Self-diffraction of laser radiation in anisotropic liquid-crystalline phototropic media

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 52, No. 4, pp. 544–550, April, 1990.     

Propagation of laser beams through inhomogeneous media

The propagation of gaussian beams in media with an arbitrary gain and/or dispersion profile is discussed using a variational method. Simple analytic formulae are derived and applied to the spin-flip laser which has a gaussian gain profile. The results are a significant improvement on the quadratic-gain approximation.     

Cerenkov radiation in anisotropic media by the methods of quantum electrodynamics

We examine the Cerenkov effect in a transparent anisotropic medium by the methods of quantum electrodynamics. We first show that in such a medium the electric field intensity is not transverse. By resolving the field we distinguish the contributions to the intensity of the radiation corresponding to the transverse and longitudinal components of the field. Focusing also on the role of the spin, we show that its effect is significant since the intensity can increase or decrease compared with that of a spinless particle.     

Certain features of radiation transport in spatially bounded media with anisotropic scattering

The problem of radiation transport (RT) in media with a nonsymmetric scattering index is examined under multiple scattering conditions. The governing influence on the nature of the RT is exerted by the integral index parameters that take account of the forward-backward radiation. Nonsymmetry of the index /, equal to three produces a relative energy redistribution through the side faces of the medium within 20% limits, where the maximum redistribution is observed for small transverse dimensions _y=_z=5. For large transverse dimensions the effect of index nonsymmetry does not appear. It is shown that the degree of anisotropy is less in spatially bounded media as compared with an unbounded layer of equal optical thickness.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 69–72, December, 1989. Original article submitted January 11, 1988.     

电力线谐波辐射在分层各向异性电离层中的传播特点

电力线谐波辐射特指在电离层或磁层中观测到的来源于地面电力系统输电线的电磁波辐射, 其在电磁场时频功率谱中表现为400 Hz至5 kHz范围内, 频率间隔为50/100 Hz或60/120 Hz 的平行谱线, 已成为近地空间环境的一种人为污染源. 对于该现象的形成机理尚缺乏定量研究. 本文研究了非理想导电大地上方由电偶极子源产生的电磁场在分层各向异性电离层中的传播模型, 提出了一种新的求解方法, 有效解决了编程计算中的数值溢出问题, 并利用已有解析解对所提方法进行了验证. 在此基础上, 利用实际电力线、大地、电离层的相关参数, 研究了偶极子源频率、电离层下边界高度、大地电导率、地磁场方向等对电力线谐波辐射在电离层中的传播的影响. 结果表明, 频率等于地-电离层波导导波模截止频率时透入电离层的电力线谐波辐射强度更大; 谐波电流一定时, 大地电导率小的地区, 电力线谐波辐射的功率更大; 电力线谐波辐射在电离层中沿地磁场方向传播. 本文所得结果有益于阐释电力线谐波辐射现象的形成机理.     

Polarization visualization of scattering media with CW laser radiation

The method of polarization visualization of a multiply scattering medium containing macroinhomogeneities based on analysis of polarization spatial distribution of a scattered linearly polarized light is discussed. The treatment is based on statistical properties of the effective optical path distribution of scattered field components. The influence of media scattering properties and the geometry of the experiment on the inhomogeneity image contrast obtained with use of polarization degree and of normalized scattered intensity of radiation as visualization parameters are discussed, as well as spatial resolution achieved in these both cases. Using the results of theoretical analysis and of the experimental model, the relationship between the shapes of spatial distributions of polarization degree and the intensity of the scattered light is considered as a function of the position of the visualized object (an absorbing half-plane immersed in a plane layer of the scattering medium). The opportunities for enhancing the quality of the images formed in this way are also discussed.     

Absorption and scattering of high-power laser radiation in low-density porous media

We have experimentally investigated the interaction of high-power neodymium laser pulses in the intensity range 10¹³–10¹⁴ W/cm² with flat low-density (0.5–10 mg/cm³) agar-agar targets under conditions of interest for problems of inertial nuclear fusion. Optical and x-ray methods with high temporal and spatial resolution were used to examine the dependence of absorption and scattering of the incident beam on the initial mean density and thickness of the irradiated samples. We show that when a porous target is irradiated, a bulk absorption layer of high-temperature plasma is produced inside the target whose dimensions are determined by the initial density of the material. The time dependence and spectral composition of the harmonics 2ω ₀ and 3ω ₀/2 observed in the plasma-scattered radiation are measured. A theoretical model is developed that describes the interaction of high-power laser pulses with a porous medium. Predictions of the model, based on the hypothesis of two stages of homogenization of the target material—a fast stage (0.1–0.3 ns) and a slow stage (1–3 ns), are in good agreement with the experimental data. Zh. éksp. Teor. Fiz. 115, 805–818 (March 1999)     

Guided waves in anisotropic media

This paper investigates the propagation of electromagnetic waves in a dielectric anisotropic medium containing conducting planes. A plane and rectangular waveguide is considered for certain particular cases of the orientation of the principal axis of the anisotropic medium relative to the waveguide coordinates. The dispersion equations for the propagation constants are deduced.In conclusion we thank D. A. Dobrotin for his advice.