Showing papers on "High harmonic generation published in 1975"
TL;DR: In this paper, a technique for phase-matched second harmonic generation using a finely layered structure with the radiation propagating parallel to the layers is analyzed. But the radiation propagation is not considered.
Abstract: A technique for obtaining phase−matched second harmonic generation using a finely layered structure with the radiation propagating parallel to the layers is analyzed.
78 citations
TL;DR: In this article, it was shown that specular second-harmonic emission from a dense, inhomogeneous plasma produced by laser irradiation of plane solid targets occurs on oblique reflection of a $p$-polarized light wave, in agreement with theoretical predictions.
Abstract: It is experimentally shown that specular second-harmonic emission from a dense, inhomogeneous plasma produced by laser irradiation of plane solid targets occurs on oblique reflection of a $p$-polarized light wave, in agreement with theoretical predictions.
44 citations
TL;DR: The electric field induced second harmonic coefficient has been measured in glass and it is concluded that the nuclear contribution is significantly smaller than the electronic contribution, and this third order effect in glass cannot be neglected when measuring the molecular hyperpolarizabilities of most organic liquids.
Abstract: The electric field induced second harmonic coefficient has been measured in glass. We have concluded that the nuclear contribution is significantly smaller than the electronic contribution, and that this third order effect in glass cannot be neglected when measuring the molecular hyperpolarizabilities of most organic liquids.
33 citations
TL;DR: The behavior of an extraordinary wave normally incident along a decreasing magnetic field gradient in a warm collisionless toroidal plasma is considered in this paper, where the second harmonic generated by this pump field is calculated, and its usefulness for poloidal magnetic field measurements in tokamaks is discussed.
Abstract: The behavior of an extraordinary wave normally incident along a decreasing magnetic field gradient in a warm collisionless toroidal plasma is considered. Full electromagnetic Vlasov theory is used and the density gradient lengths are assumed to be much larger than all wavelengths. In the case for which the upper hybrid layer is accessible, it is shown that the incident wave almost completely converts into a backward Bernstein mode at the layer. The Bernstein mode then propagates until it is absorbed near the cyclotron layer. The second harmonic generated by this pump field is calculated, and its usefulness for poloidal magnetic field measurements in tokamaks is discussed. The theory is found to be in qualitative agreement with previous experimental results.
32 citations
TL;DR: Measurements of the harmonic generation associated with a known dc field distribution gives information on the optical field distribution and indicates that dc induced second-harmonic .generation constitutes a sensitive probe of experimentally interesting mode distortios.
Abstract: The amount of optical second harmonic generated in a centrosymmetric medium in the presence of a dc electric field depends on a convolution of the optical and dc field distributions in space. Thus, measurements of the harmonic generation associated with a known dc field distribution gives information on the optical field distribution. This method has been used to investigate the focal region of a laser beam. It avoids difficulties with resolution and probe damage that arise when conventional methods are used near the focus. The detailed data are in excellent agreement with results predicted for a pure TEM00 laser beam with the notable exception that the effective confocal parameter is about a factor of 2 smaller than that indicated by conventional measurements. We believe this effect is associated with the truncation of the laser beam by the intracavity mode-selecting aperture, and indicates that dc induced second-harmonic generation constitutes a sensitive probe of experimentally interesting mode distortions.
23 citations
TL;DR: In this paper, a servo motor system was used to tune the nonlinear crystal appropriate for phase-matched second harmonic generation while the dye laser emission wavelength was tuned, and the spatial direction of the generated uv beam was used as the regulating signal.
23 citations
TL;DR: In this paper, the resonant second-harmonic generation produced by excitons in CdS and ZnO was measured using a tunable laser, and a comparison of the magnitude and sign of the exciton nonlinear coefficient determined from their measurements was found to be in good agreement with theory.
Abstract: We have measured, using a tunable laser, the resonant second-harmonic generation produced by excitons in CdS and ZnO. We find that spatial-dispersion effects are very important in the harmonic generation, and that only by including them can the data be properly understood. A comparison of the magnitude and sign of the exciton nonlinear coefficient determined from our measurements is found to be in good agreement with theory.
18 citations
TL;DR: In this article, the reflected second harmonic light from alkali metal films with the simultaneous excitation of the surface plasmon mode was calculated, and it was shown that the harmonic enhancement is closely related to the surface density and exhibits a strong dependence on the angle of incidence, film thickness, and the linear optical constants of the metal film.
18 citations
TL;DR: In this article, an extraordinary incident wave propagating along the major radius through the ST tokamak plasma is used to generate a second harmonic wave at the upper hybrid layer.
Abstract: An extraordinary incident wave propagating along the major radius through the ST tokamak plasma is used to generate a second harmonic wave at the upper hybrid layer. Remote polarization measurements of the harmonic yield the poloidal magnetic field profile. The estimated over‐all error in the measurement of the rotation angle of the total magnetic field is ≃0.3×10−2 rad. Further improvements in the accuracy of the measurements which are required to specify the current density profile unambiguously are discussed.
16 citations
TL;DR: In this paper, the third harmonic emission from a laser-created plasma, using a nanosecond TEA CO2 laser, was observed from a CO2 plasma, and the observed threshold for this emission was 6×1012 W cm−2.
Abstract: Third harmonic emission has been observed from a laser‐created plasma, using a nanosecond TEA CO2 laser. The observed threshold for this emission is 6×1012 W cm−2.
14 citations
TL;DR: In this article, the concepts of linear optics are applied to the physics of energy coupling into laser-produced plasmas currently of interest in laser-initiated fusion research.
Abstract: The concepts of linear optics are applied to the physics of energy coupling into laser‐produced plasmas currently of interest in laser‐initiated fusion research. The effects of polarization and angle of incidence upon reflection and refraction are recalled. Singular behavior occurs in the region of the plasma where the real part of the dielectric constant vanishes, the so‐called ’’critical density’’ region. The effective generation of Langmuir waves at the surfaces of bounded plasmas through the optical resonance of obliquely incident electromagnetic radiation is heuristically discussed. Enhanced electric fields, enhanced ’’collisionless’’ damping, harmonic generation, the presence of energetic electrons, and density profile modifications which result near the critical density from the excitation of these plasma waves are described. While more complex plasma processes may occur, they are not within the scope of this review.
TL;DR: The LiNbO3 parametric oscillator described in this article forms the central element in a widely tunable coherent spectrometer system and can be used for extended frequency tuning.
Abstract: The LiNbO3 parametric oscillator described here forms the central element in a widely tunable coherent spectrometer system. Efficient extended frequency tuning by harmonic generation to the visible and ultraviolet is possible in angle phase-matched crystals of LiNbO3 (1.4 μn to 0.7 μn), LiIO3 (0.7 μn to 0.35 μm) and ADP (0.35 μm to 0.26 μm), and by mixing to the extended infrared in AgGaSe2(3 μm to 12 μm), CdSe (10 μm to 25 μm), GaP (20 μm to 200 μm) and LiNbO3 (170 μm to 1 cm). We have recently carried out the doubling steps in LiNbO3 and LiIO3 and generated output wavelengths to 0.490 μm. We plan to conduct the mixing experiments in AgGaSe2 and CdSe in the near future.
TL;DR: In this paper, the authors modify harmonic generation theory to include the effect of frequency shifts in the interaction between atoms and the electromagnetic field and present closed-form expressions for generated dipole moment, absorption probability, and coherence length.
Abstract: Optical harmonic generation and mixing in the gas phase has been proposed as a technique for the generation of coherent radiation in the vacuum ultraviolet and soft X-ray spectral region. At the high field strengths required by these processes the interaction between atoms and the electromagnetic field shows intensity-dependent resonances. In this paper we modify harmonic generation theory to include the effect of these frequency shifts. Closed-form expressions for generated dipole moment, absorption probability, and coherence length are presented. The most important consequences of frequency shifts on resonantly enhanced processes are that the pump laser must be tuned away from the small-field resonance frequency, that the conversion efficiency may saturate, and that the dispersion of the medium may change sign. As an example, the generation of 198-A radiation by a five-photon mixing process in Li(+) is considered.
TL;DR: In this article, direct correlation experiments are reported which show no evidence for harmonic generation in the 1/f noise of a variety of specimens, and the authors conclude that harmonic generation is not possible.
Abstract: Direct correlation experiments are reported which show no evidence for harmonic generation in the 1/f noise of a variety of specimens.
01 May 1975
TL;DR: Second-harmonic light scattering (SHS) studies of liquid mixtures are shown to provide valuable information regarding correlations between non-centrosymmetric (e.g. dipolar) molecules and centro-smooth ones, between dipolar molecules and tetrahedral ones, as well as between the components of atomic media as discussed by the authors.
Abstract: Second-harmonic light scattering (SHS) studies of liquid mixtures are shown to provide valuable information regarding correlations between non-centrosymmetric (e. g. dipolar) molecules and centrosymmetric (e. g. quadrupolar) ones, between dipolar molecules and tetrahedral ones, as well as between the components of atomic media. Such studies moreover permit determination of nonlinear second-order and third-order molecular polarizabilities as to sign and value. LE JOURNAL DE PHYSIQUE TOME 36, OCTOBRE 1975, Classification Physics Abstracts 2.410 7.124 8.822
TL;DR: In this article, the spatial coherence of a second harmonic excited in a nonlinear crystal by multimode laser radiation was investigated and it was shown experimentally and theoretically that the harmomic field is randomly nonisotropic.
Abstract: The results are given of an investigation of the spatial coherence of a second harmonic excited in a nonlinear crystal by multimode laser radiation. It is shown experimentally and theoretically that, in general, the harmomic field is randomly nonisotropic. The correlation radius of this field is highest along the direction of sideways drift of energy in the nonlinear crystal. The characteristics of the propagation of such harmonic beams hi linear media are investigated. It is found that, during propagation, the initially circular cross section of the harmonic beam becomes strongly elongated and its field becomes randomly isotropic. These properties of harmonics should be allowed for in the design of multipliers of frequencies of high-power multimode beams and in their use in holography, heterodyne detection, etc.
TL;DR: In this paper, the second order perturbation theory based on the cold plasma equations is applied to an axially nonuniform plasma in a strong uniform axial magnetic field, and the results show that nonlinear source terms enter into the governing differential equation for the second-order potential.
Abstract: Prior experiments on the propagation of electrostatic waves on a plasma column (Gould–Trivelpiece modes) have shown linear wave reflections from an adjustable axial density gradient which scaled according to the predictions of WKB theory. For finite amplitude incident waves at radian frequency ω<ωpo, we have observed strong harmonic production at frequencies nω<ωpo where n in an integer and ωpo is the mean electron plasma frequency in the axially uniform part of the column. The harmonic production appeared to originate in the axially nonuniform plasma, and decreased markedly as the gradient was reduced experimentally. No threshold for harmonic production was observed, thus suggesting that parametric effects were not important. Second‐order perturbation theory based on the cold plasma equations is applied to an axially nonuniform plasma in a strong uniform axial magnetic field. The results show that nonlinear source terms enter into the governing differential equation for the second‐harmonic potential whic...
TL;DR: In this paper, the internal friction and the third harmonic were analyzed in terms of the dislocation models of Granato-Lucke and Peguin et al. and a dynamic dislocation multiplication mechanism was suggested for the burst type emissions.
TL;DR: In this article, a review of recent experimental work and relevant basic physical principles of V.U.V. lasers is presented, along with a detailed analysis of the photophysical properties of present and future laser systems excited by ionizing radiation.
TL;DR: In this paper, a theoretical analysis of the pulse generation of a second harmonic in a nonlinear crystal placed inside a Q-switched laser resonator is made for the saturation of the nonlinear interaction and for the inhomogeneity of the longitudinal distribution of the intensity of the fundamental frequency radiation in the active element.
Abstract: A theoretical analysis is made of the pulse generation of a second harmonic in a nonlinear crystal placed inside a Q-switched laser resonator. Allowance is made for the saturation of the nonlinear interaction and for the inhomogeneity of the longitudinal distribution of the intensity of the fundamental-frequency radiation in the active element. The following main results of a computer analysis are reported: machine oscillograms of isolated harmonic pulses often have a fine structure; for a given length of the nonlinear crystal there are, under certain conditions, two values of the pump energy which ensure optimal conversion; an increase in the pump energy causes a greater proportion of the total harmonic energy to be generated during the forward pass through the nonlinear crystal; phase-matching curves for the energy of harmonic single pulses are much wider and smoother than in the case of second harmonic generation outside the resonator.
TL;DR: In this article, a theoretical analysis is made of the generation of optical harmonics in a nonlinear medium which exhibits a two-photon transition in which the pump and harmonic photons participate.
Abstract: A theoretical analysis is made of the generation of optical harmonics in a nonlinear medium which exhibits a two-photon transition in which the pump and harmonic photons participate. Frequency doubling is discussed in detail. It is shown that free carriers formed as a result of nonlinear absorption may alter significantly the conversion of the fundamental wave into its harmonic. A discussion is given of the applicability of the proposed theory to recent experiments on the generation of the second harmonic of CO2 laser radiation in tellurium.
TL;DR: In this paper, a method based on Poincare perturbation is presented for finding the various order harmonics in a nonlinear dielectric, where the relationship between the electric field and electric displacement contains linear, quadratic, and cubic terms.
Abstract: A method based on Poincare perturbation is presented for finding the various order harmonics in a nonlinear dielectric The method is an extension of the ideas utilized by this author for finding spatial and temporal periodic solutions for elastic waves in an anharmonic lattice The method is applied here to find the generation of the first and second harmonics by a fundamental mode in a dielectric where the relationship between the electric field and electric displacement contains linear, quadratic, and cubic terms
Patent•
08 Dec 1975
TL;DR: In this paper, the authors proposed a coherent optical and infrared second harmonic generation with nonlinear crystal under noncollinear synchronism conditions and transparent for both the fundamental frequency and second harmonic.
Abstract: A device for coherent optical and infrared second harmonic generation comprising an active laser element, a cavity Q-switched to the fundamental frequency of the active laser element, thereby ensuring formation of a zone of intersection of the fundamental frequency beams, and a nonlinear crystal placed inside the fundamental frequency cavity in the fundamental frequency beams intersection zone, said crystal generating the second harmonic under noncollinear synchronism conditions and transparent for both the fundamental frequency and second harmonic. The proposed device permits second harmonic generation under non-collinear synchronism conditions in a nonlinear crystal. This allows a spectroscopically pure second harmonic to be obtained and widens the field of nonlinear crystals application.
IBM1
TL;DR: In this article, the cold plasma theory of upper hybrid harmonic generation is examined numerically and the density perturbation caused by incident wave pressure gives enhanced harmonic levels (as observed experimentally) and reveals the sensitivity of the theory to the description of the incident fields.
Abstract: The cold plasma theory of upper hybrid harmonic generation is examined numerically. Inclusion of the density perturbation caused by incident wave pressure gives enhanced harmonic levels (as observed experimentally) and reveals the sensitivity of the theory to the description of the incident fields.
TL;DR: In this paper, the second harmonic of the field was derived by an iteration procedure and the efficiency of the yield of the second harmonics was calculated, and an equation for the second-order field equation was derived.
Abstract: The generation of second harmonics of voltage and current in a space charge limited diode is considered. An equation for the second harmonic of the field is derived by an iteration procedure and the efficiency of the yield of the second harmonic is calculated.