventh-order voltage harmonics...... harmonics, especially low-order harmonics. This paper proposes a stator current harmonic suppression method using a sixth-order resonant controller to eliminate negative sequence fifth- and positive sequence seventh-order current harmonics. A stator current harmonic control loop is added to the conventional...

  20. Ultrahigh harmonics generation in a FEL with a seed laser

    Goloviznin, V.V.; Amersfoort, P.W. van

    1995-01-01

    One of the most challenging problems in modern FEL technology is to operate in the X-ray region, especially in the open-quotes water windowclose quotes. Because of the absence of optical resonators in this range of wavelengths, only a single-pass device may be suitable for this task. The Self-Amplified Spontaneous Emission (SASE) mechanism is now under active discussion as a realistic way to provide high-power coherent emission in the X-ray range. Both the undulator parameters and the electron beam parameters required for the lasing are achieveable at today's technological level. On the other hand, the SASE approach implies a very long and expensive periodic magnetic structure, typically several tens of meters long. This is mainly because of the rather long build-up time necessary to establish a coherent mode from incoherent noise. A mechanism of shortening this time would be therefore highly desirable. In the present paper we consider a scheme using two undulators and a seed-laser to produce coherent X-ray emission. The first undulator and the seed-laser provide a pre-modulation of the beam while the second undulator serves as a source of coherent spontaneous radiation at a very high harmonic of the seed-laser frequency; the whole scheme may then be considered to be an FEL-based frequency upconvertor. The total length of the periodic magnetic structure is shown to be of the order of several meters, nearly an order of magnitude shorter than in the SASE case. For the same beam quality as in the SASE scheme and with realistic seed-laser parameters, the efficiency of the beam pre-modulation at the 50-th (exclamation point) harmonic is shown to be as high as 15%. The output radiation is tunable between discrete harmonics of the seed-frequency

  1. Laser light absorption and harmonic generation due to self-generated magnetic fields

    Kruer, W.L.; Estabrook, K.G.

    1977-01-01

    It is shown that self-generated magnetic fields can play a significant role in laser light absorption. Even normally incident light will then be resonantly absorbed. Computer simulations and theoretical estimates for this absorption and the concomitant harmonic generation are given for parameters characteristic of some recent experiments

  2. Quasi-phase matching and quantum control of high harmonic generation in waveguides using counterpropagating beams

    Zhang, Xiaoshi; Lytle, Amy L.; Cohen, Oren; Kapteyn, Henry C.; Murnane, Margaret M.

    2010-11-09

    All-optical quasi-phase matching (QPM) uses a train of counterpropagating pulses to enhance high-order harmonic generation (HHG) in a hollow waveguide. A pump pulse enters one end of the waveguide, and causes HHG in the waveguide. The counterpropagation pulses enter the other end of the waveguide and interact with the pump pulses to cause QPM within the waveguide, enhancing the HHG.

  3. Integrated GaN photonic circuits on silicon (100) for second harmonic generation

    Xiong, Chi; Pernice, Wolfram; Ryu, Kevin K.; Schuck, Carsten; Fong, King Y.; Palacios, Tomas; Tang, Hong X.

    2014-01-01

    We demonstrate second order optical nonlinearity in a silicon architecture through heterogeneous integration of single-crystalline gallium nitride (GaN) on silicon (100) substrates. By engineering GaN microrings for dual resonance around 1560 nm and 780 nm, we achieve efficient, tunable second harmonic generation at 780 nm. The \\{chi}(2) nonlinear susceptibility is measured to be as high as 16 plus minus 7 pm/V. Because GaN has a wideband transparency window covering ultraviolet, visible and ...

  4. Spectral and spatial characteristics of third-harmonic generation in conical light beams

    Peet, V.E.; Shchemeljov, S.V.

    2003-01-01

    Generation of resonance-enhanced third harmonic in Bessel and other conical beams is analyzed from a simple picture, where the fundamental light field is decomposed into elementary configurations of crossed plain-wave sub-beams. We show that the overall harmonic output can be derived as a superposition of all partial harmonic components driven by elementary configurations of the fundamental field. Good agreement with experimental observations has been obtained in simulation of spectral and spatial characteristics of the generated third harmonic. Some peculiarities of harmonic generation in conical light fields are discussed

  5. Ab initio calculation of harmonic generation spectra of helium using a time-dependent non-Hermitian formalism

    Gilary, I.; Kaprálová, Petra; Moiseyev, N.

    2006-01-01

    Roč. 74, - (2006), 052505-1 ISSN 1050-2947 R&D Projects: GA AV ČR(CZ) KJB100550501; GA MŠk(CZ) LC512 Grant - others:Israel Science Foundation(IL) 1152/04 Institutional research plan: CEZ:AV0Z40550506 Keywords : high-order harmonic generation * symmetry selection rules * even harmonics * complex scaling * F-produkt Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.047, year: 2006

  6. On the possible origin of bulk third harmonic generation in skin cells

    Su, Tung-Yu; Liao, Chien-Sheng; Yang, Chih-Yuan; Zhuo, Guan-Yu; Chen, Szu-Yu; Chu, Shi-Wei

    2011-09-01

    We studied third harmonic generation (THG) of melanin solution with concentrations similar to melanocytes in human skin. In contrast to conventional observation of THG at interface, bulk THG was detected inside the solution due to the formation of melanin hydrocolloids. A linear relationship between melanin concentration and THG intensity was found, suggesting THG originated from high-order hyper-Rayleigh scattering. By fitting this linear relationship, third-order hyperpolarizability of melanin hydrocolloids was determined to be three orders larger than that of water. Our result will be useful for interpretation of THG signals in skin and other tissues containing colloidal particles.

  7. Variable pattern of high-order harmonic spectra from a laser-produced plasma by using the chirped pulses of narrow-bandwidth radiation

    Ganeev, R. A.; Suzuki, M.; Baba, M.; Kuroda, H.; Redkin, P. V.

    2007-01-01

    Various plasmas prepared by laser ablation of the surfaces of solid targets were examined by the narrow-bandwidth radiation of different chirp and pulse durations. The high-order harmonics generated during laser-plasma interaction showed different brightness, wavelength shift, harmonic cutoff, and efficiency by using variable chirps of pump radiation. An analysis of harmonic optimization at these conditions is presented. The blueshifted and redshifted harmonics observed in this case were analyzed and attributed to the abundance of free electrons and self-phase modulation of the driving pulse. The resonance-induced enhancement of the 15th harmonic from GaN-nanoparticle-containing plasma caused by the tuning of harmonic wavelength close to the ionic transition was demonstrated

  8. Second-harmonic generation imaging of collagen in ancient bone.

    Thomas, B; McIntosh, D; Fildes, T; Smith, L; Hargrave, F; Islam, M; Thompson, T; Layfield, R; Scott, D; Shaw, B; Burrell, C L; Gonzalez, S; Taylor, S

    2017-12-01

    Second-harmonic generation imaging (SHG) captures triple helical collagen molecules near tissue surfaces. Biomedical research routinely utilizes various imaging software packages to quantify SHG signals for collagen content and distribution estimates in modern tissue samples including bone. For the first time using SHG, samples of modern, medieval, and ice age bones were imaged to test the applicability of SHG to ancient bone from a variety of ages, settings, and taxa. Four independent techniques including Raman spectroscopy, FTIR spectroscopy, radiocarbon dating protocols, and mass spectrometry-based protein sequencing, confirm the presence of protein, consistent with the hypothesis that SHG imaging detects ancient bone collagen. These results suggest that future studies have the potential to use SHG imaging to provide new insights into the composition of ancient bone, to characterize ancient bone disorders, to investigate collagen preservation within and between various taxa, and to monitor collagen decay regimes in different depositional environments.

  9. Second-harmonic generation imaging of collagen in ancient bone

    B. Thomas

    2017-12-01

    Full Text Available Second-harmonic generation imaging (SHG captures triple helical collagen molecules near tissue surfaces. Biomedical research routinely utilizes various imaging software packages to quantify SHG signals for collagen content and distribution estimates in modern tissue samples including bone. For the first time using SHG, samples of modern, medieval, and ice age bones were imaged to test the applicability of SHG to ancient bone from a variety of ages, settings, and taxa. Four independent techniques including Raman spectroscopy, FTIR spectroscopy, radiocarbon dating protocols, and mass spectrometry-based protein sequencing, confirm the presence of protein, consistent with the hypothesis that SHG imaging detects ancient bone collagen. These results suggest that future studies have the potential to use SHG imaging to provide new insights into the composition of ancient bone, to characterize ancient bone disorders, to investigate collagen preservation within and between various taxa, and to monitor collagen decay regimes in different depositional environments.

  10. Static third-harmonic lines in widely variable fiber continuum generation

    Tu, Haohua; Zhao, Youbo; Liu, Yuan; Boppart, Stephen A.

    2014-01-01

    An intriguing phenomenon of third-harmonic generation under fiber continuum generation is the emission of an anharmonic signal. One popular interpretation of this effect has developed into a general theory of fiber third-harmonic generation. Here we produce "static" third-harmonic lines dictated fully by fiber properties independent of pump parameters, in contrast to the signals of all known phase-matched nonlinear optical processes that vary dynamically with these parameters. We argue that the anharmonic signal is an illusion of the continuum generation, that it is in fact harmonic, and that this theory should be reevaluated.

  11. An Improved Second-Order Generalized Integrator Based Quadrature Signal Generator

    Xin, Zhen; Wang, Xiongfei; Qin, Zian

    2016-01-01

    The second-order generalized integrator based quadrature signal generator (SOGI-QSG) is able to produce in-quadrature signals for many applications, such as frequency estimation, grid synchronization, and harmonic extraction. However, the SOGI-QSG is sensitive to input dc and harmonic components...

  12. Below-threshold harmonic generation from strong non-uniform fields

    Yavuz, I.

    2017-10-01

    Strong-field photoemission below the ionization threshold is a rich/complex region where atomic emission and harmonic generation may coexist. We studied the mechanism of below-threshold harmonics (BTH) from spatially non-uniform local fields near the metallic nanostructures. Discrete harmonics are generated due to the broken inversion symmetry, suggesting enriched coherent emission in the vuv frequency range. Through the numerical solution of the time-dependent Schrödinger equation, we investigate wavelength and intensity dependence of BTH. Wavelength dependence identifies counter-regular resonances; individual contributions from the multi-photon emission and channel-closing effects due to quantum path interferences. In order to understand the underlying mechanism of BTH, we devised a generalized semi-classical model, including the influence of Coulomb and non-uniform field interactions. As in uniform fields, Coulomb potential in non-uniform fields is the determinant of BTH; we observed that the generation of BTH are due to returning trajectories with negative energies. Due to large distance effectiveness of the non-uniformity, only long trajectories are noticeably affected.

  13. Second harmonic generation in generalized Thue-Morse ferroelectric superlattices

    Wang Longxiang; Yang Xiangbo; Chen Tongsheng

    2009-01-01

    In this paper the second harmonic generation (SHG) in generalized Thue-Morse (GTM(m, n)) ferroelectric superlattices is studied. Under the small-signal approximation, the SHG spectra in both real and reciprocal spaces are investigated. It is found that: (1) only when the structure parameters l, l A , and l B are all chosen to be proper, can SHG in GTM(m, n) ferroelectric superlattices be generated; (2) for Family A of generalized Thue-Morse, GTM(m, 1) ferroelectric systems, with the increase of parameter m, the intense peaks of SHG concentrate on the long wavelength 1.4-1.5μm (the fundamental beam (FB) wavelength is within 0.8-1.5μm), but for Family B of generalized Thue-Morse, GTM(1, n) ferroelectric superlattices, with the increase of parameter n, the intense peaks of SHG concentrate on the middle wavelength 1.1-1.2μm; and (3) for GTM(m, 1) ferroelectric superlattices, the bigger the m, the stronger the relative integral intensity (RII) of SHG would be, but for GTM(1, n) ferroelectric systems, the bigger the n, the weaker the RII of SHG would be.

  14. Experimental demonstration of efficient and robust second harmonic generation using the adiabatic temperature gradient method

    Dimova, E.; Steflekova, V.; Karatodorov, S.; Kyoseva, E.

    2018-03-01

    We propose a way of achieving efficient and robust second-harmonic generation. The technique proposed is similar to the adiabatic population transfer in a two-state quantum system with crossing energies. If the phase mismatching changes slowly, e.g., due to a temperature gradient along the crystal, and makes the phase match for second-harmonic generation to occur, then the energy would be converted adiabatically to the second harmonic. As an adiabatic technique, the second-harmonic generation scheme presented is stable to variations in the crystal parameters, as well as in the input light, crystal length, input intensity, wavelength and angle of incidence.

  15. Undulator physics and coherent harmonic generation at the MAX-lab electron storage ring

    Werin, Sverker.

    1991-01-01

    This work presents the undulator and harmonic generation project at the electron storage ring MAX-lab at University of Lund. The theory of undulator radiation, laser coherent harmonic generation, optical klystron amplifiers and FELs is treated in one uniform way, with complete solutions of the necessary equations. The permanent magnet undulator is described in some detail, along with the installation of the undulator in the storage ring. Details regarding the emitted radiation, the electron beam path in the undulator and other results are analysed. Finally harmonic generation using a Nd:YAG laser and the creation of coherent photons at the third harmonic (355 nm) is described. (author)

  16. Application of mid-infrared pulses for quasi-phase-matching of high-order harmonics in silver plasma.

    Ganeev, Rashid A; Husakou, Anton; Suzuki, Masayuki; Kuroda, Hiroto

    2016-02-22

    We demonstrate the quasi-phase-matching of a group of harmonics generated in Ag multi-jet plasma using tunable pulses in the region of 1160 - 1540 nm and their second harmonic emission. The numerical treatment of this effect includes microscopic description of the harmonic generation, propagation of the pump pulse, and the propagation of the generated harmonics. We obtained more than 30-fold growth of harmonics at the conditions of quasi-phase-matching in the region of 35 nm using eight-jet plasma compared with the case of imperforated plasma.

  17. High-harmonic generation in a quantum electron gas trapped in a nonparabolic and anisotropic well

    Hurst, Jérôme; Lévêque-Simon, Kévin; Hervieux, Paul-Antoine; Manfredi, Giovanni; Haas, Fernando

    2016-05-01

    An effective self-consistent model is derived and used to study the dynamics of an electron gas confined in a nonparabolic and anisotropic quantum well. This approach is based on the equations of quantum hydrodynamics, which incorporate quantum and nonlinear effects in an approximate fashion. The effective model consists of a set of six coupled differential equations (dynamical system) for the electric dipole and the size of the electron gas. Using this model we show that: (i) high harmonic generation is related to the appearance of chaos in the phase space, as attested to by related Poincaré sections; (ii) higher order harmonics can be excited efficiently and with relatively weak driving fields by making use of chirped electromagnetic waves.

  18. Single nano-hole as a new effective nonlinear element for third-harmonic generation

    Melentiev, P N; Konstantinova, T V; Afanasiev, A E; Balykin, V I; Kuzin, A A; Baturin, A S; Tausenev, A V; Konyaschenko, A V

    2013-01-01

    In this letter, we report on a particularly strong optical nonlinearity at the nanometer scale in aluminum. A strong optical nonlinearity of the third order was demonstrated on a single nanoslit. Single nanoslits of different aspect ratio were excited by a laser pulse (120 fs) at the wavelength 1.5 μm, leading predominantly to third-harmonic generation (THG). It has been shown that strong surface plasmon resonance in a nanoslit allows the realization of an effective nanolocalized source of third-harmonic radiation. We show also that a nanoslit in a metal film has a significant advantage in nonlinear processes over its Babinet complementary nanostructure (nanorod): the effective abstraction of heat in a film with a slit makes it possible to use much higher laser radiation intensities. (letter)

  19. Single nano-hole as a new effective nonlinear element for third-harmonic generation

    Melentiev, P. N.; Konstantinova, T. V.; Afanasiev, A. E.; Kuzin, A. A.; Baturin, A. S.; Tausenev, A. V.; Konyaschenko, A. V.; Balykin, V. I.

    2013-07-01

    In this letter, we report on a particularly strong optical nonlinearity at the nanometer scale in aluminum. A strong optical nonlinearity of the third order was demonstrated on a single nanoslit. Single nanoslits of different aspect ratio were excited by a laser pulse (120 fs) at the wavelength 1.5 μm, leading predominantly to third-harmonic generation (THG). It has been shown that strong surface plasmon resonance in a nanoslit allows the realization of an effective nanolocalized source of third-harmonic radiation. We show also that a nanoslit in a metal film has a significant advantage in nonlinear processes over its Babinet complementary nanostructure (nanorod): the effective abstraction of heat in a film with a slit makes it possible to use much higher laser radiation intensities.

  20. Time-domain analysis of second-harmonic generation of primary Lamb wave propagation in an elastic plate

    Deng Ming-Xi; Xiang Yan-Xun

    2010-01-01

    Within the second-order perturbation approximation, this paper investigates the physical process of generation of the time-domain second harmonic by a primary Lamb wave waveform in an elastic plate. The present work is performed based on the preconditions that the phase velocity matching is satisfied and that the transfer of energy from the primary Lamb wave to the double frequency Lamb wave is not zero. It investigates the influences of the difference between the group velocities of the primary Lamb wave and the double frequency Lamb wave, the propagation distance and the duration of the primary Lamb wave waveform on the envelope shape of the time-domain second harmonic. It finds that the maximum magnitude of the envelope of the second-harmonic waveform can grow within some propagation distance even if the condition of group velocity matching is not satisfied. Our analyses also indicate that the maximum magnitude of the envelope of the second-harmonic waveform is kept constant beyond a specific propagation distance. Furthermore, it concludes that the integration amplitude of the time-domain second-harmonic waveform always grows with propagation distance within the second-order perturbation. The present research yields new physical insight not previously available into the effect of generation of the time-domain second harmonic by propagation of a primary Lamb wave waveform

  1. Generation of high order modes

    Ngcobo, S

    2012-07-01

    Full Text Available with the location of the Laguerre polynomial zeros. The Diffractive optical element is used to shape the TEM00 Gassian beam and force the laser to operate on a higher order TEMp0 Laguerre-Gaussian modes or high order superposition of Laguerre-Gaussian modes...

  2. Measurement of optical-beat frequency in a photoconductive terahertz-wave generator using microwave higher harmonics.

    Murasawa, Kengo; Sato, Koki; Hidaka, Takehiko

    2011-05-01

    A new method for measuring optical-beat frequencies in the terahertz (THz) region using microwave higher harmonics is presented. A microwave signal was applied to the antenna gap of a photoconductive (PC) device emitting a continuous electromagnetic wave at about 1 THz by the photomixing technique. The microwave higher harmonics with THz frequencies are generated in the PC device owing to the nonlinearity of the biased photoconductance, which is briefly described in this article. Thirteen nearly periodic peaks in the photocurrent were observed when the microwave was swept from 16 to 20 GHz at a power of -48 dBm. The nearly periodic peaks are generated by the homodyne detection of the optical beat with the microwave higher harmonics when the frequency of the harmonics coincides with the optical-beat frequency. Each peak frequency and its peak width were determined by fitting a Gaussian function, and the order of microwave harmonics was determined using a coarse (i.e., lower resolution) measurement of the optical-beat frequency. By applying the Kalman algorithm to the peak frequencies of the higher harmonics and their standard deviations, the optical-beat frequency near 1 THz was estimated to be 1029.81 GHz with the standard deviation of 0.82 GHz. The proposed method is applicable to a conventional THz-wave generator with a photomixer.

  3. Enhanced resonant second harmonic generation in plasma based on density transition

    Kant Niti

    2015-06-01

    Full Text Available Resonant second harmonic generation of a relativistic self-focusing laser in plasma with density ramp profile has been investigated. A high intense Gaussian laser beam generates resonant second harmonic beam in plasma with density ramp profile. The second harmonic undergoes periodic focusing in the plasma channel created by the fundamental wave. The normalized second harmonic amplitude varies periodically with distance and attains maximum value in the focal region. Enhancement in the second harmonic amplitude on account of relativistic self-focusing of laser based on plasma density transition is seen. Plasma density ramp plays an important role to make self-focusing stronger which leads to enhance the second harmonic generation in plasma.

  4. Third harmonic generation of high power far infrared radiation in semiconductors

    Urban, M [Ecole Polytechnique Federale, Lausanne (Switzerland). Centre de Recherche en Physique des Plasma (CRPP)

    1996-04-01

    We investigated the third harmonic generation of high power infrared radiation in doped semiconductors with emphasis on the conversion efficiency. The third harmonic generation effect is based on the nonlinear response of the conduction band electrons in the semiconductor with respect to the electric field of the incident electromagnetic wave. Because this work is directed towards a proposed application in fusion plasma diagnostics, the experimental requirements for the radiation source at the fundamental frequency are roughly given as follows: a wavelength of the radiation at the fundamental frequency in the order of 1 mm and an incident power greater than 1 MW. The most important experiments of this work were performed using the high power far infrared laser of the CRPP. With this laser a new laser line was discovered, which fits exactly the source specifications given above: the wavelength is 676 {mu}m and the maximum power is up to 2 MW. Additional experiments were carried out using a 496 {mu}m laser and a 140 GHz (2.1 mm) gyrotron. The main experimental progress with respect to previous work in this field is, in addition to the use of a very high power laser, the possibility of an absolute calibration of the detectors for the far infrared radiation and the availability of a new type of detector with a very fast response. This detector made it possible to measure the power at the fundamental as well as the third harmonic frequency with full temporal resolution of the fluctuations during the laser pulse. Therefore the power dependence of the third harmonic generation efficiency could be measured directly. The materials investigated were InSb as an example of a narrow gap semiconductor and Si as standard material. The main results are: narrow gap semiconductors indeed have a highly nonlinear electronic response, but the narrow band gap leads at the same time to a low power threshold for internal breakdown, which is due to impact ionization. figs., tabs., refs.

  5. Squeezing and entanglement in doubly resonant, type II, second-harmonic generation

    Andersen, Ulrik Lund; Buchhave, Preben

    2003-01-01

    We investigate, theoretically, the generation of bright and vacuum-squeezed light as well as entanglement in intracavity, type II, phase-matched second-harmonic generation. The cavity in which the crystal is embedded is resonant at the fundamental frequency but not at the second-harmonic frequenc...

  6. Second harmonic generation microscopy of the living human cornea

    Artal, Pablo; Ávila, Francisco; Bueno, Juan

    2018-02-01

    Second Harmonic Generation (SHG) microscopy provides high-resolution structural imaging of the corneal stroma without the need of labelling techniques. This powerful tool has never been applied to living human eyes so far. Here, we present a new compact SHG microscope specifically developed to image the structural organization of the corneal lamellae in living healthy human volunteers. The research prototype incorporates a long-working distance dry objective that allows non-contact three-dimensional SHG imaging of the cornea. Safety assessment and effectiveness of the system were firstly tested in ex-vivo fresh eyes. The maximum average power of the used illumination laser was 20 mW, more than 10 times below the maximum permissible exposure (according to ANSI Z136.1-2000). The instrument was successfully employed to obtain non-contact and non-invasive SHG of the living human eye within well-established light safety limits. This represents the first recording of in vivo SHG images of the human cornea using a compact multiphoton microscope. This might become an important tool in Ophthalmology for early diagnosis and tracking ocular pathologies.

  7. Research of second harmonic generation images based on texture analysis

    Liu, Yao; Li, Yan; Gong, Haiming; Zhu, Xiaoqin; Huang, Zufang; Chen, Guannan

    2014-09-01

    Texture analysis plays a crucial role in identifying objects or regions of interest in an image. It has been applied to a variety of medical image processing, ranging from the detection of disease and the segmentation of specific anatomical structures, to differentiation between healthy and pathological tissues. Second harmonic generation (SHG) microscopy as a potential noninvasive tool for imaging biological tissues has been widely used in medicine, with reduced phototoxicity and photobleaching. In this paper, we clarified the principles of texture analysis including statistical, transform, structural and model-based methods and gave examples of its applications, reviewing studies of the technique. Moreover, we tried to apply texture analysis to the SHG images for the differentiation of human skin scar tissues. Texture analysis method based on local binary pattern (LBP) and wavelet transform was used to extract texture features of SHG images from collagen in normal and abnormal scars, and then the scar SHG images were classified into normal or abnormal ones. Compared with other texture analysis methods with respect to the receiver operating characteristic analysis, LBP combined with wavelet transform was demonstrated to achieve higher accuracy. It can provide a new way for clinical diagnosis of scar types. At last, future development of texture analysis in SHG images were discussed.

  8. Second harmonic generation: Effects of the multiple reflections of the fundamental and the second harmonic waves on the Maker fringes

    Tellier, Gildas; Boisrobert, Christian

    2007-11-01

    The Maker fringes technique is commonly used for the determination of nonlinear optical coefficients. In this article, we present a new formulation of Maker fringes in parallel-surface samples, using boundary conditions taking into account the anisotropy of the crystal, the refractive-index dispersion, and the reflections of the fundamental and the second harmonic waves inside the material. Complete expressions for the generated second harmonic intensity are given for birefringent crystals for the case of no pump depletion. A comparison between theory and experimental results is made, showing the accuracy of our theoretical expressions.

  9. Higher-order power harmonics of pulsed electrical stimulation modulates corticospinal contribution of peripheral nerve stimulation.

    Chen, Chiun-Fan; Bikson, Marom; Chou, Li-Wei; Shan, Chunlei; Khadka, Niranjan; Chen, Wen-Shiang; Fregni, Felipe

    2017-03-03

    It is well established that electrical-stimulation frequency is crucial to determining the scale of induced neuromodulation, particularly when attempting to modulate corticospinal excitability. However, the modulatory effects of stimulation frequency are not only determined by its absolute value but also by other parameters such as power at harmonics. The stimulus pulse shape further influences parameters such as excitation threshold and fiber selectivity. The explicit role of the power in these harmonics in determining the outcome of stimulation has not previously been analyzed. In this study, we adopted an animal model of peripheral electrical stimulation that includes an amplitude-adapted pulse train which induces force enhancements with a corticospinal contribution. We report that the electrical-stimulation-induced force enhancements were correlated with the amplitude of stimulation power harmonics during the amplitude-adapted pulse train. In an exploratory analysis, different levels of correlation were observed between force enhancement and power harmonics of 20-80 Hz (r = 0.4247, p = 0.0243), 100-180 Hz (r = 0.5894, p = 0.0001), 200-280 Hz (r = 0.7002, p harmonics. This is a pilot, but important first demonstration that power at high order harmonics in the frequency spectrum of electrical stimulation pulses may contribute to neuromodulation, thus warrant explicit attention in therapy design and analysis.

  10. Second harmonic generation at fatigue cracks by low-frequency Lamb waves: Experimental and numerical studies

    Yang, Yi; Ng, Ching-Tai; Kotousov, Andrei; Sohn, Hoon; Lim, Hyung Jin

    2018-01-01

    This paper presents experimental and theoretical analyses of the second harmonic generation due to non-linear interaction of Lamb waves with a fatigue crack. Three-dimensional (3D) finite element (FE) simulations and experimental studies are carried out to provide physical insight into the mechanism of second harmonic generation. The results demonstrate that the 3D FE simulations can provide a reasonable prediction on the second harmonic generated due to the contact nonlinearity at the fatigue crack. The effect of the wave modes on the second harmonic generation is also investigated in detail. It is found that the magnitude of the second harmonic induced by the interaction of the fundamental symmetric mode (S0) of Lamb wave with the fatigue crack is much higher than that by the fundamental anti-symmetric mode (A0) of Lamb wave. In addition, a series of parametric studies using 3D FE simulations are conducted to investigate the effect of the fatigue crack length to incident wave wavelength ratio, and the influence of the excitation frequency on the second harmonic generation. The outcomes show that the magnitude and directivity pattern of the generated second harmonic depend on the fatigue crack length to incident wave wavelength ratio as well as the ratio of S0 to A0 incident Lamb wave amplitude. In summary, the findings of this study can further advance the use of second harmonic generation in damage detection.

  11. High-order sum and difference-frequency generation in helium

    Crane, J.K.; Perry, M.D.

    1993-01-01

    High-order harmonic generation provides a new method for generating coherent, XUV radiation. These harmonics are characterized by a rapid, pertubative drop at low orders, followed by a broad plateau extending to photon energies of 150 eV in the lighter, rare gas atoms. An experimentally observed limit coincides with the theoretical limit for harmonic generation in neutral atoms given by the expression E c (eV)=IP(0)+3U p (I), where E c is the energy cutoff of the harmonic plateau, IP(O) is the field-free ionization potential and U p is the electron quiver energy at the maximum intensity, I seen by the atom. As part of an effort to develop this technique into a general purpose XUV source, extensive work to understand the phase-matching between the harmonic and driving fields, and the resulting effect on the conversion efficiency, angular distribution and spectral brightness has been undertaken at several. Though, certain aspects of the harmonically generated radiation such as the polarization, relative strength of a given harmonic, and the plateau extent, are defined by the single atom-field interaction. Specifically, the single-atom harmonic spectrum is determined primarily by the interaction of a driven, quasi-free electron with the atomic potential. Using two, independent fields one can affect the electron motion by controlling the relative strength, polarization, and phase of the fields and alter the harmonic spectrum. In this paper we discuss initial, two-color experiments where we drive the atom with two fields of different frequencies: 1053 nm (1ω) and 526 nm (2ω). In addition to the higher, odd harmonics, we observe sets of three additional peaks that we attribute to sum and difference-frequency generation between the two fields. By controlling the relative polarization between the two fields we can control the relative strength of the harmonic and mixing components, as well as the polarization of the output XUV photon

  12. Studying the universality of field induced tunnel ionization times via high-order harmonic spectroscopy

    Soifer, H; Bruner, B D; Dudovich, N; Negro, M; Devetta, M; Vozzi, C; Faccialà, D; Silvestri, S de; Stagira, S

    2014-01-01

    High-harmonic generation spectroscopy is a promising tool for resolving electron dynamics and structure in atomic and molecular systems. This scheme, commonly described by the strong field approximation, requires a deep insight into the basic mechanism that leads to the harmonic generation. Recently, we have demonstrated the ability to resolve the first stage of the process—field induced tunnel ionization—by adding a weak perturbation to the strong fundamental field. Here we generalize this approach and show that the assumptions behind the strong field approximation are valid over a wide range of tunnel ionization conditions. Performing a systematic study—modifying the fundamental wavelength, intensity and atomic system—we observed a good agreement with quantum path analysis over a range of Keldysh parameters. The generality of this scheme opens new perspectives in high harmonics spectroscopy, holding the potential of probing large, complex molecular systems. (paper)

  13. Second harmonic generation microscopy investigation of the crystalline ultrastructure of three barley starch lines affected by hydration

    Cisek, Richard; Tokarz, Danielle; Steup, Martin

    2015-01-01

    Second harmonic generation (SHG) microscopy is employed to study changes in crystalline organization due to altered gene expression and hydration in barley starch granules. SHG intensity and susceptibility ratio values (R’SHG) are obtained using reduced Stokes-Mueller polarimetric microscopy...... by ordered hydrogen and hydroxyl bond networks which increase with hydration of starch granules....

  14. New ultrafast X-ray sources and their applications. Coherent ultrashort X UV emission by harmonic generation

    Salieres, P.; Le deroff, L.; Hergott, J.F.; Merdji, H.; Carre, B.

    2000-01-01

    By focusing an intense short-pulse laser into a rare gas jet, high-order harmonics of the laser frequency are generated. Considerable progress have been made in the last few years, with the observation of harmonic orders higher that 200, extending the emission down to 3 nm. Besides its fundamental interest, this XUV emission represents a new source with unique properties of coherence and ultrashort (femtosecond) duration. A growing number of applications are reported, ranging from atomic and molecular spectroscopy to solid-state and plasma physics. (authors)

  15. Molecular frame photoemission by a comb of elliptical high-order harmonics: a sensitive probe of both photodynamics and harmonic complete polarization state.

    Veyrinas, K; Gruson, V; Weber, S J; Barreau, L; Ruchon, T; Hergott, J-F; Houver, J-C; Lucchese, R R; Salières, P; Dowek, D

    2016-12-16

    Due to the intimate anisotropic interaction between an XUV light field and a molecule resulting in photoionization (PI), molecular frame photoelectron angular distributions (MFPADs) are most sensitive probes of both electronic/nuclear dynamics and the polarization state of the ionizing light field. Consequently, they encode the complex dipole matrix elements describing the dynamics of the PI transition, as well as the three normalized Stokes parameters s 1 , s 2 , s 3 characterizing the complete polarization state of the light, operating as molecular polarimetry. The remarkable development of advanced light sources delivering attosecond XUV pulses opens the perspective to visualize the primary steps of photochemical dynamics in time-resolved studies, at the natural attosecond to few femtosecond time-scales of electron dynamics and fast nuclear motion. It is thus timely to investigate the feasibility of measurement of MFPADs when PI is induced e.g., by an attosecond pulse train (APT) corresponding to a comb of discrete high-order harmonics. In the work presented here, we report MFPAD studies based on coincident electron-ion 3D momentum imaging in the context of ultrafast molecular dynamics investigated at the PLFA facility (CEA-SLIC), with two perspectives: (i) using APTs generated in atoms/molecules as a source for MFPAD-resolved PI studies, and (ii) taking advantage of molecular polarimetry to perform a complete polarization analysis of the harmonic emission of molecules, a major challenge of high harmonic spectroscopy. Recent results illustrating both aspects are reported for APTs generated in unaligned SF 6 molecules by an elliptically polarized infrared driving field. The observed fingerprints of the elliptically polarized harmonics include the first direct determination of the complete s 1 , s 2 , s 3 Stokes vector, equivalent to (ψ, ε, P), the orientation and the signed ellipticity of the polarization ellipse, and the degree of polarization P. They are

  16. Second-harmonic generation of Lamb modes in a solid layer supported by a semi-infinite substrate

    Deng Mingxi

    2004-01-01

    Using a second-order perturbation approximation and a modal expansion analysis approach, this study develops an effective technique for studying the generation of second harmonics of Lamb modes propagating in the composite structure consisting of a solid layer supported by a semi-infinite substrate. The nonlinearity in the elastic wave motion process can result in the generation of second harmonics of primary Lamb mode propagation in the composite structure, and this nonlinearity may be treated as a second-order perturbation of the elastic response of the primary waves. There are second-order bulk and surface/interface driving sources in the composite structure wherever the primary Lamb modes propagate. These driving sources can be thought of as the forcing functions of a finite series of double-frequency Lamb modes (DFLMs) in terms of the approach of modal expansion analysis for waveguide excitation. The fields of the second harmonics of the primary Lamb modes can be regarded as superpositions of the fields of a finite series of DFLMs. Although Lamb modes are dispersive, the field of one DFLM component can have a cumulative growth effect when its phase velocity exactly or approximately equals that of a primary Lamb mode. The formal solutions for the second harmonics of Lamb modes have been obtained. The numerical simulations clearly show the physical process of the generation of second harmonics of Lamb modes in the composite structure. The complicated problems of second-harmonic generation of Lamb modes have been exactly determined within the second-order perturbation approximation

  17. More efficient second harmonic generation of whispering gallery modes by selective out-coupling

    Trainor, Luke S.; Sedlmeir, Florian; Peuntinger, Christian; Schwefel, Harald G. L.

    2017-01-01

    We demonstrate second harmonic generation (SHG) in an $x$-cut congruent lithium niobate (LN) whispering gallery mode resonator. We first show theoretically that independent control of the coupling of the pump and signal modes is optimal for high conversion rates. A scheme based on our earlier work in Ref. [1] is then implemented experimentally to verify this. Thereby we are able to improve on the efficiency of SHG by more than an order of magnitude by selectively out-coupling using a LN prism...

  18. Discrimination of collagen in normal and pathological dermis through polarization second harmonic generation

    Su, Ping-Jung; Chen, Wei-Liang; Hong, Jin-Bon; Li, Tsung-Hsien; Wu, Ruei-Jr; Chou, Chen-Kuan; Lin, Sung-Jan; Dong, Chen-Yuan

    2010-02-01

    We used polarization-resolved, second harmonic generation (P-SHG) microscopy at single pixel resolution for medical diagnosis of pathological skin dermis, and found that P-SHG can be used to distinguish normal and dermal pathological conditions of keloid, morphea, and dermal elastolysis. We find that the histograms of the d33/d31 ratio for the pathological skins to contain two peak values and to be wider than that of the normal case, suggesting that the pathological dermal collagen fibers tend to be more structurally heterogeneous. Our work demonstrates that pixel-resolved, second-order susceptibility microscopy is effective for detecting heterogeneity in spatial distribution of collagen fibers.

  19. Efficient second- and third-harmonic radiation generation from relativistic laser-plasma interactions

    Singh, Mamta; Gupta, D. N., E-mail: dngupta@physics.du.ac.in [Department of Physics and Astrophysics, University of Delhi, Delhi 110 007 (India); Suk, H. [Department of Physics and Photon Science, Gwangju Institute of Science and Technology, Gwangju 500 712 (Korea, Republic of)

    2015-06-15

    We propose an idea to enhance the efficiency of second- and third-harmonic generation by considering the amplitude-modulation of the fundamental laser pulse. A short-pulse laser of finite spot size is modeled as amplitude modulated in time. Amplitude-modulation of fundamental laser contributes in quiver velocity of the plasma electrons and produces the strong plasma-density perturbations, thereby increase in current density at second- and third-harmonic frequency. In a result, the conversion efficiency of harmonic generation increases significantly. Power conversion efficiency of harmonic generation process is the increasing function of the amplitude-modulation parameter of the fundamental laser beam. Harmonic power generated by an amplitude modulated laser is many folds higher than the power obtained in an ordinary case.

  20. Efficient second- and third-harmonic radiation generation from relativistic laser-plasma interactions

    Singh, Mamta; Gupta, D. N.; Suk, H.

    2015-01-01

    We propose an idea to enhance the efficiency of second- and third-harmonic generation by considering the amplitude-modulation of the fundamental laser pulse. A short-pulse laser of finite spot size is modeled as amplitude modulated in time. Amplitude-modulation of fundamental laser contributes in quiver velocity of the plasma electrons and produces the strong plasma-density perturbations, thereby increase in current density at second- and third-harmonic frequency. In a result, the conversion efficiency of harmonic generation increases significantly. Power conversion efficiency of harmonic generation process is the increasing function of the amplitude-modulation parameter of the fundamental laser beam. Harmonic power generated by an amplitude modulated laser is many folds higher than the power obtained in an ordinary case

  1. Crystallographic Mapping of Guided Nanowires by Second Harmonic Generation Polarimetry.

    Neeman, Lior; Ben-Zvi, Regev; Rechav, Katya; Popovitz-Biro, Ronit; Oron, Dan; Joselevich, Ernesto

    2017-02-08

    The growth of horizontal nanowires (NWs) guided by epitaxial and graphoepitaxial relations with the substrate is becoming increasingly attractive owing to the possibility of controlling their position, direction, and crystallographic orientation. In guided NWs, as opposed to the extensively characterized vertically grown NWs, there is an increasing need for understanding the relation between structure and properties, specifically the role of the epitaxial relation with the substrate. Furthermore, the uniformity of crystallographic orientation along guided NWs and over the substrate has yet to be checked. Here we perform highly sensitive second harmonic generation (SHG) polarimetry of polar and nonpolar guided ZnO NWs grown on R-plane and M-plane sapphire. We optically map large areas on the substrate in a nondestructive way and find that the crystallographic orientations of the guided NWs are highly selective and specific for each growth direction with respect to the substrate lattice. In addition, we perform SHG polarimetry along individual NWs and find that the crystallographic orientation is preserved along the NW in both polar and nonpolar NWs. While polar NWs show highly uniform SHG along their axis, nonpolar NWs show a significant change in the local nonlinear susceptibility along a few micrometers, reflected in a reduction of 40% in the ratio of the SHG along different crystal axes. We suggest that these differences may be related to strain accumulation along the nonpolar wires. We find SHG polarimetry to be a powerful tool to study both selectivity and uniformity of crystallographic orientations of guided NWs with different epitaxial relations.

  2. Inducing elliptically polarized high-order harmonics from aligned molecules with linearly polarized femtosecond pulses

    Etches, Adam; Madsen, Christian Bruun; Madsen, Lars Bojer

    2010-01-01

    A recent paper reported elliptically polarized high-order harmonics from aligned N2 using a linearly polarized driving field [X. Zhou et al., Phys. Rev. Lett. 102, 073902 (2009)]. This observation cannot be explained in the standard treatment of the Lewenstein model and has been ascribed to many...

  3. The Distortion Theorems for Harmonic Mappings with Analytic Parts Convex or Starlike Functions of Order β

    Mengkun Zhu

    2015-01-01

    Full Text Available Some sharp estimates of coefficients, distortion, and growth for harmonic mappings with analytic parts convex or starlike functions of order β are obtained. We also give area estimates and covering theorems. Our main results generalise those of Klimek and Michalski.

  4. Conformation, orientation and interaction in molecular monolayers: A surface second harmonic and sum frequency generation study

    Superfine, R.; Huang, J.Y.; Shen, Y.R.

    1988-12-01

    We have used sum frequency generation (SFG) to study the order in a silane monolayer before and after the deposition of a coadsorbed liquid crystal monolayer. We observe an increase in the order of the chain of the silane molecule induced by the interpenetration of the liquid crystal molecules. By using second harmonic generation (SHG) and SFG, we have studied the orientation and conformation of the liquid crystal molecule on clean and silane coated glass surfaces. On both surfaces, the biphenyl group is tilted by 70 degree with the alkyl chain end pointing away from the surface. The shift in the C-H stretch frequencies in the coadsorbed system indicates a significant interaction between molecules. 9 refs., 3 figs

  5. Theory of nonlinear harmonic generation in free-electron lasers with helical wigglers

    Geloni, G.; Saldin, E.; Schneidmiller, E.; Yurkov, M.

    2007-05-01

    CoherentHarmonicGeneration (CHG), and in particularNonlinearHarmonicGeneration (NHG), is of importance for both short wavelength Free-Electron Lasers (FELs), in relation with the achievement of shorter wavelengths with a fixed electron-beam energy, and high-average power FEL resonators, in relation with destructive effects of higher harmonics radiation on mirrors. In this paper we present a treatment of NHG from helical wigglers with particular emphasis on the second harmonic. Our study is based on an exact analytical solution of Maxwell's equations, derived with the help of a Green's function method. In particular, we demonstrate that nonlinear harmonic generation (NHG) fromhelicalwigglers vanishes on axis. Our conclusion is in open contrast with results in literature, that include a kinematical mistake in the description of the electron motion. (orig.)

  6. Time-resolved photoemission micro-spectrometer using higher-order harmonics of Ti:sapphire laser

    Azuma, J.; Kamada, M.; Kondo, Y.

    2004-01-01

    Full text: A new photoemission spectrometer is under construction for the photoemission microscopy and the time-resolved pump- probe experiment. The higher order harmonics of the Ti:sapphire laser is used as the light source of the VUV region in this system. Because the fundamental laser is focused tightly into the rare gas jet to generate the higher order harmonics, the spot size of the laser, in other words, the spot size of the VUV light source is smaller than a few tens of micrometer. This smallness of the spot size has advantage for the microscopy. In order to compensate the low flux of the laser harmonics, a multilayer-coated schwaltzshild optics was designed. The multilayers play also as the monochromatic filter. The spatial resolution of this schwaltzshild system is found to be less than 1 micrometer by the ray-tracing calculations. A main chamber of the system is equipped with a time-of-flight energy analyzer to improve the efficiency of the electron detection. The main chamber and the gas chamber are separated by a differential pumping chamber and a thin Al foil. The system is designed for the study of the clean surface. It will be capable to perform the sub-micron photoemission microscopy and the femto-second pump-probe photoemission study for the various photo-excited dynamics on clean surfaces

  7. Controllable excitation of higher-order rogue waves in nonautonomous systems with both varying linear and harmonic external potentials

    Jia, Heping; Yang, Rongcao; Tian, Jinping; Zhang, Wenmei

    2018-05-01

    The nonautonomous nonlinear Schrödinger (NLS) equation with both varying linear and harmonic external potentials is investigated and the semirational rogue wave (RW) solution is presented by similarity transformation. Based on the solution, the interactions between Peregrine soliton and breathers, and the controllability of the semirational RWs in periodic distribution and exponential decreasing nonautonomous systems with both linear and harmonic potentials are studied. It is found that the harmonic potential only influences the constraint condition of the semirational solution, the linear potential is related to the trajectory of the semirational RWs, while dispersion and nonlinearity determine the excitation position of the higher-order RWs. The higher-order RWs can be partly, completely and biperiodically excited in periodic distribution system and the diverse excited patterns can be generated for different parameter relations in exponential decreasing system. The results reveal that the excitation of the higher-order RWs can be controlled in the nonautonomous system by choosing dispersion, nonlinearity and external potentials.

  8. Effects of Energy Chirp on Echo-Enabled Harmonic Generation Free-Electron Lasers

    Huang, Z.

    2009-01-01

    We study effects of energy chirp on echo-enabled harmonic generation (EEHG). Analytical expressions are compared with numerical simulations for both harmonic and bunching factors. We also discuss the EEHG free-electron laser bandwidth increase due to an energy-modulated beam and its pulse length dependence on the electron energy chirp

  9. Low-order-mode harmonic multiplying gyrotron traveling-wave amplifier in W band

    Yeh, Y. S.; Chen, C. H.; Yang, S. J.; Lai, C. H.; Lin, T. Y.; Lo, Y. C.; Hong, J. W.; Hung, C. L.; Chang, T. H.

    2012-01-01

    Harmonic multiplying gyrotron traveling-wave amplifiers (gyro-TWAs) allow for magnetic field reduction and frequency multiplication. To avoid absolute instabilities, this work proposes a W-band harmonic multiplying gyro-TWA operating at low-order modes. By amplifying a fundamental harmonic TE 11 drive wave, the second harmonic component of the beam current initiates a TE 21 wave to be amplified. Absolute instabilities in the gyro-TWA are suppressed by shortening the interaction circuit and increasing wall losses. Simulation results reveal that compared with Ka-band gyro-TWTs, the lower wall losses effectively suppress absolute instabilities in the W-band gyro-TWA. However, a global reflective oscillation occurs as the wall losses decrease. Increasing the length or resistivity of the lossy section can reduce the feedback of the oscillation to stabilize the amplifier. The W-band harmonic multiplying gyro-TWA is predicted to yield a peak output power of 111 kW at 98 GHz with an efficiency of 25%, a saturated gain of 26 dB, and a bandwidth of 1.6 GHz for a 60 kV, 7.5 A electron beam with an axial velocity spread of 8%.

  10. Variable speed DFIG wind energy system for power generation and harmonic current mitigation

    Gaillard, A.; Saadate, S. [Groupe de Recherche en Electrotechnique et Electronique de Nancy, Nancy Universite - Universite Henri Poincare Nancy 1, BP239, 54506 Vandoeuvre les Nancy Cedex (France); Poure, P. [Laboratoire d' Instrumentation Electronique de Nancy, Nancy Universite - Universite Henri Poincare Nancy 1, BP239, 54506 Vandoeuvre les Nancy Cedex (France); Machmoum, M. [IREENA, 37 Boulevard de l' Universite, BP 406, 44602 Saint-Nazaire Cedex (France)

    2009-06-15

    This paper presents a novel approach for simultaneous power generation and harmonic current mitigation using variable speed WECS with DFIG. A new control strategy is proposed to upgrade the DFIG control to achieve simultaneously a green active and reactive power source with active filtering capability. To ensure high filtering performance, we studied an improved harmonic isolator in the time-domain, based on a new high selectivity filter developed in our laboratory. We examined two solutions for harmonic current mitigation: first, by compensating the whole harmonic component of the grid currents or second, by selective isolation of the predominant harmonic currents to ensure active filtering of the 5th and 7th harmonics. Simulation results for a 3 MW WECS with DFIG confirm the effectiveness and the performance of the two proposed approaches. (author)

  11. Coherent control of third-harmonic-generation by a waveform-controlled two-colour laser field

    Chen, W-J; Chen, W-F; Pan, C-L; Lin, R-Y; Lee, C-K

    2013-01-01

    We investigate generation of the third harmonic (TH; λ = 355 nm) signal by two-colour excitation (λ = 1064 nm and its second harmonic, λ = 532 nm) in argon gas, with emphasis on the influence of relative phases and intensities of the two-colour pump on the third-order nonlinear frequency conversion process. Perturbative nonlinear optics predicts that the TH signal will oscillate periodically with the relative phases of the two-colour driving laser fields due to the interference of TH signals from a direct third-harmonic-generation (THG) channel and a four-wave mixing (FWM) channel. For the first time, we show unequivocal experimental evidence of this effect. A modulation level as high as 0.35 is achieved by waveform control of the two-colour laser field. The modulation also offers a promising way to retrieve the relative phase value of the two-colour laser field. (letter)

  12. A novel harmonic control approach of distributed generation converters in a weak microgrid

    Ding, Guangqian; Gao, Feng; Tang, Yi

    2014-01-01

    as well as the long distance communication between the PCC and the converter are fully eliminated. In order to avoid overcompensation, a harmonic current limitation algorithm is implemented in the control loop. bBy properly dispatching the harmonic compensation capability, multiple DG unites can...

  13. Generalized Reduced Order Model Generation, Phase I

    National Aeronautics and Space Administration — M4 Engineering proposes to develop a generalized reduced order model generation method. This method will allow for creation of reduced order aeroservoelastic state...

  14. High-order-harmonic generation in atomic and molecular systems

    Suarez, N.; Chacon, A.; Perez-Hernandez, J.A.; Biegert, J.; Lewenstein, M.; Ciappina, Marcelo F.

    2017-01-01

    Roč. 95, č. 3 (2017), 1-20, č. článku 033415. ISSN 2469-9926 R&D Projects: GA MŠk EF15_008/0000162; GA MŠk LQ1606 EU Projects: European Commission(XE) 654148 - LASERLAB-EUROPE Grant - others:ELI Beamlines(XE) CZ.02.1.01/0.0/0.0/15_008/0000162 Institutional support: RVO:68378271 Keywords : above-threshold ionization * laser fields * ions * pulses Subject RIV: BL - Plasma and Gas Discharge Physics OBOR OECD: Fluids and plasma physics (including surface physics) Impact factor: 2.925, year: 2016

  15. Generation of even harmonics in a relativistic laser plasma of atomic clusters

    Krainov, V.P.; Rastunkov, V.S.

    2004-01-01

    It is shown that the irradiation of atomic clusters by a superintense femtosecond laser pulse gives rise to various harmonics of the laser field. They arise as a result of elastic collisions of free electrons with atomic ions inside the clusters in the presence of the laser filed. The yield of even harmonics whose electromagnetic field is transverse is attributed to the relativism of the motion of electrons and the consideration of their drift velocity associated with the internal ionization of atoms and atomic ions of a cluster. These harmonics are emitted in the same direction as odd harmonics. The conductivities and electromagnetic fields of the harmonics are calculated. The generation efficiency of the harmonics slowly decreases as the harmonic number increases. The generation of even harmonics ceases when the drift velocity of electrons becomes equal to zero and only the oscillation velocity of electrons is nonzero. The results can also be applied to the irradiation of solid-state targets inside a skin layer

  16. Robust enhancement of high harmonic generation via attosecond control of ionization.

    Bruner, Barry D; Krüger, Michael; Pedatzur, Oren; Orenstein, Gal; Azoury, Doron; Dudovich, Nirit

    2018-04-02

    High-harmonic generation (HHG) is a powerful tool to generate coherent attosecond light pulses in the extreme ultraviolet. However, the low conversion efficiency of HHG at the single atom level poses a significant practical limitation for many applications. Enhancing the efficiency of the process defines one of the primary challenges in the application of HHG as an advanced XUV source. In this work, we demonstrate a new mechanism, which in contrast to current methods, enhances the HHG conversion efficiency purely on a single particle level. We show that using a bichromatic driving field, sub-optical-cycle control and enhancement of the tunnelling ionization rate can be achieved, leading to enhancements in HHG efficiency by up to two orders of magnitude. Our method advances the perspectives of HHG spectroscopy, where isolating the single particle response is an essential component, and offers a simple route toward scalable, robust XUV sources.

  17. Passive energy jitter reduction in the cascaded third harmonic generation process

    Yan, L; Du, Y; You, Y; Sun, X; Wang, D; Hua, J; Shi, J; Lu, W; Huang, W; Chen, H; Tang, C; Huang, Z

    2014-01-01

    In free electron laser (FEL) systems with ultraviolet (UV) laser driven injectors, a highly stable UV source generated through cascaded third harmonic generation (THG) from an infrared (IR) source is a key element in guaranteeing the acceptable current jitter at the undulator. In this letter, the negative slope of the THG efficiency for high intensity ultrashort IR pulses is revealed to be a passive stabilization mechanism for energy jitter reduction in UV. A reduction of 2.5 times the energy jitter in UV is demonstrated in the experiment and simulations show that the energy jitter in UV can be reduced by more than one order of magnitude if the energy jitter in IR is less than 3%, with proper design of the THG efficiency curve, fulfilling the challenging requirement for UV laser stability in a broad scope of applications such as the photoinjector of x-ray FELs. (letter)

  18. Influences of interfacial properties on second-harmonic generation of Lamb waves propagating in layered planar structures

    Deng Mingxi; Wang Ping; Lv Xiafu

    2006-01-01

    This paper describes influences of interfacial properties on second-harmonic generation of Lamb waves propagating in layered planar structures. The nonlinearity in the elastic wave propagation is treated as a second-order perturbation of the linear elastic response. Due to the kinematic nonlinearity and the elastic nonlinearity of materials, there are second-order bulk and surface/interface driving sources in layered planar structures through which Lamb waves propagate. These driving sources can be thought of as forcing functions of a series of double frequency lamb waves (DFLWs) in terms of the approach of modal expansion analysis for waveguide excitation. The total second-harmonic fields consist of a summation of DFLWs in the corresponding stress-free layered planar structures. The interfacial properties of layered planar structures can be described by the well-known finite interfacial stiffness technique. The normal and tangential interfacial stiffness constants can be coupled with the equation governing the expansion coefficient of each DFLW component. On the other hand, the normal and tangential interfacial stiffness constants are associated with the degree of dispersion between Lamb waves and DFLWs. Theoretical analyses and numerical simulations indicate that the efficiency of second-harmonic generation by Lamb wave propagation is closely dependent on the interfacial properties of layered structures. The potential of using the effect of second-harmonic generation by Lamb wave propagation to characterize the interfacial properties of layered structures are considered. Some experimental results are presented

  19. Total internal reflection second-harmonic generation: probing the alkane water interface

    Conboy, J.C.; Daschbach, J.L.; Richmond, G.L.

    1994-01-01

    Total internal reflection Second-Harmonic Generation (SHG) has been used to study a series of neat n-alkane/water interfaces. Polarization and incident angular-dependent measurements of the SH response show good agreement with theoretical predictions. Analysis of the incident and polarization angular-dependent SH response allows for determination of the nonlinear optical properties of molecules comprising the interfacial region. Based on Kleinman symmetry, the measured surface nonlinear susceptibilities suggest a high degree of interfacial order for octane and decane with less order indicated by the odd carbon n-alkanes examined, heptane and nonane. The SH response in reflection and transmission has been measured under a Total Internal Reflection (TIR) of the fundamental. The measured nonlinear susceptibilities in each case are found to be identical. (orig.)

  20. Tunable ultraviolet radiation by second-harmonic generation in periodically poled lithium tantalate.

    Meyn, J P; Fejer, M M

    1997-08-15

    We describe electric-field poling of fine-pitch ferroelectric domain gratings in lithium tantalate and characterization of nonlinear-optical properties by single-pass quasi-phase-matched second-harmonic generation (QPM SHG). With a 7.5-microm-period grating, the observed effective nonlinear coefficient for first-order QPM SHG of 532-nm radiation is 9 pm/V, whereas for a grating with a 2.625-microm period, 2.6 pm/V was observed for second-order QPM SHG of 325-nm radiation. These values are 100% and 55% of the theoretically expected values, respectively. We derive a temperature-dependent Sellmeier equation for lithium tantalate that is valid deeper into the UV than currently available results, based on temperature-tuning experiments at different QPM grating periods combined with refractive-index data in the literature.

  1. Development of the RTP crystal applications for Q-switching operation and second harmonics generation

    Alnayli, R.Sh.

    2010-01-01

    Complete text of publication follows. A dialed theoretical studies on performances of the ideal RTP crystal for the electro optical applications as Q-switching laser operation and for nonlinear optics application as second harmonics generation are accomplished in this paper. Single or pair RTP crystal of excellent quality with dimensions 5 x 5 x 7.5 mm 3 have proposed as element model to combined Q-switching operation and frequency doublers for 1.06 μm wave length laser. In order to get and interpolate the optimum conditions to combined both of these operations by application this RTP model. The main am of this work was investigated the most influent parameters on the performance of the electro optical Q-switching laser operation such as, the voltage requirement, contrast and extinction ratios, the birefringence effective and withstand threshold on the other hand the influences of the ray walk off, thermal effective on the efficiency of the second harmonics generation as well are investigated. The results were satisfied for the goals of this paper.

  2. A feasibility study of low-order harmonics expansion applied to loading pattern search

    Shaohong, Z.; Dong, L.; Tao, W. [Shanghai Jiao Tong Univ., 1954 Hua Shan Road, Shanghai, 200030 (China); Chao, Y. A. [Westinghouse Electric Company, P. O. Box 355, Pittsburgh, PA 15230-0355 (United States)

    2006-07-01

    Despite significant progress in core loading pattern search methods over years, there still remains the issue of large computing workload and the need for improving the speed of evaluating loading pattern candidates during the search process. This paper focuses on improving the computing speed for loading pattern evaluation, rather than the method of searching for the patterns. A low order harmonics expansion method for flux distribution representation is proposed for fast LP evaluation application. The novel feature of the method is the separation of the short range local perturbation effect from the long range global tilt effect. The latter effect can be captured by low order harmonics expansion. Demonstration examples are presented to show that even for extremely large perturbations induced by fuel shuffling the proposed method can accurately calculate the flux distribution for the LP with very minimal computation. (authors)

  3. Third harmonic generation of high power far infrared radiation in semiconductors

    Urban, M.

    1996-04-01

    In this work we investigated the third harmonic generation of high power infrared radiation in doped semiconductors with emphasis on the conversion efficiency. The third harmonic generation effect is based on the nonlinear response of the conduction band electrons in the semiconductor with respect to the electric field of the incident electromagnetic wave. Because this work is directed towards a proposed application in fusion plasma diagnostics, the experimental requirements for the radiation source at the fundamental frequency are roughly given as follows: a wavelength of the radiation at the fundamental frequency in the order of 1 mm and an incident power greater than 1 MW. The most important experiments of this work were performed using the high power far infrared laser of the CRPP. With this laser a new laser line was discovered, which fits exactly the source specifications given above: the wavelength is 676 μm and the maximum power is up to 2 MW. Additional experiments were carried out using a 496 μm laser and a 140 GHz (2.1 mm) gyrotron. The main experimental progress with respect to previous work in this field is, in addition to the use of a very high power laser, the possibility of an absolute calibration of the detectors for the far infrared radiation and the availability of a new type of detector with a very fast response. This detector made it possible to measure the power at the fundamental as well as the third harmonic frequency with full temporal resolution of the fluctuations during the laser pulse. Therefore the power dependence of the third harmonic generation efficiency could be measured directly. The materials investigated were InSb as an example of a narrow gap semiconductor and Si as standard material. The main results are: narrow gap semiconductors indeed have a highly nonlinear electronic response, but the narrow band gap leads at the same time to a low power threshold for internal breakdown, which is due to impact ionization. (author) figs

  4. A novel method for detecting second harmonic ultrasonic components generated from fastened bolts

    Fukuda, Makoto; Imano, Kazuhiko

    2012-09-01

    This study examines the use of ultrasonic second harmonic components in the quality control of bolt-fastened structures. An improved method for detecting the second harmonic components, from a bolt fastened with a nut, using the transmission method is constructed. A hexagon head iron bolt (12-mm diameter and 25-mm long) was used in the experiments. The bolt was fastened using a digital torque wrench. The second harmonic component increased by approximately 20 dB before and after the bolt was fastened. The sources of second harmonic components were contact acoustic nonlinearity in the screw thread interfaces of the bolt-nut and were the plastic deformation in the bolt with fastening bolt. This result was improved by approximately 10 dB compared with previous our method. Consequently, usefulness of the novel method for detecting second harmonic ultrasonic components generated from fastened bolt was confirmed.

  5. Multiphoton excitation and high-harmonics generation in topological insulator.

    Avetissian, H K; Avetissian, A K; Avchyan, B R; Mkrtchian, G F

    2018-05-10

    Multiphoton interaction of coherent electromagnetic radiation with 2D metallic carriers confined on the surface of the 3D topological insulator is considered. A microscopic theory describing the nonlinear interaction of a strong wave and metallic carriers with many-body Coulomb interaction is developed. The set of integrodifferential equations for the interband polarization and carrier occupation distribution is solved numerically. Multiphoton excitation of Fermi-Dirac sea of 2D massless carriers is considered for a THz pump wave. It is shown that in the moderately strong pump wave field along with multiphoton interband/intraband transitions the intense radiation of high harmonics takes place.

  6. Multiphoton excitation and high-harmonics generation in topological insulator

    Avetissian, H. K.; Avetissian, A. K.; Avchyan, B. R.; Mkrtchian, G. F.

    2018-05-01

    Multiphoton interaction of coherent electromagnetic radiation with 2D metallic carriers confined on the surface of the 3D topological insulator is considered. A microscopic theory describing the nonlinear interaction of a strong wave and metallic carriers with many-body Coulomb interaction is developed. The set of integrodifferential equations for the interband polarization and carrier occupation distribution is solved numerically. Multiphoton excitation of Fermi–Dirac sea of 2D massless carriers is considered for a THz pump wave. It is shown that in the moderately strong pump wave field along with multiphoton interband/intraband transitions the intense radiation of high harmonics takes place.

  7. Modeling of second-harmonic generation of circumferential guided wave propagation in a composite circular tube

    Li, Mingliang; Deng, Mingxi; Gao, Guangjian; Xiang, Yanxun

    2018-05-01

    This paper investigated modeling of second-harmonic generation (SHG) of circumferential guided wave (CGW) propagation in a composite circular tube, and then analyzed the influences of interfacial properties on the SHG effect of primary CGW. Here the effect of SHG of primary CGW propagation is treated as a second-order perturbation to its linear wave response. Due to the convective nonlinearity and the inherent elastic nonlinearity of material, there are second-order bulk driving forces and surface/interface driving stresses in the interior and at the surface/interface of a composite circular tube, when a primary CGW mode propagates along its circumference. Based on the approach of modal expansion analysis for waveguide excitation, the said second-order driving forces/stresses are regarded as the excitation sources to generate a series of double-frequency CGW modes that constitute the second-harmonic field of the primary CGW propagation. It is found that the modal expansion coefficient of each double-frequency CGW mode is closely related to the interfacial stiffness constants that are used to describe the interfacial properties between the inner and outer circular parts of the composite tube. Furthermore, changes in the interfacial stiffness constants essentially influence the dispersion relation of CGW propagation. This will remarkably affect the efficiency of cumulative SHG of primary CGW propagation. Some finite element simulations have been implemented of response characteristics of cumulative SHG to the interfacial properties. Both the theoretical analyses and numerical simulations indicate that the effect of cumulative SHG is found to be much more sensitive to changes in the interfacial properties than primary CGW propagation. The potential of using the effect of cumulative SHG by primary CGW propagation to characterize a minor change in the interfacial properties is considered.

  8. A Low-Order Harmonic Elimination Scheme for Induction Motor Drives Using a Multilevel Octadecagonal Space Vector Structure With a Single DC Source

    Boby, Mathews; Rahul, Arun; Gopakumar, K.

    2018-01-01

    Conventional voltage-source inverters used for induction motor drives generate a hexagonal space vector structure. In the overmodulation range, the hexagonal space vector structure generates low-order harmonics in the phase voltage resulting in low-order torque ripple in the motor. Inverter...... topologies with an octadecagonal (18 sided) space vector structure eliminate fifth-, seventh-, eleventh-, and thirteenth-order harmonics from the phase voltage, and hence, the dominant sixth- and twelfth-order torque ripple generation is eliminated. Octadecagonal space vector structures proposed in the past...... require multiple dc sources, which makes four-quadrant operation of the drive system difficult and costly. In this paper, the formation of a multilevel nine-concentric octadecagonal space vector structure using a single dc source is proposed. Detailed experimental results, using open-loop V/f control...

  9. Resonant third-harmonic generation of a short-pulse laser from electron-hole plasmas

    Kant, Niti [Department of Physics, Lovely Professional University, Phagwara, Punjab 144 402 (India); Nandan Gupta, Devki [Department of Physics and Astrophysics, University of Delhi, Delhi 110 007 (India); Suk, Hyyong [Advanced Photonics Research Institute (APRI) and Graduate Program of Photonics and Applied Physics, Gwangju Institute of Science and Technology, Gwangju 500 712 (Korea, Republic of)

    2012-01-15

    In semiconductors, free carriers are created in pairs in inter-band transitions and consist of an electron and its corresponding hole. At very high carrier densities, carrier-carrier collisions dominate over carrier-lattice collisions and carriers begin to behave collectively to form plasma. Here, we apply a short-pulse laser to generate third-harmonic radiation from a semiconductor plasma (electron-hole plasma) in the presence of a transverse wiggler magnetic-field. The process of third-harmonic generation of an intense short-pulse laser is resonantly enhanced by the magnetic wiggler, i.e., wiggler magnetic field provides the necessary momentum to third-harmonic photons. In addition, a high-power laser radiation, propagating through a semiconductor imparts an oscillatory velocity to the electrons and exerts a ponderomotive force on electrons at the third-harmonic frequency of the laser. This oscillatory velocity produces a third-harmonic longitudinal current. And due to the beating of the longitudinal electron velocity and the wiggler magnetic field, a transverse third-harmonic current is produced that drives third-harmonic electromagnetic radiation. It is finally observed that for a specific wiggler wave number value, the phase-matching conditions for the process are satisfied, leading to resonant enhancement in the energy conversion efficiency.

  10. Resonant third-harmonic generation of a short-pulse laser from electron-hole plasmas

    Kant, Niti; Nandan Gupta, Devki; Suk, Hyyong

    2012-01-01

    In semiconductors, free carriers are created in pairs in inter-band transitions and consist of an electron and its corresponding hole. At very high carrier densities, carrier-carrier collisions dominate over carrier-lattice collisions and carriers begin to behave collectively to form plasma. Here, we apply a short-pulse laser to generate third-harmonic radiation from a semiconductor plasma (electron-hole plasma) in the presence of a transverse wiggler magnetic-field. The process of third-harmonic generation of an intense short-pulse laser is resonantly enhanced by the magnetic wiggler, i.e., wiggler magnetic field provides the necessary momentum to third-harmonic photons. In addition, a high-power laser radiation, propagating through a semiconductor imparts an oscillatory velocity to the electrons and exerts a ponderomotive force on electrons at the third-harmonic frequency of the laser. This oscillatory velocity produces a third-harmonic longitudinal current. And due to the beating of the longitudinal electron velocity and the wiggler magnetic field, a transverse third-harmonic current is produced that drives third-harmonic electromagnetic radiation. It is finally observed that for a specific wiggler wave number value, the phase-matching conditions for the process are satisfied, leading to resonant enhancement in the energy conversion efficiency.

  11. Coherent soft X-ray high-order harmonics using tight-focusing laser pulses in the gas mixture.

    Lu, Faming; Xia, Yuanqin; Zhang, Sheng; Chen, Deying; Zhao, Yang; Liu, Bin

    2014-01-01

    We experimentally study the harmonics from a Xe-He gas mixture using tight-focusing femtosecond laser pulses. The spectrum in the mixed gases exhibits an extended cutoff region from the harmonic H21 to H27. The potential explanation is that the harmonics photons from Xe contribute the electrons of He atoms to transmit into the excited-state. Therefore, the harmonics are emitted from He atoms easily. Furthermore, we show that there are the suppressed harmonics H15 and H17 in the mixed gases. The underlying mechanism is the destructive interference between harmonics generated from different atoms. Our results indicate that HHG from Xe-He gas mixture is an efficient method of obtaining the coherent soft X-ray source.

  12. Higher order mode damping of a higher harmonic superconducting cavity for SSRF

    Yu Haibo; Liu Jianfei; Hou Hongtao; Ma Zhenyu; Feng Xiqiang; Mao Dongqing

    2012-01-01

    Adopting a higher harmonic cavity on a synchrotron radiation facility can increase the beam lifetime and suppress the beam instability. In this paper, we report the simulation and preliminary design on higher order modes (HOMs) damping of the designed and fabricated higher harmonic superconducting cavity for Shanghai Synchrotron Radiation Facility (SSRF). The requirements for the HOM damping are analyzed, and the length and location of the HOM damper are optimized by using the SEAFISH code. The results show that the design can provide heavy damping for harmful HOMs with decreased impedance, and the beam instability requirement of SSRF can be satisfied. By using the ABCI code, the loss factor is obtained and the HOM power is estimated. (authors)

  13. Generation of µW level plateau harmonics at high repetition rate.

    Hädrich, S; Krebs, M; Rothhardt, J; Carstens, H; Demmler, S; Limpert, J; Tünnermann, A

    2011-09-26

    The process of high harmonic generation allows for coherent transfer of infrared laser light to the extreme ultraviolet spectral range opening a variety of applications. The low conversion efficiency of this process calls for optimization or higher repetition rate intense ultrashort pulse lasers. Here we present state-of-the-art fiber laser systems for the generation of high harmonics up to 1 MHz repetition rate. We perform measurements of the average power with a calibrated spectrometer and achieved µW harmonics between 45 nm and 61 nm (H23-H17) at a repetition rate of 50 kHz. Additionally, we show the potential for few-cycle pulses at high average power and repetition rate that may enable water-window harmonics at unprecedented repetition rate. © 2011 Optical Society of America

  14. Contribution of the magnetic resonance to the third harmonic generation from a fishnet metamaterial

    Reinhold, J.; Shcherbakov, M. R.; Chipouline, A.; Panov, V. I.; Helgert, C.; Paul, T.; Rockstuhl, C.; Lederer, F.; Kley, E.-B.; Tünnermann, A.; Fedyanin, A. A.; Pertsch, T.

    2012-09-01

    We investigate experimentally and theoretically the third harmonic generated by a double-layer fishnet metamaterial. To unambiguously disclose most notably the influence of the magnetic resonance, the generated third harmonic was measured as a function of the angle of incidence. It is shown experimentally and numerically that when the magnetic resonance is excited by a pump beam, the angular dependence of the third harmonic signal has a local maximum at an incidence angle of θ≃20∘. This maximum is shown to be a fingerprint of the antisymmetric distribution of currents in the gold layers. An analytical model based on the nonlinear dynamics of the electrons inside the gold shows excellent agreement with experimental and numerical results. This clearly indicates the difference in the third harmonic angular pattern at electric and magnetic resonances of the metamaterial.

  15. Harmonic Resonance Damping with a Hybrid Compensation System in Power Systems with Dispersed Generation

    Chen, Zhe; Pedersen, John Kim; Blaabjerg, Frede

    2004-01-01

    A hybrid compensation system consisting of an active filter and a group of distributed passive filters has been studied previously. The passive filters are used for each distorting load or Dispersed Generation (DG) unit to remove major harmonics and provide reactive power compensation. The active...... filter is connected in parallel with the distributed passive filters and loads/DGs to correct the system unbalance and remove the remaining harmonic components. The effectiveness of the presented compensation system has also been demonstrated. This paper studies the performance of the hybrid compensation...... demonstrated that the harmonic resonance can be damped effectively. The hybrid filter system is an effective compensation system for dispersed generation systems. In the compensation system, the passive filters are mainly responsible for main harmonic and reactive power compensation of each individual load/ DG...

  16. Tunable High Harmonic Generation driven by a Visible Optical Parametric Amplifier

    Keathley P.

    2013-03-01

    Full Text Available We studied high-harmonic generation (HHG in Ar, Ne and He gas jets using a broadly tunable, high-energy optical parametric amplifier (OPA in the visible wavelength range. We optimized the noncollinear OPA to deliver tunable, femtosecond pulses with 200-500 μJ energy at 1-kHz repetition rate with excellent spatiotemporal properties, suitable for HHG experiments. By tuning the central wavelength of the OPA while keeping energy, duration and beam size constant, we experimentally studied the scaling law of conversion efficiency and cut-off energy with the driver wavelength in argon and helium respectively. Our measurements show a λ−5.9±0.9 wavelength dependence of the conversion efficiency and a λ1.7±0.2 dependence of the HHG cut-off photon energy over the full visible range in agreement with previous experiments of near- and mid-IR wavelengths. By tuning the central wavelength of the driver source and changing the gas, the high order harmonic spectra in the extreme ultraviolet cover the full range of photon energy between ~25 eV and ~100 eV. Due to the high coherence intrinsic in HHG, as well as the broad and continuous tunability in the extreme UV range, a high energy, high repetition rate version of this source might be an ideal seed for free electron lasers.

  17. Field-controllable second harmonic generation at a graphene oxide heterointerface

    Fernandes, Gustavo E.; Kim, Jin Ho; Osgood, Richard, III; Xu, Jimmy

    2018-03-01

    We report on the voltage-dependent SHG signal obtained in a reduced-graphene oxide (rGO)/p-type Si heterointerface. A simple qualitative model considering the interaction between the heterointerface depletion region potential and the naturally occurring surface dipole layer on the rGO is introduced to account for the characteristics of the SHG signal, specifically, a minimum point at ≈ -3 V bias on the rGO side of the interface. This feature-rich system has the potential to provide field-controllable surface-dipole moments and second-order nonlinearities, which may find applications in tunable nonlinear photonic devices for realizing second-harmonic generation and optical-rectification.

  18. Vibrational excitation of hydrogen molecules by two-photon absorption and third-harmonic generation

    Miyamoto, Yuki; Hara, Hideaki; Hiraki, Takahiro; Masuda, Takahiko; Sasao, Noboru; Uetake, Satoshi; Yoshimi, Akihiro; Yoshimura, Koji; Yoshimura, Motohiko

    2018-01-01

    We report the coherent excitation of the vibrational state of hydrogen molecules by two-photon absorption and the resultant third-harmonic generation (THG). Parahydrogen molecules cooled by liquid nitrogen are irradiated by mid-infrared nanosecond pulses at 4.8 μm with a nearly Fourier-transform-limited linewidth. The first excited vibrational state of parahydrogen is populated by two-photon absorption of the mid-infrared photons. Because of the narrow linewidth of the mid-infrared pulses, coherence between the ground and excited states is sufficient to induce higher-order processes. Near-infrared photons from the THG are observed at 1.6 μm. The dependence of the intensity of the near-infrared radiation on mid-infrared pulse energy, target pressure, and cell length is determined. We used a simple formula for THG with consideration of realistic experimental conditions to explain the observed results.

  19. Second-harmonic and sum-frequency generation for surface studies

    Hunt, J.H.; Guyot-Sionnest, P.; Shen, Y.R.

    1987-07-01

    Second harmonic generation (SHG) has now been well established as a versatile surface-sensitive probe. It has been used to study electrochemical processes at electrode surfaces, molecular adsorption and desorption at metal and semiconductor surfaces, orientational phase transition of molecular monolayers on water, surface reconstruction and epitaxial growth, and so on. More recently, it has been employed as a tool to monitor monolayer polymerization and other surface reactions, to probe polar order of molecules at interfaces, and to measure molecular nonlinearity. While most surface techniques are restricted to the solid/vacuum environment, SHG is applicable to nearly all interfaces as long as the interfaces are accessible by light. In addition, SHG has the advantages of being capable of in-situ measurements with high temporal, spatial, and spectral resolutions

  20. Optically induced second-harmonic generation in CdI sub 2 -Cu layered nanocrystals

    Voolless, F; Hydaradjan, W

    2003-01-01

    A large enhancement (up to 0.40 pm V sup - sup 1) of the second-order optical susceptibility was observed in CdI sub 2 -Cu single-layered nanocrystals for the Nd:YAG fundamental laser beam lambda = 1.06 mu m. The Cu impurity content and nanolayer thickness of the cleaved layers (about several nanometres) play a crucial role in the observed effect. The temperature dependence of the optical second-harmonic generation (SHG) together with its correlation with Raman spectra of low-frequency modes indicate a key role for the UV-induced anharmonic electron-phonon interactions in the observed effect. The maximal output UV-induced SHG was achieved for a Cu content of about 0.5% and at liquid helium temperatures.

  1. Cumulative Second Harmonic Generation in Lamb Waves for the Detection of Material Nonlinearities

    Bermes, Christian; Jacobs, Laurence J.; Kim, Jin-Yeon; Qu, Jianmin

    2007-01-01

    An understanding of the generation of higher harmonics in Lamb waves is of critical importance for applications such as remaining life prediction of plate-like structural components. The objective of this work is to use nonlinear Lamb waves to experimentally investigate inherent material nonlinearities in aluminum plates. These nonlinearities, e.g. lattice anharmonicities, precipitates or vacancies, cause higher harmonics to form in propagating Lamb waves. The amplitudes of the higher harmonics increase with increasing propagation distance due to the accumulation of nonlinearity while the Lamb wave travels along its path. Special focus is laid on the second harmonic, and a relative nonlinearity parameter is defined as a function of the fundamental and second harmonic amplitude. The experimental setup uses an ultrasonic transducer and a wedge for the Lamb wave generation, and laser interferometry for detection. The experimentally measured Lamb wave signals are processed with a short-time Fourier transformation (STFT), which yields the amplitudes at different frequencies as functions of time, allowing the observation of the nonlinear behavior of the material. The increase of the relative nonlinearity parameter with propagation distance as an indicator of cumulative second harmonic generation is shown in the results for the alloy aluminum 1100-H14

  2. Second-harmonic generation circular dichroism spectroscopy from tripod-like chiral molecular films

    Wang Xiao-Ou; Chen Li-An; Chen Li-Xue; Sun Xiu-Dong; Li Jun-Qing; Li Chun-Fei

    2010-01-01

    The second-harmonic generation (SHG) circular dichroism in the light of reflection from chiral films of tripod-like chiral molecules is investigated. The expressions of the second-harmonic generation circular dichroism are derived from our presented three-coupled-oscillator model for the tripod-like chiral molecules. Spectral dependence of the circular dichroism of SHG from film surface composed of tripod-like chiral molecules is simulated numerically and analysed. Influence of chiral parameters on the second-harmonic generation circular dichroism spectrum in chiral films is studied. The result shows that the second-harmonic generation circular dichroism is a sensitive method of detecting chirality compared with the ordinary circular dichroism in linear optics. All of our work indicates that the classical molecular models are very effective to explain the second-harmonic generation circular dichroism of chiral molecular system. The classical molecular model theory can give us a clear physical picture and brings us very instructive information about the link between the molecular configuration and the nonlinear processes

  3. Vector model for polarized second-harmonic generation microscopy under high numerical aperture

    Wang, Xiang-Hui; Chang, Sheng-Jiang; Lin, Lie; Wang, Lin-Rui; Huo, Bing-Zhong; Hao, Shu-Jian

    2010-01-01

    Based on the vector diffraction theory and the generalized Jones matrix formalism, a vector model for polarized second-harmonic generation (SHG) microscopy is developed, which includes the roles of the axial component P z , the weight factor and the cross-effect between the lateral components. The numerical results show that as the relative magnitude of P z increases, the polarization response of the second-harmonic signal will vary from linear polarization to elliptical polarization and the polarization orientation of the second-harmonic signal is different from that under the paraxial approximation. In addition, it is interesting that the polarization response of the detected second-harmonic signal can change with the value of the collimator lens NA. Therefore, it is more advantageous to adopt the vector model to investigate the property of polarized SHG microscopy for a variety of cases

  4. Dynamics of injection locking in a solid-state laser with intracavity second-harmonic generation

    Zolotoverkh, I I; Lariontsev, E G

    2000-01-01

    The dynamics of oscillation in a solid-state laser with intracavity second-harmonic generation under the influence of an external signal at the second-harmonic frequency injected into its cavity in the presence of feedback at the double frequency is theoretically studied. Boundaries of the regions of injection locking for three stationary laser states differing in the nonlinear phase incursion caused by radiation conversion into the second harmonic are found. Relaxation oscillations in the stationary state of injection locking are studied. It is shown that the second relaxation frequency, which is related to phase perturbations of the second harmonic and perturbations of the phase difference of waves in a nonlinear crystal, is excited in a single-mode solid-state laser in addition to the fundamental frequency of relaxation oscillations. Conditions are found under which relaxation oscillations at the second relaxation frequency are excited. (lasers)

  5. Study and development of a soft X-ray laser seeded by high-order harmonic

    Goddet, J.Ph.

    2009-05-01

    The work in this thesis aimed to study a geometry of X-UV lasers inspired by high power laser. This architecture, consisting of an injector (a source of high-order harmonics) coupled to an amplifier (plasma created by laser), corresponds to that of a laser chain in the spectral range of the X-UV. The laser at 32.8 nm studied here, is produced by the injection of high-order harmonic in a krypton plasma created by Optical Field Ionization (OFI). This scheme, initially tested by T. Ditmire in 1995, was validated in 2003 with a plasma amplifier created by the interaction of intense laser and a gaseous medium. This thesis is a continuation of that work in trying to address different aspects, not only a better understanding of the physical processes involved, but also of the spatio-temporal characterization of this type of source. We have demonstrated experimentally for the first time a source in the X-UV, which can be highly compact, energetic (1 μJ per pulse), close to the diffraction limit and Fourier transform limited. Indeed, through the spatial filtering of harmonics by the amplifying medium, the injected X-UV laser at 32.8 nm shows a Gaussian spatial profile with a divergence of 0.7 mrad (at 1/e 2 ). The wavefront was measured with a Hartmann sensor and presents a value of λ/17 in standard deviation, demonstrating that the X-UV source is diffraction limited. The temporal characterization of laser shows that the coherence time is of the order of the duration of spontaneous emission of the amplifier. The temporal coherence presents a Gaussian profile with a relative spectral width Δλ/λ equal to 10 -5 (FWHM) corresponding to a pulse duration of about 5 ps. (author)

  6. Second- and third-harmonic generation as a local probe for nanocrystal-doped polymer materials with a suppressed optical breakdown threshold

    Konorov, S. O.; Fedotov, A. B.; Ivanov, A. A.; Alfimov, M. V.; Zabotnov, S. V.; Naumov, A. N.; Sidorov-Biryukov, D. A.; Podshivalov, A. A.; Petrov, A. N.; Fornarini, L.; Carpanese, M.; Ferrante, G.; Fantoni, R.; Zheltikov, A. M.

    2003-09-01

    Second- and third-harmonic generation processes are shown to allow the detection of absorptive agglomerates of nanocrystals in transparent materials and the visualization of optical breakdown in nanocomposite materials. Correlations between laser-induced breakdown and the behavior of the second- and third-harmonic signals produced in SiC/PMMA nanocomposite films are studied. The potential of second- and third-harmonic generation for the on-line visualization of laser breakdown in nanocomposite polymer materials is revealed, with the ablative material removal being monitored by the decay of the second- and third-harmonic signals. The second and third harmonics generated around the optical breakdown threshold by 75-fs pulses of 1.25-μm Cr:forsterite laser radiation are respectively more than two and four orders of magnitude more intense than the second and third harmonics produced under identical conditions by 40-ps pulses of a Nd:YAG laser. The breakdown threshold for PMMA films doped with 10-20-nm SiC nanocrystals forming absorptive agglomerates are demonstrated to be more than an order of magnitude lower than the breakdown threshold for crystalline SiC and about an order of magnitude lower than that for nondoped PMMA films.

  7. An isoparametric shell of revolution finite element for harmonic loadings of any order

    Johnson, J.J.; Charman, C.M.

    1981-01-01

    A general isoparametric shell of revolution finite element subjected to any order harmonic loading is presented. Derivation of the element properties, its implementation in a general purpose finite element program, and its application to a sample problem are discussed. The element is isoparametric, that is, the variation of the displacements along the meridian of the shell and the shape of the meridian itself are approximated in an identical manner. The element has been implemented in the computer program MODSAP. A sample problem of a cooling tower subjected to wind loading is presented. (orig./HP)

  8. Injection of harmonics generated in gas in a free-electron laser providing intense and coherent extreme-ultraviolet light

    Lambert, G; Garzella, D; Labat, M; Carre, B; Bougeard, M; Salieres, P; Merdji, H; Gobert, O [CEA Saclay, DSM, DRECAM, Serv. Photons Atomes Mol., F-91191 Gif sur Yvette, (France); Lambert, G; Hara, T; Tanikawa, T; Kitamura, H; Shintake, T; Tanaka, Y; Tahara, K [RIKEN SPring Centre, Harima Inst., Hyogo 679-5148, (Japan); Lambert, G; Labat, M; Chubar, O; Couprie, M E [Groupe Magnetisme et Insertion, Synchrotron Soleil, F-91192 Gif sur Yvette, (France); Hara, T; Kitamura, H; Shintake, T; Inoue, S; Tanaka, Y [XFEL Project Head Office, RIKEN, Hyogo 679-5148, (Japan)

    2008-07-01

    Conventional synchrotron radiation sources enable the structure of matter to be studied at near-atomic spatial resolution and picosecond temporal resolution. Free-electron lasers promise to extend this down to femtosecond timescales. The process by which free-electron lasers amplify synchrotron light-known as self-amplified spontaneous emission - is only partially temporally coherent, but this can be improved by seeding it with an external laser. Here we explore the use of seed light produced by high-order harmonic generation in a gas, covering wavelengths from the ultraviolet to soft X-rays. Using the SPring-8 Compact SASE Source test accelerator, we demonstrate an increase of three orders of magnitude in the intensity of the fundamental radiation at 160 nm, halving of the free-electron laser saturation length, and the generation of nonlinear harmonics at 54 nm and 32 nm. The low seed level used in this demonstration suggests that nonlinear harmonic schemes should enable the generation of fully coherent soft X-rays at wavelengths down to the so-called 'water window', vital for the study of biological samples. (authors)

  9. Phase-coded multi-pulse technique for ultrasonic high-order harmonic imaging of biological tissues in vitro

    Ma Qingyu; Zhang Dong; Gong Xiufen; Ma Yong

    2007-01-01

    Second or higher order harmonic imaging shows significant improvement in image clarity but is degraded by low signal-noise ratio (SNR) compared with fundamental imaging. This paper presents a phase-coded multi-pulse technique to provide the enhancement of SNR for the desired high-order harmonic ultrasonic imaging. In this technique, with N phase-coded pulses excitation, the received Nth harmonic signal is enhanced by 20 log 10 N dB compared with that in the single-pulse mode, whereas the fundamental and other order harmonic components are efficiently suppressed to reduce image confusion. The principle of this technique is theoretically discussed based on the theory of the finite amplitude sound waves, and examined by measurements of the axial and lateral beam profiles as well as the phase shift of the harmonics. In the experimental imaging for two biological tissue specimens, a plane piston source at 2 MHz is used to transmit a sequence of multiple pulses with equidistant phase shift. The second to fifth harmonic images are obtained using this technique with N = 2 to 5, and compared with the images obtained at the fundamental frequency. Results demonstrate that this technique of relying on higher order harmonics seems to provide a better resolution and contrast of ultrasonic images

  10. QED effects induced harmonics generation in extreme intense laser foil interaction

    Yu, J. Y.; Yuan, T.; Liu, W. Y.; Chen, M.; Luo, W.; Weng, S. M.; Sheng, Z. M.

    2018-04-01

    A new mechanism of harmonics generation (HG) induced by quantum electrodynamics (QED) effects in extreme intense laser foil interaction is found and investigated by particle-in-cell (PIC) simulations. When two laser pulses with identical intensities of 1.6× {10}24 {{W}} {{{cm}}}-2 are counter-incident on a thin foil target, harmonics emission is observed in their reflected electromagnetic waves. Such harmonics radiation is excited due to transversely oscillating electric currents coming from the vibration of QED effect generated {e}-{e}+ pairs. The effects of laser intensity and polarization were studied. By distinguishing the cascade depth of generated photons and pairs, the influence of QED cascades on HG was analyzed. Although the current HG is not an efficient way for radiation source applications, it may provide a unique way to detect the QED processes in the near future ultra-relativistic laser solid interactions.

  11. Second harmonic generation by a relativistic annular electron beam propagating through a cylindrical waveguide

    Yasumoto, Kiyotoshi; Abe, Hiroshi

    1983-01-01

    The second harmonic generated by a relativistic annular electron beam propagating through a cylindrical waveguide immersed in a strong axial magnetic field is investigated on the basis of the relativistic hydrodynamic equations for cold electrons. The efficiency of second harmonic generation is calculated separately for the pump by the TM electromagnetic wave and for the pump by the slow space-charge wave, by assuming that the electron beam is thin and of low density and the pump wave is azimuthally symmetric. It is shown that, in the case of slow space-charge wave pump, an appreciably large efficiency of second harmonic generation is achieved in the high frequency region, whereas the efficiency by the TM electromagnetic wave pump is relatively small over the whole frequency range.(author)

  12. Stator Current Harmonic Reduction in a Novel Half Quasi-Z-Source Wind Power Generation System

    Shoudao Huang

    2016-09-01

    Full Text Available The generator stator current gets distorted with unacceptable levels of total harmonic distortion (THD because impedance-source wind power generation systems use three-phase diode rectifiers. The stator current harmonics will cause increasing losses and torque ripple, which reduce the efficiency and stability of the system. This paper proposes a novel half quasi-Z-source inverter (H-qZSI for grid-connected wind power generation systems, which can reduce the generator stator current harmonics a great deal. When H-qZSI operates in the shoot-through zero state, the derivative of the generator stator current is only determined by the instantaneous value of the generator stator voltage, so the nonlinear relationship between generator stator current and stator voltage is improved compared with the traditional impedance-source inverter. Theoretically, it is indicated that the stator current harmonics can be reduced effectively by means of the proposed H-qZSI. Finally, simulation and experimental results are given to verify the theoretical analysis.

  13. Rotating-coil calibration in a reference quadrupole, considering roll-angle misalignment and higher-order harmonics

    AUTHOR|(CDS)2075492; Buzio, Marco; Köster, Oliver; Russenschuck, Stephan; Severino, Giordana

    2016-01-01

    A method is proposed for calibrating the radius of a rotating coil sensor by relaxing the metrological constraints on alignment and field errors of the reference quadrupole. A coil radius calibration considering a roll-angle misalignment of the measurement bench, the magnet, and the motor-drive unit is analyzed. Then, the error arising from higher-order harmonic field imperfections in the reference quadrupole is assessed. The method is validated by numerical field computation for both the higher-order harmonic errors and the roll-angle misalignment. Finally, an experimental proof-of-principle demonstration is car-ried out in a calibration magnet with sextupole harmonic.

  14. Stator current harmonics evolution by neural network method based on CFE/SS algorithm for ACEC generator of Rey Power Plant

    Soleymani, S.; Ranjbar, A.M.; Mirabedini, H.

    2001-01-01

    One method for on-line fault diagnosis in synchronous generator is stator current harmonics analysis. Then artificial neural network is considered in this paper in order to evaluate stator current harmonics in different loads. Training set of artificial neural network is made ready by generator modeling, finite element method and state space model. Many points from generator capability curve are used in order to complete this set. Artificial neural network which is used in this paper is a percept ron network with a single hidden layer, Eight hidden neurons and back propagation algorithm. Results are indicated that the trained artificial neural network can identify stator current harmonics for arbitrary load from the capability curve. The error is less than 10% in comparison with values obtained directly from the CFE-SS algorithm. The rating parameters of modeled generator are 43950 (kV A), 11(KV), 3000 (rpm), 50 (H Z), (P F=0.8)

  15. Retrieving molecular structural information and tracking HNC/HCN isomerization process with high harmonic generation by ultrashort laser pulses

    Nguyen Ngoc Ty; Le Van Hoang; Vu Ngoc Tuoc; Le Anh Thu

    2010-01-01

    We investigate the possibility of applying the iterative method, suggested in our previous work, for HCN molecule and its HNC isomer. We found that the high-order harmonic generation (HHG) spectra are quite insensitive to the change of H-C (or H-N) bond length so that only the inter-nuclear C-N distance can be retrieved from the high-order harmonic spectra using ultrashort intense lasers. Furthermore, by analyzing the HHG spectra emitted by HCN during the chemical reaction path of isomerization we identify the intensity peaks nearby the stable, metastable and transition states. this finding can be useful for tracking the HNC/HNC isomerization process. (author)

  16. Effect of self-focusing on resonant third harmonic generation of laser in a rippled density plasma

    Kaur, Sukhdeep; Sharma, A. K.; Yadav, Sushila

    2010-01-01

    Resonant third harmonic generation by a Gaussian laser beam in a rippled density plasma is studied. The laser ponderomotive force induces second harmonic longitudinal velocity on electrons that couples with the static density ripple to produce a density perturbation at 2ω,2k+q, where ω and k are the frequency and wave number of the laser and q is the ripple wave number of the laser. This density perturbation beats with electron oscillatory velocity at ω,k-vector to produce a nonlinear current driving the third harmonic generation. In the regime of quadratic nonlinearity, the self-focusing of the laser enhances the third harmonic power. However, at higher intensity, plasma density is significantly reduced on the axis, detuning the third harmonic resonance and weakening the harmonic yield. Self-focusing causes enhancement in the efficiency of harmonic generation.

  17. Detecting a pronounced delocalized state in third-harmonic generation phenomenon; a quantum chaos approach

    Behnia, S.; Ziaei, J.; Khodavirdizadeh, M.

    2018-06-01

    Nonlinear optics (NLO) deserves special attention in new optical devices, making it possible to generate coherent light more efficiently. Among the various NLO phenomena the third-harmonic generation (THG) is at the core of the effective operating mechanism of broadband wavelength conversion, in all-optical devices. Here, we aim to understand how the third-order susceptibility and the electric field may be effectively effect on the localization properties of the light in the THG process when included in a two-mode cavity coherently perturbed by a classical field. We address a stable-unstable transition due to the combination effect of the aforementioned factors. We report a reliable evidence confirming the appearance of chaos in THG under suitable conditions. By tracing the signatures of adjacent-spectral-spacing-ratio (ASSR) distribution and participation ratio, we also find a critical point (ɛc ,κc) =(3 . 1 , 0 . 35) for which a pronounced delocalized response is seen. This study may have profound findings for practical devices, and ushers in new opportunities for practical exploitation of the electric field and the third-order susceptibility effect in nonlinear optical devices.

  18. Impact of electron-electron Coulomb interaction on the high harmonic generation process in graphene

    Avetissian, H. K.; Mkrtchian, G. F.

    2018-03-01

    Generation of high harmonics in a monolayer graphene initiated by a strong coherent radiation field, taking into account electron-electron Coulomb interaction, is investigated. A microscopic theory describing the nonlinear optical response of graphene is developed. The Coulomb interaction of electrons is treated in the scope of dynamic Hartree-Fock approximation. The closed set of integrodifferential equations for the single-particle density matrix of a graphene quantum structure is solved numerically. The obtained solutions show the significance of many-body Coulomb interaction on the high harmonic generation process in graphene.

  19. Fabrication of Multi-Harmonic Buncher for Pulsed Proton Beam Generation

    Kim, H. S.; Kwon, H. J.; Cho, Y. S. [Korea Multipurpose Accelerator Complex, Gyeongju (Korea, Republic of)

    2015-05-15

    Fast neutrons with a broad spectrum can be generated by irradiating the proton beams on target materials. To measure the neutron energy by time of flight (TOF) method, the short pulse width of the proton beam is preferred because the neutron energy uncertainty is proportional to the pulse width. In addition, the pulse repetition rate should be low enough to extend the lower limit of the available neutron energy. Pulsed proton beam generation system is designed based on an electrostatic deflector and slit system as shown in Fig. 1. In a simple deflector with slit system, most of the proton beam is blocked by slit, especially when the beam pulse width is short. The ideal field pattern inside the buncher cavity is saw-tooth wave. To make the field pattern similar to the saw-tooth waveform, we adopted a multi-harmonic buncher (MHB). The design for the multi-harmonic buncher including 3D electromagnetic calculation has been performed. Based on the design, a multi-harmonic buncher cavity was fabricated. It consists of two resonators, two drift tubes and a vacuum chamber. The resonator is a quarter-wave coaxial resonator type. The drift tube is connected to the resonator by using a coaxial vacuum feedthrough. Design summary and detailed fabrication method of the multi-harmonic buncher is presented in this paper. A multi-harmonic buncher for a proton beam chopper system to generate a short pulse neutron beam was designed, fabricated and assembled.

  20. A Case Study of Harmonic Impact on a Motor-Generator Set System

    Joung, Pil-Bum [KHNP CRI, Daejeon (Korea, Republic of)

    2016-10-15

    Motor-Generator Sets are usually used to supply power to a Control Element Drive Mechanism Control System (CEDMCS) at nuclear power plants with pressurized water reactors. Two Motor-Generator Sets, which have 100% capacity, are operated in parallel to improve the reliability of the power supply to the CEDMCS. Fig. 1 presents a diagram of a Motor- Generator Set system. The system of a Motor-Generator Set is composed of electrical equipment, such as a motor, a fly-wheel, and a generator, an exciter and protection-control device, such as a protective relay, synchro check relay, and an auto voltage regulator. In general, the harmonic impact of electrical equipment increases the deterioration of the equipment, the motor, and the generator’s lifetime, which can also be caused by vibration and over-heating and maloperation of the protection-control device. In this paper, we came to understand the harmonic impact on the Motor-Generator Set system through a study of delaying parallel operation by non-operation of the synchro check relay and the fault of under voltage protective relay. Thus, KHNP has established and applied the measures of harmonic reduction by the CEDMCS, such as limiting the voltage harmonic distortion to less than 10%, which is described in IEEE Std 519.

  1. Selectively Plasmon-Enhanced Second-Harmonic Generation from Monolayer Tungsten Diselenide on Flexible Substrates

    Wang, Zhuo

    2018-01-04

    Monolayer two-dimensional transition metal dichalcogenides (2D TMDCs) exhibit promising characteristics in miniaturized nonlinear optical frequency converters, due to their inversion asymmetry and large second-order nonlinear susceptibility. However, these materials usually have a very short light interaction lengths with the pump laser because they are atomically thin, such that second-harmonic generation (SHG) is generally inefficient. In this paper, we fabricate a judiciously structured 150-nm-thick planar surface consisting of monolayer tungsten diselenide and sub-20-nm-wide gold trenches on flexible substrates, reporting ~7000-fold SHG enhancement without peak broadening or background in the spectra as compared to WSe2 on as-grown sapphire substrates. Our proof-of-concept experiment yields effective second-order nonlinear susceptibility of 2.1 × 104 pm/V. Three orders of magnitude enhancement is maintained with pump wavelength ranging from 800 nm to 900 nm, breaking the limitation of narrow pump wavelength range for cavity-enhanced SHG. In addition, SHG amplitude can be dynamically controlled via selective excitation of the lateral gap plasmon by rotating the laser polarization. Such fully open, flat and ultrathin profile enables a great variety of functional samples with high SHG from one patterned silicon substrate, favoring scalable production of nonlinear converters. The surface accessibility also enables integration with other optical components for information processing in an ultrathin and flexible form.

  2. Selectively Plasmon-Enhanced Second-Harmonic Generation from Monolayer Tungsten Diselenide on Flexible Substrates

    Wang, Zhuo; Dong, Zhaogang; Zhu, Hai; Jin, Lei; Chiu, Ming-Hui; Li, Lain-Jong; Xu, Qing-Hua; Eda, Goki; Maier, Stefan A.; Wee, Andrew T. S.; Qiu, Cheng-Wei; Yang, Joel K.W.

    2018-01-01

    Monolayer two-dimensional transition metal dichalcogenides (2D TMDCs) exhibit promising characteristics in miniaturized nonlinear optical frequency converters, due to their inversion asymmetry and large second-order nonlinear susceptibility. However, these materials usually have a very short light interaction lengths with the pump laser because they are atomically thin, such that second-harmonic generation (SHG) is generally inefficient. In this paper, we fabricate a judiciously structured 150-nm-thick planar surface consisting of monolayer tungsten diselenide and sub-20-nm-wide gold trenches on flexible substrates, reporting ~7000-fold SHG enhancement without peak broadening or background in the spectra as compared to WSe2 on as-grown sapphire substrates. Our proof-of-concept experiment yields effective second-order nonlinear susceptibility of 2.1 × 104 pm/V. Three orders of magnitude enhancement is maintained with pump wavelength ranging from 800 nm to 900 nm, breaking the limitation of narrow pump wavelength range for cavity-enhanced SHG. In addition, SHG amplitude can be dynamically controlled via selective excitation of the lateral gap plasmon by rotating the laser polarization. Such fully open, flat and ultrathin profile enables a great variety of functional samples with high SHG from one patterned silicon substrate, favoring scalable production of nonlinear converters. The surface accessibility also enables integration with other optical components for information processing in an ultrathin and flexible form.

  3. Development of a 3D FEL code for the simulation of a high-gain harmonic generation experiment

    Biedron, S. G.

    1999-01-01

    Over the last few years, there has been a growing interest in self-amplified spontaneous emission (SASE) free-electron lasers (FELs) as a means for achieving a fourth-generation light source. In order to correctly and easily simulate the many configurations that have been suggested, such as multi-segmented wigglers and the method of high-gain harmonic generation, we have developed a robust three-dimensional code. The specifics of the code, the comparison to the linear theory as well as future plans will be presented

  4. Sensitivity of echo enabled harmonic generation to sinusoidal electron beam energy structure

    E. Hemsing

    2017-06-01

    Full Text Available We analytically examine the bunching factor spectrum of a relativistic electron beam with sinusoidal energy structure that then undergoes an echo-enabled harmonic generation (EEHG transformation to produce high harmonics. The performance is found to be described primarily by a simple scaling parameter. The dependence of the bunching amplitude on fluctuations of critical parameters is derived analytically, and compared with simulations. Where applicable, EEHG is also compared with high gain harmonic generation (HGHG and we find that EEHG is generally less sensitive to several types of energy structure. In the presence of intermediate frequency modulations like those produced by the microbunching instability, EEHG has a substantially narrower intrinsic bunching pedestal.

  5. New results of the high-gain harmonic generation free-electron laser experiment

    Doyuran, A.; Babzien, M.; Shaftan, T.; Biedron, S.G.; Yu, L.H.; Ben-Zvi, I.; DiMauro, L.F.; Graves, W.; Johnson, E.; Krinsky, S.; Malone, R.; Pogorelsky, I.; Skaritka, J.; Rakowsky, G.; Wang, X.J.; Woodle, M.; Yakimenko, V.; Jagger, J.; Sajaev, V.; Vasserman, I.

    2001-01-01

    We report on the experimental investigation of high-gain harmonic generation carried out at the Accelerator Test Facility at Brookhaven National Laboratory. A seed CO 2 laser at a wavelength of 10.6 μm was used to generate FEL output at a 5.3-μm wavelength. The duration of the output pulse was measured using a second-harmonic intensity autocorrelator, and the coherence length was measured using an interferometer. We also measured the energy distribution of the electron beam after it exited the second undulator, observing behavior consistent with that is expected at saturation. The intensity of the harmonic components of the output at 2.65 and 1.77 μm was determined relative to that of the 5.3-μm fundamental. Finally, using a corrector magnet upstream of the radiator, steering effects on the trajectories of the electron and light beams were studied

  6. Third harmonic generation of shear horizontal guided waves propagation in plate-like structures

    Li, Wei Bin [School of Aerospace Engineering, Xiamen University, Xiamen (China); Xu, Chun Guang [School of Mechanical Engineering, Beijing Institute of Technology, Beijing (China); Cho, Youn Ho [School of Mechanical Engineering, Pusan National University, Busan (Korea, Republic of)

    2016-04-15

    The use of nonlinear ultrasonics wave has been accepted as a promising tool for monitoring material states related to microstructural changes, as it has improved sensitivity compared to conventional non-destructive testing approaches. In this paper, third harmonic generation of shear horizontal guided waves propagating in an isotropic plate is investigated using the perturbation method and modal analysis approach. An experimental procedure is proposed to detect the third harmonics of shear horizontal guided waves by electromagnetic transducers. The strongly nonlinear response of shear horizontal guided waves is measured. The accumulative growth of relative acoustic nonlinear response with an increase of propagation distance is detected in this investigation. The experimental results agree with the theoretical prediction, and thus providing another indication of the feasibility of using higher harmonic generation of electromagnetic shear horizontal guided waves for material characterization.

  7. Effects of voltage unbalance and system harmonics on the performance of doubly fed induction wind generators

    Kiani, Morgan Mozhgan

    Inherent difficulties in management of electric power in the presence of an increasing demand for more energy, non-conventional loads such as digital appliances, and non-sustainable imported fossil fuels has initiated a multi-folded effort by many countries to restructure the way electric energy is generated, dispatched, and consumed. Smart power grid is the manifestation of many technologies that would eventually transforms the existing power grid into a more flexible, fault resilient, and intelligent system. Integration of distributed renewable energy sources plays a central role in successful implementation of this transformation. Among the renewable options, wind energy harvesting offers superior engineering and economical incentives with minimal environmental impacts. Doubly fed induction generators (DFIG) have turned into a serious contender for wind energy generators due to their flexibility in control of active and reactive power with minimal silicon loss. Significant presence of voltage unbalance and system harmonics in finite inertia transmission lines can potentially undermine the reliability of these wind generators. The present dissertation has investigated the impacts of system unbalances and harmonics on the performance of the DFIG. Our investigation indicates that these effects can result in an undesirable undulation in the rotor shaft which can potentially invoke mechanical resonance, thereby causing catastrophic damages to the installations and the power grid. In order to remedy the above issue, a control solution for real time monitoring of the system unbalance and optimal excitation of the three phase rotor currents in a DFIG is offered. The optimal rotor currents will create appropriate components of the magneto-motive force in the airgap that will actively compensate the undesirable magnetic field originated by the stator windings. Due to the iterative nature of the optimization procedure, field reconstruction method has been incorporated

  8. Evaluation of the optical axis tilt of zinc oxide films via noncollinear second harmonic generation

    Bovino, F. A.; Larciprete, M. C.; Belardini, A.; Sibilia, C.

    2009-01-01

    We investigated noncollinear second harmonic generation form zinc oxide films, grown on glass substrates by dual ion beam sputtering technique. At a fixed incidence angle, the generated signal is investigated by scanning the polarization state of both fundamental beams. We show that the map of the generated signal as a function of polarization states of both pump beams, together with the analytical curves, allows to retrieve the orientation of the optical axis and eventually, its angular tilt, with respect to the surface normal.

  9. A New Second-Order Generalized Integrator Based Quadrature Signal Generator With Enhanced Performance

    Xin, Zhen; Qin, Zian; Lu, Minghui

    2016-01-01

    Due to the simplicity and flexibility of the structure of the Second-Order Generalized Integrator based Quadrature Signal Generator (SOGI-QSG), it has been widely used over the past decade for many applications such as frequency estimation, grid synchronization, and harmonic extraction. However......, the SOGI-QSG will produce errors when its input signal contains a dc component or harmonic components with unknown frequencies. The accuracy of the signal detection methods using it may hence be compromised. To overcome the drawback, the First-Order System (FOS) concept is first used to illustrate...

  10. Microbubble generator excited by fluidic oscillator's third harmonic frequency

    Tesař, Václav

    2014-01-01

    Roč. 92, č. 9 (2014), s. 1603-1615 ISSN 0263-8762 R&D Projects: GA ČR GA13-23046S Institutional support: RVO:61388998 Keywords : fluidic oscillator * microbubble generation * fluidic feedback loop Subject RIV: BK - Fluid Dynamics Impact factor: 2.348, year: 2014 http://dx.doi.org/10.1016/j.cherd.2013.12.004

  11. High bandwidth second-harmonic generation in partially deuterated KDP

    Webb, M.S.; Eimerl, D.; Velsko, S.P.

    1992-01-01

    We have experimentally determined the spectrally noncritical phasematching behavior of Type I frequency doubling in KDP and its dependence on deuteration level in partially deuterated KDP. The first order wavelength sensitivity parameter∂Δk/∂γ for Type I doubling of 1.053 μm light vanishes for a KD*P crystal with a deuteration level between 10 and 14%. Very high bandwidth frequency doubling of Nd:glass lasers is possible with such a crystal

  12. Bulk characterization methods for non-centrosymmetric materials: second-harmonic generation, piezoelectricity, pyroelectricity, and ferroelectricity.

    Ok, Kang Min; Chi, Eun Ok; Halasyamani, P Shiv

    2006-08-01

    Characterization methods for bulk non-centrosymmetric compounds are described. These methods include second-harmonic generation, piezoelectricity, pyroelectricity, and ferroelectricity. In this tutorial review with each phenomenon, details are given of the measurement techniques along with a brief history and background. Finally, data interpretation is discussed.

  13. Local excitation of surface plasmon polaritons by second-harmonic generation in crystalline organic nanofibers

    Skovsen, Esben; Søndergaard, Thomas; Fiutowski, Jacek

    2012-01-01

    Coherent local excitation of surface plasmon polaritons (SPPs) by second-harmonic generation (SHG) in aligned crystalline organic functionalized para-phenylene nanofibers deposited on a thin silver film is demonstrated. The excited SPPs are characterized using angle-resolved leakage radiation...

  14. Third harmonic generation of CO2 laser radiation in AgGaSe2 crystal

    journal of. September 2000 physics pp. 405–412. Third harmonic generation of .... cell, the short pulse is accompanied by an unavoidable background pulse of 216 ns dura- ... the long pulse laser interacts with only a small number of SF molecules. ... illuminates the discharge region and produces electrons by ionization of ...

  15. Continuous-variable Einstein-Podolsky-Rosen paradox with traveling-wave second-harmonic generation

    Olsen, M.K.

    2004-01-01

    The Einstein-Podolsky-Rosen paradox and quantum entanglement are at the heart of quantum mechanics. Here we show that single-pass traveling-wave second-harmonic generation can be used to demonstrate both entanglement and the paradox with continuous variables that are analogous to the position and momentum of the original proposal

  16. Effect of loss on slow-light-enhanced second-harmonic generation in periodic nanostructures

    Saravi, Sina; Quintero-Bermudez, Rafael; Setzpfandt, Frank

    2016-01-01

    We theoretically analyze the dependence of second-harmonic generation efficiency on the group index in periodic optical waveguides with loss. We investigate different possible scenarios of using slow light to enhance the efficiency of this process and show that in some cases there exists a maxima...

  17. Observation of self-pulsing in singly resonant optical second-harmonic generation with competing nonlinearities

    Bache, Morten; Lodahl, Peter; Mamaev, Alexander V.

    2002-01-01

    We predict and experimentally observe temporal self-pulsing in singly resonant intracavity second-harmonic generation under conditions of simultaneous parametric oscillation. The threshold for self-pulsing as a function of cavity tuning and phase mismatch are found from analysis of a three...

  18. Extracting morphologies from third harmonic generation images of structurally normal human brain tissue

    Zhang, Zhiqing; Kuzmin, Nikolay V.; Groot, Marie Louise; de Munck, Jan C.

    2017-01-01

    Motivation: The morphologies contained in 3D third harmonic generation (THG) images of human brain tissue can report on the pathological state of the tissue. However, the complexity of THG brain images makes the usage of modern image processing tools, especially those of image filtering,

  19. Evidence of multipolar response of Bacteriorhodopsin by noncollinear second harmonic generation.

    Bovino, F A; Larciprete, M C; Sibilia, C; Váró, G; Gergely, C

    2012-06-18

    Noncollinear second harmonic generation from a Bacteriorhodopsin (BR) oriented multilayer film was systematically investigated by varying the polarization state of both fundamental beams. Both experimental results and theoretical simulations, show that the resulting polarization mapping is an useful tool to put in evidence the optical chirality of the investigated film as well as the corresponding multipolar contributions to the nonlinear.

  20. Plasmonic enhancement of High Harmonic Generation revisited: Predominance of Atomic Line Emission

    Ropers C.

    2013-03-01

    Full Text Available We demonstrate nanostructure-enhanced extreme ultraviolet fluorescence from noble gases driven by low-energy, few-cycle light pulses. Despite sufficient local intensities, plasmon-enhanced high harmonic generation is not observed, which follows from the small, nanometer-size coherent source volume.

  1. A structure and second-harmonic generation of crystals Li B3O5

    Burak, Ya.V.

    1997-01-01

    Projections of atoms of nonlinear optical crystals Li B 3 O 5 onto planes perpendicular to directions of the phase matching of type-1 and type-2 for second-harmonic generation (SHG) in a YAG:Nd laser are constructed. Analyses of the interdependence of orientations of (B 3 O 7 ) 5 -complexes and of the effectiveness of SHG are conducted

  2. Second-Harmonic Generation Scanning Microscopy on Domains in Al Surfaces

    Pedersen, Kjeld; Bozhevolnyi, Sergey I.

    1999-01-01

    Scanning optical second-harmonic generation microscopy has been used to investigate domains in the surface of polycrystaline Al. Strong contrast among the crystalline grains is obtained due to variations in their crystallographic orientations and thus also nonlinear response. The origin of the co...

  3. High harmonic generation in H2 and HD by two-colour femtosecond ...

    We have argued that for these combinations, the harmonic generation due to transitions in the electronic continuum by tunnelling or multiphoton ionization may be neglected and only the electronic transitions within the two lowest electronic states would be important. Thus, the characteristic features of HHG spectra in the ...

  4. Direct detection of the parametrically generated half-harmonic voltage in a Josephson tunnel junction

    Mygind, Jesper; Pedersen, Niels Falsig; Sørensen, O. H.

    1976-01-01

    The first direct observation of the parametrically generated half-harmonic voltage in a Josephson tunnel junction is reported. A microwave signal at f=17.25 GHz is applied to the junction dc current biased at zero voltage such that the Josephson plasma resonance fp=f/2. Under these conditions...

  5. Generation of ultrahigh harmonics with a two-stage free electron laser and a seed laser

    Goloviznin, V. V.; van Amersfoort, P. W.

    1997-01-01

    We consider the possibility to premodulate an ultrarelativistic electron beam on the nanometer length scale, so that it can produce coherent spontaneous radiation in the x-ray range. The scheme that uses the same basic elements as the high gain harmonic generation (HGHG) scheme, two wigglers and a

  6. Quantum properties of transverse pattern formation in second-harmonic generation

    Bache, Morten; Scotto, P.; Zambrini, R.

    2002-01-01

    these equations through extensive numerical simulations and analytically in the linearized limit. Our study, made below and above the threshold of pattern formation, is guided by a microscopic scheme of photon interaction underlying pattern formation in second-harmonic generation. Close to the threshold...

  7. Optimum third harmonic generation efficiency in the far infrared in Si, GaAs and InP

    Brazis, R.; Raguotis, R.; Siegrist, M.R.

    1997-12-01

    We investigate by means of a Monte Carlo technique the nonlinear drift response of electrons to high power electromagnetic waves in Si, GaAs and InP. The first and third harmonic drift velocity amplitudes and phases are presented as function of the pumping wave frequency in the range of 200 to 500 GHz. The third harmonic generation efficiency is found to reach a maximum at a pumping wave amplitude of 10-25 kV/cm depending on the material and the lattice temperature. Cooling down to liquid nitrogen temperature results in an improvement of the efficiency by a factor of 2 to 10, depending on the material and the pumping wave amplitude. Cooled GaAs and InP are both an order of magnitude more efficient than Si at ambient temperature, for which to date the best measured performance has been reported. (author) 2 figs., 5 refs

  8. InSe monolayer: synthesis, structure and ultra-high second-harmonic generation

    Zhou, Jiadong; Shi, Jia; Zeng, Qingsheng; Chen, Yu; Niu, Lin; Liu, Fucai; Yu, Ting; Suenaga, Kazu; Liu, Xinfeng; Lin, Junhao; Liu, Zheng

    2018-04-01

    III–IV layered materials such as indium selenide have excellent photoelectronic properties. However, synthesis of materials in such group, especially with a controlled thickness down to monolayer, still remains challenging. Herein, we demonstrate the successful synthesis of monolayer InSe by physical vapor deposition (PVD) method. The high quality of the sample was confirmed by complementary characterization techniques such as Raman spectroscopy, atomic force microscopy (AFM) and high resolution annular dark field scanning transmission electron microscopy (ADF-STEM). We found the co-existence of different stacking sequence (β- and γ-InSe) in the same flake with a sharp grain boundary in few-layered InSe. Edge reconstruction is also observed in monolayer InSe, which has a distinct atomic structure from the bulk lattice. Moreover, we discovered that the second-harmonic generation (SHG) signal from monolayer InSe shows large optical second-order susceptibility that is 1–2 orders of magnitude higher than MoS2, and even 3 times of the largest value reported in monolayer GaSe. These results make atom-thin InSe a promising candidate for optoelectronic and photosensitive device applications.

  9. Third harmonic generation by Bloch-oscillating electrons in a quasioptical array

    Ghosh, A.W.; Wanke, M.C.; Allen, S.J.; Wilkins, J.W.

    1999-01-01

    We compute the third harmonic field generated by Bloch-oscillating electrons in a quasioptical array of superlattices under THz irradiation. The third harmonic power transmitted oscillates with the internal electric field, with nodes associated with Bessel functions in eEd/ℎω. The nonlinear response of the array causes the output power to be a multivalued function of the incident laser power. The output can be optimized by adjusting the frequency of the incident pulse to match one of the Fabry-Pacute erot resonances in the substrate. Within the transmission-line model of the array, the maximum conversion efficiency is 0.1%. copyright 1999 American Institute of Physics

  10. Second harmonic generation in anisotropic Langmuir-Blodgett films of N-docosyl-4-nitroaniline

    Geisler, T.; Rosenkilde, S.; Ramanujam, P.S.

    1992-01-01

    Langmuir-Blodgett (LB) films of N-docosyl-4-nitroaniline have been made and their nonlinear optical properties studied by second harmonic generation (SHG) measurements. A significant enhancement of the intensity of the second harmonic of the 1.064-mu-m YAG was observed when a two layer Y-type film...... structure. Both of these observations are not common for Y-type LB films and the usual assumption of C(infinity nu) symmetry is therefore not valid. The results make us suggest that these LB films possess C(s) and C2-nu symmetry for mono- and multilayers, respectively. Theoretical expressions...

  11. Ultrashort pulse chirp measurement via transverse second-harmonic generation in strontium barium niobate crystal

    Trull, J.; Wang, B.; Parra, A.; Vilaseca, R.; Cojocaru, C. [Departament de Física i Enginyeria Nuclear, Universitat Politècnica Catalunya, Terrassa 08222 (Spain); Sola, I. [Grupo de Investigación en Óptica Extrema (GIOE), Departamento de Física Aplicada, Universidad de Salamanca, Plaza de la Merced s/n, 37008 Salamanca (Spain); Krolikowski, W. [Laser Physics Centre, Research School of Physics and Engineering, Australian National University, Canberra ACT 0200 (Australia); Science Program, Texas A and M University at Qatar, Doha (Qatar); Sheng, Y. [Laser Physics Centre, Research School of Physics and Engineering, Australian National University, Canberra ACT 0200 (Australia)

    2015-06-01

    Pulse compression in dispersive strontium barium niobate crystal with a random size and distribution of the anti-parallel orientated nonlinear domains is observed via transverse second harmonic generation. The dependence of the transverse width of the second harmonic trace along the propagation direction allows for the determination of the initial chirp and duration of pulses in the femtosecond regime. This technique permits a real-time analysis of the pulse evolution and facilitates fast in-situ correction of pulse chirp acquired in the propagation through an optical system.

  12. Ultrashort pulse chirp measurement via transverse second-harmonic generation in strontium barium niobate crystal

    Trull, J.; Wang, B.; Parra, A.; Vilaseca, R.; Cojocaru, C.; Sola, I.; Krolikowski, W.; Sheng, Y.

    2015-01-01

    Pulse compression in dispersive strontium barium niobate crystal with a random size and distribution of the anti-parallel orientated nonlinear domains is observed via transverse second harmonic generation. The dependence of the transverse width of the second harmonic trace along the propagation direction allows for the determination of the initial chirp and duration of pulses in the femtosecond regime. This technique permits a real-time analysis of the pulse evolution and facilitates fast in-situ correction of pulse chirp acquired in the propagation through an optical system

  13. Suppression and nonlinear excitation of parasitic modes in second harmonic gyrotrons operating in a very high order mode

    Nusinovich, Gregory S.; Pu, Ruifeng; Granatstein, Victor L.

    2015-01-01

    In recent years, there was an active development of high-power, sub-terahertz (sub-THz) gyrotrons for numerous applications. For example, a 0.67 THz gyrotron delivering more than 200 kW with about 20% efficiency was developed. This record high efficiency was achieved because the gyrotron operated in a high-order TE 31,8 -mode with the power of ohmic losses less than 10% of the power of outgoing radiation. That gyrotron operated at the fundamental cyclotron resonance, and a high magnetic field of about 27 T was created by a pulse solenoid. For numerous applications, it is beneficial to use gyrotrons at cyclotron harmonics which can operate in available cryomagnets with fields not exceeding 15 T. However, typically, the gyrotron operation at harmonics faces severe competition from parasitic modes at the fundamental resonance. In the present paper, we consider a similar 0.67 THz gyrotron designed for operation in the same TE 31,8 -mode, but at the second harmonic. We focus on two nonlinear effects typical for interaction between the fundamental and second harmonic modes, viz., the mode suppression and the nonlinear excitation of the mode at the fundamental harmonic by the second harmonic oscillations. Our study includes both the analytical theory and numerical simulations performed with the self-consistent code MAGY. The simulations show that stable second harmonic operation in the TE 31,8 mode is possible with only modest sacrifice of efficiency and power

  14. Measurement of electrodynamics characteristics of higher order modes for harmonic cavity at 2400 MHz

    Shashkov, Ya V.; Sobenin, N. P.; Gusarova, M. A.; Lalayan, M. V.; Bazyl, D. S.; Donetskiy, R. V.; Orlov, A. I.; Zobov, M. M.; Zavadtsev, A. A.

    2016-09-01

    In the frameworks of the High Luminosity Large Hadron Collider (HL-LHC) upgrade program an application of additional superconducting harmonic cavities operating at 800 MHz is currently under discussion. As a possible candidate, an assembly of two cavities with grooved beam pipes connected by a drift tube and housed in a common cryomodule, was proposed. In this article we discuss measurements of loaded Q-factors of higher order modes (HOM) performed on a scaled aluminium single cell cavity prototype with the fundamental frequency of 2400 MHz and on an array of two such cavities connected by a narrow beam pipe. The measurements were performed for the system with and without the matching load in the drift tube..

  15. Variable order spherical harmonic expansion scheme for the radiative transport equation using finite elements

    Surya Mohan, P.; Tarvainen, Tanja; Schweiger, Martin; Pulkkinen, Aki; Arridge, Simon R.

    2011-01-01

    Highlights: → We developed a variable order global basis scheme to solve light transport in 3D. → Based on finite elements, the method can be applied to a wide class of geometries. → It is computationally cheap when compared to the fixed order scheme. → Comparisons with local basis method and other models demonstrate its accuracy. → Addresses problems encountered n modeling of light transport in human brain. - Abstract: We propose the P N approximation based on a finite element framework for solving the radiative transport equation with optical tomography as the primary application area. The key idea is to employ a variable order spherical harmonic expansion for angular discretization based on the proximity to the source and the local scattering coefficient. The proposed scheme is shown to be computationally efficient compared to employing homogeneously high orders of expansion everywhere in the domain. In addition the numerical method is shown to accurately describe the void regions encountered in the forward modeling of real-life specimens such as infant brains. The accuracy of the method is demonstrated over three model problems where the P N approximation is compared against Monte Carlo simulations and other state-of-the-art methods.

  16. Can even-order laser harmonics exhibited by Bohmian trajectories in symmetric potentials be observed?

    Peatross, J; Johansen, J

    2014-01-13

    Strong-field laser-atom interactions provide extreme conditions that may be useful for investigating the de Broglie-Bohm quantum interpretation. Bohmian trajectories representing bound electrons in individual atoms exhibit both even and odd harmonic motion when subjected to a strong external laser field. The phases of the even harmonics depend on the random initial positions of the trajectories within the wave function, making the even harmonics incoherent. In contrast, the phases of odd harmonics remain for the most part coherent regardless of initial position. Under the conjecture that a Bohmian point particle plays the role of emitter, this suggests an experiment to determine whether both even and odd harmonics are produced at the atomic level. Estimates suggest that incoherent emission of even harmonics may be detectable out the side of an intense laser focus interacting with a large number of atoms.

  17. Concept for power scaling second harmonic generation using a cascade of nonlinear crystals

    Hansen, Anders Kragh; Tawfieq, Mahmoud; Jensen, Ole Bjarlin

    2015-01-01

    for efficient power scaling of single-pass SHG beyond such limits using a cascade of nonlinear crystals, in which the first crystal is chosen for high nonlinear efficiency and the subsequent crystal(s) are chosen for power handling ability. Using this highly efficient singlepass concept, we generate 3.7 W...... successfully combines the high efficiency of the first stage with the good power handling properties of the subsequent stages. The concept is generally applicable and can be expanded with more stages to obtain even higher efficiency, and extends also to other combinations of nonlinear media suitable for other......Within the field of high-power second harmonic generation (SHG), power scaling is often hindered by adverse crystal effects such as thermal dephasing arising from the second harmonic (SH) light, which imposes limits on the power that can be generated in many crystals. Here we demonstrate a concept...

  18. Mode matching in multiresonant plasmonic nanoantennas for enhanced second harmonic generation

    Celebrano, Michele; Wu, Xiaofei; Baselli, Milena; Großmann, Swen; Biagioni, Paolo; Locatelli, Andrea; de Angelis, Costantino; Cerullo, Giulio; Osellame, Roberto; Hecht, Bert; Duò, Lamberto; Ciccacci, Franco; Finazzi, Marco

    2015-05-01

    Boosting nonlinear frequency conversion in extremely confined volumes remains a challenge in nano-optics research, but can enable applications in nanomedicine, photocatalysis and background-free biosensing. To obtain brighter nonlinear nanoscale sources, approaches that enhance the electromagnetic field intensity and counter the lack of phase matching in nanoplasmonic systems are often employed. However, the high degree of symmetry in the crystalline structure of plasmonic materials (metals in particular) and in nanoantenna designs strongly quenches second harmonic generation. Here, we describe doubly-resonant single-crystalline gold nanostructures with no axial symmetry displaying spatial mode overlap at both the excitation and second harmonic wavelengths. The combination of these features allows the attainment of a nonlinear coefficient for second harmonic generation of ˜5 × 10-10 W-1, enabling a second harmonic photon yield higher than 3 × 106 photons per second. Theoretical estimations point toward the use of our nonlinear plasmonic nanoantennas as efficient platforms for label-free molecular sensing.

  19. Ultrafast third-harmonic generation from textured aluminum nitride-sapphire interfaces

    Stoker, D. S.; Keto, J. W.; Baek, J.; Wang, W.; Becker, M. F.; Kovar, D.

    2006-01-01

    We measured and modeled third-harmonic generation (THG) from an AlN thin film on sapphire using a time-domain approach appropriate for ultrafast lasers. Second-harmonic measurements indicated that polycrystalline AlN contains long-range crystal texture. An interface model for third-harmonic generation enabled an analytical representation of scanning THG (z-scan) experiments. Using it and accounting for Fresnel reflections, we measured the AlN-sapphire susceptibility ratio and estimated the susceptibility for aluminum nitride, χ xxxx (3) (3ω;ω,ω,ω)=1.52±0.25x10 -13 esu. The third-harmonic (TH) spectrum strongly depended on the laser focus position and sample thickness. The amplitude and phase of the frequency-domain interference were fit to the Fourier transform of the calculated time-domain field to improve the accuracy of several experimental parameters. We verified that the model works well for explaining TH signal amplitudes and spectral phase. Some anomalous features in the TH spectrum were observed, which we attributed to nonparaxial effects

  20. Spatio-spectral analysis of ionization times in high-harmonic generation

    Soifer, Hadas, E-mail: hadas.soifer@weizmann.ac.il [Department of Physics of Complex Systems, Weizmann Institute of Science, Rehovot 76100 (Israel); Dagan, Michal; Shafir, Dror; Bruner, Barry D. [Department of Physics of Complex Systems, Weizmann Institute of Science, Rehovot 76100 (Israel); Ivanov, Misha Yu. [Department of Physics, Imperial College London, South Kensington Campus, SW7 2AZ London (United Kingdom); Max-Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, Max-Born-Strasse 2A, D-12489 Berlin (Germany); Serbinenko, Valeria; Barth, Ingo; Smirnova, Olga [Max-Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, Max-Born-Strasse 2A, D-12489 Berlin (Germany); Dudovich, Nirit [Department of Physics of Complex Systems, Weizmann Institute of Science, Rehovot 76100 (Israel)

    2013-03-12

    Graphical abstract: A spatio-spectral analysis of the two-color oscillation phase allows us to accurately separate short and long trajectories and reconstruct their ionization times. Highlights: ► We perform a complete spatio-spectral analysis of the high harmonic generation process. ► We analyze the ionization times across the entire spatio-spectral plane of the harmonics. ► We apply this analysis to reconstruct the ionization times of both short and long trajectories. - Abstract: Recollision experiments have been very successful in resolving attosecond scale dynamics. However, such schemes rely on the single atom response, neglecting the macroscopic properties of the interaction and the effects of using multi-cycle laser fields. In this paper we perform a complete spatio-spectral analysis of the high harmonic generation process and resolve the distribution of the subcycle dynamics of the recolliding electron. Specifically, we focus on the measurement of ionization times. Recently, we have demonstrated that the addition of a weak, crossed polarized second harmonic field allows us to resolve the moment of ionization (Shafir, 2012) [1]. In this paper we extend this measurement and perform a complete spatio-spectral analysis. We apply this analysis to reconstruct the ionization times of both short and long trajectories showing good agreement with the quantum path analysis.

  1. High-order harmonics from an ultraintense laser pulse propagating inside a fiber

    Bulanov, S.V.; Esirkepov, T. Zh.; Naumova, N.M.; Sokolov, I.V.

    2003-01-01

    A strong effect of high harmonic radiation during the propagation of a high intensity short laser pulse in a thin wall hollow channel ('fiber') is found and studied via relativistic particle-in-cell simulations. The fiber has finite width walls comprised of an overdense plasma. Only the harmonic radiation with the harmonic number above critical value, for which the fiber walls are transparent, propagates outwards in the form of a coherent ultrashort pulse with very short wavelength

  2. Enhanced Cerenkov second-harmonic generation in a planar nonlinear waveguide that reproduces a one-dimensional photonic bandgap structure

    Pezzetta, D.; Sibilia, C.; Bertolotti, M.; Ramponi, R.; Osellame, R.; Marangoni, M.; Haus, J. W.; Scalora, M.; Bloemer, M. J.; Bowden, C. M.

    2002-01-01

    Second-harmonic generation in the Cerenkov configuration is investigated under conditions for which the use of a linear grating fabricated on top of the waveguide reproduces a photonic bandgap structure. The fundamental mode of the guide at the fundamental frequency is tuned at the photonic band-edge resonance, thus producing great confinement and enhancement of the electromagnetic field inside the structure. The conversion efficiency achieved in both the forward and the backward directions is at least 1 order of magnitude greater than that of a conventional Cerenkov emission in a waveguide of the same length. An analysis of the tolerances of the grating period on the conversion efficiency is presented

  3. Experimental Observation of Cumulative Second-Harmonic Generation of Circumferential Guided Wave Propagation in a Circular Tube

    Deng Ming-Xi; Gao Guang-Jian; Li Ming-Liang

    2015-01-01

    The experimental observation of cumulative second-harmonic generation of the primary circumferential guided wave propagation is reported. A pair of wedge transducers is used to generate the primary circumferential guided wave desired and to detect its fundamental-frequency and second-harmonic amplitudes on the outside surface of the circular tube. The amplitudes of the fundamental waves and the second harmonics of the circumferential guided wave propagation are measured for different separations between the two wedge transducers. At the driving frequency where the primary and the double-frequency circumferential guided waves have the same linear phase velocities, the clear second-harmonic signals can be observed. The quantitative relationships between the second-harmonic amplitudes and circumferential angle are analyzed. It is experimentally verified that the second harmonics of primary circumferential guided waves do have a cumulative growth effect with the circumferential angle. (paper)

  4. Second-Order Harmonic Reduction Technique for Photovoltaic Power Conditioning Systems Using a Proportional-Resonant Controller

    Hae-Gwang Jeong

    2013-01-01

    Full Text Available This paper proposes a second-order harmonic reduction technique using a proportional-resonant (PR controller for a photovoltaic (PV power conditioning system (PCS. In a grid-connected single-phase system, inverters create a second-order harmonic at twice the fundamental frequency. A ripple component unsettles the operating points of the PV array and deteriorates the operation of the maximum power point tracking (MPPT technique. The second-order harmonic component in PV PCS is analyzed using an equivalent circuit of the DC/DC converter and the DC/AC inverter. A new feed-forward compensation technique using a PR controller for ripple reduction is proposed. The proposed algorithm is advantageous in that additional devices are not required and complex calculations are unnecessary. Therefore, this method is cost-effective and simple to implement. The proposed feed-forward compensation technique is verified by simulation and experimental results.

  5. A large enhancement of photoinduced second harmonic generation in CdI2--Cu layered nanocrystals.

    Miah, M Idrish

    2009-02-12

    Photoinduced second harmonic generation (PISHG) in undoped as well as in various Cu-doped (0.05-1.2% Cu) CdI2 nanocrystals was measured at liquid nitrogen temperature (LNT). It was found that the PISHG increases with increasing Cu doping up to approximately 0.6% and then decreases almost to that for the undoped CdI2 for doping higher than approximately 1%. The values of the second-order susceptibility ranged from 0.50 to 0.67 pm V(-1) for the Cu-doped nanocrystals with a thickness of 0.5 nm. The Cu-doping dependence shown in a parabolic fashion suggests a crucial role of the Cu agglomerates in the observed effects. The PISHG in crystals with various nanosizes was also measured at LNT. The size dependence demonstrated the quantum-confined effect with a maximum PISHG for 0.5 nm and with a clear increase in the PISHG with decreasing thickness of the nanocrystal. The Raman scattering spectra at different pumping powers were taken for thin nanocrystals, and the phonon modes originating from interlayer phonons were observed in the spectra. The results were discussed within a model of photoinduced electron-phonon anharmonicity.

  6. High Harmonic Generation XUV Spectroscopy for Studying Ultrafast Photophysics of Coordination Complexes

    Ryland, Elizabeth S.; Lin, Ming-Fu; Benke, Kristin; Verkamp, Max A.; Zhang, Kaili; Vura-Weis, Josh

    2017-06-01

    Extreme ultraviolet (XUV) spectroscopy is an inner shell technique that probes the M_{2,3}-edge excitation of atoms. Absorption of the XUV photon causes a 3p→3d transition, the energy and shape of which is directly related to the element and ligand environment. This technique is thus element-, oxidation state-, spin state-, and ligand field specific. A process called high-harmonic generation (HHG) enables the production of ultrashort (˜20fs) pulses of collimated XUV photons in a tabletop instrument. This allows transient XUV spectroscopy to be conducted as an in-lab experiment, where it was previously only possible at accelerator-based light sources. Additionally, ultrashort pulses provide the capability for unprecedented time resolution (˜50fs IRF). This technique has the capacity to serve a pivotal role in the study of electron and energy transfer processes in materials and chemical biology. I will present the XUV transient absorption instrument we have built, along with ultrafast transient M_{2,3}-edge absorption data of a series of small inorganic molecules in order to demonstrate the high specificity and time resolution of this tabletop technique as well as how our group is applying it to the study of ultrafast electronic dynamics of coordination complexes.

  7. Kinetic Modeling of Accelerated Stability Testing Enabled by Second Harmonic Generation Microscopy.

    Song, Zhengtian; Sarkar, Sreya; Vogt, Andrew D; Danzer, Gerald D; Smith, Casey J; Gualtieri, Ellen J; Simpson, Garth J

    2018-04-03

    The low limits of detection afforded by second harmonic generation (SHG) microscopy coupled with image analysis algorithms enabled quantitative modeling of the temperature-dependent crystallization of active pharmaceutical ingredients (APIs) within amorphous solid dispersions (ASDs). ASDs, in which an API is maintained in an amorphous state within a polymer matrix, are finding increasing use to address solubility limitations of small-molecule APIs. Extensive stability testing is typically performed for ASD characterization, the time frame for which is often dictated by the earliest detectable onset of crystal formation. Here a study of accelerated stability testing on ritonavir, a human immunodeficiency virus (HIV) protease inhibitor, has been conducted. Under the condition for accelerated stability testing at 50 °C/75%RH and 40 °C/75%RH, ritonavir crystallization kinetics from amorphous solid dispersions were monitored by SHG microscopy. SHG microscopy coupled by image analysis yielded limits of detection for ritonavir crystals as low as 10 ppm, which is about 2 orders of magnitude lower than other methods currently available for crystallinity detection in ASDs. The four decade dynamic range of SHG microscopy enabled quantitative modeling with an established (JMAK) kinetic model. From the SHG images, nucleation and crystal growth rates were independently determined.

  8. Analysis of human knee osteoarthritic cartilage using polarization sensitive second harmonic generation microscopy

    Kumar, Rajesh; Grønhaug, Kirsten M.; Romijn, Elisabeth I.; Drogset, Jon O.; Lilledahl, Magnus B.

    2014-05-01

    Osteoarthritis is one of the most prevalent joint diseases in the world. Although the cause of osteoarthritis is not exactly clear, the disease results in a degradation of the quality of the articular cartilage including collagen and other extracellular matrix components. We have investigated alterations in the structure of collagen fibers in the cartilage tissue of the human knee using mulitphoton microscopy. Due to inherent high nonlinear susceptibility, ordered collagen fibers present in the cartilage tissue matrix produces strong second harmonic generation (SHG) signals. Significant morphological differences are found in different Osteoarthritic grades of cartilage by SHG microscopy. Based on the polarization analysis of the SHG signal, we find that a few locations of hyaline cartilage (mainly type II collagen) is being replaced by fibrocartilage (mainly type I cartilage), in agreement with earlier literature. To locate the different types and quantify the alteration in the structure of collagen fiber, we employ polarization-SHG microscopic analysis, also referred to as _-tensor imaging. The image analysis of p-SHG image obtained by excitation polarization measurements would represent different tissue constituents with different numerical values at pixel level resolution.

  9. Transformation between surface spherical harmonic expansion of arbitrary high degree and order and double Fourier series on sphere

    Fukushima, Toshio

    2018-02-01

    In order to accelerate the spherical harmonic synthesis and/or analysis of arbitrary function on the unit sphere, we developed a pair of procedures to transform between a truncated spherical harmonic expansion and the corresponding two-dimensional Fourier series. First, we obtained an analytic expression of the sine/cosine series coefficient of the 4 π fully normalized associated Legendre function in terms of the rectangle values of the Wigner d function. Then, we elaborated the existing method to transform the coefficients of the surface spherical harmonic expansion to those of the double Fourier series so as to be capable with arbitrary high degree and order. Next, we created a new method to transform inversely a given double Fourier series to the corresponding surface spherical harmonic expansion. The key of the new method is a couple of new recurrence formulas to compute the inverse transformation coefficients: a decreasing-order, fixed-degree, and fixed-wavenumber three-term formula for general terms, and an increasing-degree-and-order and fixed-wavenumber two-term formula for diagonal terms. Meanwhile, the two seed values are analytically prepared. Both of the forward and inverse transformation procedures are confirmed to be sufficiently accurate and applicable to an extremely high degree/order/wavenumber as 2^{30} {≈ } 10^9. The developed procedures will be useful not only in the synthesis and analysis of the spherical harmonic expansion of arbitrary high degree and order, but also in the evaluation of the derivatives and integrals of the spherical harmonic expansion.

  10. Harmonic US imaging of vesicoureteric reflux in children: usefulness of a second generation US contrast agent.

    Ascenti, Giorgio; Zimbaro, Giovanni; Mazziotti, Silvio; Chimenz, Roberto; Fede, Carmelo; Visalli, Carmela; Scribano, Emanuele

    2004-06-01

    Contrast-enhanced voiding urosonography (VUS) is largely accepted both for the diagnosis and follow-up of vesicoureteric reflux (VUR) in children. To evaluate the usefulness of contrast-enhanced second-harmonic VUS in the diagnosis and grading of VUR, using a second-generation contrast agent. Eighty consecutive children were prospectively studied with contrast-enhanced second-harmonic VUS. All children received a second-generation contrast medium, constituted by phospholipid-stabilized microbubbles of sulphur-hexafluoride (SonoVue, Bracco, Milan, Italy). US monitoring of the bladder, of the retrovesical space and of the kidneys was performed using, alternatively, both tissue-harmonic and contrast-harmonic modes. In those young boys where VUR was depicted at VUS, examination was completed with transperineal, sagittal urethral exploration during micturition. VUR was graded in five steps and diagnoses were compared with voiding cystourethrography (VCUG). VUR was diagnosed in 52 reno-ureteral units with VUS. In 49 of these reno-ureteral units, VCUG confirmed the presence of VUR. In comparison to VUS, sensitivity and negative predictive value of VCUG were inferior. The grade of VUR detected at VUS was higher than that detected at VCUG in three units. In no case was the grade of VUR detected at VCUG higher than the one detected at VUS. The differences between VUS and VCUG in grading VUR were statistically significant (p=0.02). Imaging of the normal posterior urethra was skilfully demonstrated with US in 15 young boys with VUR. No statistically significant differences were found between tissue-harmonic and contrast-harmonic mode (p=0.102). Contrast-enhanced second-harmonic VUS is a sensitive and easy technique for the evaluation of VUR. A second-generation US contrast medium such as SonoVue, if available, should be the first choice as the dose required for one examination is much lower and consequently significant reduction of contrast agent cost is possible. Copyright

  11. Higher-order approximate solutions to the relativistic and Duffing-harmonic oscillators by modified He's homotopy methods

    Belendez, A; Pascual, C; Fernandez, E; Neipp, C; Belendez, T

    2008-01-01

    A modified He's homotopy perturbation method is used to calculate higher-order analytical approximate solutions to the relativistic and Duffing-harmonic oscillators. The He's homotopy perturbation method is modified by truncating the infinite series corresponding to the first-order approximate solution before introducing this solution in the second-order linear differential equation, and so on. We find this modified homotopy perturbation method works very well for the whole range of initial amplitudes, and the excellent agreement of the approximate frequencies and periodic solutions with the exact ones has been demonstrated and discussed. The approximate formulae obtained show excellent agreement with the exact solutions, and are valid for small as well as large amplitudes of oscillation, including the limiting cases of amplitude approaching zero and infinity. For the relativistic oscillator, only one iteration leads to high accuracy of the solutions with a maximal relative error for the approximate frequency of less than 1.6% for small and large values of oscillation amplitude, while this relative error is 0.65% for two iterations with two harmonics and as low as 0.18% when three harmonics are considered in the second approximation. For the Duffing-harmonic oscillator the relative error is as low as 0.078% when the second approximation is considered. Comparison of the result obtained using this method with those obtained by the harmonic balance methods reveals that the former is very effective and convenient

  12. Mapping the nonlinear optical susceptibility by noncollinear second-harmonic generation.

    Larciprete, M C; Bovino, F A; Giardina, M; Belardini, A; Centini, M; Sibilia, C; Bertolotti, M; Passaseo, A; Tasco, V

    2009-07-15

    We present a method, based on noncollinear second-harmonic generation, to evaluate the nonzero elements of the nonlinear optical susceptibility. At a fixed incidence angle, the generated signal is investigated by varying the polarization state of both fundamental beams. The resulting polarization charts allows us to verify if Kleinman's symmetry rules can be applied to a given material or to retrieve the absolute value of the nonlinear optical tensor terms, from a reference measurement. Experimental measurements obtained from gallium nitride layers are reported. The proposed method does not require an angular scan and thus is useful when the generated signal is strongly affected by sample rotation.

  13. High gain harmonic generation free electron lasers enhanced by pseudoenergy bands

    Takashi Tanaka

    2017-08-01

    Full Text Available We propose a new scheme for high gain harmonic generation free electron lasers (HGHG FELs, which is seeded by a pair of intersecting laser beams to interact with an electron beam in a modulator undulator located in a dispersive section. The interference of the laser beams gives rise to a two-dimensional modulation in the energy-time phase space because of a strong correlation between the electron energy and the position in the direction of dispersion. This eventually forms pseudoenergy bands in the electron beam, which result in efficient harmonic generation in HGHG FELs in a similar manner to the well-known scheme using the echo effects. The advantage of the proposed scheme is that the beam quality is less deteriorated than in other existing schemes.

  14. Soft X-Ray Second Harmonic Generation as an Interfacial Probe

    Lam, R. K.; Raj, S. L.; Pascal, T. A.; Pemmaraju, C. D.; Foglia, L.; Simoncig, A.; Fabris, N.; Miotti, P.; Hull, C. J.; Rizzuto, A. M.; Smith, J. W.; Mincigrucci, R.; Masciovecchio, C.; Gessini, A.; Allaria, E.; De Ninno, G.; Diviacco, B.; Roussel, E.; Spampinati, S.; Penco, G.; Di Mitri, S.; Trovò, M.; Danailov, M.; Christensen, S. T.; Sokaras, D.; Weng, T. -C.; Coreno, M.; Poletto, L.; Drisdell, W. S.; Prendergast, D.; Giannessi, L.; Principi, E.; Nordlund, D.; Saykally, R. J.; Schwartz, C. P.

    2018-01-01

    Nonlinear optical processes at soft x-ray wavelengths have remained largely unexplored due to the lack of available light sources with the requisite intensity and coherence. Here we report the observation of soft x-ray second harmonic generation near the carbon K edge (~284 eV) in graphite thin films generated by high intensity, coherent soft x-ray pulses at the FERMI free electron laser. Our experimental results and accompanying first-principles theoretical analysis highlight the effect of resonant enhancement above the carbon K edge and show the technique to be interfacially sensitive in a centrosymmetric sample with second harmonic intensity arising primarily from the first atomic layer at the open surface. This technique and the associated theoretical framework demonstrate the ability to selectively probe interfaces, including those that are buried, with elemental specificity, providing a new tool for a range of scientific problems.

  15. Generation of high harmonic free electron laser with phase-merging effect

    Li, Heting, E-mail: liheting@ustc.edu.cn; Jia, Qika; Zhao, Zhouyu

    2017-03-01

    An easy-to-implement scheme is proposed to produce the longitudinal electron bunch density modulation with phase-merging phenomenon. In this scheme an electron bunch is firstly transversely dispersed in a modified dogleg to generate the exact dependence of electron energy on the transverse position, then it is modulated in a normal modulator. After travelling through a modified chicane with specially designed transfer matrix elements, the density modulation with phase-merging effect is generated which contains high harmonic components of the seed laser. We present theoretical analysis and numerical simulations for seeded soft x-ray free-electron laser. The results demonstrate that this technique can significantly enhance the frequency up-conversion efficiency and allow a seeded FEL operating at very high harmonics.

  16. Effect of composition and temperature on the second harmonic generation in silver phosphate glasses

    Konidakis, I.; Psilodimitrakopoulos, S.; Kosma, K.; Lemonis, A.; Stratakis, E.

    2018-01-01

    We herein employ nonlinear laser imaging microscopy to explicitly study the dynamics of second harmonic generation (SHG) in silver iodide phosphate glasses. While glasses of this family have gained extensive scientific attention over the years due to their superior conducting properties, considerably less attention has been paid to their unique nonlinear optical characteristics. In the present study, firstly, it is demonstrated that SHG signal intensity is enhanced upon increasing silver content due to the random formation of silver microstructures within the glass network. Secondly, the SHG temperature dynamics were explored near the glass transition temperature (Tg) regime, where significant glass relaxation phenomena occur. It is found that heating towards the Tg improves the SHG efficiency, whereas above Tg, the capacity of glasses to generate second harmonic radiation is drastically suppressed. The novel findings of this work are considered important in terms of the potential employment of these glasses for the realization of advanced photonic applications like optical-switches and wavelength conversion devices.

  17. Green bright squeezed light from a cw periodically poled KTP second harmonic generator

    Andersen, Ulrik Lund; Buchhave, Preben

    2002-01-01

    We present the experimental observation of bright amplitude squeezed light from a singly resonant second harmonic generator (SHG) based on a periodically poled potassium titanyl phosphate (KTP) crystal. Contrary to conventional SHG, the interacting waves in this device couple efficiently using qu...... reduction is greater than what could be expected using normal birefringence phase matched KTP with the same experimental parameters. Excellent agreement between experiment and theory is found. (C)2002 Optical Society of America....... quasi phase matching (QPM) and more importantly QPM allows access to higher valued elements of the nonlinear tensor than is possible under the constraint of birefringence phase matching. We observe a noise reduction of 13% below the shot noise limit in the generated second harmonic field. This noise...

  18. First lasing of a high-gain harmonic generation free-electron laser experiment.

    Babzien, M.; Ben-Zvi, I.; Biedron, S. G.; DiMauro, L. F.; Douryan, A.; Galayda, J. N.; Gluskin, E.; Graves, W.; Jagger, J.; Johnson, E.; Krinsky, S.; Malone, R.; Pogorelsky, I.; Rakowsky, G.; Sajaev, V.; Skaritka, J.; Solomon, L.; Vasserman, I.; Wang, X. L.; Woodle, M.; Yakimenko, V.; Yu, L.-H.

    1999-09-11

    We report on the first lasing of a high-gain harmonic generation (HGHG) free-electron laser (FEL). The experiment was conducted at the Accelerator Test Facility (ATF) at Brookhaven National Laboratory (BNL). This is a BNL experiment in collaboration with the Advanced Photon Source (APS) at Argonne National Laboratory. A preliminary measurement gives a high-gain harmonic generation (HGHG) pulse energy that is 2 x 10{sup 7} times larger than the spontaneous radiation, In a purely self-amplified spontaneous emission (SASE) mode of operation, the signal was measured as 10 times larger than the spontaneous radiation in the same distance ({approximately}2 m) through the same wiggler. This means the HGHG signal is 2 x 10{sup 6} times larger than the SASE signal. To obtain the same saturated output power by the SASE process, the radiator would have to be 3 times longer (6 m).

  19. Comparative investigation of third- and fifth-harmonic generation in atomic and molecular gases driven by midinfrared ultrafast laser pulses

    Ni Jielei; Yao Jinping; Zeng Bin; Chu Wei; Li Guihua; Zhang Haisu; Jing Chenrui [State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, P.O. Box 800-211, Shanghai 201800 (China); Graduate School of the Chinese Academy of Sciences, Beijing 100039 (China); Chin, S. L. [Department of Physics, Engineering Physics and Optics, and Center for Optics, Photonics and Laser (COPL), Laval University, Laval, Quebec, G1K 7P4 (Canada); Cheng, Y.; Xu, Z. [State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, P.O. Box 800-211, Shanghai 201800 (China)

    2011-12-15

    We report on the comparative experimental investigation on third- and fifth-harmonic generation (THG and FHG) in atomic and molecular gases driven by midinfrared ultrafast laser pulses at a wavelength of {approx}1500 nm. We observe that the conversion efficiencies of both the THG and FHG processes saturate at similar peak intensities close to {approx}1.5 x 10{sup 14} W/cm{sup 2} for argon, nitrogen, and air, whose ionization potentials are close to each other. Near the saturation intensity, the ratio of yields of the FHG and THG reaches {approx}10{sup -1} for all the gases. Our results show that high-order Kerr effect seems to exist; however, contribution from the fourth-order Kerr refractive index coefficient alone is insufficient to balance the Kerr self-focusing without the assistance of plasma generation.

  20. Atomic systems with one and two active electrons in electromagnetic fields: Ionization and high harmonics generation

    Ivanov, I A; Kheifets, A S

    2010-01-01

    We describe a theoretical procedure for solving the time-dependent Schroedinger equation (TDSE) for atomic systems with one or two valence electrons. Motion of the valence electrons is described by means of the Hartree-Fock potential including the exchange interaction. We apply the procedure to various physical phenomena occurring in atoms exposed to strong electromagnetic fields. As an illustration, we consider below the processes of high harmonics generation and attosecond pulses production.

  1. High-contrast imaging of mycobacterium tuberculosis using third-harmonic generation microscopy

    Kim, Bo Ram; Lee, Eungjang; Park, Seung-Han

    2015-07-01

    Nonlinear optical microcopy has become an important tool in investigating biomaterials due to its various advantages such as label-free imaging capabilities. In particular, it has been shown that third-harmonic generation (THG) signals can be produced at interfaces between an aqueous medium (e.g. cytoplasm, interstitial fluid) and a mineralized lipidic surface. In this work, we have demonstrated that label-free high-contrast THG images of the mycobacterium tuberculosis can be obtained using THG microscopy.

  2. Optical second harmonic generation phase measurement at interfaces of some organic layers with indium tin oxide

    Ngah Demon, Siti Zulaikha; Miyauchi, Yoshihiro; Mizutani, Goro; Matsushima, Toshinori; Murata, Hideyuki

    2014-08-01

    We observed phase shift in optical second harmonic generation (SHG) from interfaces of indium tin oxide (ITO)/copper phthalocyanine (CuPc) and ITO/pentacene. Phase correction due to Fresnel factors of the sample was taken into account. The phase of SHG electric field at the ITO/pentacene interface, ϕinterface with respect to the phase of SHG of bare substrate ITO was 160°, while the interface of ITO/CuPc had a phase of 140°.

  3. Optical second harmonic generation phase measurement at interfaces of some organic layers with indium tin oxide

    Ngah Demon, Siti Zulaikha; Miyauchi, Yoshihiro; Mizutani, Goro; Matsushima, Toshinori; Murata, Hideyuki

    2014-01-01

    We observed phase shift in optical second harmonic generation (SHG) from interfaces of indium tin oxide (ITO)/copper phthalocyanine (CuPc) and ITO/pentacene. Phase correction due to Fresnel factors of the sample was taken into account. The phase of SHG electric field at the ITO/pentacene interface, ϕ_ with respect to the phase of SHG of bare substrate ITO was 160°, while the interface of ITO/CuPc had a phase of 140°.

  4. Grain size effect of monolayer MoS2 transistors characterized by second harmonic generation mapping

    Lin, Chih-Pin

    2015-08-27

    We investigated different CVD-synthesized MoS2 films, aiming to correlate the device characteristics with the grain size. The grain size of MoS2 can be precisely characterized through nondestructive second harmonic generation mapping based on the degree of inversion symmetry. The devices with larger grains at the channel region show improved on/off current ratio, which can be explained by the less carrier scattering caused by the grain boundaries.

  5. The Ultraviolet Surprise. Efficient Soft X-Ray High Harmonic Generation in Multiply-Ionized Plasmas

    Popmintchev, Dimitar; Hernandez-Garcia, Carlos; Dollar, Franklin; Mancuso, Christopher; Perez-Hernandez, Jose A.; Chen, Ming-Chang; Hankla, Amelia; Gao, Xiaohui; Shim, Bonggu; Gaeta, Alexander L.; Tarazkar, Maryam; Romanov, Dmitri A.; Levis, Robert J.; Gaffney, Jim A.; Foord, Mark; Libby, Stephen B.; Jaron-Becker, Agnieskzka; Becker, Andreas; Plaja, Luis; Muranane, Margaret M.; Kapteyn, Henry C.; Popmintchev, Tenio

    2015-01-01

    High-harmonic generation is a universal response of matter to strong femtosecond laser fields, coherently upconverting light to much shorter wavelengths. Optimizing the conversion of laser light into soft x-rays typically demands a trade-off between two competing factors. Reduced quantum diffusion of the radiating electron wave function results in emission from each species which is highest when a short-wavelength ultraviolet driving laser is used. But, phase matching - the constructive addition of x-ray waves from a large number of atoms - favors longer-wavelength mid-infrared lasers. We identified a regime of high-harmonic generation driven by 40-cycle ultraviolet lasers in waveguides that can generate bright beams in the soft x-ray region of the spectrum, up to photon energies of 280 electron volts. Surprisingly, the high ultraviolet refractive indices of both neutral atoms and ions enabled effective phase matching, even in a multiply ionized plasma. We observed harmonics with very narrow linewidths, while calculations show that the x-rays emerge as nearly time-bandwidt-limited pulse trains of ~100 attoseconds

  6. Beam position diagnostics with higher order modes in third harmonic superconducting accelerating cavities

    Zhang, Pei

    2013-02-01

    Higher order modes (HOM) are electromagnetic resonant fields. They can be excited by an electron beam entering an accelerating cavity, and constitute a component of the wakefield. This wakefield has the potential to dilute the beam quality and, in the worst case, result in a beam-break-up instability. It is therefore important to ensure that these fields are well suppressed by extracting energy through special couplers. In addition, the effect of the transverse wakefield can be reduced by aligning the beam on the cavity axis. This is due to their strength depending on the transverse offset of the excitation beam. For suitably small offsets the dominant components of the transverse wakefield are dipole modes, with a linear dependence on the transverse offset of the excitation bunch. This fact enables the transverse beam position inside the cavity to be determined by measuring the dipole modes extracted from the couplers, similar to a cavity beam position monitor (BPM), but requires no additional vacuum instrumentation. At the FLASH facility in DESY, 1.3 GHz (known as TESLA) and 3.9 GHz (third harmonic) cavities are installed. Wakefields in 3.9 GHz cavities are significantly larger than in the 1.3 GHz cavities. It is therefore important to mitigate the adverse effects of HOMs to the beam by aligning the beam on the electric axis of the cavities. This alignment requires an accurate beam position diagnostics inside the 3.9 GHz cavities. It is this aspect that is focused on in this thesis. Although the principle of beam diagnostics with HOM has been demonstrated on 1.3 GHz cavities, the realization in 3.9 GHz cavities is considerably more challenging. This is due to the dense HOM spectrum and the relatively strong coupling of most HOMs amongst the four cavities in the third harmonic cryo-module. A comprehensive series of simulations and HOM spectra measurements have been performed in order to study the modal band structure of the 3.9 GHz cavities. The dependencies of

  7. Beam position diagnostics with higher order modes in third harmonic superconducting accelerating cavities

    Zhang, Pei

    2013-02-15

    Higher order modes (HOM) are electromagnetic resonant fields. They can be excited by an electron beam entering an accelerating cavity, and constitute a component of the wakefield. This wakefield has the potential to dilute the beam quality and, in the worst case, result in a beam-break-up instability. It is therefore important to ensure that these fields are well suppressed by extracting energy through special couplers. In addition, the effect of the transverse wakefield can be reduced by aligning the beam on the cavity axis. This is due to their strength depending on the transverse offset of the excitation beam. For suitably small offsets the dominant components of the transverse wakefield are dipole modes, with a linear dependence on the transverse offset of the excitation bunch. This fact enables the transverse beam position inside the cavity to be determined by measuring the dipole modes extracted from the couplers, similar to a cavity beam position monitor (BPM), but requires no additional vacuum instrumentation. At the FLASH facility in DESY, 1.3 GHz (known as TESLA) and 3.9 GHz (third harmonic) cavities are installed. Wakefields in 3.9 GHz cavities are significantly larger than in the 1.3 GHz cavities. It is therefore important to mitigate the adverse effects of HOMs to the beam by aligning the beam on the electric axis of the cavities. This alignment requires an accurate beam position diagnostics inside the 3.9 GHz cavities. It is this aspect that is focused on in this thesis. Although the principle of beam diagnostics with HOM has been demonstrated on 1.3 GHz cavities, the realization in 3.9 GHz cavities is considerably more challenging. This is due to the dense HOM spectrum and the relatively strong coupling of most HOMs amongst the four cavities in the third harmonic cryo-module. A comprehensive series of simulations and HOM spectra measurements have been performed in order to study the modal band structure of the 3.9 GHz cavities. The dependencies of

  8. Autonomous control of inverter-interfaced Distributed Generation units for harmonic current filtering and resonance damping in an islanded microgrid

    Wang, Xiongfei; Blaabjerg, Frede; Chen, Zhe

    2012-01-01

    Harmonic current filtering and resonance damping have become important concerns on the control of an islanded microgrids. To address these challenges, this paper proposes a control method of inverter-interfaced Distributed Generation (DG) units, which can autonomously share harmonic currents and ...

  9. Generation of Bright, Spatially Coherent Soft X-Ray High Harmonics in a Hollow Waveguide Using Two-Color Synthesized Laser Pulses.

    Jin, Cheng; Stein, Gregory J; Hong, Kyung-Han; Lin, C D

    2015-07-24

    We investigate the efficient generation of low-divergence high-order harmonics driven by waveform-optimized laser pulses in a gas-filled hollow waveguide. The drive waveform is obtained by synthesizing two-color laser pulses, optimized such that highest harmonic yields are emitted from each atom. Optimization of the gas pressure and waveguide configuration has enabled us to produce bright and spatially coherent harmonics extending from the extreme ultraviolet to soft x rays. Our study on the interplay among waveguide mode, atomic dispersion, and plasma effect uncovers how dynamic phase matching is accomplished and how an optimized waveform is maintained when optimal waveguide parameters (radius and length) and gas pressure are identified. Our analysis should help laboratory development in the generation of high-flux bright coherent soft x rays as tabletop light sources for applications.

  10. Third order harmonic imaging for biological tissues using three phase-coded pulses.

    Ma, Qingyu; Gong, Xiufen; Zhang, Dong

    2006-12-22

    Compared to the fundamental and the second harmonic imaging, the third harmonic imaging shows significant improvements in image quality due to the better resolution, but it is degraded by the lower sound pressure and signal-to-noise ratio (SNR). In this study, a phase-coded pulse technique is proposed to selectively enhance the sound pressure of the third harmonic by 9.5 dB whereas the fundamental and the second harmonic components are efficiently suppressed and SNR is also increased by 4.7 dB. Based on the solution of the KZK nonlinear equation, the axial and lateral beam profiles of harmonics radiated from a planar piston transducer were theoretically simulated and experimentally examined. Finally, the third harmonic images using this technique were performed for several biological tissues and compared with the images obtained by the fundamental and the second harmonic imaging. Results demonstrate that the phase-coded pulse technique yields a dramatically cleaner and sharper contrast image.

  11. Generation of five phase-locked harmonics by implementing a divide-by-three optical frequency divider.

    Suhaimi, Nurul Sheeda; Ohae, Chiaki; Gavara, Trivikramarao; Nakagawa, Ken'ichi; Hong, Feng-Lei; Katsuragawa, Masayuki

    2015-12-15

    We report the generation of five phase-locked harmonics, f₁:2403  nm, f₂:1201  nm, f₃:801  nm, f₄:600  nm, and f₅:480  nm with an exact frequency ratio of 1:2:3:4:5 by implementing a divide-by-three optical frequency divider in the high harmonic generation process. All five harmonics are generated coaxially with high phase coherence in time and space, which are applicable for various practical uses.

  12. Measurement and control of the frequency chirp rate of high-order harmonic pulses

    Mauritsson, J.; Johnsson, P.; Lopez-Martens, R.; Varju, K.; L'Huillier, A.; Kornelis, W.; Biegert, J.; Keller, U.; Gaarde, M.B.; Schafer, K.J.

    2004-01-01

    We measure the chirp rate of harmonics 13 to 23 in argon by cross correlation with a 12 femtosecond probe pulse. Under low ionization conditions, we directly measure the negative chirp due to the atomic dipole phase, and show that an additional chirp on the pump pulse is transferred to the qth harmonic as q times the fundamental chirp. Our results are in accord with simulations using the experimentally measured 815 nm pump and probe pulses. The ability to measure and manipulate the harmonic chirp rate is essential for the characterization and optimization of attosecond pulse trains

  13. A comprehensive study and analysis of second order harmonic ripple in DC microgrid feeding single phase PWM inverter loads

    Gautam, Aditya R.; Fulwani, Deepak; Guerrero, Josep M.

    2016-01-01

    The paper presents a detailed analysis of second order harmonic ripple in a DC microgrid. A boost converter feeding PWM inverter load is considered and equivalent circuit is proposed. The effect of the size of input capacitor, output capacitor and inductor of boost converter, on this ripple has...

  14. One-third (period three) harmonic generation in microwave-driven Josephson tunnel junctions

    Hansen, Jørn Bindslev; Clarke, J.; Mygind, Jesper

    1986-01-01

    One-third harmonic signals have been generated in the zero voltage state of a Josephson tunnel junction driven with a microwave current in the frequency range 8–20 GHz. The signal was as much as 50 dB above the noise level of the detector with a linewidth of less than 100 Hz. The junction...... parameters and microwave current were measured in situ in separate experiments. The subharmonic generation occurred for ranges of microwave current and frequency that were in reasonable agreement with the results of digital computer simulations. Applied Physics Letters is copyrighted by The American...

  15. A concept of a new undulator that will generate irrational higher harmonics in synchrotron radiation

    Hashimoto, Shinya; Sasaki, Shigemi

    1994-03-01

    A preliminary consideration has been made on an undulator with magnetic poles quasi-periodically aligned along the path of electron beams to discriminate the rational higher harmonics of radiation that are harmful in some synchrotron radiation experiments. The harmonics with irrational ratios in energy generated by the undulator is never simultaneously reflected by a crystal monochromator in the same orientation. A combination of the new undulator and high-resolution crystal monochromator is expected to be very useful on beamlines of high energy radiation in which X-ray mirrors are useless because of too small critical angles of total reflection. Further, a possibility of manufacturing the new undulator has been discussed. (author)

  16. In-phased second harmonic wave array generation with intra-Talbot-cavity frequency-doubling.

    Hirosawa, Kenichi; Shohda, Fumio; Yanagisawa, Takayuki; Kannari, Fumihiko

    2015-03-23

    The Talbot cavity is one promising method to synchronize the phase of a laser array. However, it does not achieve the lowest array mode with the same phase but the highest array mode with the anti-phase between every two adjacent lasers, which is called out-phase locking. Consequently, their far-field images exhibit 2-peak profiles. We propose intra-Talbot-cavity frequency-doubling. By placing a nonlinear crystal in a Talbot cavity, the Talbot cavity generates an out-phased fundamental wave array, which is converted into an in-phase-locked second harmonic wave array at the nonlinear crystal. We demonstrate numerical calculations and experiments on intra-Talbot-cavity frequency-doubling and obtain an in-phase-locked second harmonic wave array for a Nd:YVO₄ array laser.

  17. Nonlinear Optical Magnetism Revealed by Second-Harmonic Generation in Nanoantennas.

    Kruk, Sergey S; Camacho-Morales, Rocio; Xu, Lei; Rahmani, Mohsen; Smirnova, Daria A; Wang, Lei; Tan, Hark Hoe; Jagadish, Chennupati; Neshev, Dragomir N; Kivshar, Yuri S

    2017-06-14

    Nonlinear effects at the nanoscale are usually associated with the enhancement of electric fields in plasmonic structures. Recently emerged new platform for nanophotonics based on high-index dielectric nanoparticles utilizes optically induced magnetic response via multipolar Mie resonances and provides novel opportunities for nanoscale nonlinear optics. Here, we observe strong second-harmonic generation from AlGaAs nanoantennas driven by both electric and magnetic resonances. We distinguish experimentally the contribution of electric and magnetic nonlinear response by analyzing the structure of polarization states of vector beams in the second-harmonic radiation. We control continuously the transition between electric and magnetic nonlinearities by tuning polarization of the optical pump. Our results provide a direct observation of nonlinear optical magnetism through selective excitation of multipolar nonlinear modes in nanoantennas.

  18. A Perturbation Analysis of Harmonics Generation from Saturated Elements in Power Systems

    Kumano, Teruhisa

    Nonlinear phenomena such as saturation in magnetic flux give considerable effects in power system analysis. It is reported that a failure in a real 500kV system triggered islanding operation, where resultant even harmonics caused malfunctions in protective relays. It is also reported that the major origin of this wave distortion is nothing but unidirectional magnetization of the transformer iron core. Time simulation is widely used today to analyze this type of phenomena, but it has basically two shortcomings. One is that the time simulation takes two much computing time in the vicinity of inflection points in the saturation characteristic curve because certain iterative procedure such as N-R (Newton-Raphson) should be used and such methods tend to be caught in an ill conditioned numerical hunting. The other is that such simulation methods sometimes do not help intuitive understanding of the studied phenomenon because the whole nonlinear equations are treated in a matrix form and not properly divided into understandable parts as done in linear systems. This paper proposes a new computation scheme which is based on so called perturbation method. Magnetic saturation in iron cores in a generator and a transformer are taken into account. The proposed method has a special feature against the first shortcoming of the N-R based time simulation method stated above. In the proposed method no iterative process is used to reduce the equation residue but uses perturbation series, which means free from the ill condition problem. Users have only to calculate each perturbation terms one by one until he reaches necessary accuracy. In a numerical example treated in the present paper the first order perturbation can make reasonably high accuracy, which means very fast computing. In numerical study three nonlinear elements are considered. Calculated results are almost identical to the conventional Newton-Raphson based time simulation, which shows the validity of the method. The

  19. Optimal conditions for the generation of the third harmonic of focused radiation in a self-interaction regime

    Kulagin, I A; Usmanov, T

    1998-01-01

    A method developed for the analysis of the interaction of wave beams in a self-interaction regime is used to determine the changes in the optimal conditions for third-harmonic generation with changes in the degree of focusing of the fundamental-frequency radiation in isotropic media. Conditions under which a redistribution of the intensities and phases of the interacting wave beams reduces the efficiency of third-harmonic generation are identified. It is shown that, under strong focusing conditions, there may be additional extrema in the dependence of the intensity of the harmonic on the density of the medium. (nonlinear optical phenomena)

  20. Propagation dynamics and X-pulse formation in phase-mismatched second-harmonic generation

    Valiulis, G.; Jukna, V.; Jedrkiewicz, O.; Clerici, M.; Rubino, E.; DiTrapani, P.

    2011-01-01

    This paper concerns the theoretical, numerical, and experimental study of the second-harmonic-generation (SHG) process under conditions of phase and group-velocity mismatch and aims to demonstrate the dimensionality transition of the SHG process caused by the change of the fundamental wave diameter. We show that SHG from a narrow fundamental beam leads to the spontaneous self-phase-matching process with, in addition, the appearance of angular dispersion for the off-axis frequency components generated. The angular dispersion sustains the formation of the short X pulse in the second harmonic (SH) and is recognized as three-dimensional (3D) dynamics. On the contrary, the large-diameter fundamental beam reduces the number of the degrees of freedom, does not allow the generation of the angular dispersion, and maintains the so-called one-dimensional (1D) SHG dynamics, where the self-phase-matching appears just for axial components and is accompanied by the shrinking of the SH temporal bandwidth, and sustains a long SH pulse formation. The transition from long SH pulse generation typical of the 1D dynamics to the short 3D X pulse is illustrated numerically and experimentally by changing the conditions from the self-defocusing to the self-focusing regime by simply tuning the phase mismatch. The numerical and experimental verification of the analytical results are also presented.

  1. Ultimate waveform reproducibility of extreme-ultraviolet pulses by high-harmonic generation in quartz

    Garg, M.; Kim, H. Y.; Goulielmakis, E.

    2018-05-01

    Optical waveforms of light reproducible with subcycle precision underlie applications of lasers in ultrafast spectroscopies, quantum control of matter and light-based signal processing. Nonlinear upconversion of optical pulses via high-harmonic generation in gas media extends these capabilities to the extreme ultraviolet (EUV). However, the waveform reproducibility of the generated EUV pulses in gases is inherently sensitive to intensity and phase fluctuations of the driving field. We used photoelectron interferometry to study the effects of intensity and carrier-envelope phase of an intense single-cycle optical pulse on the field waveform of EUV pulses generated in quartz nanofilms, and contrasted the results with those obtained in gas argon. The EUV waveforms generated in quartz were found to be virtually immune to the intensity and phase of the driving field, implying a non-recollisional character of the underlying emission mechanism. Waveform-sensitive photonic applications and precision measurements of fundamental processes in optics will benefit from these findings.

  2. Modulating optical rectification, second and third harmonic generation of doped quantum dots: Interplay between hydrostatic pressure, temperature and noise

    Ganguly, Jayanta; Saha, Surajit; Bera, Aindrila; Ghosh, Manas

    2016-10-01

    We examine the profiles of optical rectification (OR), second harmonic generation (SHG) and third harmonic generation (THG) of impurity doped QDs under the combined influence of hydrostatic pressure (HP) and temperature (T) in presence and absence of Gaussian white noise. Noise has been incorporated to the system additively and multiplicatively. In order to study the above nonlinear optical (NLO) properties the doped dot has been subjected to a polarized monochromatic electromagnetic field. Effect of application of noise is nicely reflected through alteration of peak shift (blue/red) and variation of peak height (increase/decrease) of above NLO properties as temperature and pressure are varied. All such changes again sensitively depends on mode of application (additive/multiplicative) of noise. The remarkable influence of interplay between noise strength and its mode of application on the said profiles has also been addressed. The findings illuminate fascinating role played by noise in tuning above NLO properties of doped QD system under the active presence of both hydrostatic pressure and temperature.

  3. Nonlinear optical rectification and second and third harmonic generation in GaAs δ-FET systems under hydrostatic pressure

    Martínez-Orozco, J.C.; Mora-Ramos, M.E.; Duque, C.A.

    2012-01-01

    The GaAs n-type delta-doped field effect transistor is proposed as a source for nonlinear optical responses such as second order rectification and second and third harmonic generation. Particular attention is paid to the effect of hydrostatic pressure on these properties, related with the pressure-induced modifications of the energy level spectrum. The description of the one-dimensional potential profile is made including Hartree and exchange and correlation effects via a Thomas–Fermi-based local density approximation. The allowed energy levels are calculated within the effective mass and envelope function approximations by means of an expansion over an orthogonal set of infinite well eigenfunctions. The results for the coefficients of nonlinear optical rectification and second and third harmonic generation are reported for several values of the hydrostatic pressure. - Highlights: ► GaAs n-type delta-doped field effect transistor. ► NOR and SHG are enhanced as a result of the pressure. ► THG is quenched as a result of the pressure. ► The zero pressure situation is the best scenario for the THG.

  4. Anharmonic phonons and second-order phase-transitions by the stochastic self-consistent harmonic approximation

    Mauri, Francesco

    Anharmonic effects can generally be treated within perturbation theory. Such an approach breaks down when the harmonic solution is dynamically unstable or when the anharmonic corrections of the phonon energies are larger than the harmonic frequencies themselves. This situation occurs near lattice-related second-order phase-transitions such as charge-density-wave (CDW) or ferroelectric instabilities or in H-containing materials, where the large zero-point motion of the protons results in a violation of the harmonic approximation. Interestingly, even in these cases, phonons can be observed, measured, and used to model transport properties. In order to treat such cases, we developed a stochastic implementation of the self-consistent harmonic approximation valid to treat anharmonicity in the nonperturbative regime and to obtain, from first-principles, the structural, thermodynamic and vibrational properties of strongly anharmonic systems. I will present applications to the ferroelectric transitions in SnTe, to the CWD transitions in NbS2 and NbSe2 (in bulk and monolayer) and to the hydrogen-bond symmetrization transition in the superconducting hydrogen sulfide system, that exhibits the highest Tc reported for any superconductor so far. In all cases we are able to predict the transition temperature (pressure) and the evolution of phonons with temperature (pressure). This project has received funding from the European Union's Horizon 2020 research and innovation programme under Grant agreement No. 696656 GrapheneCore1.

  5. Effect of pulse slippage on resonant second harmonic generation of a short pulse laser in a plasma

    Nitikant; Sharma, A K

    2004-01-01

    The process of second harmonic generation of an intense short pulse laser in a plasma is resonantly enhanced by the application of a magnetic wiggler. The wiggler of suitable wave number k-vector 0 provides necessary momentum to second harmonic photons to make harmonic generation a resonant process. The laser imparts an oscillatory velocity to electrons and exerts a longitudinal ponderomotive force on them at (2ω 1 ,2k-vector 1 ), where ω 1 and k-vector 1 are the frequency and the wave number of the laser, respectively. As the electrons acquire oscillatory velocity at the second harmonic, the wiggler magnetic field beats with it to produce a transverse second harmonic current at (2ω 1 ,2k-vector 1 +k-vector 0 ), driving the second harmonic electromagnetic radiation. However, the group velocity of the second harmonic wave is greater than that of the fundamental wave, hence, the generated pulse slips out of the main laser pulse and its amplitude saturates

  6. Extreme UV harmonic production by free-electron generators of coherent radiation

    Ortega, J.M.

    1986-01-01

    The bunching phenomenon is the basic process occurring in a free-electron generator of coherent generation such as the Klystron in the mm-wave-length range or the free-electron laser (FEL) in the optical region. During interaction with the incident electromagnetic wave the electrons are progressively gathered into small packets separated by a length equal to its wavelength λ/sub L/. Once the electrons are bunched there is a given phase relationship between them and the field of any wave which wavelength is an harmonic of λ/sub L/. This is the source of the gain (electrons decelerated by the field) or of the absorption (electrons accelerated by the laser) mechanisms. In the FEL case the electrons are passing through an undulator (spatially varying periodic magnetic field). Since one uses high-energy electrons (E≅100-1000 MeV) they emit synchrotron radiation called in this case undulator radiation or spontaneous emission. This radiation coexists with the stimulated emission giving rise to the gain mechanism and to the FEL oscillation. When the electrons are bunched the spontaneous emission becomes coherent at the wavelength harmonic of λ/sub L/, and there is an increase in the emission intensity which ideally would be N/sub e/. (Number of electrons is typically ≅10/sup 10/.) Thus bursts of photons are emitted at frequencies harmonic of an incident wave which may be an external laser or the FEL itself. This is likely to extend the spectral range of the free-electron generation of coherent radiation toward the extreme UV λ<1000A). The advantages and limitations of the various solutions (linear or circular accelerator, FEL, or external laser) are discussed. The authors summarize the various experimental results obtained to date and the prospects for the synchrotron radiation dedicated ring super-ACO presently under construction at LURE at Orsay

  7. Third-harmonic generation of a laser-driven quantum dot with impurity

    Sakiroglu, S.; Kilic, D. Gul; Yesilgul, U.; Ungan, F.; Kasapoglu, E.; Sari, H.; Sokmen, I.

    2018-06-01

    The third-harmonic generation (THG) coefficient for a laser-driven quantum dot with an on-center Gaussian impurity under static magnetic field is theoretically investigated. Laser field effect is treated within the high-frequency Floquet approach and the analytical expression of the THG coefficient is deduced from the compact density-matrix approach. The numerical results demonstrate that the application of intense laser field causes substantial changes on the behavior of THG. In addition the position and magnitude of the resonant peak of THG coefficient is significantly affected by the magnetic field, quantum dot size and the characteristic parameters of the impurity potential.

  8. Second Harmonic Generation characterization of SOI wafers: Impact of layer thickness and interface electric field

    Damianos, D.; Vitrant, G.; Lei, M.; Changala, J.; Kaminski-Cachopo, A.; Blanc-Pelissier, D.; Cristoloveanu, S.; Ionica, I.

    2018-05-01

    In this work, we investigate Second Harmonic Generation (SHG) as a non-destructive characterization method for Silicon-On-Insulator (SOI) materials. For thick SOI stacks, the SHG signal is related to the thickness variations of the different layers. However, in thin SOI films, the comparison between measurements and optical modeling suggests a supplementary SHG contribution attributed to the electric fields at the SiO2/Si interfaces. The impact of the electric field at each interface of the SOI on the SHG is assessed. The SHG technique can be used to evaluate interfacial electric fields and consequently interface charge density in SOI materials.

  9. Label-free three-dimensional imaging of cell nucleus using third-harmonic generation microscopy

    Lin, Jian; Zheng, Wei; Wang, Zi; Huang, Zhiwei, E-mail: biehzw@nus.edu.sg [Optical Bioimaging Laboratory, Department of Biomedical Engineering, Faculty of Engineering, National University of Singapore, Singapore 117576 (Singapore)

    2014-09-08

    We report the implementation of the combined third-harmonic generation (THG) and two-photon excited fluorescence (TPEF) microscopy for label-free three-dimensional (3-D) imaging of cell nucleus morphological changes in liver tissue. THG imaging shows regular spherical shapes of normal hepatocytes nuclei with inner chromatin structures while revealing the condensation of chromatins and nuclear fragmentations in hepatocytes of diseased liver tissue. Colocalized THG and TPEF imaging provides complementary information of cell nuclei and cytoplasm in tissue. This work suggests that 3-D THG microscopy has the potential for quantitative analysis of nuclear morphology in cells at a submicron-resolution without the need for DNA staining.

  10. Label-free three-dimensional imaging of cell nucleus using third-harmonic generation microscopy

    Lin, Jian; Zheng, Wei; Wang, Zi; Huang, Zhiwei

    2014-01-01

    We report the implementation of the combined third-harmonic generation (THG) and two-photon excited fluorescence (TPEF) microscopy for label-free three-dimensional (3-D) imaging of cell nucleus morphological changes in liver tissue. THG imaging shows regular spherical shapes of normal hepatocytes nuclei with inner chromatin structures while revealing the condensation of chromatins and nuclear fragmentations in hepatocytes of diseased liver tissue. Colocalized THG and TPEF imaging provides complementary information of cell nuclei and cytoplasm in tissue. This work suggests that 3-D THG microscopy has the potential for quantitative analysis of nuclear morphology in cells at a submicron-resolution without the need for DNA staining.

  11. Atomically Phase-Matched Second-Harmonic Generation in a 2D Crystal

    2016-08-26

    OPEN ORIGINAL ARTICLE Atomically phase-matched second-harmonic generation in a 2D crystal Mervin Zhao1,2,*, Ziliang Ye1,2,*, Ryuji Suzuki3,4,*, Yu...photoluminescence mapping, Raman spectroscopy and atomic -force microscopy. (b) Image produced via scanning and gathering the SH light produced by the 3R-MoS2...arising from a single atomic layer, where the SH light elucidated important information such as the grain boundaries and electronic structure in these ultra

  12. A superconducting short period undulator for a harmonic generation FEL experiment

    Ingold, G.; Solomon, L.; Ben-Zvi, I.; Krinsky, S.; Li, D.; Lynch, D.; Sheehan, J.; Woodle, M.; Qiu, X.Z.; Yu, L.H.

    1993-01-01

    A three stage superconducting (SC) undulator for a high gain harmonic generation (HGE) FEL experiment in the infrared is under construction at the NSLS in collaboration with Grumman Corporation. A novel undulator technology suitable for short period (6-40mm) undulators will be employed for all three stages, the modulator, the dispersive section and the radiator. The undulator triples the frequency of a 10.4μm CO 2 seed laser. So far a 27 period (one third of the final radiator) prototype radiator has been designed, built and tested

  13. High efficiency fourth-harmonic generation from nanosecond fiber master oscillator power amplifier

    Mu, Xiaodong; Steinvurzel, Paul; Rose, Todd S.; Lotshaw, William T.; Beck, Steven M.; Clemmons, James H.

    2016-03-01

    We demonstrate high power, deep ultraviolet (DUV) conversion to 266 nm through frequency quadrupling of a nanosecond pulse width 1064 nm fiber master oscillator power amplifier (MOPA). The MOPA system uses an Yb-doped double-clad polarization-maintaining large mode area tapered fiber as the final gain stage to generate 0.5-mJ, 10 W, 1.7- ns single mode pulses at a repetition rate of 20 kHz with measured spectral bandwidth of 10.6 GHz (40 pm), and beam qualities of Mx 2=1.07 and My 2=1.03, respectively. Using LBO and BBO crystals for the second-harmonic generation (SHG) and fourth-harmonic generation (FHG), we have achieved 375 μJ (7.5 W) and 92.5 μJ (1.85 W) at wavelengths of 532 nm and 266 nm, respectively. To the best of our knowledge these are the highest narrowband infrared, green and UV pulse energies obtained to date from a fully spliced fiber amplifier. We also demonstrate high efficiency SHG and FHG with walk-off compensated (WOC) crystal pairs and tightly focused pump beam. An SHG efficiency of 75%, FHG efficiency of 47%, and an overall efficiency of 35% from 1064 nm to 266 nm are obtained.

  14. High Order Voltage and Current Harmonic Mitigation Using the Modular Multilevel Converter STATCOM

    Kontos, E.; Tsolaridis, Georgios; Teodorescu, Remus; Bauer, P.

    2017-01-01

    Due to the increase of power electronic-based loads, the maintenance of high power quality poses a challenge in modern power systems. To limit the total harmonic distortion in the line voltage and currents at the point of the common coupling (PCC), active power filters are commonly employed. This

  15. New performance in harmonic analysis device generation used for magnetic fields measurements

    Evesque, C.; Tkatchenko, M.

    1996-01-01

    In particle accelerator, correcting high multipole components of magnets are of high importance for quality magnet: to get a pure quadrupole to within 10 -4 , we have to know the field quality to 10 -5 through the 30. order. Our laboratory needed such a very sharp device to find small harmonic components of magnetic field. For harmonic analysis of magnetic field, we adopted the standard method, i.e. a rotating coil connected to a flux integrator. Nowadays, coils measuring azimuthal component of magnetic field are used. In order to obtain correct and accurate measurements, we were guided by two imperatives: first, optimisation of construction constraints and second, comparison of azimuthal and radial component measurements. With this background, this article describes both new technological solutions adopted and new performance obtained. We also discuss the most suitable geometric structure for the coils. We obtained a noiseless signal, a repeatability of 10 -5 and a sensitivity up to 10 -8 Weber for both types of coils. Our device is able to find and measure main component, normal and skew multipole components up to the 32. order, when simulating local defects. The magnetic axis is located within 5 μm. The central gradient is also measured and magnetic length deduced. Complementary functions of two types of coils were noticed in detecting local defects of magnetic structure. (authors)

  16. New performance in harmonic analysis device generation used for magnetic fields measurements

    Evesque, C.; Tkatchenko, M.

    1996-12-31

    In particle accelerator, correcting high multipole components of magnets are of high importance for quality magnet: to get a pure quadrupole to within 10{sup -4}, we have to know the field quality to 10{sup -5} through the 30. order. Our laboratory needed such a very sharp device to find small harmonic components of magnetic field. For harmonic analysis of magnetic field, we adopted the standard method, i.e. a rotating coil connected to a flux integrator. Nowadays, coils measuring azimuthal component of magnetic field are used. In order to obtain correct and accurate measurements, we were guided by two imperatives: first, optimisation of construction constraints and second, comparison of azimuthal and radial component measurements. With this background, this article describes both new technological solutions adopted and new performance obtained. We also discuss the most suitable geometric structure for the coils. We obtained a noiseless signal, a repeatability of 10{sup -5} and a sensitivity up to 10{sup -8} Weber for both types of coils. Our device is able to find and measure main component, normal and skew multipole components up to the 32. order, when simulating local defects. The magnetic axis is located within 5 {mu}m. The central gradient is also measured and magnetic length deduced. Complementary functions of two types of coils were noticed in detecting local defects of magnetic structure. (authors).

  17. A novel intravital multi-harmonic generation microscope for early diagnosis of oral cancer

    Cheng, Yu-Hsiang; Lin, Chih-Feng; Shih, Ting-Fang; Sun, Chi-Kuang

    2013-03-01

    Oral cancer is one of the most frequently diagnosed human cancers and leading causes of cancer death all over the world, but the prognosis and overall survival rate are still poor because of delay in diagnosis and lack of early intervention. The failure of early diagnosis is due to insufficiency of proper diagnostic and screening tools and most patients are reluctant to undergo biopsy. Optical virtual biopsy techniques, for imaging cells and tissues at microscopic details capable of differentiating benign from malignant lesions non-invasively, are thus highly desirable. A novel multi-harmonic generation microscope, excited by a 1260 nm Cr:forsterite laser, with second and third harmonic signals demonstrating collagen fiber distribution and cell morphology in a sub-micron resolution, was developed for clinical use. To achieve invivo observation inside the human oral cavity, a small objective probe with a suction capability was carefully designed for patients' comfort and stability. By remotely changing its focus point, the same objective can image the mucosa surface with a low magnification, illuminated by side light-emitting diodes, with a charge-coupled device (CCD) for site location selection before the harmonic generation biopsy was applied. Furthermore, the slow galvanometer mirror and the fast resonant mirror provide a 30 fps frame rate for high-speed real-time observation and the z-motor of this system is triggered at the same rate to provide fast 3D scanning, again ensuring patients' comfort. Focusing on the special cytological and morphological changes of the oral epithelial cells, our preliminary result disclosed excellent consistency with traditional histopathology studies.

  18. Harmonics generation of a terahertz wakefield free-electron laser from a dielectric loaded waveguide excited by a direct current electron beam.

    Li, Weiwei; Lu, Yalin; He, Zhigang; Jia, Qika; Wang, Lin

    2016-06-01

    We propose to generate high-power terahertz (THz) radiation from a cylindrical dielectric loaded waveguide (DLW) excited by a direct-current electron beam with the harmonics generation method. The DLW supports a discrete set of modes that can be excited by an electron beam passing through the structure. The interaction of these modes with the co-propagating electron beam results in micro-bunching and the coherent enhancement of the wakefield radiation, which is dominated by the fundamental mode. By properly choosing the parameters of DLW and beam energy, the high order modes can be the harmonics of the fundamental one; thus, high frequency radiation corresponding to the high order modes will benefit from the dominating bunching process at the fundamental eigenfrequency and can also be coherently excited. With the proposed method, high power THz radiation can be obtained with an easily achievable electron beam and a large DLW structure.

  19. Observation of spectral gain narrowing in a high-order harmonic seeded soft-x-ray amplifier

    Tissandier, F.; Sebban, S.; Ribière, M.; Gautier, J.; Zeitoun, Ph.; Lambert, G.; Barszczak Sardinha, A.; Goddet, J.Ph.; Burgy, F.; Lefrou, T.; Valentin, C.; Rousse, A.; Guilbaud, O.; Klisnick, A.; Nejdl, Jaroslav; Mocek, Tomáš; Maynard, G.

    2010-01-01

    Roč. 81, č. 6 (2010), 063833/1-063833/4 ISSN 1050-2947 R&D Projects: GA AV ČR IAA100100911 Institutional research plan: CEZ:AV0Z10100523 Keywords : high-order harmonic * soft-x-ray * amplification * OFI * gain narrowing * Ni-like krypton plasma Subject RIV: BH - Optics, Masers, Lasers Impact factor: 2.861, year: 2010 http://pra.aps.org/abstract/PRA/v81/i6/e063833

  20. Third-harmonic generation and self-channeling in air using high-power femtosecond laser pulses

    Akoezbek, N.; Iwasaki, A.; Chin, S.L.; Becker, A.; Scalora, M.; Bowden, C.M.

    2002-01-01

    It is shown, both theoretically and experimentally, that during laser pulse filamentation in air an intense ultrashort third-harmonic pulse is generated forming a two-colored filament. The third-harmonic pulse maintains both its peak intensity and energy over distances much longer than the characteristic coherence length. We argue that this is due to a nonlinear phase-locking mechanism between the two pulses in the filament and is independent of the initial material wave-vector mismatch. A rich spatiotemporal propagation dynamics of the third-harmonic pulse is predicted. Potential applications of this phenomenon to other parametric processes are discussed

  1. Investigation of phase matching for third-harmonic generation in silicon slow light photonic crystal waveguides using Fourier optics.

    Monat, Christelle; Grillet, Christian; Corcoran, Bill; Moss, David J; Eggleton, Benjamin J; White, Thomas P; Krauss, Thomas F

    2010-03-29

    Using Fourier optics, we retrieve the wavevector dependence of the third-harmonic (green) light generated in a slow light silicon photonic crystal waveguide. We show that quasi-phase matching between the third-harmonic signal and the fundamental mode is provided in this geometry by coupling to the continuum of radiation modes above the light line. This process sustains third-harmonic generation with a relatively high efficiency and a substantial bandwidth limited only by the slow light window of the fundamental mode. The results give us insights into the physics of this nonlinear process in the presence of strong absorption and dispersion at visible wavelengths where bandstructure calculations are problematic. Since the characteristics (e.g. angular pattern) of the third-harmonic light primarily depend on the fundamental mode dispersion, they could be readily engineered.

  2. Towards protein-crystal centering using second-harmonic generation (SHG) microscopy

    Kissick, David J.; Dettmar, Christopher M.; Becker, Michael; Mulichak, Anne M.; Cherezov, Vadim; Ginell, Stephan L.; Battaile, Kevin P.; Keefe, Lisa J.; Fischetti, Robert F.; Simpson, Garth J.

    2013-01-01

    The potential of second-harmonic generation (SHG) microscopy for automated crystal centering to guide synchrotron X-ray diffraction of protein crystals has been explored. The potential of second-harmonic generation (SHG) microscopy for automated crystal centering to guide synchrotron X-ray diffraction of protein crystals was explored. These studies included (i) comparison of microcrystal positions in cryoloops as determined by SHG imaging and by X-ray diffraction rastering and (ii) X-ray structure determinations of selected proteins to investigate the potential for laser-induced damage from SHG imaging. In studies using β 2 adrenergic receptor membrane-protein crystals prepared in lipidic mesophase, the crystal locations identified by SHG images obtained in transmission mode were found to correlate well with the crystal locations identified by raster scanning using an X-ray minibeam. SHG imaging was found to provide about 2 µm spatial resolution and shorter image-acquisition times. The general insensitivity of SHG images to optical scatter enabled the reliable identification of microcrystals within opaque cryocooled lipidic mesophases that were not identified by conventional bright-field imaging. The potential impact of extended exposure of protein crystals to five times a typical imaging dose from an ultrafast laser source was also assessed. Measurements of myoglobin and thaumatin crystals resulted in no statistically significant differences between structures obtained from diffraction data acquired from exposed and unexposed regions of single crystals. Practical constraints for integrating SHG imaging into an active beamline for routine automated crystal centering are discussed

  3. Modified Perfect Harmonics Cancellation Control of a Grid Interfaced SPV Power Generation

    Singh, B.; Shahani, D. T.; Verma, A. K.

    2015-03-01

    This paper deals with a grid interfaced solar photo voltaic (SPV) power generating system with modified perfect harmonic cancellation (MPHC) control for power quality improvement in terms of mitigation of the current harmonics, power factor correction, control of point of common coupling (PCC) voltage with reactive power compensation and load balancing in a three phase distribution system. The proposed grid interfaced SPV system consists of a SPV array, a dc-dc boost converter and a voltage source converter (VSC) used for the compensation of other connected linear and nonlinear loads at PCC. The reference grid currents are estimated using MPHC method and control signals are derived by using pulse width modulation (PWM) current controller of VSC. The SPV power is fed to the common dc bus of VSC and dc-dc boost converter using maximum power point tracking (MPPT). The dc link voltage of VSC is regulated by using dc voltage proportional integral (PI) controller. The analysis of the proposed SPV power generating system is carried out under dc/ac short circuit and severe SPV-SX and SPV-TX intrusion.

  4. Quantitative second-harmonic generation imaging to detect osteogenesis imperfecta in human skin samples

    Adur, J.; Ferreira, A. E.; D'Souza-Li, L.; Pelegati, V. B.; de Thomaz, A. A.; Almeida, D. B.; Baratti, M. O.; Carvalho, H. F.; Cesar, C. L.

    2012-03-01

    Osteogenesis Imperfecta (OI) is a genetic disorder that leads to bone fractures due to mutations in the Col1A1 or Col1A2 genes that affect the primary structure of the collagen I chain with the ultimate outcome in collagen I fibrils that are either reduced in quantity or abnormally organized in the whole body. A quick test screening of the patients would largely reduce the sample number to be studied by the time consuming molecular genetics techniques. For this reason an assessment of the human skin collagen structure by Second Harmonic Generation (SHG) can be used as a screening technique to speed up the correlation of genetics/phenotype/OI types understanding. In the present work we have used quantitative second harmonic generation (SHG) imaging microscopy to investigate the collagen matrix organization of the OI human skin samples comparing with normal control patients. By comparing fibril collagen distribution and spatial organization, we calculated the anisotropy and texture patterns of this structural protein. The analysis of the anisotropy was performed by means of the two-dimensional Discrete Fourier Transform and image pattern analysis with Gray-Level Co-occurrence Matrix (GLCM). From these results, we show that statistically different results are obtained for the normal and disease states of OI.

  5. Influence of crack opening and incident wave angle on second harmonic generation of Lamb waves

    Yang, Yi; Ng, Ching-Tai; Kotousov, Andrei

    2018-05-01

    Techniques utilising second harmonic generation (SHG) have proven their great potential in detecting contact-type damage. However, the gap between the practical applications and laboratory studies is still quite large. The current work is aimed to bridge this gap by investigating the effects of the applied load and incident wave angle on the detectability of fatigue cracks at various lengths. Both effects are critical for practical implementations of these techniques. The present experimental study supported by three-dimensional (3D) finite element (FE) modelling has demonstrated that the applied load, which changes the crack opening and, subsequently, the contact nonlinearity, significantly affects the amplitude of the second harmonic generated by the fundamental symmetric mode (S0) of Lamb wave. This amplitude is also dependent on the length of the fatigue crack as well as the incident wave angle. The experimental and FE results correlate well, so the modelling approach can be implemented for practical design of damage monitoring systems as well as for the evaluation of the severity of the fatigue cracks.

  6. Second harmonic generation in nanoscale films of transition metal dichalcogenide: Accounting for multipath interference

    A. V. Kudryavtsev

    2016-09-01

    Full Text Available The transfer matrix method has been widely used to calculate wave propagation through the layered structures consisting entirely of either linear or nonlinear optical materials. In the present work, we develop the transfer matrix method for structures consisting of alternating layers of linear and nonlinear optical materials. The result is presented in a form that allows one to directly substitute the values of material constants, refractive index and absorption coefficient, into the expressions describing the second harmonic generation (SHG field. The model is applied to the calculation of second harmonic (SH field generated in nano-thin layers of transition metal dichalcogenides exfoliated on top of silicon oxide/silicon Fabry-Perot cavity. These structures are intensively studied both in view of their unique properties and perspective applications. A good agreement between experimental and numerical results can be achieved by small modification of optical constants, which may arise in an experiment due to a strong electric field of an incident focused pump laser beam. By considering the SHG effect, this paper completes the series of works describing the role of Fabry-Perot cavity in different optical effects (optical reflection, photoluminescence and Raman scattering in 2D semiconductors that is extremely important for characterization of these unique materials.

  7. Direct-substitution method for studying second harmonic generation in arbitrary optical superlattices

    Ying Chen

    Full Text Available In this paper, we present the direct-substitution (DS method to study the second-harmonic generation (SHG in arbitrary one-dimensional optical superlattices (OS. Applying this method to Fibonacci and generalized Fibonacci systems, we obtain the relative intensity of SHG and compare them with previous works. We confirmed the validity of the proposed DS method by comparing our results of SHG in quasiperiodic Fibonacci OS with previous works using analytical Fourier transform method. Furthermore, the three-dimension SHG spectra obtained by DS method present the properties of SHG in Fibonacci OS more distinctly. What’s more important, the DS method demands very few limits and can be used to compute directly and conveniently the intensity of SHG in arbitrary OS where the quasi-phase-matching (QPM can be achieved. It shows that the DS method is powerful for the calculation of electric field and intensity of SHG and can help experimentalists conveniently to estimate the distributions of SHG in any designed polarized systems. Keywords: Second-harmonic generation, Direct-substitution, Fibonacci

  8. Cut-off scaling of high-harmonic generation driven by a femtosecond visible optical parametric amplifier

    Cirmi, Giovanni; Lai, Chien-Jen; Granados, Eduardo; Huang, Shu-Wei; Sell, Alexander; Hong, Kyung-Han; Moses, Jeffrey; Keathley, Phillip; Kärtner, Franz X

    2012-01-01

    We studied high-harmonic generation (HHG) in Ar, Ne and He gas jets using a broadly tunable, high-energy optical parametric amplifier (OPA) in the visible wavelength range. We optimized the noncollinear OPA to deliver tunable, femtosecond pulses with 200-500 µJ energy at the 1 kHz repetition rate with excellent spatiotemporal properties, suitable for HHG experiments. By tuning the central wavelength of the OPA while keeping other parameters (energy, duration and beam size) constant, we experimentally studied the scaling law of cut-off energy with the driver wavelength in helium. Our measurements show a λ 1.7+0.2 dependence of the HHG cut-off photon energy over the full visible range in agreement with previous experiments of near- and mid-IR wavelengths. By tuning the central wavelength of the driver source, the high-order harmonic spectra in the extreme ultraviolet cover the full range of photon energy between ∼25 and ∼100 eV. Due to the high coherence intrinsic in HHG, as well as the broad and continuous tunability in the extreme UV range, a high energy, high repetition rate version of this source might be an ideal seed for free electron lasers.

  9. Second Harmonic Generation of Violet Light in Femtosecond-Laser-Inscribed BiB3O6 Cladding Waveguides

    Jia Yuechen

    2013-11-01

    Full Text Available We report on the second harmonic generation of violet light of a nonlinear cladding waveguide in BiB3O6 crystal produced by femtosecond laser inscription. Under continuous-wave pump laser at 800 nm, the guided second harmonic wave at 400 nm with a conversion efficiency of ~0.32% has been realized through the Type I birefringence phase matching configuration.

  10. Probing the longitudinal electric field of Bessel beams using second-harmonic generation from nano-objects

    Turquet, Léo; Kakko, Joona-Pekko; Karvonen, Lasse; Jiang, Hua; Kauppinen, Esko; Lipsanen, Harri; Kauranen, Martti; Bautista, Godofredo

    2017-08-01

    Non-diffractive Bessel beams are receiving significant interest in optical microscopy due to their remarkably large depth of field. For example, studies have shown the superiority of Bessel beams over Gaussian beams for volumetric imaging of three-dimensionally thick or extended samples. However, the vectorial aspects of the focal fields of Bessel beams are generally obscured when traditional methods are used to characterize their three-dimensional point-spread function in space, which contains contributions from all optical field components. Here, we show experimentally the three-dimensional spatial distribution and enhanced depth of field of the longitudinal electric field components of a focused linearly-polarized Bessel beam. This is done through second-harmonic generation from well-defined vertically-aligned gallium-arsenide nanowires, whose second-order response is primarily driven by the longitudinal fields at the beam focus.

  11. Development of blue lasers, from second harmonic generation using a Nd:YAG laser emitting at 946 nm

    Nogueira, Gustavo Bernardes

    2010-01-01

    Blue lasers have attracted much attention for applications such as blue-ray, displays and as pumped source for the Ti:sapphire laser. A Nd:YAG crystal with diffusion bonded end-caps was used together with a pump wavelength of 802,3 nm, detuned from the absorption peak at 808 nm in order to minimize the thermal lens effect by providing for a better temperature distribution inside the crystal. Using different input mirror radii, the best relation between pump waist and laser was achieved in a linear cavity and resulted in 6.75W cw (continuous wave) laser power at 946 nm and slope efficiency of 48%. In a second step, a second harmonic generation crystal for blue emission at 473 nm was inserted into different types of resonators, and the blue output power at 473 nm was measured as a function of absorbed pump power. (author)

  12. Second Harmonic Generation Imaging Analysis of Collagen Arrangement in Human Cornea.

    Park, Choul Yong; Lee, Jimmy K; Chuck, Roy S

    2015-08-01

    To describe the horizontal arrangement of human corneal collagen bundles by using second harmonic generation (SHG) imaging. Human corneas were imaged with an inverted two photon excitation fluorescence microscope. The excitation laser (Ti:Sapphire) was tuned to 850 nm. Backscatter signals of SHG were collected through a 425/30-nm bandpass emission filter. Multiple, consecutive, and overlapping image stacks (z-stacks) were acquired to generate three dimensional data sets. ImageJ software was used to analyze the arrangement pattern (irregularity) of collagen bundles at each image plane. Collagen bundles in the corneal lamellae demonstrated a complex layout merging and splitting within a single lamellar plane. The patterns were significantly different in the superficial and limbal cornea when compared with deep and central regions. Collagen bundles were smaller in the superficial layer and larger in deep lamellae. By using SHG imaging, the horizontal arrangement of corneal collagen bundles was elucidated at different depths and focal regions of the human cornea.

  13. Optical second harmonic generation from V-shaped chromium nanohole arrays

    Khoa Quang, Ngo; Miyauchi, Yoshihiro; Mizutani, Goro; Charlton, Martin D.; Chen, Ruiqi; Boden, Stuart; Rutt, Harvey

    2014-02-01

    We observed rotational anisotropy of optical second harmonic generation (SHG) from an array of V-shaped chromium nanoholes fabricated by electron beam lithography. Phenomenological analysis indicated that the effective nonlinear susceptibility element \\chi _{313}^{(2)} had a characteristic contribution to the observed anisotropic SHG intensity patterns. Here, coordinate 1 is in the direction of the tip of V shapes in the substrate plane, and 3 indicates the direction perpendicular to the sample surface. The SHG intensity for the S-polarized output light was very weak, probably owing to the cancellation effect of the image dipoles generated at the metal-air boundary. The possible origin of the observed nonlinearity is discussed in terms of the susceptibility elements obtained.

  14. Life Cycle Greenhouse Gas Emissions of Nuclear Electricity Generation: Systematic Review and Harmonization

    Warner, E.S.; Heath, G.A.

    2012-01-01

    A systematic review and harmonization of life cycle assessment (LCA) literature of nuclear electricity generation technologies was performed to determine causes of and, where possible, reduce variability in estimates of life cycle greenhouse gas (GHG) emissions to clarify the state of knowledge and inform decision making. LCA literature indicates that life cycle GHG emissions from nuclear power are a fraction of traditional fossil sources, but the conditions and assumptions under which nuclear power are deployed can have a significant impact on the magnitude of life cycle GHG emissions relative to renewable technologies. Screening 274 references yielded 27 that reported 99 independent estimates of life cycle GHG emissions from light water reactors (LWRs). The published median, interquartile range (IQR), and range for the pool of LWR life cycle GHG emission estimates were 13, 23, and 220 grams of carbon dioxide equivalent per kilowatt-hour (g CO 2 -eq/kWh), respectively. After harmonizing methods to use consistent gross system boundaries and values for several important system parameters, the same statistics were 12, 17, and 110 g CO 2 -eq/kWh, respectively. Harmonization (especially of performance characteristics) clarifies the estimation of central tendency and variability. To explain the remaining variability, several additional, highly influential consequential factors were examined using other methods. These factors included the primary source energy mix, uranium ore grade, and the selected LCA method. For example, a scenario analysis of future global nuclear development examined the effects of a decreasing global uranium market-average ore grade on life cycle GHG emissions. Depending on conditions, median life cycle GHG emissions could be 9 to 110 g CO 2 -eq/kWh by 2050.

  15. Second harmonic generation of off axial vortex beam in the case of walk-off effect

    Chen, Shunyi; Ding, Panfeng; Pu, Jixiong

    2016-07-01

    Process of off axial vortex beam propagating in negative uniaxial crystal is investigated in this work. Firstly, we get the formulae of the normalized electric field and calculate the location of vortices for second harmonic beam in two type of phase matching. Then, numerical analysis verifies that the intensity distribution and location of vortices of the first order original vortex beam depend on the walk-off angle and off axial magnitude. It is shown that, in type I phase matching, the distribution of vortices is symmetrical about the horizontal axis, the separation distance increases as the off axial magnitude increases or the off axial magnitude deceases. However, in type II phase matching, the vortices are symmetrical along with some vertical axis, and increase of the walk-off angle or off axial magnitude leads to larger separation distance. Finally, the case of high order original off axial vortex beam is also investigated.

  16. A research technique for the effect of higher harmonic voltages on the operating parameters of a permanent magnet synchronous generator

    Hasanova L. H.

    2017-12-01

    Full Text Available Nowadays permanent magnet synchronous machines those frequency-controlled from stator side with frequency inverters made on the basis of power transistors or fully controlled thyristors, are widely used as motors and generators. In future they are also promising a good application in transport, including marine. Modern frequency inverters are equipped with a control system based on sine-shaped pulse width modulation. While shaping the voltage in the output of the inverter, in addition to the fundamental harmonic, higher harmonic components are also included in the voltage shape, which certainly affect the operating parameters of the generator (electromagnetic torque, power, currents. To determine this effect the modeling and investigation technique of higher harmonic voltages in the "electric network – frequency converter – synchronous machine with permanent magnets" system has been developed. The proposed equations of a frequency-controlled permanent magnet synchronous machine allow relatively simply reproduce the harmonic composition of the voltage in the output of a frequency inverter equipped with the control system based on a sinusoidal pulse width modulation. The developed research technique can be used for inverters with any number and composition of voltage harmonic components feeding a stator winding of a permanent magnet synchronous machine. On a particular case, the efficiency of the research technique of the higher harmonics influence on the operating parameters of the generator has been demonstrated. At the same time, the study has been carried out taking into account the shape of the voltage curve feeding the windings of the synchronous machine containing in addition to the fundamental harmonic the 8, 10, 11, 13, 14 and 16-th harmonic components, and the rated active power of the synchronous machine has been equal to 1 500 kW.

  17. Three-dimensional analysis of harmonic generation in high-gain free-electron lasers

    Huang, Zhirong; Kim, Kwang-Je

    2000-01-01

    In a high-gain free-electron laser (FEL) employing a planar undulator, strong bunching at the fundamental wavelength can drive substantial bunching and power levels at the harmonic frequencies. In this paper we investigate the three-dimensional evolution of harmonic radiation based on the coupled Maxwell-Klimontovich equations that take into account nonlinear harmonic interactions. Each harmonic field is a sum of a linear amplification term and a term driven by nonlinear harmonic interactions. After a certain stage of exponential growth, the dominant nonlinear term is determined by interactions of the lower nonlinear harmonics and the fundamental radiation. As a result, the gain length, transverse profile, and temporal structure of the first few harmonics are eventually governed by those of the fundamental. Transversely coherent third-harmonic radiation power is found to approach 1% of the fundamental power level for current high-gain FEL projects

  18. Investigation on fibrous collagen modifications during corneal laser welding by second harmonic generation microscopy

    Matteini, Paolo; Ratto, Fulvio; Rossi, Francesca; Cicchi, Riccardo; Stringari, Chiara; Kapsokalyvas, Dimitrios; Pavone, Francesco S.; Pini, Roberto

    2009-02-01

    The structural modifications in the collagen lattice of corneal stroma induced by near-infrared laser welding were investigated with second-harmonic generation (SHG) imaging. The corneal laser welding procedure is performed by staining the wound edges with a saturated water solution of Indocyanine Green (ICG) followed by irradiation with a 810 nm diode laser operated in continuous (CWLW: continuous wave laser welding) or pulsed (PLW: pulsed laser welding) mode. Both these procedures can provide closure of corneal wounds by inducing different structural modifications in the extracellular matrix. SHG imaging of native corneal stroma revealed collagen bundles composed of many regularly aligned collagen fibrils. After CWLW the regular lamellar arrangement was lost; collagen bundles appeared densely packed with an increasing disordered arrangement toward the welded cut. The weld was characterized by a loss of details; nevertheless, the observation of the second harmonic signal at this site indicated the lack of collagen denaturation. By contrast, PLW mode produced welding spots at the interface between donor and recipient corneal layers, which were characterized by a severe loss of the SHG signal, suggesting the occurrence of a complete collagen denaturation. SHG imaging appeared to be a powerful tool for visualizing the supramolecular morphological modifications in the collagen matrix after laser welding.

  19. Modelling and Analysis of DFIG Wind Turbine Harmonics Generated in Grids

    A.Chilambuchelvan; B.BabyPriya,

    2010-01-01

    In this paper an analytic technique for modelling harmonics is proposed for a DFIG wind turbine connected to the grid. An algorithm based on Hilbert transform for the analysis of harmonics in power systems isdeveloped. The simulation results prove the effectiveness of the Hilbert Transform (HT) for power harmonic analysis in DFIG wind turbine connected to a grid.

  20. Bismuth-, Tin-, and Lead-Containing Metal-Organic Materials: Synthesis, Structure, Photoluminescence, Second Harmonic Generation, and Ferroelectric Properties

    Wibowo, Arief Cahyo

    polymer ranging from 1D supramolecular structures to true 3D coordination polymers is covered in Chapter 4. The observation of a new 2D Kagome lattice and unique layered perovskite-type bismuth-based coordination polymers and their photoluminescence properties is the focus of Chapter 5. In chapters 6 and 7, a successful approach to implement our novel hybrid strategy for synthesizing enantiomerically pure single crystals consisting of Second Order Jahn Teller (SOJT)-possessing main group metal cations, specifically bismuth and tin, and homochiral ligands or unsymmetric ligands is discussed. The new MOMs with polar space groups exhibit second harmonic generation and have potential for ferroelectric properties.

  1. Generation of second-harmonic radiations of a self-focusing laser from a plasma with density-transition

    Kant, Niti; Gupta, Devki Nandan; Suk, Hyyong

    2011-01-01

    A Gaussian laser-beam resonantly generates a second-harmonic wave in a plasma in the presence of a wiggler magnetic-field of suitable period. The self-focusing of the fundamental pulse enhances the intensity of the second-harmonic pulse. An introduction of an upward plasma-density ramp strongly enhances the self-focusing of the fundamental laser pulse. The laser pulse attains a minimum spot size and propagates up to several Rayleigh lengths without divergence. Due to the strong self-focusing of the fundamental laser pulse, the second-harmonic intensity enhances significantly. A considerable enhancement of the intensity of the second-harmonic is observed from the proposed mechanism. -- Highlights: → An upward plasma-density ramp is very important for laser propagation in plasmas. → As the plasma density increases, effect of self-focusing becomes stronger. → We utilize this self-focused laser to generate second-harmonic radiations. → The self-focusing laser enhances the intensity of the second-harmonic pulse.

  2. Generation of second-harmonic radiations of a self-focusing laser from a plasma with density-transition

    Kant, Niti [Department of Physics, Lovely Professional University, Phagwara 144 402, Punjab (India); Gupta, Devki Nandan, E-mail: dngupta@physics.du.ac.in [Department of Physics and Astrophysics, University of Delhi, Delhi 110 007 (India); Suk, Hyyong [Advanced Photonics Research Institute (APRI) and Graduate Program of Photonics and Applied Physics, Gwangju Institute of Science and Technology, Gwangju 500 712 (Korea, Republic of)

    2011-08-15

    A Gaussian laser-beam resonantly generates a second-harmonic wave in a plasma in the presence of a wiggler magnetic-field of suitable period. The self-focusing of the fundamental pulse enhances the intensity of the second-harmonic pulse. An introduction of an upward plasma-density ramp strongly enhances the self-focusing of the fundamental laser pulse. The laser pulse attains a minimum spot size and propagates up to several Rayleigh lengths without divergence. Due to the strong self-focusing of the fundamental laser pulse, the second-harmonic intensity enhances significantly. A considerable enhancement of the intensity of the second-harmonic is observed from the proposed mechanism. -- Highlights: → An upward plasma-density ramp is very important for laser propagation in plasmas. → As the plasma density increases, effect of self-focusing becomes stronger. → We utilize this self-focused laser to generate second-harmonic radiations. → The self-focusing laser enhances the intensity of the second-harmonic pulse.

  3. Circularly polarized harmonic generation by intense bicircular laser pulses: electron recollision dynamics and frequency dependent helicity

    Bandrauk, André D.; Mauger, François; Yuan, Kai-Jun

    2016-12-01

    Numerical solutions of time-dependent Schrödinger equations for one and two electron cyclic molecules {{{H}}}nq+ exposed to intense bichromatic circularly polarized laser pulses of frequencies {ω }1 and {ω }2, such that {ω }1/{ω }2={n}1/{n}2 (integer) produce circularly polarized high order harmonics with a cut-off recollision maximum energy at and greater than the linear polarization law (in atomic units) {N}m{ω }1={I}p+3.17{U}p, where I p is the ionization potential and {U}p={(2{E}0)}2/4{ω }2 is the ponderomotive energy defined by the field E 0 (intensity I={{cE}}02/8π ) from each pulse and mean frequency ω =({ω }1+{ω }2)/2 . An electron recollision model in a rotating frame at rotating frequency {{Δ }}ω =({ω }1-{ω }2)/2 predicts this simple result as a result of recollision dynamics in a combination of bichromatic circularly polarized pulses. The harmonic helicities and their intensities are shown to depend on compatible symmetries of the net pulse electric fields with that of the molecules.

  4. Nanotwin Detection and Domain Polarity Determination via Optical Second Harmonic Generation Polarimetry.

    Ren, Ming-Liang; Agarwal, Rahul; Nukala, Pavan; Liu, Wenjing; Agarwal, Ritesh

    2016-07-13

    We demonstrate that optical second harmonic generation (SHG) can be utilized to determine the exact nature of nanotwins in noncentrosymmetric crystals, which is challenging to resolve via conventional transmission electron or scanned probe microscopies. Using single-crystalline nanotwinned CdTe nanobelts and nanowires as a model system, we show that SHG polarimetry can distinguish between upright (Cd-Te bonds) and inverted (Cd-Cd or Te-Te bonds) twin boundaries in the system. Inverted twin boundaries are generally not reported in nanowires due to the lack of techniques and complexity associated with the study of the nature of such defects. Precise characterization of the nature of defects in nanocrystals is required for deeper understanding of their growth and physical properties to enable their application in future devices.

  5. Optical second harmonic generation phase measurement at interfaces of some organic layers with indium tin oxide

    Ngah Demon, Siti Zulaikha; Miyauchi, Yoshihiro; Mizutani, Goro; Matsushima, Toshinori; Murata, Hideyuki

    2014-01-01

    Highlights: • SHG phase from the interfaces of ITO/CuPc and ITO/pentacene was observed. • Optical dispersion of the organic thin film was taken into account. • Phase shift from bare ITO was 140° for ITO/CuPc and 160° for ITO/pentacene. - Abstract: We observed phase shift in optical second harmonic generation (SHG) from interfaces of indium tin oxide (ITO)/copper phthalocyanine (CuPc) and ITO/pentacene. Phase correction due to Fresnel factors of the sample was taken into account. The phase of SHG electric field at the ITO/pentacene interface, ϕ interface with respect to the phase of SHG of bare substrate ITO was 160°, while the interface of ITO/CuPc had a phase of 140°

  6. Second-harmonic generation as a DNA malignancy indicator of prostate glandular epithelial cells

    Zheng-Fei, Zhuang; Han-Ping, Liu; Zhou-Yi, Guo; Xiao-Yuan, Deng; Shuang-Mu, Zhuo; Bi-Ying, Yu

    2010-01-01

    This paper first demonstrates second-harmonic generation (SHG) in the intact cell nucleus, which acts as an optical indicator of DNA malignancy in prostate glandular epithelial cells. Within a scanning region of 2.7 μm×2.7 μm in cell nuclei, SHG signals produced from benign prostatic hyperplasia (BPH) and prostate carcinoma (PC) tissues (mouse model C57BL/6) have been investigated. Statistical analyses (t test) of a total of 405 measurements (204 nuclei from BPH and 201 nuclei from PC) show that SHG signals from BPH and PC have a distinct difference (p < 0.05), suggesting a potential optical method of revealing very early malignancy in prostate glandular epithelial cells based upon induced biochemical and/or biophysical modifications in DNA. (geophysics, astronomy and astrophysics)

  7. Application of Fourier transform-second-harmonic generation imaging to the rat cervix.

    Lau, T Y; Sangha, H K; Chien, E K; McFarlin, B L; Wagoner Johnson, A J; Toussaint, K C

    2013-07-01

    We present the application of Fourier transform-second-harmonic generation (FT-SHG) imaging to evaluate the arrangement of collagen fibers in five nonpregnant rat cervices. Tissue slices from the mid-cervix and near the external orifice of the cervix were analyzed in both two-dimensions (2D) and three-dimensions (3D). We validate that the cervical microstructure can be quantitatively assessed in three dimensions using FT-SHG imaging and observe collagen fibers oriented both in and out-of-plane in the outermost and the innermost layers, which cannot be observed using 2D FT-SHG analysis alone. This approach has the potential to be a clinically applicable method for measuring progressive changes in collagen organization during cervical remodeling in humans. © 2013 The Authors Journal of Microscopy © 2013 Royal Microscopical Society.

  8. Controllable nonlocal behaviour by cascaded second-harmonic generation of fs pulses

    Bache, Morten; Bang, Ole; Krolikowski, Wieslaw

    2008-01-01

    Second-harmonic generation (SHG) of ultra-short pulses can act as a prototypical nonlocal nonlinear model, since the strength and nature of the temporal nonlocality can be controlled through the phase-mismatch parameter. The presence of a group-velocity mismatch namely implies that when the phase...... mismatch is small the nonlocal response function becomes oscillatory, while for large phase mismatch it becomes localized. In the transition between the two regimes the strength of the nonlocality diverges, and the system goes from a weakly nonlocal to a strongly nonlocal state. When simulating soliton...... compression to few-cycle pulses in the cascaded quadratic soliton compressor, the spectral content of the full coupled SHG model is predicted by the nonlocal model even when few-cycle pulses are interacting....

  9. Photoinduced second harmonic generation of LaFe4Sb12near spin fluctuated critical points

    Nouneh, K.; Viennois, R.; Kityk, I.V.; Terki, F.; Charar, S.; Benet, S.; Paschen, S.

    2004-01-01

    The temperature dependence of the resistivity, the Seebeck coefficient and photoinduced second harmonic generation (PISHG) are studied near the quantum critical point in the skutterudite compound LaFe 4 Sb 12 , possessing increased spin fluctuations. We observed a large maximum of the PISHG at a temperature of about 15 K. The PISHG signal increases substantially below 35 K. We found a correlation between the temperature dependences of PISHG, resistivity and Seebeck coefficient. We proposed a phenomenological explanation for the occurrence of the PISHG signal in LaFe 4 Sb 12 implying strong spin fluctuations exist in this system, which may present some interest for the study of other spin fluctuation systems. Physical insight into the phenomenon observed is grounded in the participation of anharmonic electron-phonon and electron-paramagnon interactions stimulated by inducing light in the interactions with the photoexcited dipole moments. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  10. Second-harmonic generation in atomic vapor with picosecond laser pulses

    Kim, D.; Mullin, C.S.; Shen, Y.R.

    1997-01-01

    Picosecond laser pulses were used to study the highly forbidden resonant second-harmonic generation (SHG) in potassium vapor. The input intensity dependence, vapor density dependence, buffer-gas pressure dependence, and spatial profile of the SHG were measured. A pump - probe experiment was conducted to probe the time dependence of the SHG signal. The experimental results can be understood from an ionization-initiated dc-field-induced SHG model. A theory of a dc-field-induced SHG model is developed that takes into account the time development of the dc electric field in detail. This temporal buildup of the dc field along with transient coherent excitation between two-photon-allowed transitions can explain the experimental results quantitatively, including the previous vapor SHG results with nanosecond laser pulses. copyright 1997 Optical Society of America

  11. Analysis of the superconducting wiggler magnets for the ATF Harmonic Generation FEL experiment

    Zhang, X.; Ben-Zvi, I.; Ingold, G.; Krinsky, S.; Yu, L.H.

    1992-01-01

    In this paper, we consider the superconducting wiggler magnet under construction for the High Gain Harmonic Generation experiment (HGHG) at the Accelerator Test Facility (ATF) at BNL. This wiggler consists of an energy modulation section, a dispersion magnet and a radiator section. We present an analysis of the dispersion magnet and the end effects in the other wiggler sections. The purpose of the dispersion magnet is to convert energy modulation of the electron beam into spatial bunching. For the dispersion magnet, we discuss the physical requirements, analyze the magnetic design, determine the focusing properties, and consider the effect of departures from ideal behavior on the FEL gain. In the modulator and radiator wigglers we analyze the effects due to the ends of the wiggler and discuss their correction. In addition, the localized field produced by a trim coil for horizontal beam steering is investigated

  12. Low-temperature anomalies of photoinduced second harmonic generation in skutterudites

    Viennois, R; Kityk, I V; Terki, F; Charar, S; Muntzer, A; Kasperczyk, J; Ravot, D; Tedenac, J C

    2003-01-01

    Photoinduced second harmonic generation (PISHG) was found in skutterudite compounds of CeFe 4 Sb 12 and Ce 0.7 Fe 3.5 Ni 0.5 Sb 12 . Measurements versus temperature, pump-probe delaying time and external magnetic field were performed. The studied compounds belong to moderate heavy fermion compounds (HFC) in the ground state. The PISHG signals appear at 6.8 and 4.9 K for CeFe 4 Sb 12 and Ce 0.7 Fe 3.5 Ni 0.5 Sb 12 , respectively. We suspect that these signals are due to anharmonic electron-phonon interactions creating a charge density non-centrosymmetry. The observed effects are caused either by a possible phase transition or by drastic changes in the electron structure of the HFC with decreasing temperature

  13. Two-Photon Luminescence and Second Harmonic Generation from Gold Micro-Plates

    Xu Wang

    2014-09-01

    Full Text Available Micron-sized gold plates were prepared by reducing chloroauric acid with lemongrass extract. Their two-photon luminescence (TPL and second harmonic generation (SHG were investigated. The results show that the TPL and SHG intensity of gold plates is dependent on the wavelength and polarization of excitation laser. The TPL intensity of gold plates decreases with the increase of the excitation wavelength except for a small peak around 820–840 nm, while SHG intensity increases with the excitation wavelength redshift. In addition, it is found that the TPL intensity of the gold plate’s edge is related with the angle between the edge orientation and the polarization direction of the excitation light. The TPL intensity increases with the angle increase from 0° to 90°.

  14. Identification of stacking faults in silicon carbide by polarization-resolved second harmonic generation microscopy.

    Hristu, Radu; Stanciu, Stefan G; Tranca, Denis E; Polychroniadis, Efstathios K; Stanciu, George A

    2017-07-07

    Although silicon carbide is a highly promising crystalline material for a wide range of electronic devices, extended and point defects which perturb the lattice periodicity hold deep implications with respect to device reliability. There is thus a great need for developing new methods that can detect silicon carbide defects which are detrimental to device functionality. Our experiment demonstrates that polarization-resolved second harmonic generation microscopy can extend the efficiency of the "optical signature" concept as an all-optical rapid and non-destructive set of investigation methods for the differentiation between hexagonal and cubic stacking faults in silicon carbide. This technique can be used for fast and in situ characterization and optimization of growth conditions for epilayers of silicon carbide and similar materials.

  15. Optical second harmonic generation phase measurement at interfaces of some organic layers with indium tin oxide

    Ngah Demon, Siti Zulaikha [School of Materials Science, Japan Advanced Institute of Science and Technology, 923-1292 Ishikawa (Japan); Department of Physics, Centre of Defence Foundation Studies, National Defence University of Malaysia, 53 000 Kuala Lumpur (Malaysia); Miyauchi, Yoshihiro [Department of Applied Physics, School of Applied Sciences, National Defense Academy of Japan, 239-8686 Kanagawa (Japan); Mizutani, Goro, E-mail: mizutani@jaist.ac.jp [School of Materials Science, Japan Advanced Institute of Science and Technology, 923-1292 Ishikawa (Japan); Matsushima, Toshinori; Murata, Hideyuki [School of Materials Science, Japan Advanced Institute of Science and Technology, 923-1292 Ishikawa (Japan)

    2014-08-30

    Highlights: • SHG phase from the interfaces of ITO/CuPc and ITO/pentacene was observed. • Optical dispersion of the organic thin film was taken into account. • Phase shift from bare ITO was 140° for ITO/CuPc and 160° for ITO/pentacene. - Abstract: We observed phase shift in optical second harmonic generation (SHG) from interfaces of indium tin oxide (ITO)/copper phthalocyanine (CuPc) and ITO/pentacene. Phase correction due to Fresnel factors of the sample was taken into account. The phase of SHG electric field at the ITO/pentacene interface, ϕ{sub interface} with respect to the phase of SHG of bare substrate ITO was 160°, while the interface of ITO/CuPc had a phase of 140°.

  16. Spectral Phase Modulation and chirped pulse amplification in High Gain Harmonic Generation

    Wu, Zilu; Krinsky, Sam; Loos, Henrik; Murphy, James; Shaftan, Timur; Sheehy, Brian; Shen, Yuzhen; Wang, Xijie; Yu Li Hua

    2004-01-01

    High Gain Harmonic Generation (HGHG), because it produces longitudinally coherent pulses derived from a coherent seed, presents remarkable possibilities for manipulating FEL pulses. If spectral phase modulation imposed on the seed modulates the spectral phase of the HGHG in a deterministic fashion, then chirped pulse amplification, pulse shaping, and coherent control experiments at short wavelengths become possible. In addition, the details of the transfer function will likely depend on electron beam and radiator dynamics and so prove to be a useful tool for studying these. Using the DUVFEL at the National Synchrotron Light Source at Brookhaven National Laboratory, we present spectral phase analyses of both coherent HGHG and incoherent SASE ultraviolet FEL radiation, applying Spectral Interferometry for Direct Electric Field Reconstruction (SPIDER), and assess the potential for employing compression and shaping techniques.

  17. Bulk quadrupole and interface dipole contribution for second harmonic generation in Si(111)

    Reitböck, Cornelia; Stifter, David; Alejo-Molina, Adalberto; Hingerl, Kurt; Hardhienata, Hendradi

    2016-01-01

    The second harmonic generation (SHG) response was measured for arbitrarily oriented linear input polarization on Si(111) surfaces in rotational anisotropy experiments. We show for the first time, using the simplified bond hyperpolarizability model (SBHM), that the observed angular shifts of the nonlinear peaks and symmetry features—related to changes in the input polarization—help to identify the corresponding interface dipolar and bulk quadrupolar SHG sources, yielding excellent agreement with the experiment. Additionally, we evaluate for the s-in/p-out (sp) and p-in/p-out (pp)-polarization SHG intensities the contributions from the individual Si bonds. Furthermore, a relation between the four parameters arising from SBHM and six coefficients of the phenomenological SHG theory needed to reproduce experimental data is established. (paper)

  18. Automatic transfer function generation using contour tree controlled residue flow model and color harmonics.

    Zhou, Jianlong; Takatsuka, Masahiro

    2009-01-01

    Transfer functions facilitate the volumetric data visualization by assigning optical properties to various data features and scalar values. Automation of transfer function specifications still remains a challenge in volume rendering. This paper presents an approach for automating transfer function generations by utilizing topological attributes derived from the contour tree of a volume. The contour tree acts as a visual index to volume segments, and captures associated topological attributes involved in volumetric data. A residue flow model based on Darcy's Law is employed to control distributions of opacity between branches of the contour tree. Topological attributes are also used to control color selection in a perceptual color space and create harmonic color transfer functions. The generated transfer functions can depict inclusion relationship between structures and maximize opacity and color differences between them. The proposed approach allows efficient automation of transfer function generations, and exploration on the data to be carried out based on controlling of opacity residue flow rate instead of complex low-level transfer function parameter adjustments. Experiments on various data sets demonstrate the practical use of our approach in transfer function generations.

  19. Towards protein-crystal centering using second-harmonic generation (SHG) microscopy

    Kissick, David J.; Dettmar, Christopher M. [Purdue University, West Lafayette, IN 47907 (United States); Becker, Michael [Argonne National Laboratory, Argonne, IL 60439 (United States); Mulichak, Anne M. [Hauptman–Woodward Medical Research Institute, Argonne, IL 60439 (United States); Cherezov, Vadim [The Scripps Research Institute, La Jolla, CA 92037 (United States); Ginell, Stephan L. [Argonne National Laboratory, Argonne, IL 60439 (United States); Battaile, Kevin P.; Keefe, Lisa J. [Hauptman–Woodward Medical Research Institute, Argonne, IL 60439 (United States); Fischetti, Robert F. [Argonne National Laboratory, Argonne, IL 60439 (United States); Simpson, Garth J., E-mail: gsimpson@purdue.edu [Purdue University, West Lafayette, IN 47907 (United States)

    2013-05-01

    The potential of second-harmonic generation (SHG) microscopy for automated crystal centering to guide synchrotron X-ray diffraction of protein crystals has been explored. The potential of second-harmonic generation (SHG) microscopy for automated crystal centering to guide synchrotron X-ray diffraction of protein crystals was explored. These studies included (i) comparison of microcrystal positions in cryoloops as determined by SHG imaging and by X-ray diffraction rastering and (ii) X-ray structure determinations of selected proteins to investigate the potential for laser-induced damage from SHG imaging. In studies using β{sub 2} adrenergic receptor membrane-protein crystals prepared in lipidic mesophase, the crystal locations identified by SHG images obtained in transmission mode were found to correlate well with the crystal locations identified by raster scanning using an X-ray minibeam. SHG imaging was found to provide about 2 µm spatial resolution and shorter image-acquisition times. The general insensitivity of SHG images to optical scatter enabled the reliable identification of microcrystals within opaque cryocooled lipidic mesophases that were not identified by conventional bright-field imaging. The potential impact of extended exposure of protein crystals to five times a typical imaging dose from an ultrafast laser source was also assessed. Measurements of myoglobin and thaumatin crystals resulted in no statistically significant differences between structures obtained from diffraction data acquired from exposed and unexposed regions of single crystals. Practical constraints for integrating SHG imaging into an active beamline for routine automated crystal centering are discussed.

  20. SOFT X-RAY FEL BY CASCADING STAGES OF HIGH GAIN HARMONIC GENERATION.

    YU,L.H.

    2003-04-17

    Short wavelength Free-Electron Lasers are perceived as the next generation of synchrotron light sources. In the past decade, significant advances have been made in the theory and technology of high brightness electron beams and single pass FELs. These developments facilitate the construction of practical VUV FELs and make x-ray FELs possible. Self-Amplified Spontaneous Emission (SASE) and High Gain Harmonic Generation (HGHG)[17-19] are the two leading candidates for x-ray FELs. The first lasing of HGHG proof-of-principle experiment succeeded in August, 1999 in Brookhaven National Laboratory. The experimental results agree with the theory prediction. Compared with SASE FEL, the following advantages of HGHG FEL were confirmed; (1) Better longitudinal coherence, and hence, much narrower bandwidth than SASE. (2) More stable central wavelength, (3) More stable output energy. In this introduction, we will first briefly describe the principle of HGHG in Section A. Then in Section B, we give a general description about how to produce soft x-ray by cascading HGHG scheme. In section 2, we give a detailed description of the system design. Then, in section 3, we give a description of an analytical estimate for the HGHG process, and the calculation of the parameters of different parts of the system. The estimate is found to agree with simulation within about a factor 2 for most cases we studied. The stability issue, the sensitivity to parameter variation, the harmonic contents of the final output, and the noise degradation issue of such HGHG scheme are discussed in Section 4. The results are presented in Section 4. Finally, in Section 5, we will give some discussion of the challenges in development of the system. The conclusion is given in Section 6.

  1. Experimental investigation of the generation of harmonic photons from the interaction of free electrons with intense laser radiation

    Englert, T.J.

    1983-01-01

    An experimental investigation of the generation of second harmonic photons through the interaction of free electrons with an intense laser beam has been performed. Second harmonic photons with a wavelength of 530nm generated from the interaction of free electrons with 1060nm photons from a neodymium-glass laser are implied by observing Doppler shifted photons with wavelengths of 490nm and 507nm. The observed photon wavelengths results from a Doppler shift of the laser photon wavelengths as viewed in the rest frame of the electrons combined with a Doppler shift of the second harmonic photons emitted from 1600eV and 500eV electrons. Comparison of experimental results with those predicted by cross sections, derived using classical and quantum electrodynamics, shows reasonable agreement with both theories. Although second harmonic photons are created, the dynamics of second harmonic photon generation (accelerated electron motion due to the electromagnetic field or actual two-photon interaction with the electron) cannot be resolved without further experiment

  2. Texture analysis applied to second harmonic generation image data for disease classification and development of a multi-view second harmonic generation imaging platform

    Wen, Lianggong

    Many diseases, e.g. ovarian cancer, breast cancer and pulmonary fibrosis, are commonly associated with drastic alterations in surrounding connective tissue, and changes in the extracellular matrix (ECM) are associated with the vast majority of cellular processes in disease progression and carcinogenesis: cell differentiation, proliferation, biosynthetic ability, polarity, and motility. We use second harmonic generation (SHG) microscopy for imaging the ECM because it is a non-invasive, non-linear laser scanning technique with high sensitivity and specificity for visualizing fibrillar collagen. In this thesis, we are interested in developing imaging techniques to understand how the ECM, especially the collagen architecture, is remodeled in diseases. To quantitate remodeling, we implement a 3D texture analysis to delineate the collagen fibrillar morphology observed in SHG microscopy images of human normal and high grade malignant ovarian tissues. In the learning stage, a dictionary of "textons"---frequently occurring texture features that are identified by measuring the image response to a filter bank of various shapes, sizes, and orientations---is created. By calculating a representative model based on the texton distribution for each tissue type using a training set of respective mages, we then perform classification between normal and high grade malignant ovarian tissues classification based on the area under receiver operating characteristic curves (true positives versus false positives). The local analysis algorithm is a more general method to probe rapidly changing fibrillar morphologies than global analyses such as FFT. It is also more versatile than other texture approaches as the filter bank can be highly tailored to specific applications (e.g., different disease states) by creating customized libraries based on common image features. Further, we describe the development of a multi-view 3D SHG imaging platform. Unlike fluorescence microscopy, SHG excites

  3. Life cycle water use for electricity generation: a review and harmonization of literature estimates

    Meldrum, J; Nettles-Anderson, S; Heath, G; Macknick, J

    2013-01-01

    This article provides consolidated estimates of water withdrawal and water consumption for the full life cycle of selected electricity generating technologies, which includes component manufacturing, fuel acquisition, processing, and transport, and power plant operation and decommissioning. Estimates were gathered through a broad search of publicly available sources, screened for quality and relevance, and harmonized for methodological differences. Published estimates vary substantially, due in part to differences in production pathways, in defined boundaries, and in performance parameters. Despite limitations to available data, we find that: water used for cooling of thermoelectric power plants dominates the life cycle water use in most cases; the coal, natural gas, and nuclear fuel cycles require substantial water per megawatt-hour in most cases; and, a substantial proportion of life cycle water use per megawatt-hour is required for the manufacturing and construction of concentrating solar, geothermal, photovoltaic, and wind power facilities. On the basis of the best available evidence for the evaluated technologies, total life cycle water use appears lowest for electricity generated by photovoltaics and wind, and highest for thermoelectric generation technologies. This report provides the foundation for conducting water use impact assessments of the power sector while also identifying gaps in data that could guide future research. (letter)

  4. A new approach to theoretical investigations of high harmonics generation by means of fs laser interaction with overdense plasma layers. Combining particle-in-cell simulations with machine learning

    Mihailescu, A.

    2016-01-01

    Within the past decade, various experimental and theoretical investigations have been performed in the field of high-order harmonics generation (HHG) by means of femtosecond ( fs ) laser pulses interacting with laser produced plasmas. Numerous potential future applications thus arise. Beyond achieving higher conversion efficiency for higher harmonic orders and hence harmonic power and brilliance, there are more ambitious scientific goals such as attaining shorter harmonic wavelengths or reducing harmonic pulse durations towards the attosecond and even the zeptosecond range. High order harmonics are also an attractive diagnostic tool for the laser-plasma interaction process itself. Particle-in-Cell (PIC) simulations are known to be one of the most important numerical instruments employed in plasma physics and in laser-plasma interaction investigations. The novelty brought by this paper consists in combining the PIC method with several machine learning approaches. For predictive modelling purposes, a universal functional approximator is used, namely a multi-layer perceptron (MLP), in conjunction with a self-organizing map (SOM). The training sets have been retrieved from the PIC simulations and also from the available literature in the field. The results demonstrate the potential utility of machine learning in predicting optimal interaction scenarios for gaining higher order harmonics or harmonics with particular features such as a particular wavelength range, a particular harmonic pulse duration or a certain intensity. Furthermore, the author will show how machine learning can be used for estimations of electronic temperatures, proving that it can be a reliable tool for obtaining better insights into the fs laser interaction physics.

  5. Harmonic Analyzing of the Double PWM Converter in DFIG Based on Mathematical Model

    Jing Liu

    2017-12-01

    Full Text Available Harmonic pollution of double fed induction generators (DFIGs has become a vital concern for its undesirable effects on power quality issues of wind generation systems and grid-connected system, and the double pulse width modulation (PWMconverter is one of the main harmonic sources in DFIGs. Thus the harmonic analysis of the converter in DFIGs is a necessary step to evaluate their harmonic pollution of DFIGs. This paper proposes a detailed harmonic modeling method to discuss the main harmonic components in a converter. In general the harmonic modeling could be divided into the low-order harmonic part (up to 30th order and the high-order harmonic part (greater than order 30 parts in general. The low-order harmonics are produced by the circuit topology and control algorithm, and the harmonic component will be different if the control strategy changes. The high-order harmonics are produced by the modulation of the switching function to the dc variable. In this paper, the low-order harmonic modeling is established according to the directions of power flow under the vector control (VC, and the high-order harmonic modeling is established by the switching function of space vector PWM and dc currents. Meanwhile, the simulations of harmonic a components in a converter are accomplished in a real time digital simulation system. The results indicate that the proposed modeling could effectively show the harmonics distribution of the converter in DFIGs.

  6. Enhanced high harmonic generation driven by high-intensity laser in argon gas-filled hollow core waveguide

    Cassou, Kevin; Daboussi, Sameh; Hort, Ondrej; Descamps, Dominique; Petit, Stephane; Mevel, Eric; Constant, Eric; Guilbaud, Oilvier; Kazamias, Sophie

    2014-01-01

    We show that a significant enhancement of the photon flux produced by high harmonic generation can be obtained through guided configuration at high laser intensity largely above the saturation intensity. We identify two regimes. At low pressure, we observe an intense second plateau in the high harmonic spectrum in argon. At relatively high pressure, complex interplay between strongly time-dependent ionization processes and propagation effects leads to important spectral broadening without loss of spectral brightness. We show that the relevant parameter for this physical process is the product of laser peak power by gas pressure. We compare source performances with high harmonic generation using a gas jet in loose focusing geometry and conclude that the source developed is a good candidate for injection devices such as seeded soft x-ray lasers or free electron lasers in the soft x-ray range. (authors)

  7. Dramatic dwindling of the power spectrum of high order harmonics by shrinking of the gap size in bowtie nanostructures

    Hosseinzadeh, F.; Batebi, S., E-mail: s-batebi@guilan.ac.ir [University of Guilan, Department of Faculty of Science (Iran, Islamic Republic of); Soofi, M. Q. [Shahid Beheshti University, Laser and Plasma Research Institute (Iran, Islamic Republic of)

    2017-03-15

    Our work is based on high harmonic generation in a gaseous medium (helium ion), by exploiting gold bowtie nanostructures as laser field amplifiers. As the result of emission of a laser pulse, the wave function of the atom varies with time; so, it is necessary to solve 1D time-dependent Schrödinger equation by means of split operator method. By illumination of a short duration, long wavelength three color laser pulse inside the gap, the enhanced field not only changes with time, but also varies in space. In this work we considered this space inhomogeneity in linear and nonlinear schemes. We show that in nonlinear case, the plateau region is more extended. We also show that in larger gaps, cutoff occurs on higher frequencies. But limitation of electron motion in bowtie nanostructures leads to the choice of an optimum 16 nm gap size in our case. We predict that, by the superposition of supercontinuum harmonics, a 26 attosecond pulse can be generated.

  8. Four New Applications of Second-Order Generalized Integrator Quadrature Signal Generator

    Xin, Zhen; Zhao, Rende; Wang, Xiongfei

    2016-01-01

    The Second-Order Generalized Integrator (SOGI) was used as a building block for the SOGI-Quadrature-Signal Generator (SOGI-QSG) which has been widely used for grid synchronization, frequency estimation, and harmonic extraction over the past decade. This paper further investigates its integration...... and differentiation characteristics, with four new integrators and differentiators proposed. Theoretical analysis shows that the proposed SOGI-QSG based integration and differentiation methods can effectively overcome the drawbacks of the pure integrator and differentiator. The proposed four new methods...

  9. Efficient third harmonic generation of a CW-fibered 1.5 µm laser diode

    Philippe, Charles; Chea, Erick; Nishida, Yoshiki; du Burck, Frédéric; Acef, Ouali

    2016-10-01

    We report on frequency tripling of CW-Telecom laser diode using two cascaded PPLN ridge nonlinear crystals, both used in single-pass configuration. All optical components used for this development are fibered, leading to a very compact and easy to use optical setup. We have generated up to 290 mW optical power in the green range, from 800 mW only of infrared power around 1.54 µm. This result corresponds to an optical conversion efficiency P 3 ω / P ω > 36 %. To our knowledge, this is best value ever demonstrated up today for a CW-third harmonic generation in single-pass configuration. This frequency tripling experimental setup was tested over more than 2 years of continuous operation, without any interruption. The compactness and the reliability of our device make it very suitable as a transportable optical oscillator. In particular, it paves the way for embedded applications thanks to the high level of long-term stability of the optical alignments.

  10. Sum frequency and second harmonic generation from the surface of a liquid microjet

    Smolentsev, Nikolay; Chen, Yixing; Roke, Sylvie, E-mail: sylvie.roke@epfl.ch [Laboratory for Fundamental Biophotonics (LBP), Institute of Bioengineering (IBI), School of Engineering STI, École Polytechnique Fédérale de Lausanne EPFL, 1015 Lausanne (Switzerland); Jena, Kailash C. [Laboratory for Fundamental Biophotonics (LBP), Institute of Bioengineering (IBI), School of Engineering STI, École Polytechnique Fédérale de Lausanne EPFL, 1015 Lausanne (Switzerland); Department of Physics, Indian Institute of Technology Ropar, Rupnagar, 140001 (India); Brown, Matthew A. [Laboratory for Surface Science and Technology, Department of Materials, ETH Zürich, CH-8093 Zurich (Switzerland)

    2014-11-14

    The use of a liquid microjet as a possible source of interest for Second Harmonic Generation (SHG) and Sum Frequency Generation (SFG) spectroscopy is examined. We measured non-resonant SHG scattering patterns from the air/water interface of a microjet of pure water and observe a strong enhancement of the SHG signal for certain scattering angles. These enhancements can be explained by the optical properties and the shape of the liquid microjet. SFG experiments at the surface of a liquid microjet of ethanol in air show that it is also possible to measure the coherent vibrational SFG spectrum of the ethanol/air interface in this way. Our findings are useful for future far-UV or X-ray based nonlinear optical surface experiments on liquid jets. In addition, combined X-ray photoelectron spectroscopy and SHG/SFG measurements are feasible, which will be very useful in improving our understanding of the molecular foundations of electrostatic and chemical surface properties and phenomena.

  11. Sum frequency and second harmonic generation from the surface of a liquid microjet

    Smolentsev, Nikolay; Chen, Yixing; Jena, Kailash C.; Brown, Matthew A.; Roke, Sylvie

    2014-11-01

    The use of a liquid microjet as a possible source of interest for Second Harmonic Generation (SHG) and Sum Frequency Generation (SFG) spectroscopy is examined. We measured non-resonant SHG scattering patterns from the air/water interface of a microjet of pure water and observe a strong enhancement of the SHG signal for certain scattering angles. These enhancements can be explained by the optical properties and the shape of the liquid microjet. SFG experiments at the surface of a liquid microjet of ethanol in air show that it is also possible to measure the coherent vibrational SFG spectrum of the ethanol/air interface in this way. Our findings are useful for future far-UV or X-ray based nonlinear optical surface experiments on liquid jets. In addition, combined X-ray photoelectron spectroscopy and SHG/SFG measurements are feasible, which will be very useful in improving our understanding of the molecular foundations of electrostatic and chemical surface properties and phenomena.

  12. Sum frequency and second harmonic generation from the surface of a liquid microjet

    Smolentsev, Nikolay; Chen, Yixing; Roke, Sylvie; Jena, Kailash C.; Brown, Matthew A.

    2014-01-01

    The use of a liquid microjet as a possible source of interest for Second Harmonic Generation (SHG) and Sum Frequency Generation (SFG) spectroscopy is examined. We measured non-resonant SHG scattering patterns from the air/water interface of a microjet of pure water and observe a strong enhancement of the SHG signal for certain scattering angles. These enhancements can be explained by the optical properties and the shape of the liquid microjet. SFG experiments at the surface of a liquid microjet of ethanol in air show that it is also possible to measure the coherent vibrational SFG spectrum of the ethanol/air interface in this way. Our findings are useful for future far-UV or X-ray based nonlinear optical surface experiments on liquid jets. In addition, combined X-ray photoelectron spectroscopy and SHG/SFG measurements are feasible, which will be very useful in improving our understanding of the molecular foundations of electrostatic and chemical surface properties and phenomena

  13. Third-harmonic generation and scattering in combustion flames using a femtosecond laser filament.

    Zang, Hong-Wei; Li, He-Long; Su, Yue; Fu, Yao; Hou, Meng-Yao; Baltuška, Andrius; Yamanouchi, Kaoru; Xu, Huailiang

    2018-02-01

    Coherent radiation in the ultraviolent (UV) range has high potential applicability to the diagnosis of the formation processes of soot in combustion because of the high scattering efficiency in the UV wavelength region, even though the UV light is lost largely by the absorption within the combustion flames. We show that the third harmonic (TH) of a Ti:sapphire 800 nm femtosecond laser is generated in a laser-induced filament in a combustion flame and that the conversion efficiency of the TH varies sensitively by the ellipticity of the driver laser pulse but does not vary so much by the choice of alkanol species introduced as fuel for the combustion flames. We also find that the TH recorded from the side direction of the filament is the Rayleigh scattering of the TH by soot nanoparticles within the flame and that the intensity of the TH varies depending on the fuel species as well as on the position of the laser filament within the flame. Our results show that a remote and in situ measurement of distributions of soot nanoparticles in a combustion flame can be achieved by Rayleigh scattering spectroscopy of the TH generated by a femtosecond-laser-induced filament in the combustion flame.

  14. Chiral crystal of a C2v-symmetric 1,3-diazaaulene derivative showing efficient optical second harmonic generation

    Ma, Xiaohua; Fu, Limin; Zhao, Yunfeng; Ai, Xicheng; Zhang, Jianping; Han, Yu; Guo, Zhixin

    2011-01-01

    the moderate static first hyperpolarizabilities (β0) for both APNA [(136 ± 5) à - 10-30 esu] and DPAPNA [(263 ± 20) à - 10-30 esu], only APNA crystal shows a powder efficiency of second harmonic generation (SHG) of 23 times that of urea. It is shown

  15. The application of the symmetry properties of optical second harmonic generation to studies of interfaces and gases

    Feller, M.B.

    1991-11-01

    Optical second harmonic generation has proven to be a powerful tool for studying interfaces. The symmetry properties of the process allow for surface sensitivity not available with other optical methods. In this thesis, we take advantage of these symmetry properties SHG to study a variety of interesting systems not previously studied with this technique. We show that optical second harmonic generation is an effective surface probe with a submonolayer sensitivity for media without inversion symmetry. We demonstrate the technique at a gallium arsenide surface, exploiting the different symmetry properties of the bulk and surface of the crystal to isolate the surface contribution. We also demonstrate that optical second harmonic generation can be used to determine the anisotropic orientational distribution of a surface monolayer of molecules. We apply the technique to study homogeneously aligned liquid crystal cells. To further explore the LC-polymer interface, we used SHG to study the surface memory effect. The surface memory effect is the rendering of an isotropic interface anisotropic by putting it in contact with an anisotropic bulk. Last, we describe some preliminary measurements of a time-resolved spectroscopic study of the phenomenon of second harmonic generation in a gas. The construction of a 500 microjoule pulsed, tunable laser source is described

  16. The application of the symmetry properties of optical second harmonic generation to studies of interfaces and gases

    Feller, Marla Beth [Univ. of California, Berkeley, CA (United States)

    1991-11-01

    Optical second harmonic generation has proven to be a powerful tool for studying interfaces. The symmetry properties of the process allow for surface sensitivity not available with other optical methods. In this thesis, we take advantage of these symmetry properties SHG to study a variety of interesting systems not previously studied with this technique. We show that optical second harmonic generation is an effective surface probe with a submonolayer sensitivity for media without inversion symmetry. We demonstrate the technique at a gallium arsenide surface, exploiting the different symmetry properties of the bulk and surface of the crystal to isolate the surface contribution. We also demonstrate that optical second harmonic generation can be used to determine the anisotropic orientational distribution of a surface monolayer of molecules. We apply the technique to study homogeneously aligned liquid crystal cells. To further explore the LC-polymer interface, we used SHG to study the surface memory effect. The surface memory effect is the rendering of an isotropic interface anisotropic by putting it in contact with an anisotropic bulk. Last, we describe some preliminary measurements of a time-resolved spectroscopic study of the phenomenon of second harmonic generation in a gas. The construction of a 500 microjoule pulsed, tunable laser source is described.

  17. Quantitative Characterization of Collagen in the Fibrotic Capsule Surrounding Implanted Polymeric Microparticles through Second Harmonic Generation Imaging.

    Akilbekova, Dana; Bratlie, Kaitlin M

    2015-01-01

    The collagenous capsule formed around an implant will ultimately determine the nature of its in vivo fate. To provide a better understanding of how surface modifications can alter the collagen orientation and composition in the fibrotic capsule, we used second harmonic generation (SHG) microscopy to evaluate collagen organization and structure generated in mice subcutaneously injected with chemically functionalized polystyrene particles. SHG is sensitive to the orientation of a molecule, making it a powerful tool for measuring the alignment of collagen fibers. Additionally, SHG arises from the second order susceptibility of the interrogated molecule in response to the electric field. Variation in these tensor components distinguishes different molecular sources of SHG, providing collagen type specificity. Here, we demonstrated the ability of SHG to differentiate collagen type I and type III quantitatively and used this method to examine fibrous capsules of implanted polystyrene particles. Data presented in this work shows a wide range of collagen fiber orientations and collagen compositions in response to surface functionalized polystyrene particles. Dimethylamino functionalized particles were able to form a thin collagenous matrix resembling healthy skin. These findings have the potential to improve the fundamental understanding of how material properties influence collagen organization and composition quantitatively.

  18. Quantitative Characterization of Collagen in the Fibrotic Capsule Surrounding Implanted Polymeric Microparticles through Second Harmonic Generation Imaging.

    Dana Akilbekova

    Full Text Available The collagenous capsule formed around an implant will ultimately determine the nature of its in vivo fate. To provide a better understanding of how surface modifications can alter the collagen orientation and composition in the fibrotic capsule, we used second harmonic generation (SHG microscopy to evaluate collagen organization and structure generated in mice subcutaneously injected with chemically functionalized polystyrene particles. SHG is sensitive to the orientation of a molecule, making it a powerful tool for measuring the alignment of collagen fibers. Additionally, SHG arises from the second order susceptibility of the interrogated molecule in response to the electric field. Variation in these tensor components distinguishes different molecular sources of SHG, providing collagen type specificity. Here, we demonstrated the ability of SHG to differentiate collagen type I and type III quantitatively and used this method to examine fibrous capsules of implanted polystyrene particles. Data presented in this work shows a wide range of collagen fiber orientations and collagen compositions in response to surface functionalized polystyrene particles. Dimethylamino functionalized particles were able to form a thin collagenous matrix resembling healthy skin. These findings have the potential to improve the fundamental understanding of how material properties influence collagen organization and composition quantitatively.

  19. Analytic model of bunched beams for harmonic generation in the low-gain free electron laser regime

    G. Penn

    2006-06-01

    Full Text Available One scheme for harmonic generation employs free electron lasers (FELs with two undulators: the first uses a seed laser to modulate the energy of the electron beam; following a dispersive element which acts to bunch the beam, the second undulator radiates at a higher harmonic. These processes are currently evaluated using extensive calculations or simulation codes which can be slow to evaluate and difficult to set up. We describe a simple algorithm to predict the output of a harmonic generation beam line in the low-gain FEL regime, based on trial functions for the output radiation. Full three-dimensional effects are included. This method has been implemented as a Mathematica® package, named CAMPANILE, which runs rapidly and can be generalized to include effects such as asymmetric beams and misalignments. This method is compared with simulation results using the FEL code GENESIS, both for single stages of harmonic generation and for the LUX project, a design concept for an ultrafast x-ray facility, where multiple stages upshift the input laser frequency by factors of up to 200.

  20. Tracking the ultrafast XUV optical properties of x-ray free-electron-laser heated matter with high-order harmonics

    Williams, Gareth O.; Künzel, S.; Daboussi, S.; Iwan, B.; Gonzalez, A. I.; Boutu, W.; Hilbert, V.; Zastrau, U.; Lee, H. J.; Nagler, B.; Granados, E.; Galtier, E.; Heimann, P.; Barbrel, B.; Dovillaire, G.; Lee, R. W.; Dunn, J.; Recoules, V.; Blancard, C.; Renaudin, P.; de la Varga, A. G.; Velarde, P.; Audebert, P.; Merdji, H.; Zeitoun, Ph.; Fajardo, M.

    2018-02-01

    We present measurements of photon absorption by free electrons as a solid is transformed to plasma. A femtosecond x-ray free-electron laser is used to heat a solid, which separates the electron and ion heating time scales. The changes in absorption are measured with an independent probe pulse created through high-order-harmonic generation. We find an increase in electron temperature to have a relatively small impact on absorption, contrary to several predictions, whereas ion heating increases absorption. We compare the data to current theoretical and numerical approaches and find that a smoother electronic structure yields a better fit to the data, suggestive of a temperature-dependent electronic structure in warm dense matter.