Markovian non-Gaussian approximation for light propagation in a random medium

A theory is presented for wave propagation in a random medium that generalizes the Markovian-Gaussian approximation to the case of a non-Gaussian probability distribution of refractivity fluctuations. A Poissonian model of refractivity fluctuations that are statistically independent in non-overlapping intervals in the x-direction is used. This model turns out to be Gaussian under appropriate conditions. General solutions are obtained for the mean field and the mutual coherence function of a plane, partially coherent incident wave. These solutions contain a new functional parameter, a characteristic function of the amplitude of dielectric permittivity fluctuations, that affects the shape of the coherence function as well as its spectrum.     

Additional electromagnetic waves in a uniaxial crystal with anisotropy fluctuations

It has been shown that the inclusion of orientational fluctuations of the axes of nonpolar axially symmetric molecules leads to a spatial dispersion of the permittivity of a uniaxial crystal. Expressions for the local field, polarization, and principal values of the permittivity tensor of the crystal have been derived. An estimate has been made of the wavelength above which the contribution to the spatial dispersion of orientational fluctuations of the molecular axes dominates. The phase velocities of the ordinary and extraordinary electromagnetic waves in a uniaxial crystal have been determined. It has been demonstrated that additional slow extraordinary electromagnetic waves can exist near the zeros of the principal values of the permittivity tensor of the crystal in particular ranges of angles between the wave vector and the optic axis of the crystal.     

A comparison of the results of a numerical simulation and an approximate calculation of the statistical characteristics of radio waves in a layer with random inhomogeneities of dielectric permittivity

We consider the formation algorithm for a random inhomogeneity field of dielectric permittivity of a medium that is used in simulations of the statistical characteristics of a wave that has propagated through a randomly inhomogeneous layer. We carry out a comparison of the statistical characteristics of a geometrical-optics wave, obtained via a numerical simulation, with the results of calculations of these characteristics by approximate formulae obtained using perturbation theory. It is pointed out that the applicability limits of the perturbation method, when solving geometrical-optics equations in a randomly inhomogeneous medium, depend on the formulation (one- or two-point) of the trajectory problem. It is shown that a calculation of the spatial correlation function of the field can be carried out using the perturbation method, even in the case of relatively strong fluctuations of dielectric permittivity. This is due to the fact that, in the region where this function differs markedly from zero, the correlation function of the eikonal obtained by the perturbation method is sufficiently accurate, and amplitude fluctuations are small.     

Beam wave propagation within the second Rytov perturbation approximation

The applicability of the classical Rytov method in statistical wave propagation problems is reconsidered and expanded by demanding results that are of second order in the permittivity fluctuations, rather than limiting them to just the first Rytov perturbation approximation, as is traditionally done. It is shown that one must augment the well-known second order statistics (e.g., log-amplitude variance), as calculated from the first Rytov approximation, with first-order statistics (e.g., the average log-amplitude), as calculated from the second Rytov approximation. Thus, a complete solution is derived for the second Rytov approximation for general beam wave propagation through turbulent media, the permittivity fluctuations of which are described by the Kolmogorov-Obukhov spectrum. This then allows a complete and consistent treatment that yields the fact that the average log-amplitude is, in the general beam wave case, not equal to the additive inverse of the log-amplitude variance. This gives results from the Rytov method that are then in exact agreement with the corresponding limiting case of strong fluctuation theory, as well as a simplified analytical expression for beam wave broadening, and the correct theoretical explanation of the well-known applicability limit for the Rytov method.     

Dielectric Characteristics for Radio Frequency Waves in a Laboratory Dipole Plasma

Transverse and parallel dielectric permittivity elements have been derived for radio frequency waves in a laboratory dipole magnetic field plasma. Vlasov equation is resolved for both the trapped and untrapped particles as a boundary value problem to define their separate contributions to the dielectric tensor components. To estimate the wave power absorbed in the plasma volume the perturbed electric field and current density components are decomposed in a Fourier series over the poloidal angle. In this case, the dielectric characteristics can be analyzed independently of the solution of the Maxwell's equations. As usual, imaginary part of the parallel permittivity elements is necessary to estimate the electron Landau damping of radio frequency waves, whereas imaginary part of the transverse permittivity elements is important to estimate the wave dissipation by the cyclotron resonances. Computations of the imaginary part of the parallel permittivity elements are carried out in a wide range of the wave frequencies. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Enhancement of electron density in the interaction of high-power electromagnetic waves with inhomogeneous magnetized plasma

Propagation characteristics of a high-power electromagnetic wave through an inhomogeneous magnetized plasma is investigated. Considering the momentum transfer equations for electrons and ions and taking into account the ponderomotive force, the distribution of electron density and dielectric permittivity are obtained. Using non-linear dielectric permittivity and Maxwell's equations in the absence of external current and charge densities, non-linear wave equations are achieved. The results indicate that the external static magnetic field can modify the profiles of both the electric and magnetic fields. It is also shown that the external static magnetic field enhances the amplitude of the electron density and the non-linear dielectric permittivity.     

Electromagnetic wave scattering from a random medium layer with a random interface

Abstract

The problem of electromagnetic wave scattering from a random medium layer with a random interface is considered. The layer has planar boundaries on average. Assuming that both the random perturbations of the interface and the random fluctuations of permittivity of the medium are small, a first-order perturbation solution to the scattered field is obtained. Using this solution, the bistatic scattering coefficients γ_αβ are calculated and expressed in a compact and meaningful form. The various terms that constitute γ_αβ are identified with distinct scattering processes. Since it is often of particular interest, the special case of backscattering is considered. Finally, the results are compared with those of others.     

Fluctuational spatial dispersion in achiral liquid crystals

An investigation is made of the spatial dispersion of the permittivity of achiral liquid crystals with large-scale fluctuations. It is observed that for large correlation lengths the terms with spatial dispersion are anomalously large. The specific form of these terms is obtained for orientational fluctuations in a nematic and fluctuations of the deformations of the smectic layers in a smectic-A in an orienting magnetic field. It is shown that these effects may be observed optically by means of accurate measurements of the angular dependence of the refractive indices of electromagnetic waves. Zh. éksp. Teor. Fiz. 114, 182–190 (July 1998)     

Distinct current-carrying charge density wave states in NbSe3

We have performed detailed measurements of the dc current-voltage (I–V) characteristics of NbSe₃ in the hysteretic switching regime. Within the hysteresis loop, we observe a series of well-defined and quasi-stable current-carrying states, each with a unique I–V relationship. Transitions between the states, induced by both the applied electric field and thermal fluctuations, are observed. Rapid and random transitions between closely spaced levels are suggested to result in excessive current or voltage noise for the depinned charge density wave condensate.     

一种简化非Gauss场模型在随机介质中光传播问题中的应用

为了研究大气湍流间歇性的光传播效应，构造出一种比较简单的非Gauss场模型(Poission场 )用于描述大气介电常数(或折射率)随机起伏.模型特征泛函含有四个待定函数，根据大气湍 流的统计均匀性，介电起伏的单点概率分布函数，以及介电起伏能谱可以选择或确定它们. 对在这种简化湍流中传播的光波平均场及二阶统计矩性质进行了理论分析，并给出数值模拟 的一个简单例子. 关键词： 光波传播 大气湍流 间歇性     

Light scattering by extraordinarily polarized polaritons

The objective of this work is to investigate how the anisotropy of the interaction between dipole-active vibrations of a crystal lattice and infrared electromagnetic waves is manifested in the spontaneous parametric light scattering spectra of polaritons (Raman scattering by small angles). The case where scattering occurs by extraordinarily polarized polaritons—quasiparticles formed as a result of the coupling of the wave polarized in the symmetry plane of a biaxial crystal simultaneously with two phonons possessing orthogonal dipolar moments—is studied. A series of spectra of equilibrium fluctuations of the electromagnetic (infrared) field, each of which represents an intensity distribution in frequency-wave number coordinates for a fixed direction of the wave vector, are constructed on the basis of a scattering model that takes account of the tensor character of the permittivity and the quadratic and cubic susceptibilities of the crystal. Analysis of the computed spectra identified the basic laws and dependences which are determined by the anisotropy of the electromagnetic susceptibilities of various orders and made it possible to explain previous experimental results which cannot be interpreted on the basis of the generally accepted model of transversely polarized polaritons. A method is proposed for determining the contributions of the dipole-active vibrations of the crystal lattice to the permittivity and the quadratic and cubic susceptibilities, as well as the absorption of the material from the spectra of the extraordinarily polarized polaritons.     

On the statistical moments of the wave field in the presence of caustics

The diffraction of a scalar wave field by a screen causing random and regular phase modulation is considered. The regular phase advance causes focusing of the field (i.e., the development of foci or caustic surfaces). It is shown that for strong phase fluctuations geometric optics is suitable for calculating the statistical moments of the field even in focusing regions if the singularity of the moment on the caustic is integrable. This is valid specifically for the average intensity. In calculating the higher moments it is necessary to take diffraction effects into account. Estimates are obtained of the intensity fluctuations in the region of the caustic shadow.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 15, No. 4, pp. 550–556, April, 1972.In conclusion the author is pleased to thank P. V. Bliokh for his constant interest in the work and his help, and likewise F. G. Bass and I. M. Fuks for their helpful advice.     

Determination of the relative permittivity of the AlGaN barrier layer in strained AlGaN/GaN heterostructures

Using the measured capacitance--voltage curves and the photocurrent spectrum obtained from the Ni Schottky contact on a strained Al_0.3Ga_0.7N/GaN heterostructure, the value of the relative permittivity of the AlGaN barrier layer was analysed and calculated by self-consistently solving Schr?dinger's and Poisson's equations. It is shown that the calculated values of the relative permittivity are different from those formerly reported, and reverse biasing the Ni Schottky contact has an influence on the value of the relative permittivity. As the reverse bias increases from 0 V to --3~V, the value of the relative permittivity decreases from 7.184 to 7.093.     

Conformal Fluctuations of the Interior Schwarzschild Solution

The basic formalism for conformal fluctuations of the gravitational field is presented. After developing a master propagator for the interior Schwarzschild solution, the time development of the gravitational wave function is considered. The effect of the two classical singularities (resp. pseudo-singularities) of the Schwarzschild solution on the quantum wave function for the gravitational field is studied using a wave function initially localized on the classical solution. While the true singularity at r = 0 imparts consequences on the wave function that cannot be ignored, the pseudo-singularity at the event horizon does not seem to cause any divergences on the interior fluctuations of the Schwarzschild solution.     

On ponderomotive forces in laser beams

The close connection is established between the ponderomotive force potential and the wave radiated by an electron oscillating in the electromagnetic field of a laser beam and in the magnetostatic field.One of the authors (V. P.) would like to thank the University of N. S. W. for the kind hospitality during his stay there; this author also thanks S. N. Lozovski for bringing some aspects of this problem to his attention as early as in the year 1975. The authors thank R. Klíma for his valuable comments.     

Transformation of a monochromatic plane wane by the pulse-periodic time modulation of an infinite medium

An exact solution to the problem of the transformation of a monochromatic plane wave by a finite train of equally spaced rectangular pulses of permittivity and conductivity of an infinite medium is considered. The permittivity pulse train is shifted relative to the conductivity pulse train by an arbitrary time. The problem is studied analytically in terms of the second-order Volterra integral equation describing the electromagnetic wave transformation in a medium with time-dependent parameters. The equation is solved using the resolvent technique. Expressions for the amplitude of the transformed electric field component for any time instant at any spatial point are derived and analyzed.     

一种结构简单的二维左手材料设计及仿真研究

基于产生负介电常数的周期性金属线单元结构,讨论了金属线长度和宽度的变化对负介电常数的影响.在入射波的波矢k方向上放置两个单元结构,使两单元中的金属线响应入射波的磁场产生负磁导率,就可得到一维左手材料.若保持电边界条件的位置不变而调换波端口和磁边界条件位置,即入射波的波矢k转过90°角,两单元结构同样具有左手特性,从而可实现二维左手材料.