Showing papers on "High harmonic generation published in 1990"
TL;DR: A nonlinear theory of intense laser-plasma interactions is developed and used to describe relativistic optical guiding, coherent harmonic radiation production, and nonlinear plasma wakefield generation.
Abstract: A nonlinear theory of intense laser-plasma interactions is developed and used to describe relativistic optical guiding, coherent harmonic radiation production, and nonlinear plasma wakefield generation. Relativistic optical guiding is found to be ineffective in preventing the leading portion (\ensuremath{\le} a plasma wavelength) of a laser pulse from diffracting. Coherent harmonic generation is found to be most efficient for short laser pulses. Optical guiding and harmonic generation may be enhanced by the presence of large amplitude plasma wakefields. These phenomena may be important in laser-driven plasma accelerators, x-ray sources, and fusion schemes.
444 citations
TL;DR: In this article, a nonlinear one-dimensional theory is developed that describes some important aspects of intense laser-plasma interactions, including nonlinear plasma wake-field generation, relativistic optical guiding, coherent harmonic radiation production, as well as other related phenomena.
Abstract: A nonlinear one-dimensional theory is developed that describes some important aspects of intense laser-plasma interactions. The self-consistent laser-plasma analysis includes nonlinear plasma wake-field generation, relativistic optical guiding, coherent harmonic radiation production, as well as other related phenomena. Relativistic optical guiding is found to be most effective for long laser pulses having slow rise times. Short laser pulses are shown to be weakly guided. Coherent harmonic generation using a linearly polarized laser is found to be most efficient for short laser pulses and can be enhanced by the presence of large amplitude plasma wake fields. Aspects of particle acceleration by laser pulses as well as possible methods for upshifting the frequency of laser pulses are also discussed.
269 citations
TL;DR: In this paper, a model using those properties that have been developed shows the presence of a large number of odd harmonics, which can be described by using the dc tunneling limit.
Abstract: In cases in which the ponderomotive energy is much larger than the ionization energy, which correspond to the highintensity limit or to the low-frequency limit, harmonic generation in gases near the ionization threshold can be understood from a plasma-physics point of view. Multiphoton ionization, which can be described by using the dc tunneling limit, takes place in a time interval localized around the maximum of the electric field. The plasma current thus generated varies on the same fast time scale and is responsible for harmonic generation. A model using those properties that has been developed shows the presence of a large number of odd harmonics.
170 citations
TL;DR: In this paper, a monolithic ring resonator of KNbO3 was used for efficient frequency doubling of a 856 nm GaAlAs diode laser and a special electronic servo technique was devised to lock the laser frequency to the cavity so that stable generation of blue output was obtained.
Abstract: A monolithic ring resonator of KNbO3 was used for efficient frequency doubling of a 856 nm GaAlAs diode laser. A special electronic servo technique was devised to lock the diode laser frequency to the KNbO3 cavity so that stable generation of blue output was obtained. With 105 mW of incident near‐infrared power, 41 mW of 428 nm radiation were produced. The conversion efficiency from electrical input power into the diode laser to blue output was ∼10%.
152 citations
TL;DR: The first measurements of the phase of the infrared-visible sum-frequency generation signal are presented, and two techniques are introduced and applied to the determination of the polar orientation of a selected group of atoms within an adsorbed molecule.
Abstract: We present what are to our knowledge the first measurements of the phase of the infrared-visible sum-frequency generation signal. We introduce two techniques and apply the measurements to the determination of the polar orientation of a selected group of atoms within an adsorbed molecule.
125 citations
TL;DR: A simple two-state model is presented illustrating the fact that the most prominent features observed in high-order harmonic generation are generic to strongly driven systems.
Abstract: We present a simple two-state model illustrating the fact that the most prominent features observed in high-order harmonic generation are generic to strongly driven systems. We also address two important questions that arise in the comparison of theory and experiment.
122 citations
TL;DR: The second harmonic of the 842-nm output of a GaAlAs diode laser is generated in a KNbO(3) crystal in a resonant, external ring cavity and used to perform saturation spectroscopy on narrow transitions in rubidium.
Abstract: The second harmonic of the 842-nm output of a GaAlAs diode laser is generated in a KNbO3 crystal in a resonant, external ring cavity. The diode laser is optically stabilized to the ring cavity through feedback from the counterpropagating fundamental wave, which is weakly excited in the resonator. We have produced 6.7 mW of tunable, narrowband radiation at 421 nm and have used that light to perform saturation spectroscopy on narrow transitions in rubidium.
102 citations
TL;DR: In this article, a theoretical and experimental investigation of the operation of a high-power harmonic gyrotron at submillimeter wavelengths is reported using a waveguide cavity with an iris at the output end of the straight section, using 14 different second-harmonic modes with frequencies of 301-503 GHz, output powers of 1-22 kW, and a 12-MHz emission frequency bandwidth.
Abstract: A theoretical and experimental investigation of the operation of a harmonic gyrotron at submillimeter wavelengths is reported. Using a waveguide cavity with an iris at the output end of the straight section, 14 different second-harmonic modes were observed with frequencies of 301-503 GHz, output powers of 1-22 kW, and a 12-MHz emission frequency bandwidth. The highest output power was 22 kW, with a total efficiency of 3.5% at 467 GHz, and an output power of 15 kW with a 6% efficiency was obtained at 417 GHz. Research was conducted using a 65-75 kV up to 10-A electron gun with a 1/1.5- mu s pulse length and a 4-Hz repetition rate, which produced a helical electron beam in magnetic fields of up to 14 T. These results represent the first operation of a high-power harmonic gyrotron in the submillimeter region. >
88 citations
TL;DR: In this article, the relativistic wake-field generation by laser pulses with realistic shapes is investigated and a nonlinear scheme of the laser wakefield accelerator is suggested. But it is not shown that longitudinal plasma waves with relativistically amplitudes and phase velocities close to the speed of light can be excited in the wake of a strong single laser pulse in a cold plasma.
83 citations
TL;DR: In this article, the role of propagation effects in high-order harmonic generation experiments was studied and the phase-matching integrals were calculated in the weak-field limit by taking into account the dispersion of the rare-gas medium at each harmonic frequency and the absorption of the harmonics.
Abstract: We study the role of propagation effects in high-order harmonic-generation experiments. The phase-matching integrals are calculated in the weak-field limit by taking into account the dispersion of the rare-gas medium at each harmonic frequency and the absorption of the harmonics. The refractive indices of the rare gases are deduced from a calculation of the dynamic polarizabilities within the framework of many-body perturbation theory and the random phase approximation. We also study the influence of the ionization of the gaseous medium and the presence of free electrons on the harmonic conversion efficiency by numerically integrating the propagation equation. These results are compared with experimental data.
81 citations
TL;DR: It has been found that group-velocity dispersion can be used to advantage by predelaying the ordinary and extraordinary polarizations appropriately in a thin KDP crystal with its axes aligned at 90{degree} to the main conversion crystal.
Abstract: A computer model has been used to investigate frequency doubling of 1-psec duration high-power pulses in potassium dihydrogen phosphate (KDP) for type-II phase matching. It has been found that group-velocity dispersion can be used to advantage by predelaying the ordinary and extraordinary polarizations appropriately in a thin KDP crystal with its axes aligned at 90\ifmmode^\circ\else\textdegree\fi{} to the main conversion crystal. In that situation power conversion g100% from the fundamental to the second harmonic can be obtained with simultaneous ``compression'' of the output pulse duration by up to a factor of 5.
TL;DR: In this article, a single-mode buried-heterostructure InGaAsP laser at 1.3 mu m was used to evaluate the parameters of the rate equations and the nonlinear gain coefficient and the electrical response of the packaged laser were simultaneously determined from small-signal characteristics.
Abstract: The theoretical analysis is based on rate equations including gain-compression effects. General criteria are established to predict the existence of irregular behaviors. Experiments are performed on a single-mode buried-heterostructure InGaAsP laser at 1.3 mu m. An original method is proposed to evaluate the parameters of the rate equations. Fully optical measurements are used. The nonlinear gain coefficient and the electrical response of the packaged laser are simultaneously determined from small-signal characteristics. Time-domain measurements show the three behaviors achieved with the laser, i.e., simple periodic, periodic with multiple spikes, and periodic doubling. Excellent agreement is found between experiments and calculations. Frequency-domain measurements are focused on distortions in periodic regimes. A quantitative limit of perturbation theories is given which corresponds to a second-order harmonic level exceeding -15 dB. >
TL;DR: In this paper, a 10 million fold enhancement for surface emitting harmonic generation over a normal GaAs film was obtained by using AlGaAs resonant multilayers embedded in a waveguide geometry.
Abstract: By using AlGaAs resonant multilayers embedded in a wave-guide geometry a ten million fold enhancement for surface emitting harmonic generation over a normal GaAs film was obtained. The multilayer system allows compensation for material losses at the harmonic and the use of thick films for efficient coupling of communication fibres to the device. The experimental results agree closely with theory and a monolithic implementation of visible, surface emitting solid state diode lasers is presented for InGaAs, InP and GaAs geometries.
TL;DR: In this paper, high-order harmonic generation in xenon, using a Nd:YAG laser (1064 nm), was studied as a function of the laser intensity in the 1013 W/cm2 range.
Abstract: We present experimental results on high-order harmonic generation in xenon, using a Nd:YAG laser (1064 nm). The harmonic generation efficiency is studied as a function of the laser intensity in the 1013 W/cm2 range. The harmonic conversion rates show a significant change of behavior when the medium becomes ionized (∼1013 W/cm2). This effect can be understood as the change of the nonlinear response of the medium from neutral atoms to ions and also as the influence of free electrons. We study the role of propagation effects (phase matching) by performing experiments using three different lenses (75, 200, and 300 mm) to focus the incident laser beam, thus changing the interaction geometry. Although for each harmonic the conversion rate is strongly dependent on the confocal parameter b (as b3), the behavior of the harmonic frequency distribution shows almost no influence of the focusing geometry.
TL;DR: In this article, a large single crystal (18×40×15 mm3) of a new nonlinear optical material "chalcone derivative" was grown by an evaporation method.
Abstract: A large single crystal (18×40×15 mm3) of a new nonlinear optical material ‘‘chalcone derivative’’ has been grown by an evaporation method. This crystal was relatively easy to grow to a large size and was chemically stable. The cutoff wavelength was 430 nm. The calculated phase matching angles for the second‐harmonic generation (SHG) of Nd:YAG lasers agreed with the experimental data. Effective nonlinear optical coefficients deff of type I and type II for SHG have been measured to be 3.5 pm/V for type I and 5.7 pm/V for type II.
TL;DR: InP TED oscillators have been experimentally investigated for frequencies between 170 and 279 GHz as mentioned in this paper, and it has been found that output powers of more than 7 and 0.2 mW are possible at 180 and 272 GHz using second-and third-harmonic mode operation, respectively.
Abstract: InP TED (transferred electron device) oscillators have been experimentally investigated for frequencies between 170 and 279 GHz. It has been found that output powers of more than 7 and 0.2 mW are possible at 180 and 272 GHz using second- and third-harmonic mode operation, respectively. Conversion efficiencies of more than 13% and 0.3% between fundamental and second harmonic and fundamental and third harmonic, respectively, have been found. The conversion efficiencies are comparable to GaAs TEDs. The output powers, conversion efficiencies, and tuning ranges (more than 22%) are the biggest reported for InP TEDs at these frequencies. The output power at third harmonic was sufficient for supplying a superconducting mixer with local oscillator power. >
TL;DR: Using time-dependent Hartree-Fock theory, the results of calculations of dipole moments induced in xenon by 1.064-nm radiation of intensities in the range 1013-1014 W/cm2 were described in this article.
Abstract: Using time-dependent Hartree–Fock theory, we describe the results of calculations of dipole moments induced in xenon by 1.064-nm radiation of intensities in the range 1013–1014 W/cm2. The calculated spectrum comprises sharply defined optical harmonics to order 61. We comment on the three-dimensional properties of our calculated induced dipole moments and on the spectral background underlying these harmonics.
TL;DR: In this article, a stable state modeling, analysis, and solution of transistor-controlled systems are developed and experimentally verified over a wide range of operation, and the effects of the chopping frequency on the performance parameters and harmonic generation are thoroughly investigated.
Abstract: Steady-state modeling, analysis, and solution of transistor-controlled systems are developed and experimentally verified over a wide range of operation. General features of the system performance and the effects of the chopping frequency on the performance parameters and harmonic generation are thoroughly investigated. Over most of the control range, and for chopping frequencies in the order of several hundred hertz and higher, it is demonstrated that the harmonic contents of the load current are almost negligible, providing highly desired operating conditions for many applications where the fundamental current is the only useful component. >
TL;DR: In this article, the response of a hydrogen atom to an intense nonresonant laser field is investigated by direct numerical solution of the time-dependent Schrodinger equation, which is nonperturbative and does not involve the eigenstates of the field-free atom.
Abstract: The response of a hydrogen atom to an intense nonresonant laser field is investigated by direct numerical solution of the time-dependent Schrodinger equation. This calculation is nonperturbative and does not involve the eigenstates of the field-free atom. An ionization rate for three-photon ionization is calculated and found to be in excellent agreement with previous values. The time-dependent electric dipole moment is calculated; its Fourier transform yields the spectrum of scattered light. Odd-order harmonic peaks through at least the 25th order are present in the spectrum.
TL;DR: In this paper, a theory for the special complex cavity is proposed, which is in the form of a single resonant circuit having a TE/sub 0n/ from or to TE/ sub 0,n+p/ mode converter and it features excellent mode selectivity, high power capability, and an asymmetric triangle profile of the RF field that is favorable to efficient operation for a 35 GHz second-harmonic gyromonotron employing this complex cavity with TE sub 03/ mode output.
Abstract: A theory is proposed for the special complex cavity; it is in the form of a single resonant circuit having a TE/sub 0n/ from or to TE/sub 0,n+p/ mode converter and it features excellent mode selectivity, high power capability, and an asymmetric triangle profile of the RF field that is favourable to efficient operation for a 35-GHz second-harmonic gyromonotron employing this complex cavity with TE/sub 03/ mode output are numerically illustrated and experimentally demonstrated. Power as high as 200 kW and efficiency as high as 30% have been obtained. These experimental results are record values for a gyrotron operating at the second-harmonic millimeter wavelength. Implications of the single-resonant complex cavity for the fundamental harmonic and third-harmonic high-average-power gyrotron design are discussed. >
TL;DR: In this article, rotational anisotropy in the optical second harmonic generation from Ag(111 and Ag(110) single-crystal electrodes is used to measure relative changes in the components of the nonlinear susceptibility of the interface during charging and adsorption processes.
Abstract: Rotational anisotropy in the optical second harmonic generation from Ag(111) and Ag(110) single-crystal electrodes is used to measure relative changes in the components of the nonlinear susceptibility of the interface during charging and adsorption processes. The application of a dc field and underpotential deposition of lead and thallium are studied.
TL;DR: The results of a calculation of high-order harmonic generation by a classical hydrogen atom, submitted to an intense, single-mode, radiation field are presented.
Abstract: We present the results of a calculation of high-order harmonic generation by a classical hydrogen atom, submitted to an intense, single-mode, radiation field. The spectra showing these harmonics associated with different kinds of trajectories as well as with an ensemble average of trajectories are discussed.
TL;DR: In this article, the threshold conditions under which a spatial subharmonic beam may arise when a Bi12SiO20 crystal is illuminated by two pump beams, and a nonlinear theory based on the material equations leads to good qualitative agreement with experiments.
Abstract: The threshold conditions, under which a spatial subharmonic beam may arise when a Bi12SiO20 crystal is illuminated by two pump beams, are investigated. It is shown that a nonlinear theory based on the material equations leads to good qualitative agreement with experiments
TL;DR: In this article, a review examines the nonlinear optical properties of highly excited and ionized gaseous media and low-temperature plasmas, focusing particularly on the role of excited atomic and ionised states, as well as continuum states.
Abstract: This review examines the nonlinear optical properties of highly excited and ionized gaseous media and low-temperature plasmas. The authors concentrate particularly on the role of excited atomic and ionized states, as well as continuum states. The authors cite and discuss experimental results of coherent anti-Stokes Raman scattering and optical harmonic generation in media consisting of excited atoms and ions. Nonlinear optical experiments involving the continuum states in intense optical fields are examined. In this connection the authors also discuss above-threshold ionization and the multiphoton stripping of atoms.
TL;DR: In this article, the application of time-resolved surface second harmonic generation (TRSSHG) as a surface-specific probe of picosecond reaction kinetics has been studied.
Abstract: The application of time-resolved surface second harmonic generation (TRSSHG) as a surface-specific probe of picosecond reaction kinetics has been studied. The method was tested by comparing the measured dynamics with those obtained from the time-resolved fluorescence (TRF) technique. The agreement between the two methods was good. It is concluded that the TRSSHG method is a useful probe of picosecond surface chemistry. Small differences between fluorescence and second harmonic data are explained by a consideration of the different natures of the two experiments. The surface-specific method is essentially an analogue of transient absorption spectroscopy, except that induced changes in hyperpolarizability are measured.
TL;DR: In this paper, a 3D laser beam focused through H2 or CH4/H2 plasmas induced THG at 121.5 nm, near the atomic hydrogen 2p 2PoJ→1s 2S 1/2 Lyman-α transition.
Abstract: Third‐harmonic generation (THG) was used to monitor ground‐state atomic hydrogen H(1s 2S1/2) in a dc plasma system. A 364.6 nm laser beam focused through H2 or CH4/H2 plasmas induced THG at 121.5 nm, near the atomic hydrogen 2p 2PoJ→1s 2S1/2 Lyman‐α transition. Both the intensity and frequency shift of the excitation spectra exhibited dependence on the plasma power. Absolute H atom concentration was estimated by comparing the frequency shift to that obtained in a calibrated microwave discharge flow system. The sensitivity was ∼4×1013 cm−3 (100 ppm). The measured atomic hydrogen densities were substantially less than in other diamond chemical vapor deposition methods and may explain the lower diamond deposition rates obtained with dc plasma systems of this type.
TL;DR: In this paper, a scheme for harmonic wave generation using a prebunched electron beam has been demonstrated using a high-harmonic gyrotron, where the beam was used to further increase the efficiency.
Abstract: A scheme for harmonic wave generation using a prebunched electron beam has been demonstrated. The prebunched electron beam has been used to further increase the efficiency of the authors' axis-encircling high-harmonic gyrotron. The proof-of-principle experiment was performed at the third harmonic with a TE/sub 312/ mode at 27.7 GHz. The conversion power of 6.7 kW was significantly greater than that used in the nonprebunched experiment. Also, mode competition was effectively suppressed. As expected, the unsaturated output power is proportional to the square of the electron beam current and the start of oscillation current is essentially zero. A linear theory, derived by taking into account the spread of the guiding center and the spread of the axial velocity, gives good agreement with the experimental results. >
TL;DR: Second- and third-harmonic generation from a cell containing xenon gas is observed using a tightly focused laser beam with intensities of up to 4\ifmmode\times\else\texttimes\fi{}${10}^{13}$ W/${\mathrm{cm}}^{2}$.
Abstract: We observe experimentally and explain theoretically second- and third-harmonic generation from a cell containing xenon gas using a tightly focused laser beam with intensities of up to 4\ifmmode\times\else\texttimes\fi{}${10}^{13}$ W/${\mathrm{cm}}^{2}$. Both processes are forbidden according to standard lowest-order theories.
TL;DR: In this article, accurate wave functions of the James-Coolidge type were used to calculate for H2 and D2 the dynamic second hyperpolarizabilities (γ) which mediate the nonlinear optical processes.
Abstract: Accurate wave functions of the James–Coolidge type, which account for electron correlation, are used to calculate for H2 and D2 the dynamic second hyperpolarizabilities (γ) which mediate the nonlinear optical processes: dc Kerr, dc electric‐field‐induced second‐harmonic generation and third‐harmonic generation. Values are given for a range of frequencies (ω=0 to ω=0.05 a.u.) as well as for some common laser frequencies. The effects of vibration are explicitly considered. As well, values of the dynamic field‐gradient polarizabilities B and C are found. The results are more accurate than those previously published.
TL;DR: In this article, the authors proposed a solution algorithm based on Newton's method with improved convergence characteristics for computing harmonic levels, and a parametric study is presented to illustrate the effects of the AC power system model and the converter control system on the harmonic generation.
Abstract: Electronic switching in AC/DC converters generate harmonics. The level of the harmonics depends on the interaction of the interconnected AC and DC systems. In analysis methods for computing harmonic levels, the modeling of the AC power system and its effect on the computed harmonic spectrum, and the convergence of the solution method have not been adequately researched. A method which addresses these issues is proposed. The method is used to show that the choice of the AC system model is very critical since the harmonic distortion at the interface bus is the result of an interaction between the converter and the AC-system. The method consists of a comprehensive model of a converter substation, the AC power system, and the DC-system equivalent. A solution algorithm based on Newton's method is proposed with improved convergence characteristics. A parametric study is presented to illustrate the effects of the AC power system model and the converter control system on the harmonic generation. >