Showing papers on "High harmonic generation published in 1985"
TL;DR: The squeezing spectra for the output fields of several intracavity nonlinear optical systems are obtained and it is shown that at critical points, e.g., the turning points for optical bistability, the threshold for parametric oscillation, and the self-pulsing instability in second-harmonic generation, perfect squeezing is, in principle, possible.
Abstract: The squeezing spectra for the output fields of several intracavity nonlinear optical systems are obtained. It is shown that at critical points, e.g., the turning points for optical bistability, the threshold for parametric oscillation, and the self-pulsing instability in second-harmonic generation, perfect squeezing in the output field is, in principle, possible.
240 citations
TL;DR: In this paper, the alternating sign of the effective nonlinear optical (nlo) coefficient enables efficient frequency mixing independent of the constraints of birefringence for periodic laminar ferroelectric domain superstructures in chromium-doped LiNbO3.
Abstract: Periodic laminar ferroelectric domain superstructures in chromium‐doped LiNbO3 have been grown by modulating the bias current during Czochralski growth. Periodic domain patterns stacked along the y axis with domain thicknesses as low as 8 μm have been prepared. The alternating sign of the effective nonlinear optical (nlo) coefficient enables efficient frequency mixing independent of the constraints of birefringence. This is demonstrated by realizing frequency doubling of 1.06‐μm YAG : Nd laser radiation using the largest nlo coefficient, d33. For domain thicknesses equal to an odd multiple of the coherence length, d=(2m+1)lc, the second harmonic intensity varies as the square of the domain number. For the optimum case, d=lc, an improvement of the nlo efficiency, as compared to the 90° phase‐matched process, by the factor [(2/π)d33/d31]2=15 is inferred.
134 citations
TL;DR: In this paper, it was shown theoretically that the directly modulated laser diode, with the modulation frequency of its injection current comparable to the relaxation oscillation frequency, exhibits period doubling route to chaos as the modulation index of current is increased.
Abstract: It is shown theoretically that the directly modulated laser diode, with the modulation frequency of its injection current comparable to the relaxation oscillation frequency, exhibits period doubling route to chaos as the modulation index of current is increased. The effect of spontaneous emission factor on the chaotic behavior in the laser diode is also studied.
118 citations
TL;DR: Optical second harmonic generation for surface and interface studies is briefly reviewed in this article, with numerous examples illustrating how powerful and versatile this new surface analytical technique can be for surface analysis.
Abstract: Optical second harmonic generation for surface and interface studies is briefly reviewed, with numerous examples illustrating how powerful and versatile this new surface analytical technique can be.
103 citations
62 citations
TL;DR: In this article, a conical antenna was found to be superior to the conventional long-wire antenna at wavelengths shorter than 10 μm, and the sensitivity and high-speed response of WNiO−Ni point contact diodes were investigated at different laser frequencies and mixing orders as a function of tip radius, resistance, and coupling.
Abstract: Dramatic improvements in the stability of the metal‐insulator‐metal point contact diode has been achieved by the use of blunter whisker tips. The optimum values for tip radius and diode resistance were experimentally determined. Both sensitivity and high‐speed response of W‐NiO‐Ni point contact diodes were investigated at different laser frequencies and mixing orders as a function of tip radius, resistance, and coupling. The tip radii were changed by more than an order of magnitude, and surprisingly, the sensitivity and the harmonic generation up to 88 THz were not significantly affected. A conical antenna was found to be superior to the conventional long‐wire antenna at wavelengths shorter than 10 μm. Responsivity measurements as a function of the diode resistance showed evidence for two different physical mechanisms responsible for the operation of the diode.
61 citations
TL;DR: In this paper, the basic mechanisms, linear and non-linear, for light absorption are reviewed and the processes responsible for harmonic generation are investigated in connection with the ponderomotive force, soliton formation, wavebreaking, etc.
56 citations
TL;DR: In this paper, the phase matched generation of the optical second harmonic was investigated in the chiral smectic C* phase of a classical ferroelectric liquid crystal (DOBAMBC).
Abstract: The phase-matched generation of the optical second harmonic was investigated in the chiral smectic C* phase of a classical ferroelectric liquid crystal (DOBAMBC). The phase-matching was achieved either by incidence angle or by temperature tuning. The temperature behaviour of the second order nonlinear susceptibility was studied.
53 citations
TL;DR: The Brillouin reflectivity is numerically found to display a chaotic time evolution at laser fluxes below those at which ion sound-wave harmonic generation takes place.
Abstract: Low reflectivity of stimulated Brillouin scattering is shown to result from wave-interaction incoherency caused by the ion sound-wave nonlinearity. The Brillouin reflectivity is numerically found to display a chaotic time evolution at laser fluxes below those at which ion sound-wave harmonic generation takes place. At these fluxes, the scattered light exhibits a spiky frequency spectrum. Scaling laws for the reflectivity are given.
31 citations
TL;DR: Optimization of crystal thickness, based on numerical simulations is discussed, and overall conversion efficiencies in excess of 40% have been achieved for incident laser intensities between 1 and 2.5 GW/cm2.
Abstract: Basic properties of the fourth harmonic conversion of 1.053-μm laser radiation with KDP crystals are experimentally determined. Optimization of crystal thickness, based on numerical simulations is discussed. A large aperture conversion cell combining second and fourth harmonic generators has been designed. Overall conversion efficiencies (ω → 4ω) in excess of 40% have been achieved for incident laser intensities between 1 and 2.5 GW/cm2.
28 citations
TL;DR: In this article, a nonlinear Schrodinger equation for linearly polarized electromagnetic waves propagating across the ambient magnetic field in an electron-positron plasma was obtained, and the nonlinearities arising from wave intensity induced particle mass modulation, as well as harmonic generation were incorporated.
Abstract: A nonlinear Schrodinger equation is obtained for linearly polarized electromagnetic waves propagating across the ambient magnetic field in an electron-positron plasma. The nonlinearities arising from wave intensity induced particle mass modulation, as well as harmonic generation are incorporated. Modulational instability and localization of pulsar radiation are investigated.
TL;DR: In this article, the interference effects for second-harmonic generation within a resonant cavity were investigated and the dependence of the second harmonic phase on the fundamental phases and coupling efficiency on the overlap of the harmonic polarization wave with the cavity-mode function was shown.
Abstract: An experiment is described that investigates certain interference effects for second-harmonic generation within a resonant cavity. By employing a noncollinear geometry, the phases of two fundamental beams from a frequency-stabilized dye laser can be controlled unrestricted by the boundary conditions imposed in an optical cavity containing a KDP crystal and resonant at the second harmonic. The fundamental beams are either traveling or standing waves and generate either one or two coherent sources of ultraviolet radiation within the cavity. The experiment demonstrates explicitly the dependence of second-harmonic phase on the fundamental phases and the dependence of coupling efficiency on the overlap of the harmonic polarization wave with the cavity-mode function. The measurements agree well with a simple theory.
TL;DR: In this paper, the problems concerning the development of high f -number spectrographs with high spectral and spatial resolution using holographic reflecting gratings, for the study of processes of harmonic generation in laser plasmas are considered.
Abstract: The problems concerning the development of high f -number spectrographs with high spectral and spatial resolution using holographic reflecting gratings, for the study of processes of harmonic generation in laser plasmas are considered. The concave holographic gratings and spectrograph schemes used in the “Delfin-1” installation are described. The anomalous generation of ω 0 and 2ω 0 harmonics from the subcritical density plasma region has been observed experimentally. Possible interpretations of the observed effect are given.
TL;DR: In this article, the frequency doubling performance of CdGeAs2 as a function of wavelength has been characterised using a representative selection of lines from the 9 and 10 μm bands of a single mode TEA CO2 laser.
Abstract: The frequency-doubling performance of CdGeAs2 as a function of wavelength has been characterised using a representative selection of lines from the 9 and 10 μm bands of a single mode TEA CO2 laser Results are shown to be in good agreement with theory in which wavelength dependent absorption, most significant for the generated signal, is taken into account
TL;DR: Transients in resonantly coupled three-level systems are studied, finding that free-induction decay is strongly dominated by population-induced effects; Raman-like peaks introduced by Stark shifts may show large instantaneous gain.
Abstract: We study transients in resonantly coupled three-level systems. Two of the levels are coupled by intense two-photon pumping, and the third one provides a probing level. Adiabatically eliminated levels appear in effective system parameters. Experimentally, this model is applicable, e.g., in resonantly enhanced parametric and harmonic generation in atomic vapors. A distinguishing feature in the system is the appearance of ac Stark shifts in the probe spectra when pumping at the two-photon resonance. The nutation signal is shown to give information on the effective two-photon Rabi frequency and on the decay rate of the dipole-forbidden two-photon coherence. Free-induction decay is strongly dominated by population-induced effects; Raman-like peaks introduced by Stark shifts may show large instantaneous gain. Gaussian pump pulses are investigated to investigate effects arising from the temporal sweeping of the two-photon Rabi flipping and the modulation of the Stark shifts. The results also provide relevant information on the gain dynamics of coherently pumped lasers.
01 Jan 1985
TL;DR: In this paper, the acoustic n onlinearity parameter has been determined in the heat treatable aluminum alloys 6U61-T6, 2024-T4 and 7075-T551 using the ultrasonic harmonic generation technique.
Abstract: The acoustic n onlinearity parameter has been determined in the heat treatable aluminum alloys 6U61-T6, 2024-T4 and 7075-T551 using the ultrasonic harmonic generation technique . The measurements were made using a 10 MHz longitudinal u ltrasonic transducer for transmission and a capacitive transducer for the detection of the second harmonic. Preliminary results i ndicate a linear relationship between the n onlinearity parameter and the volume fraction of second phase precipitates in these alloys. This finding is consistent with the ordered dependence of the nonlinearity parameter on the molecular structure of cubic crystals for a given propagation mode. Independent measurements made of the acoustoelastic constants in the same alloys are found to exhibit a similar dependence o n second phase.
15 Jun 1985-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this paper, absolute and relative energy spread measurements have been made on the ACO storage ring using two different methods: spectral analysis of the electron bunch length based on the proportionality of the longitudinal bunch length versus energy spread and direct measurement using the on axis synchrotron radiation emitted by an optical klystron.
Abstract: Absolute and relative energy spread measurements have been made on the ACO storage ring using two different methods. The first one consists of a spectral analysis of the electron bunch length based on the proportionality of the longitudinal bunch length versus energy spread. The second one constitutes a direct measurement using the on axis synchrotron radiation emitted by an optical klystron. The two measurement techniques present a very high signal/noise ratio allowing time resolved records. Examples are presented of the energy spread time evolution in the FEL oscillator and of harmonic generation experiments.
TL;DR: In this paper, an analytic expression for the efficiency of harmonic generation in focused beams allowing for the second-order Kerr effect was derived for the case of the third harmonic and the results show good agreement with known experimental data.
Abstract: An analytic expression is derived for the efficiency of harmonic generation in focused beams allowing for the second-order Kerr effect. A specific analysis is made for the case of the third harmonic. The results show good agreement with known experimental data.
TL;DR: Second harmonic detection in fluorescence spectrometry is shown to be capable of suppressing interfering scattering features which are up to 150 times more intense than the underlying fluorescence as discussed by the authors, which is a major benefit in optical alignment of the instrument.
Abstract: Harmonic generation in saturated fluorescence is shown to reduce the scattered light background in laser-induced fluorescence. In the harmonic generation technique, the fluorescence is excited with sinusoidal amplitude modulation and the nonlinear response of saturated fluorescence generates harmonics of the excitation frequency. Detection at the second harmonic is shown to completely suppress the amplitude of Raman scattering background. The suppression occurs with no decrease in background noise for detection systems at the statistical noise limit and, since second harmonic detection decreases the fluorescence signal, signal-to-noise is degraded. For systems with nonstatistical noise, the noise in the background is decreased with second harmonic detection, and improved analytical detection limits may result. Second harmonic detection in fluorescence spectrometry is shown to be capable of suppressing interfering scattering features which are up to 150 times more intense than the underlying fluorescence. Fluorescence spectra from a steady-state concentration of 210 molecules in the probe volume are shown. A major benefit in optical alignment of the instrument is obtained through second harmonic detection. 10 references, 8 figures, 2 tables.
01 Jan 1985
TL;DR: In this article, electric-field induced second harmonic generation measurements on thin polydiacetylene films performed at 1.064 and 1.907 μm are reported.
Abstract: Results of electric-field induced second harmonic generation measurements on thin polydiacetylene films performed at 1.064 μm and 1.907 μm are reported. At 1.064 μm one observes large internal polarization fields depending on the polymer thin film morphology. No such polarization effects are observed at 1.907 μm.
01 Jan 1985
TL;DR: In this paper, the spectral properties of the VUV and XUV spectral regions were investigated using laser-based sources of high energy radiation. But, the spectroscopy community and particularly, those in molecular spectrography, have been less active in fully exploiting the level of sophistication now available using laser techniques for studies of excited states in the spectral regions.
Abstract: Over the past ten years enormous strides have been made towards producing novel sources of VUV and XUV radiation using lasers. This work has been motivated by many factors, including studies of highly-excited atomic states; interest in nonlinear optical phenomena; the development of x-ray lasers; and, the long-term prospect of applications of high energy radiation to photolithography in the production of integrated circuits. The spectroscopy community and, particularly, those in molecular spectroscopy, have been less active in fully exploiting the level of sophistication now available using laser techniques for studies of excited states in the VUV and XUV spectral regions. First, we now have the capability of producing high intensity [1–7], continously-tunable, coherent and narrow line width VUV radiation, spanning the 100 nm - 200 nm region, with laboratory-scale dye laser systems.
TL;DR: In this article, particle simulations are used to understand the nonlinear characteristics of this instability and the instability saturates by beam trapping, nonlinear electron effects, and nonlinear motion parallel to the density gradient.
Abstract: Recent experiments on the TMX‐U device, at the Lawrence Livermore National Laboratory have indicated the possibility of a drift wave being driven unstable by the injection of neutral beams in the thermal barrier region. A review of linear theory is presented in the local approximation. In addition, particle simulations are used to understand the nonlinear characteristics of this instability. The particle simulations are performed using 1d‐3v and 2d‐3v electrostatic particle simulation codes. The instability is shown to saturate by beam trapping, nonlinear electron effects, and nonlinear motion parallel to the density gradient. Resonant E×B motion is a significant process for some of the beam particles. This process is closely associated with the trapping of beam ions. Harmonic generation is also observed, as appears in some of the experimental data. Qualitative nonlinear theory is presented in support of the particle simulations.
TL;DR: It is found that the effect of beam size on second harmonic intensity should be taken into account in actual experiments.
Abstract: Second harmonic generation of long-range surface plasmon polaritons excited by a finite 1-D beam are discussed. To simplify the analysis of second harmonic generation, we adopt the “pole cancellation” method originally developed by Sipe. A numerical calculation of second harmonic intensity is presented. It is found that the effect of beam size on second harmonic intensity should be taken into account in actual experiments.
01 Mar 1985
TL;DR: In this article, the process of optical 2nd harmonic generation in thin surface layers between centrosym materials was studied and the surface susceptibilities were dominated by the electronic properties of adsorbed monolayers of dye mols.
Abstract: The process was studied of optical 2nd harmonic generation in thin surface layers between centrosym materials The surface susceptibilities are dominated by the electronic properties of adsorbed monolayers of dye mols Through the appropriate choice of dye, 1 or 2 electronic resonances can be used in the process leading to dramatic enhancement of the generated signal
27 Mar 1985
TL;DR: In this paper, the second harmonic and difference frequency generators as well as parametric amplifiers and oscillators are presented as efficient devices for frequency conversion of coherent radiation, and third order devices for signal processing and optical logic applications are discussed.
Abstract: Nonlinear integrated optical devices based on second and third order nonlinearities of Ti:LiNbO3 waveguides are reviewed. Second harmonic and difference frequency generators as well as parametric amplifiers and oscillators are presented as efficient devices for frequency conversion of coherent radiation. Furthermore, third order devices for signal processing and optical logic applications are discussed.
01 Oct 1985
TL;DR: In this paper, the Jones matrix technique is used to calculate losses due to optical isolators in laser cavities with a linear phase anisotropy, and practical recommendations for designing optical isolateators are formulated.
Abstract: The Jones matrix technique is used to calculate losses due to optical isolators in laser cavities with a linear phase anisotropy. The behavior of YAG:Nd lasers when the cavity is tuned, when the pump power changes, or when a nonlinear frequency-doubling crystal is inserted inside the cavity, is explained by considering the effects of a phase plate, and practical recommendations for designing optical isolators are formulated. In particular, the calculated results can be used to find tolerances on the alignment of the polarizer and the principal axes of the nonlinear crystal. It is also shown that a half-wave plate must be used to rotate the polarization plane for optimum performance of optical isolators in YAG:Nd laser cavities.
01 Jan 1985
TL;DR: In this paper, it was shown that larger bubbles give rise to a stronger echo than bubbles at resonance, giving rise to ambiguities which would make it difficult to measure the size distribution of bubbles covering a range of sizes.
Abstract: The detection and sizing of microbubbles in fluids has potential applications in industry and medicine. Non-invasive techniques using ultrasound appear attractive compared to optical techniques. Different methods employing ultrasound have been shown to be capable of detecting bubbles in fluids and of estimating their sizes. These include those using the Doppler effect (Nishi, 1972)1 , resonant scattering (Fairbanks and Scully, 1977)2 and second harmonic generation (Miller, 1981)3. There are some major drawbacks in these techniques. In the Doppler technique there is no way of distinguishing echoes from a cluster of small bubbles from those of a large bubble occupying the same volume. The Doppler technique is also incapable of detecting stationary bubbles, such as those trapped in tissues. The resonant scattering and the second harmonic generation techniques work on the basis of the fact that bubbles have a characteristic resonant frequency dependent on their sizes. In resonant scattering, however, it is found that larger bubbles give rise to a stronger echo than bubbles at resonance, giving rise to ambiguities which would make it difficult to measure the size distribution of bubbles covering a range of sizes. Both the resonant scattering and the second harmonic generation methods suffer from poor spatial resolution.
01 Jan 1985
TL;DR: In this paper, both continuously and step tunable nonlinear infrared frequency generation has many potential applications in remote sensing, and it is essential that the technology exists to reliably grow the material in adequate size and quality.
Abstract: Both continuously and step tunable nonlinear infrared frequency generation have many potential applications in remote sensing. Nonlinear frequency conversion in the infrared, however, has been limited by the properties of available nonlinear optical materials. The required material characteristics include low absorption, good optical quality, and dispersion and birefingence properties which allow phasematching in addition to nonlinear properties of high resistance to optical damage and a usefull nonlinear optical coefficient. Furthermore, it is essential that the technology exists to reliably grow the material in adequate size and quality.
01 Jun 1985
TL;DR: In this paper, the first experiment of surface second-harmonic generation with a CW laser was carried out with a simple inexpensive CW diode laser and the results showed that it is possible to obtain a nonlinear optical effect at a surface without using a high laser intensity.
Abstract: Optical second-harmonic generation (SHG) can be an extremely sensitive tool for surface studies. The technique is capable of probing adsorbed molecules at various interfaces [1]. It is based on the idea that SHG is forbidden in a medium with inversion symmetry, but necessarily allowed at a surface. To see such a surface nonlinear optical effect, high laser intensity is often needed. Thus, in the experiments reported so far, pulsed lasers were used exclusively. From the consideration for practical applications, however, the technique would look much more attractive if the bulky pulsed laser can be replaced by a simple inexpensive CW diode laser. We demonstrate here at this conference that this is indeed possible. The work, described below, also constitutes the first experiment of surface SHG carried out with a CW laser.