非线性左手材料中的二次谐波

基于电磁场理论，推导了无耗非线性左手材料中二次谐波的曼利－诺关系，及相位匹配条件下正向基波与逆向二次谐波的能量转换过程及其空间分布.验证了可将无耗非线性左手材料的入射面作为反射镜，把能量以二次谐波的形式反射.同时分别给出有限厚度介质板中基波和二次谐波的场强分布数值结果，验证了结论的正确性.最后从相位失配角度说明了相位匹配是分析非线性左手材料二次谐波的重要条件.这为研究左手材料的非线性理论奠定了基础.     

Second-harmonic generation in a layer with variable susceptibility

The weak nonlinearity limit of the second-harmonic generation in a medium with variable second-order susceptibility, changing along the direction of propagation of interacting waves according to the hyperbolic secant law, is considered. It is shown that the variation of the second harmonic’s normalized intensity with the spatial coordinate is given in terms of the solution to an auxiliary linear problem, which is known as the Rosen-Zener quantum two-level model. The final intensity of the second harmonic at the exit from the medium is calculated and analyzed. It is shown that, for the particular Rosen-Zener profile under consideration, because of its inherent properties, the variation range of the peak susceptibility of the layer for which the medium can be strictly considered as weakly nonlinear is narrower than the corresponding parameter range for a homogeneous medium.     

Second-harmonic generation in periodically poled nonlinear polymer waveguides

We demonstrate quasi-phase-matched (QPM) second-harmonic generation (SHG) at the optical communication wavelengths with side-chain polymer waveguides. A ridge waveguide structure is designed to support fundamental mode guiding at both the pump and the second harmonics, leading to a high field overlap integral of the guided modes. The nonlinearity contrast in the +/0 type QPM waveguide is maximized under a QPM poling electrode width of nearly half the coherence length. Using these configurations, we record a normalized SHG efficiency of 2.2% W(-1) cm(-2) in the polymer waveguide.     

Second-harmonic generation in poled films of nonlinear optical polymer composites

The second-harmonic generation (SHG) has been measured for studying the molecular ordering and its relaxation process in poled states of two different nonlinear optical (NLO) polymer composites.p-Nitroaniline (pNA) and the azo dye Disperse Orange 3 (DO3) are uniformly dispersed in photopolymer matrices followed by poling. Two different composites made-up of 1 wt% of pNA and 2.5 wt% of DO3 are poled at 200 MV m^-1 and 80 MV m^-1, respectively. One of the second-order NLO coefficients,d ₃₃, was found to be 0.27 pm V^-1 for the pNA-doped film and 0.20 pm V^-1 for the DO3-doped film. While for the latter the ratiod ₃₃/d ₃₃ (3.1) is consistent with the value of 3 in the low-field approximation, for the former the value of 3.5 indicates that higher-order effects of the poling field play a significant role in the NLO process. It is suggested that the SHG relaxation dynamics is also closely related to the UV absorption of the NLO molecules in a photopolymer matrix.     

Modulation instability of a continuous signal in an optical fiber taking into account third-order dispersion

Moscow Institute of Electronics. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 33, No. 1, pp. 111–117, January, 1990.     

Photon-electron scattering taking vacuum energy into account

We deal with photon-electron scattering between the two uncharged conducting parallel plates. The electromagnetic vacuum field between the two plates is defined by the configuration of space and also interacts with the electrons. We first deal with the relevant operators for the electron and photon fields and with the Feynman propagator. We compute theS-matrix for photon-electron scattering, taking into account the influence of the vacuum field. The computed photon-electron scattering cross section also manifests the influence of the vacuum field. We give an example for low-energy scattering of the influence of the vacuum field upon the scattering cross section.     

Second-harmonic generation at interfaces

Second-harmonic light can be generated at dye coated surfaces of fused silica. By changing either the angle of incidence or the frequency of the fundamental, phase matching of signals produced at the two surfaces of a plane-parallel plate has been achieved. The interaction of light from multiple internal reflections has also been studied.     

Second-harmonic generation at periodic second-order susceptibility gratings with self-phase and cross-phase modulation

Quasi-phase-matched second-harmonic generation at periodic quadratic susceptibility gratings with self-phase and cross-phase modulation owing to Kerr nonlinearities is investigated. A model of interaction of monochromatic plane travelling waves is considered. The solution assumes a nondepleted pump and results for a numerical computation of second-harmonic conversion efficiency for a highly efficient process are presented. It is shown that for high spatial-frequency gratings the efficiency of second-harmonic generation depends on the reduced detuning and the Kerr-nonlinearity coefficient only. In some cases, if the signs of and are opposite, the Kerr nonlinearity can enhance the second-harmonic conversion efficiency due to the compensation of the phase mismatch attained in the below-half-conversion stage by the reversed phase mismatch in the above-half-conversion stage of the process. The computed maximum conversion efficiencies for various values of and are plotted in a contour map on the - plane.     

Second-harmonic generation by elliptic Bessel light beams in periodically polarized nonlinear crystals

The features of the frequency doubling of elliptic Bessel light beams under quasi-synchronous interaction in periodically polarized nonlinear crystals have been investigated. The overlap integrals describing the efficiency of second-harmonic generation by elliptic Bessel light beams have been investigated numerically. Reported at the Vth International Scientific-Technical Conference on Quantum Electronics, November 22–25, 2004, Minsk, Belarus. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 6, pp. 752–755, November–December, 2005.     

Solution of polarization eigenvalue problems taking depolarization into account

The shape of the transmission band of an active interferometer, a resonator with amplification and absorption cells excited by an external signal, is studied. Upon tuning the external signal frequency, the narrow saturated absorption resonances can be observed in the transmission band of the interferometer. It is shown that, by varying the gain, the resonance absorption amplitude can be compensated for one order of smallness in pressure. The effect of amplitude and frequency noises of the external signal on the results obtained is studied.     

Cylindrically symmetric distributions of matter taking into account pressure

A cylindrically symmetric distribution of matter under pressure which evolves with time is considered. A new class of non-steady-state solutions to the Einstein equations with cylindrical symmetry is found (for cases when the matter is under zero, constant, and time-dependent pressure). A homogeneous, anisotropic universe and an analog of the Schwarzschild solution are considered as particular cases.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 33–36, December, 1985.     

Second-harmonic generation of polarization singularities

Second-harmonic generation was studied theoretically for the vector singularities (daisy modes) of linearly polarized light and for the elliptic singularities (C points) of elliptically polarized light. Topological charge doubling for C points and daisy modes, similar to that found for vortices, was found. Unlike for vortices, however, it was found that for both C points and daisy modes the sign of the charge is reversed; for C points the photon spin or handedness (right or left) is also reversed; and for daisy modes the number of intensity petals is not doubled. These findings are all unexpected because neither charge nor spin nor orbital angular momentum is conserved for C points, whereas a daisy mode in which the number of intensity petals does not equal twice the magnitude of the charge is anomalous.     

Second-harmonic generation in a double-tuned microwave cavity partly filled with nonlinear dielectric crystals

The conditions for optimal second-harmonic generation using dielectric crystals in a microwave cavity are investigated. The general relations, obtained by a vector Green's theorem, are specified to a rectangular cavity, where the eigenfunctions can be calculated explicitely. A good agreement is found between theory and experiments performed at a fundamental frequency of 9 GHz using LiNbO₃ as the crystal.     

Leontovich-Levin equation taking into account finite conductivity of a conductor

A generalization of the Leontovich-Levin equation for current in an ideally conducting linear vibrator to the case of a finite-conductivity conductor is considered. This generalization is valid for strong and weak skin effects, as well as for inhomogeneous conductors with an axisymmetric conductivity distribution (in particular, for carbon nanotubes, CNTs). The internal structure of the conductor is fully described by the internal impedance per unit length. A recurrent scheme is proposed for calculating such an impedance for layer-inhomogeneous conductors. A particular case of the impedance for metallic achiral CNTs is considered, and substantial differences between this case and the macroscopic model of a conductor with full skin effect are indicated.     

Second-harmonic generation in centro-symmetric semiconductors

Summary The crystallographic dependence of optical-second-harmonic generation (SHG) in Si and Ge single crystals is obtained with 10 ps pulses at 527 nm and at incident fluences above the threshold for laser melting of the crystal lattice. We find that the experimentally observed dependence of SHG on crystal orientation remains unchanged up to the damage limit. Observed selection rules are analysed in terms of various possible contributions.

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Riassunto Generazione della seconda armonica ottica è ottenuta nei monocristalli di Si e Ge con impulsi laser di 10 ps, a 527 nm, e con densità di energia inpingente superiore all soglia per la fuzione del reticolo cristallino. Si osserva che la seconda armonica mantiene la propria dipendenza dall' orientazione cristallografica, indipendente dal valore della densità di energia che è incidente sulla superficie cristallina, fino alla soglia del danno. Il mutamento d'intensità di generazione a secondo orientazione cristallografica e piano di polarizzazione è stato analizzato in funzione di vari contributi probabili.

     

Second-harmonic generation with traveling-wave pulses

We experimentally studied properties of traveling-wave excitation and traveling-wave pulse compression for a Nd : glass laser system with a streak camera. These properties were extended to second-harmonic generation with a type-11 KDP crystal. We found that the second-harmonic pulse generated from the chirped-fundamental pulse also has a good chirp linearity, but the spectral bandwidth and temporal duration were reduced. We demonstrated the effective subpulse suppression in the compressed pulse with the second-harmonic generation. The pulse with tilted wave front, short wavelength and high contrast ratio can be obtained by the second-harmonic generation of traveling-wave pulse.     

Second-harmonic generation in vortex-induced waveguides

We study the second-harmonic generation and localization of light in a reconfigurable waveguide induced by an optical vortex soliton in a defocusing Kerr medium. We show that the vortex-induced waveguide greatly improves conversion efficiency from the fundamental to the second-harmonic field.