Showing papers on "High harmonic generation published in 1988"
TL;DR: In this paper, a theory of external doubling with a resonant fundamental is presented and compared to experimental results for three monolithic cavities of nonlinear MgO:LiNbO/sub 3.
Abstract: 56% efficient external-cavity-resonant second-harmonic generation of a diode-laser pumped, CW single-axial-mode Nd:YAG laser is reported. A theory of external doubling with a resonant fundamental is presented and compared to experimental results for three monolithic cavities of nonlinear MgO:LiNbO/sub 3/. The best conversion efficiency was obtained with a 12.5-mm-long monolithic ring cavity doubler, which produced 29.7 mW of CW, single-axial mode 532-nm radiation from an input of 52.5 mW. >
238 citations
TL;DR: It is shown that optical second-harmonic generation can also be used as an effective surface probe with a submonolayer sensitivity for media without inversion symmetry.
Abstract: We show that optical second-harmonic generation can also be used as an effective surface probe with a submonolayer sensitivity for media without inversion symmetry. The adsorption of Sn on GaAs is used as an example. A detailed summary of all accessible elements of the surface nonlinear susceptibility tensor χ(2) for the various crystal faces of GaAs is provided.
95 citations
TL;DR: In this paper, self-generated light beam at the half-angle between the two pumps is as high as 40% of the pump beam intensity, which is probably a spatial analog of the temporal subharmonics obtained in a cavity containing a nonlinear medium.
Abstract: Self‐generation of spatial subharmonics when two coherent, almost collinear, pump beams propagate in a nonlinear photorefractive crystal of Bi12 SiO20, is reported. The intensity of the self‐generated light beam at the half‐angle between the two pumps is as high as 40% of the pump beam intensity. This phenomenon is probably a spatial analog of the temporal subharmonics obtained in a cavity containing a nonlinear medium. Application of the subharmonic of half‐spatial frequency to collinear Bragg diffraction of a near infrared beam is demonstrated.
93 citations
TL;DR: In this article, a significant improvement in frequency doubling efficiency of a cw output of a GaAlAs laser diode was described, up to 0.72 mW of 421 nm power was generated by illuminating a KNbO3 crystal with a 270 mW diffraction-limited beam generated by an externally injection-locked laser dioder array, operating in a singlemode and single-far field lobe.
Abstract: Significant improvement in frequency doubling efficiency of a cw output of a GaAlAs laser diode is described. Up to 0.72 mW of 421 nm power was generated by illuminating a KNbO3 crystal with a 270 mW diffraction‐limited beam generated by an externally injection‐locked laser diode array, operating in a single‐mode and single‐far‐field lobe.
89 citations
TL;DR: The magnetic behavior of a sintered Y•Ba•Cu•O superconductor has been investigated by monitoring the harmonic components of its magnetic response to an alternating field.
Abstract: The magnetic behavior of a sintered Y‐Ba‐Cu‐O superconductor has been investigated by monitoring the harmonic components of its magnetic response to an alternating field. As the steady bias field is incrementally raised, a transition from a linear, reversible behavior of the magnetization to a nonlinear, irreversible behavior is indicated by the appearance of magnetic losses and odd harmonic components in the response. These harmonics disappear as the bias field or the temperature is increased above a certain point, indicating a linear behavior. The disappearance of the odd harmonics, while the magnetic losses persist, is interpreted as signifying a transition to a state of dissipative flux motion without pinning. These measurements demonstrate a new technique for determination of the lower critical field and the ‘‘irreversibility’’ field below which irreversibility in the magnetization sets in as a result of flux pinning.
72 citations
51 citations
TL;DR: In this article, a laser-based source and detection scheme for performing time-resolved photoemission studies of materials is described, where a pulsed laser source produces intense picosecond pulses of coherent radiation that are nearly continuously tunable from the near infrared to photon energies up to 13 eV.
Abstract: This article describes a laser‐based source and detection scheme for performing time‐resolved photoemission studies of materials. The pulsed laser source produces intense picosecond pulses of coherent radiation that are nearly continuously tunable from the near infrared to photon energies up to 13 eV. To achieve high sensitivity, a novel multianode time‐of‐flight spectrometer has been built that generates an angularly resolved intensity versus kinetic energy spectrum with better than 100‐meV resolution. The source and detector provide an opportunity to study the electronic dynamics of excited systems on a picosecond time scale.
49 citations
TL;DR: In this article, a theory of nonlinear optical properties of fractals is developed and a giant enhancement of optical susceptibilities is predicted for impurities bound to a fractal, which occurs if the exciting radiation frequency lies within the absorption band of the fractal.
Abstract: A theory of nonlinear optical properties of fractals is developed. Giant enhancement of optical susceptibilities is predicted for impurities bound to a fractal. This enhancement occurs if the exciting radiation frequency lies within the absorption band of the fractal. The giant optical nonlinearities are due to existence of high local electric fields in the sites of impurity locations. Such fields are due to the inhomogeneously broadened character of a fractal spectrum, i.e. partial conservation of individuality of fractal-forming particles (monomers). The field enhancement is proportional to theQ-factor of the resonance of a monomer. The effects of coherent anti-Stokes Raman scattering (CARS) and phase conjugation (PC) of light waves are enhanced to a much greater degree than generation of higher harmonics. In a general case the susceptibility of a higher-order is enhanced in the maximum way if the process includes “substraction” of photons (at least one of the strong field frequencies enters the susceptibility with the minus sign). Alternatively, enhancement for the highest-order harmonic generation (when all the photons are “accumulated”) is minimal. The predicted phenomena bear information on spectral properties of both impurity molecules and a fractal. In particular, in the CARS spectra a narrow (with the natural width) resonant structure, which is proper to an isolated monomer of a fractal, is predicted to be observed.
48 citations
Patent•
21 Jun 1988TL;DR: In this article, the optical resonator is made sufficiently low such that the dominant loss presented to the resonated mode of the optical resonance is the conversion loss to the generated harmonic, and the reflectance of the input mirror is impedance matched to the losses of the resonator including the harmonic conversion loss.
Abstract: TEM OOq laser radiation derived from a diode-pumped ring laser is directed into a faceted member of nonlinear optical material defining either a standing wave or ring monolithic optical resonator to generate harmonic laser radiation. The losses of the optical resonator, exclusive of the conversion loss to the harmonic, are made sufficiently low such that the dominant loss presented to the resonated mode of the optical resonator is the conversion loss to the generated harmonic. The reflectance of the input mirror of the optical resonator is impedance matched to the losses of the resonator including the harmonic conversion loss for optimum conversion efficiency. The length of the nonlinear optical material is shortened to the point where the bulk losses are less than ten times the sum of the surface and mirror losses, yielding conversion efficiencies of greater than 20 percent.
45 citations
TL;DR: The planar orotron as discussed by the authors is a slow-wave structure consisting of a rectangular metal grating which is opposed by a planar conducting boundary, and it operates in surface harmonic mode: electrons interact with axially traveling waves which evanesce above the grating surface, and the amplified radiation leaves the resonator in parallel with the beam axis.
Abstract: The planar orotron is introduced and shown to be a viable source of moderate power and of millimeter and submillimeter wavelength radiation. The resonator is a slow-wave structure consisting of a rectangular metal grating which is opposed by a planar conducting boundary. The device operates in the surface harmonic mode: electrons interact with axially traveling waves which evanesce above the grating surface, and the amplified radiation leaves the resonator in parallel with the beam axis. Operation in both the forward and backward mode is possible. The resonator cavity is designed to enhance longitudinal reflections, and thereby enhance the output power and efficiency. The output frequency and tuning range are determined by the grating parameters. Experiments performed in the backward mode have produced radiation from 30 to 110 GHz at power levels ranging from 100 W to 2 kW. The efficiencies vary from 1 to 7%. The measured frequencies are closely predicted by a theory which is also presented. >
43 citations
TL;DR: The d32 coefficient of potassium niobate was used in a 90-deg, temperature-tuned, Type I phase-matching configuration to generate the second harmonic of the 946-nm intracavity field.
Abstract: We report the first observation to our knowledge of coherent emission at 473 nm from an intracavity-doubled Nd:YAG microlaser. The d32 coefficient of potassium niobate was used in a 90-deg, temperature-tuned, Type I phase-matching configuration to generate the second harmonic of the 946-nm intracavity field. Output powers in excess of 5 mW at optical conversion efficiencies of approximately 2% have been observed with dye-laser pumping at 588 nm.
TL;DR: In this paper, the use of resonant-tunneling diodes as varistors for harmonic multiplication was demonstrated and it was shown that even harmonics do not appear because of the antisymmetry of the current-voltage (I-V) curve.
Abstract: This paper demonstrates the use of resonant-tunneling diodes as varistors for harmonic multiplication. It is shown that efficient odd-harmonic conversion is possible and that even harmonics do not appear because of the antisymmetry of the current-voltage (I-V) curve. It is also shown that, with the proper choice of resonant-tunneling structure and pump amplitude, most of the harmonic output power can be confined to a single odd-harmonic frequency. Fifth-harmonic multiplication was demonstrated with an output at 21.75 GHz and a power conversion efficiency of 0.5 percent, and a fifth-harmonic efficiency of 2.7 percent was achieved in a circuit simulation using an improved I-V curve.
TL;DR: In this article, the authors proposed using the scanning tunneling microscope (STM) in new experiments on laser frequency synthesis and laser rectification at optical frequencies, where the authors introduced the subject of harmonic generation and mixing of laser beams by the related tunneling device called the point contact diode.
Abstract: This paper elaborates on the idea, recently advanced by the authors, of using the scanning tunneling microscope (STM) in new experiments on laser frequency synthesis and laser rectification at optical frequencies. We first introduce the subject of harmonic generation and mixing of laser beams by the related tunneling device called ‘‘point contact diode.’’ Then, we present new quasistatic current–voltage characteristics of several STM junctions, emphasizing their nonlinear and rectifying aspects. The physical origin of the observed asymmetrical I–V curves is discussed. Finally, we describe the proposed rectification experiment which should result in an operationally meaningful definition of a tunneling time for electrons crossing an STM junction and we present some very preliminary results.
TL;DR: In this paper, experimental studies of harmonic generation in Xe using a 1064 nm Nd-YAG laser were conducted using a positively dispersive medium, using a tight-focusing geometry.
Abstract: We report experimental studies of harmonic generation in Xe using a 1064 nm Nd-YAG laser Third-harmonic conversion is observed in a positively dispersive medium, using a tight-focusing geometry The intensity of third-harmonic generation in a gas cell varies much more steeply with the laser intensity than a cubic law The reason for the breaking of the phase matching condition is discussed
TL;DR: In this paper, the unstable oscillations of a virtual cathode, which forms when a magnetized relativistic electron beam is injected into a circular waveguide, generates the microwave radiation.
Abstract: A description is given of experiments demonstrating a method for producing high-power microwave emission. The unstable oscillations of a virtual cathode, which forms when a magnetized relativistic electron beam is injected into a circular waveguide, generates the microwave radiation. In contrast to other virtual-cathode microwave-generation techniques, electrons in the waveguide are prevented from reflexing back into the diode region by use of a slotted range-thick anode. Electrons injected into the waveguide are guided through the slot by an applied magnetic field, while reflected electrons, under the proper conditions, are intercepted by the anode. Several advantages of this approach are described, and experimental confirmation of this mode of high-power microwave generation is demonstrated. Data showing frequency scaling with beam parameters and magnetic field are also presented. Using this technique, 1.4 GW was produced at 3.9 GHz with several hundred megawatts radiated in harmonic radiation. >
TL;DR: In this article, the effects of higher harmonic generation and self-demodulation of signals over a large range of distances from a source were studied and a conclusion is that nonlinear properties of the medium should be taken into account in corresponding physical models used in seismology and seismic prospecting.
TL;DR: In this article, the authors investigated the frequency mixing of infrared laser radiation in the tunneling junction of a scanning tunneling microscope (STM) and demonstrated a considerable extension of the frequency range accessible with the STM.
Abstract: Frequency mixing of infrared laser radiation in the tunneling junction of a scanning tunneling microscope (STM) was investigated. The dependence of the mixing signal on the tunneling current, the bias voltage, the power and polarization of the laser radiation, and on the difference frequency was studied using a W–Au STM junction. From the frequency dependence of the signals observed up to 90 MHz, the difference frequency generation is attributed to a thermal process. In addition, the generation of harmonics of the beat signal and mixing with a radio frequency signal is reported. The mixing experiments demonstrate a considerable extension of the frequency range accessible with the STM.
01 Oct 1988-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this paper, the authors summarize the various achievements made at Orsay on the coherent harmonic generation, using an external laser focused in an optical klystron, and the perspectives offered for VUV production by the new storage ring Super-ACO, taking into account the parameters recently measured on this ring.
Abstract: In this paper we summarize the various achievements made at Orsay on the “coherent harmonic generation”, using an external laser focused in an optical klystron. First we observed in 1984 the third harmonic (3547 A) of a NdYAG laser, on our storage ring ACO. In a later experiment, performed in 1987 on the same machine, VUV photons (1770 and 1064 A) have been generated by the same method, on the third and fifth harmonic of a doubled NdYAG laser. The perspectives offered for VUV production by the new storage ring Super-ACO are discussed, taking into account the parameters recently measured on this ring.
TL;DR: The severe cavity-matching requirement for optimum short-pulse generation is addressed by an active cavity-length stabilization scheme based on second-harmonic generation, which allows pulses ~100 fsec in duration to be maintained for periods of several hours.
Abstract: We report on the cavity-length detuning characteristics of a synchronously pumped femtosecond linear-resonator cw dye laser. The severe cavity-matching requirement (to within 0.2 μm) for optimum short-pulse generation is addressed by an active cavity-length stabilization scheme based on second-harmonic generation. This allows pulses ~100 fsec in duration to be maintained for periods of several hours.
TL;DR: In this article, a detailed model of two-photon-resonant four-wave mixing that includes the consideration of efficiency-limiting processes is presented, and the model provides a generally applicable systematic approach for maximizing conversion efficiencies for both exact and near-twophoton resonance.
Abstract: A detailed model of two-photon-resonant four-wave mixing that includes the consideration of efficiency-limiting processes is presented. The model provides a generally applicable systematic approach for maximizing conversion efficiencies for both exact and near two-photon resonance. For exact two-photon resonance, an interference effect limits efficiency to a value determined by ratios of nonlinear susceptibilities and input intensities. For near two-photon resonance, nonlinear refractive indices limit efficiencies unless input intensities are properly balanced. For the specific case of 130.2-nm generation in Hg, we examine a number of potential additional efficiency-limiting processes, including amplified spontaneous emission, stimulated Raman and hyper-Raman gain, parametric gain, linear absorption, and population transfer. We include isotopic effects and Gaussian-profile beams. From our analysis, we conclude that efficiencies of approximately 10% should be feasible by using collimated light beams in an energy-scalable system.
TL;DR: In this article, the authors considered surface enhanced second harmonic generation through delocalized electromagnetic resonances such as surface plasmons or guided waves at bare or coated metallic gratings, and showed that there exists an optimum groove depth of the grating for which the enhancement of the second harmonic efficiency, as compared to the flat case, is the greatest.
Abstract: This paper is concerned with surface enhanced second harmonic generation through delocalized electromagnetic resonances such as surface plasmons or guided waves at bare or coated metallic gratings. The formalisms presented are rigorous in the sense that the groove depth of the grating is not considered as a perturbative parameter. This allows us to show that there exists an optimum groove depth of the grating for which the enhancement of the second harmonic efficiency, as compared to the flat case, is the greatest. Shallow modulated gratings (10 -1) lead to optimum enhancement as high as 105. Emphasis is placed on the effect of the periodicity and of the profile of the grating on this optimum enhancement.
TL;DR: In this paper, the results of a study of fifth-harmonic production in neon and argon irradiated with 248-nm picosecond laser pulses are presented and compared with theory.
Abstract: The results of a study of fifth-harmonic production in neon and argon irradiated with 248-nm picosecond laser pulses are presented. Focused intensities range from 1013 to 1015 W/cm2. Data for fifth-harmonic intensity as a function of both target density and focused laser intensity are presented and compared with theory. For the laser intensities and medium densities studied, estimates for the linear and nonlinear components of Δk, the wave-vector mismatch between the fundamental and harmonic waves, indicate that the nonlinear component is much greater than the linear component.
TL;DR: Using a molecular theory of harmonic generation developed within the framework of quantum electrodynamics, it is proved that second-harmonic generation is forbidden in isotropic fluids to all levels of multipolar approximation.
Abstract: Using a molecular theory of harmonic generation developed within the framework of quantum electrodynamics, we prove that second-harmonic generation is forbidden in isotropic fluids to all levels of multipolar approximation.
TL;DR: In this paper, a comprehensive theoretical investigation of the third-order susceptibilities for the nonlinear optical processes dc Kerr and dc electric field-induced second-harmonic generation is reported for H2 and D2.
Abstract: A comprehensive theoretical investigation of the third‐order susceptibilities for the nonlinear optical processes dc Kerr and dc electric‐field‐induced second‐harmonic generation is reported for H2 and D2. Accurate wave functions of the J ames–Coolidge‐type, which account for electronic correlation, are utilized and particular attention is given to the effects of vibration. Results for both the parallel and perpendicular components of the susceptibilities are given for λ=∞, 10 640, 6943, 6328, 5900, 5145, and 4880 A. These are sufficient to enable a direct comparison with certain experimental data and, in general, the agreement is within the expected error bounds.
TL;DR: In this article, the angular distribution of the second harmonic generation (SHG) in disordered nonlinear media is shown to exhibit sharp peaks due to the weak localization of photons, and the shape of these peaks is related to the spatial structure of the electric field for strongly scattered second harmonic (SH) radiation and is sensitive to Anderson localization effects.
TL;DR: In this article, a systematic explanation of the pressure-dependent multiphoton ionization spectra of argon is given in terms of the phase matching requirements of third-harmonic generation.
Abstract: A systematic explanation of the pressure‐dependent multiphoton ionization spectra of argon is given in terms of the phase matching requirements of third‐harmonic generation. Two‐color sum‐frequency generation in a highly dispersive medium and its effects on normal three‐photon excitation process are analyzed, using argon as an example. Finally an anomaly in the resonance line shapes of the two laser MPI spectra of argon is reported and attributed to the displacement of the foci of the two counterpropagating laser beams.
TL;DR: In this article, an efficient and tunable coherent ultraviolet (360-390 nm) generation in beta-BaB(2)O(4) crystals using type-I phase matching at room temperature is presented.
Abstract: Efficient and tunable coherent ultraviolet (360-390 nm) generation in beta-BaB(2)O(4) crystals using type-I phase matching at room temperature is presented. The phase-matching angle is characterized with an alexandrite laser with a wavelength tuning range of 725-785 nm. The crystal angular bandwidth of 0.9 mrad-cm and spectralbandwidth of 1.15 nm-cm are also measured. UV output pulse energy of 105 mJ at 378 nm with 31% energy conversion efficiency is achieved.
TL;DR: In this paper, a low-energy, axis-rotating beam of 28-30 kV, 0.8-3.5 A, 4 mu s, and 60 pps interacts with a single RF mode, both in a circular cavity and in a six-vane circuit by the negative mass instability.
Abstract: Microwave radiation at the fundamental and harmonic electron cyclotron frequencies generated by a cusptron oscillator is reported. A low-energy, axis-rotating beam of 28-30 kV, 0.8-3.5 A, 4 mu s, and 60 pps interacts with a single RF mode, both in a circular cavity and in a six-vane circuit by the negative mass instability. In fundamental and second-harmonic frequency generation with a circular circuit, the independently excited modes are TE/sub 11/s and TE/sub 21/s, with radiation power of more than 1.8 kW and an electronic efficiency of approximately 7.5%. Employing a six-vane circuit, microwave radiation of 6.0 GHz (sixth harmonic) and 3.9 GHz (fourth harmonic) is also independently generated with more than 10.4 and 4.0 kW radiation power, respectively. Corresponding electronic efficiencies are approximately 10.0 and 9.5%. >
TL;DR: In this paper, an experimental four-cavity, fifth-harmonic gyroklystron was described, which separates at 11.3 GHz in a 1.2-KG magnetic field.
Abstract: An experimental four-cavity, fifth-harmonic gyroklystron is described that separates at 11.3 GHz in a 1.2-KG magnetic field. This device used longer drift regions than previous configurations. Principal results reported include 45 dB of small-signal gain and 0.6 kW of output power. Other results include the measurement of phase noise characteristics and the identification of spurious output signals. An improved beam diagnostic which determines the pitch of the electron orbits was used together with a fluorescent uranium-glass witness plate and beam-current diagnostics to characterize the electron beam. This information was used to perform analytic modelling and computer simulation of the amplifier. The experimental results are compared with the predictions of the analytic theory and simulation, and substantial agreement is demonstrated. >
01 Jan 1988
TL;DR: In this article, the second-order electric susceptibility tensor tensor (x(2) is defined as the coupling coefficient of a dielectric tensor for the material X(2):EE, and the secondorder nonlinear optical (NLO) processes are viewed via the molecular polarization p which is induced by an electric field e local to the molecular environment.
Abstract: Second-order nonlinear optical (NLO) processes, including harmonic generation and the electrooptic effect, are the result of a nonlinear response in the polarization P of a dielectric which is quadratic in the applied electric field of the light beams E P = X(2):EE.The coupling coefficient x(2) is the second-order electric susceptibility tensor for the material. Maximizing the nonlinear susceptibility coefficients can result in large NLO effects. However, understanding the origins of x(2) often requires examination of these interactions on the microscopic level. Here, the process can be viewed via the molecular polarization p which is induced by an electric field e local to the molecular environment.