Showing papers on "High harmonic generation published in 1986"
TL;DR: In this paper, a rate-equation theory of a multilongitudinal-mode laser oscillator with an intracavity-doubling crystal is presented that includes terms modeling the sum-frequency and frequency-dubling processes.
Abstract: The output of a laser-diode-pumped Nd:YAG laser with an intravcavity-doubling crystal exhibits large-amplitude fluctuations and longitudinal-mode instabilities. The results of an experimental and theoretical investigation of these instabilities are described. The instabilities arise from coupling of the longitudinal modes of the laser oscillator by sum-frequency generation in the nonlinear crystal. A rate-equation theory of a multilongitudinal-mode laser oscillator with an intracavity-doubling crystal is presented that includes terms modeling the sum-frequency and frequency-doubling processes.
365 citations
TL;DR: In this article, the phase matchability of BaB 2 O 4 has been shown to be phase matchable for second-harmonic generation down to 2048 A at room temperature.
Abstract: \Beta -BaB 2 O 4 has been found to be phase matchable for second-harmonic generation down to 2048 A at room temperature. Sellmeier's equations, which are highly accurate from 1.064 μm to 2050 A, are reported.
264 citations
TL;DR: In this paper, the phase-matching angular acceptance bandwidth, damage-threshold observations, and a measurement of effective susceptibility relative to KD*P are also reported, and various doubling schemes are investigated to avoid reconversion effects observed in 9mm-long crystals.
Abstract: Conversion efficiencies in excess of 50% have been measured in frequency-doubling experiments in KTP using divergent fundamental 1.064-μm beams. Various doubling schemes have been investigated to avoid reconversion effects observed in 9-mm-long crystals. The phase-matching angular acceptance bandwidth, damage-threshold observations, and a measurement of effective susceptibility relative to KD*P are also reported.
195 citations
Patent•
15 Aug 1986TL;DR: In this article, a second harmonic, optical generator is disclosed in which a laser diode produces an output pumping beam which is focused by means of a graded, refractive index rod lens into a rod of lasant material, such as Nd:YAG, disposed within an optical resonator to pump the lasant materials and to excite the optical resonators at a fundamental wavelength.
Abstract: A second harmonic, optical generator is disclosed in which a laser diode produces an output pumping beam which is focused by means of a graded, refractive index rod lens into a rod of lasant material, such as Nd:YAG, disposed within an optical resonator to pump the lasant material and to excite the optical resonator at a fundamental wavelength. A non-linear electro-optic material such as MgO:LiNbO3 is coupled to the excited, fundamental mode of the optical resonator to produce a non-linear interaction with the fundamental wavelength producing a harmonic. In one embodiment, the gain medium and the non-linear material are disposed within an optical resonator defined by a pair of reflectors, one of which is formed on a face of the gain medium and the second of which is formed on a face of the non-linear medium. In another embodiment, the non-linear, electro-optic material is doped with the lasant ion such that the gain medium and the non-linear doubling material are co-extensive in volume. In another embodiment, a non-linear, doubling material is disposed in an optical resonator external of the laser gai medium for improved stability of the second harmonic generation process. In another embodiment, the laser gain medium andthe non-linear material are bonded together by means of an optically transparent cement to form a mechanically stable, monolithic structure. In another embodiment, the non-linear material has reflective faces formed thereon to define a ring resonator to decouple reflections from the non-linear medium back to the gain medium for improved stability.
85 citations
65 citations
TL;DR: A harmonic-generation mechanism that relies on the coupling modulation between an electron orbit and an electromagnetic mode is proposed and predicts the emission of even-harmonic radiation in the forward direction primarily in the TEM/sub 01/ mode.
Abstract: A harmonic-generation mechanism that relies on the coupling modulation between an electron orbit and an electromagnetic mode is proposed. Applications of this mechanism to harmonic generation in linearly polarized free-electron lasers predicts the emission of even-harmonic radiation in the forward direction primarily in the ${\mathrm{TEM}}_{01}$ mode.
43 citations
Patent•
30 Oct 1986TL;DR: In this paper, a monolithic phasematched harmonic generator is obtained by optically pumping an optically nonlinear lasant member having reflective faces defining the monolithic optical resonator.
Abstract: A monolithic phasematched harmonic generator is obtained by optically pumping an optically nonlinear lasant member having reflective faces defining the monolithic optical resonator. Phasematching is achieved, in one case, by inclining a totally internally reflective face of the resonator at a proper angle relative to other faces of the resonator to angularly separate and resonate lasant waves of the proper polarization. In a second case, a clad fiber resonator of optically nonlinear lasant material has its cladding arranged to guide and thus resonate only lasant waves of the correct polarization. In a third case, the optical nonlinear coefficient of the optically nonlinear lasant material is spatially modulated with a period equal to an odd integer number of coherence lengths, of the harmonic generation process, to obtain quasi-phasematched operation. Phasematched operation improves the efficiency of the harmonic generation process.
42 citations
Patent•
12 Nov 1986
TL;DR: In this article, a method for exciting harmonic generation of radio frequency in a tank resonant circuit by bipolar spaced, half-cycle pulses was proposed. But the method was not suitable for high frequency applications, since the period of the resonant frequency oscillations is 1/N the period between successive pulses of similar polarity.
Abstract: A method of and apparatus for exciting harmonic generation of radio frequency in a tank resonant circuit by bipolar spaced, half-cycle pulses, wherein the period of the tank resonant frequency oscillations is 1/N the period between successive pulses of similar polarity, where N is an odd integer greater than unity.
38 citations
03 Nov 1986
TL;DR: In this article, the use of periodic modulation of lithium niobate waveguide properties to achieve phase-matching for second harmonic generation has been investigated both theoretically and experimentally, and a compact expression for the conversion efficiency has been derived for the case when simultaneous modulation of both the linear and nonlinear properties are taken into account.
Abstract: Use of periodic modulation of lithium niobate waveguide properties to achieve phase-matching for second harmonic generation has been investigated both theoretically and experimentally. The mathematical description has been reduced to the same form of differential equations as for the unperturbed case, but with a modified coupling coefficient. A compact expression for the conversion efficiency has been derived for the case when simultaneous modulation of both the linear and nonlinear properties are taken into account. For the case of modulation of only the linear properties, second harmonic light has been obtained experimentally.
31 citations
TL;DR: The method can measure the index difference to better than 0.1%, which for gases such as helium represents an absolute accuracy of ∼10−9.2%, much better than previously reported.
Abstract: Measurements of the dispersion of the refractive index using a nonlinear interferometer are described. A sample of the optical material to be measured is interposed between two optically nonlinear crystals, and a moderately intense laser is passed through the combination. By observing the interference between the second harmonics produced in the two nonlinear crystals, the difference between the refractive indices of the sample at the laser frequency and its second harmonic frequency can be determined very precisely. We have used the interferometer to measure the dispersion in several gases between 1064 and 532 nm. We have also used it to determine the dispersion of two transparent solids. The method can measure the index difference to better than 0.1%, which for gases such as helium represents an absolute accuracy of ∼10−9.
30 citations
TL;DR: In this paper, the beam-steering grid is a programmable reflector, where the diode bias controls the phase shift of the reflection, and the variation of the phase across the grating sets the direction of the reflected beam.
Abstract: Loading a grid with diodes offers the possibility of two-dimensional control of millimeter waves that is analogous to holography and nonlinear optics. These grids are attractive because they are suitable for monolithic integration with gallium-arsenide Schottky diodes and for high-power operation. Here we present grid designs for electronic beam-steering and harmonic generation. The beam-steering grid is a programmable reflector, where the diode bias controls the phase shift of the reflection. The variation of the phase across the grating sets the direction of the reflected beam. The reflection loss in computer simulations is 3dB at 90GHz. The harmonic-generating grid acts as a nonlinear reactive surface, where the nonlinear capacitance of the diodes produces the harmonic frequencies. Quasioptical filters select the desired harmonic. Computer simulations predict that a 65GHz-to-130GHz doubler would have an output power of 0.56W/cm2 and a conversion efficiency of 35%.
TL;DR: In this article, the process of second-harmonic generation when the nonlinear crystal is in an active laser cavity is studied both analytically and numerically, characterized by isolated bifurcations (steady and Hopf) but also by interacting bifurlcations.
Abstract: We study the process of second-harmonic generation when the nonlinear crystal is in an active laser cavity. This system is characterized by isolated bifurcations (steady and Hopf) but also by interacting bifurcations. They are studied both analytically and numerically.
TL;DR: Optical second-harmonic generation was used to probe the structure of freely suspended films of 4'-n-octyl-4-cyanobiphenyl (8CB) in the smectic-A phase, and its behavior suggested no modifications of molecular arrangement in the layers in the presence of the two ''free'' surfaces.
Abstract: Optical second-harmonic generation (SHG) was used to probe the structure of freely suspended films of 4'-n-octyl-4-cyanobiphenyl (8CB) in the smectic-A phase. The intensity of the SHG from ultrathin films with thickness varying from 2 to 10 molecular layers appeared quantized, but its behavior suggested no modifications of molecular arrangement in the layers in the presence of the two ''free'' surfaces. A macroscopic theory for the SHG from a film with stratified nonlinear susceptibility is presented and compared with the experimental observation.
26 Sep 1986
TL;DR: In this article, the authors considered the use of GaAs Schottky diodes for detecting up to 10 THz with circular or non-circular geometries, tunable sideband generation from a laser source by using the power back radiated by a wire antenna connected to the diode.
Abstract: The interest given to GaAs Schottky diodes having small junction sizes has been continuously growing during the last decade to realize fast devices for detection, mixing, harmonic generation or sideband conversion in the terahertz domain. The studies carried out at LDIR on those devices cover both experimental and theoretical aspects. The following topics are considered here: Videodetection up to 10 THz with diodes having circular or non-circular geometries, tunable sideband generation from a laser source by using the power back radiated by a wire antenna connected to the diode, and detectormixer block development to improve the electromagnetic coupling efficiency between the submillimeter wave radiation and the antenna.
26 Sep 1986
TL;DR: The second and third harmonic generation of far infrared radiation in bulk solids is reported in this article, where single pulses with power of 100 KW and duration of 40 ns are focused on dielectrics or semi-conductors.
Abstract: Far -infrared nonlinear opticsFritz KeilmannMax -Planck -Institut fur FestkorperforschungHeisenbergstr. 1, 7000 Stuttgart 80, FRGAbstractSecond and third harmonic generation of far -infrared radiation in bulk solids is reportedThe far -infrared source is a step -tunable gas laser emitting in the range 8.2 to 57 cm-1.Single pulses with power of 100 KW and duration of 40 ns are focused on dielectrics or semi-conductors. Harmonic power is selectively transmitted through perforated metal cutoff fil-ters and detected with a GaAs photoconductor. Harmonic powers up to 100 W are obtained.QuantitY1ve measurement53allow to determine absolute values of the nonlinear susceptibili-
TL;DR: In this article, the authors investigated the possibility of optical harmonic generation in gaseous media with positive dispersion and showed that the dependence of the third-harmonic generation efficiency on the intensity of incident beam (η∼W4) is explained by the second-order Kerr effect.
Abstract: Third-harmonic generation in gaseous media with positive dispersion is investigated. Using the example of the 351.7–117.2 nm conversion process in rare gases the possibility of optical harmonic generation in media with positive dispersion was first experimentally obtained and theoretically substantiated. Unusual dependence of the thirdharmonic generation efficiency on the intensity of incident beam (η∼W4) is explained due to the second-order Kerr effect.
TL;DR: Treatment of the multiphoton-ionization problem involving phase-matched, third-harmonic fields is generalized to include quantitative effects of index changes due to a buffer gas, absorption due to dimers, and collisional dephasing of coherent excitations.
Abstract: Several extensions are made in theoretical studies of multiphoton ionization associated with third-harmonic fields that are generated near three-photon resonances in gaseous media. The treatment includes the strong coherent cancellation effect which occurs between three-photon pumping of a resonant level and pumping by the third-harmonic field that is generated in the same medium. The incomplete spoiling of the cancellation effect with counterpropagating beams is quantitatively described. Also, treatment of the multiphoton-ionization problem involving phase-matched, third-harmonic fields is generalized to include quantitative effects of index changes due to a buffer gas, absorption due to dimers, and collisional dephasing of coherent excitations. Finally, we show how measurements of linewidths, phase-matching positions, and pressure dependences of ionization yields associated with third-harmonic generation and subsequent absorption can be used to determine oscillator strengths of a resonant level, absorption coefficients for a resonant species and a buffer-gas species, and the refractive index of the buffer gas at the third-harmonic frequency.
TL;DR: The passive mode locking of a cw Rhodamine 110 dye laser is reported, in a simple uncompensated linear cavity, subpicosecond pulse generation was achieved over the spectral range 553–570 nm.
Abstract: The passive mode locking of a cw Rhodamine 110 dye laser is reported. In a simple uncompensated linear cavity, subpicosecond pulse generation was achieved over the spectral range 553–570 nm. Pulses as short as 150 fsec were recorded using standard second-harmonic autocorrelation measurement techniques. Two saturable-absorbing species were found to operate successfully in this region.
TL;DR: In this article, a two-fluid model of plasmas with collisions is presented, which permits the calculation of dynamic electric fields and double layers inside of plaasmas including oscillations and damping.
Abstract: A genuine two-fluid model of plasmas with collisions permits the calculation of dynamic electric fields and double layers inside of plasmas including oscillations and damping. For the first time, a macroscopic model for coupling of electromagnetic and Langmuir waves was achieved with realistic damping. Starting points were laser-produced plasmas showing very high dynamic electric fields in nonlinear force-produced cavitons and inverted layers, in agreement with experiments. Applications for any inhomogeneous plasma as in laboratory or in astrophysical plasmas can then be followed up by a transparent hydrodynamic description. We find the rotation of plasmas in magnetic fields and a new second harmonic resonance. Explanation of inverted double layers, second harmonic emission from laser-produced plasmas, and laser acceleration of charged particles by the very high fields of the double layers is given.
TL;DR: It is shown how detailed information on multiphoton ionization involving phase-matched third-harmonic photons can be used to obtain optical constants in the vacuum-ultraviolet region.
Abstract: Unfocused linearly polarized laser beams, in single-pass and counterpropagating configurations, are used in conjunction with absolute ionization measurements in calibrated proportional counters to examine the nature of multiphoton ionization of xenon near three-photon resonances. Mixtures of xenon with other noble gases are also used to incorporate phase matching in order to elucidate additional characteristics of multiphoton ionization in the presence of third-harmonic fields. Point-by-point comparisons are made between theoretically predicted and experimentally observed features of the study. We also show how detailed information on multiphoton ionization involving phase-matched third-harmonic photons can be used to obtain optical constants in the vacuum-ultraviolet region.
TL;DR: In this article, the first passive mode locking of a continuous-wave energy transfer dye laser was reported using an argon ion laser-pumped mixture of rhodamine 6G and sulphur rhodamines 101 as the active medium, pulses of less than 500 fs duration were generated over the spectral range 652-694 nm using two different saturable absorbers in a simple linear cavity without dispersion optimization.
Abstract: The first passive mode locking of a continuous-wave energy transfer dye laser is reported. Using an argon ion laser-pumped mixture of rhodamine 6G and sulphur rhodamine 101 as the active medium, pulses of less than 500 fs duration have been generated over the spectral range 652-694 nm using two different saturable absorbers in a simple linear cavity without dispersion optimization. Pulses as short as 120 fs have been measured using standard second-harmonic generation autocorrelation techniques.
01 Sep 1986-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this article, the harmonic generation rate of an optical klystron placed on a storage ring has been calculated in the VUV spectral range in three cases: (i) when the pump laser is an external pulsed laser; (ii) when this FEL is Q-switched instead of cw. Although the first case will provide the maximum coherent power, the second case will produce a noticeable amount of harmonics with a simpler experimental setup.
Abstract: The harmonic generation rate of an optical klystron placed on a storage ring has been calculated in the VUV spectral range in 3 cases: (i) when the pump laser is an external pulsed laser; (ii) when the pump laser is an FEL working on the ring; and (iii) when this FEL is Q-switched instead of cw. Although the first case will provide the maximum coherent power it appears that the Q-switched FEL will produce a noticeable amount of harmonics with a simpler experimental setup. An output power of the order of 1 kW should be produced between typically 300 and 1500 A on a standard VUV ring like Super-ACO at Orsay.
TL;DR: In this paper, the authors present a theoretical analysis of coax excitation and plasma impedance for a dielectric-filled rectangular waveguide, where the plasma reflection coefficient is obtained by matching plasma and waveguide fields at the interface.
Abstract: Dielectric-filled waveguides may be advantageous for heating reactor-grade tokamak plasmas, due to their compactness and power-handling capability. We present a theoretical analysis of coax excitation and plasma impedance for a dielectric-filled rectangular waveguide. The plasma reflection coefficient is obtained by matching plasma and waveguide fields at the interface. The numerical results show that the reflection coefficients can be made small by careful tailoring of the waveguide dimensions to the density profile for heating at the second or third harmonic of deuterium. We present a scattering matrix approach for the design of a coaxial feed to match the waveguide in the presence of a wide range of plasma loading. For a waveguide filled with a high permittivity dielectric, a shorted probe gives better coupling than an open-ended probe.
04 Mar 1986
TL;DR: In this paper, polyacetylene films were used to generate optical third harmonics and other nonlinear optical effects using a Nd-YAG pulsed laser operating at 1.06 microns.
Abstract: Polyacetylene films were used to generate optical third harmonics and other nonlinear optical effects. The source was a Nd-YAG pulsed laser operating at 1.06 microns. The poly-acetylene films were prepared using the Shirakawa synthesis procedure. The films were free standing, one micron to 100 microns in thickness. Nonlinear optical effects were observed using non-Bragg angle scattering. The films were mounted in a vacuum tight sample holder, nevertheless, the measurements resulted in heat damage to the films.
01 Oct 1986
TL;DR: In this article, the results of a comparative study of three solution methods: harmonic balance, modified SPICE, and time domain methods are presented for the analysis of large-signal devices.
Abstract: Lumped-element circuit models, modified to include RF voltage-dependent elements may be used to describe the large-signal performance of a MESFET. Several solution methods exist for the analysis of amplifier circuits incorporating the large-signal device model. The paper reports the results of a comparative study of three solution methods: harmonic balance, modified SPICE and time domain methods. A simple amplifier, with 50 Ω generator and load impedances is used to show the importance of the nonlinear gate-source capacitance and avalanche breakdown in predicting harmonic generation in the MESFET. An amplifier, with cascaded transmission-line input and output matching sections, illustrates the effect on the large-signal analysis, of using the three alternative solution methods with their associated descriptions of the distributed external microwave circuits. It is concluded that, for this application, the harmonic balance method is faster and more accurate than the other solution methods.
09 Jun 1986
TL;DR: In this paper, a GaAs waveguide was used to phase match the difference frequency generation in an integrated optical parametric oscillator in GaAs, and the phase matching was achieved by using the waveguide mode dispersion or material birefringence.
Abstract: In the early days of integrated optics the attractive features of nonlinear optical devices using a guided wave structure have been recognized very soon [1–4]. Due to the concentration of optical fields in a long waveguide structure with crosssection dimensions of the order of a wavelength, very efficient nonlinear interactions could be expected to generate new optical frequencies. Especially the possibility to achieve phase matching even in isotropic materials, utilizing the waveguide mode structure, stimulated the interest in integrated, nonlinear devices. Anderson and Mc Mullen [5] were the first who demonstrated experimentally phase matched difference frequency generation in a GaAs (isotropic!) waveguide. Suematsu [6] and Boyd [7] both predicted a very low threshold power for an integrated optical parametric oscillator in GaAs. Despite these promising aspects, no experimental efforts have been reported up to now, to obtain parametric oscillation in a GaAs waveguide structure. Probably the required high waveguide quality (low losses, extremely good homogeneity, no optical damage) and the need for a suitable index profile to yield a good overlap of the interacting fields prevented the development of efficient nonlinear devices in that material. Nevertheless, in a number of other material systems nonlinear effects, mainly second harmonic generation, were studied [8]. In particular, several methods to achieve phase matching in optical waveguides were demonstrated. Somekh and Yariv [9] and Tang et al. [10,11] used periodic structures; Burns, Andrews and Lee [12,13] developed a waveguide composition yielding “noncritical” phase matching; other authors used the waveguide mode dispersion or the material birefringence to get phase matching of the interacting modes.
TL;DR: In this article, the authors summarize some of the principal characteristics of emission from targets at half-harmonics of the laser frequency, including Raman conversion and the direct linear conversion of plasmons generated by two-plasmon decay.
Abstract: After a brief review of stimulated Raman scattering and two-plasmon decay, which dominate the physics of laser–plasma interactions at and below the quarter-critical density, we summarize some of the principal characteristics of emission from targets at half-harmonics of the laser frequency. Two mechanisms in particular are thought to contribute to the emission; Raman conversion and the direct linear conversion of plasmons generated by two-plasmon decay. Both processes are reviewed and the implications of each for the emission spectra examined.The effect of strong self-generated magnetic fields on harmonic generation is considered briefly and attention is drawn to ways in which the coincidence of interactions in the underdense plasma may influence their basic characteristics. A finite-amplitude ion wave, for example, modifies the spectrum of Raman scattered light, including significant frequency splitting.