Propagation of an arbitrary incident light in a uniaxially planar slab

Similarly to the Jones calculus, a propagation formulation of an arbitrary incident light in a uniaxially planar slab with any orientation of the optic axis is derived, where both the multi-reflections and multi-refractions and the phase difference between the ordinary and extraordinary waves arising at the interface are considered. Unlike the case of propagation in the stratified isotropic media, the elements of the reflection and transmission matrices not only include the reflection and transmission coefficients, but also comprise phase differences caused by the mutual couples between ordinary (O) and extraordinary (E) waves. At this point, the propagation of an arbitrary light in a stratified uniaxially anisotropic media may be viewed as the multi-reflections and multi-refractions of a compound wave composed of one O wave and one E wave.     

Light propagation in stratified anisotropic media

Light propagation in stratified anisotropic media with arbitrary orientation of optic axes smoothly varying from layer to layer is considered. In the WKB approximation, a general expression for the field is obtained. For the case of a uniaxial medium, the normal waves are found and specific features of the light propagation are analyzed. General conditions are obtained that determine the turning points and forbidden zones. It is shown that the developed approach allows one to find trajectories of rays in anisotropic media with arbitrary layered structure.     

Transient acoustic wave propagation in rigid porous media: a time-domain approach

Wave propagation of acoustic waves in porous media is considered. The medium is assumed to have a rigid frame, so that the propagation takes place in the air which fills the material. The Euler equation and the constitutive relation are generalized to take into account the dispersive nature of these media. It is shown that the connection between the fractional calculus and the behavior of materials with memory allows time-domain wave equations, the coefficients of which are no longer frequency dependent, to be worked out. These equations are suited for direct and inverse scattering problems, and lead to the complete determination of the porous medium parameters.     

光在二维无序介质中的动态传播过程

用有限时域差分 FDTD 法研究了光在二维无序介质中的动态传播过程.数值模拟了某一高斯脉冲光束入射到无序介质中光场的空间分布随时间的演化,结果表明：在光束入射的初期,能量从光源区向外传播并出现了清晰的波前传播的特点;经过一定的时间后,有部分能量从光源区向外扩散,而大部分能量逐渐聚集在介质中的一些小区域内,这与整体散射模型关于无序介质中光子局域化的研究相吻合,而且更清晰地呈现了形成光子局域化过程中的物理现象及整体散射干涉效应的重要机理作用.     

Electromagnetically induced coherent backscattering

We demonstrate a strong coherent backward wave oscillation using forward propagating fields only. This is achieved by applying laser fields to an ultradispersive medium with proper chosen detunings to excite a molecular vibrational coherence that corresponds to a backward propagating wave. The physics then has much in common with the propagation of ultraslow light. Applications to coherent scattering and remote sensing are discussed.     

On the velocity of propagation of a signal in nonlinear optical media

The maximum velocity of propagation of a signal, which is defined as the velocity of propagation of the wave front, is considered for electromagnetic waves in nonlinear media. It is shown that the magnitude of velocity is determined to a considerable extent on the form of the constitutive equation defining the relation between the polarization of the medium with the radiation field strength. In the noninertial nonlinearity model, this velocity may be smaller (in media with self-focusing nonlinearity) or larger (defocusing nonlinearity) than the velocity of light in vacuum. For real nonlinear media, for which the inertia of their response is taken into account, the wave front velocity coincides with the velocity of light in vacuum.     

水平极化光在单轴吸收晶体中的传播

根据光在各向同性吸收介质中传播的分析方法,引入了波法线矢量传播常量,讨论了水平极化光在单轴吸收晶体中的传播规律,得到了波法线折射率、光线折射率、吸收系数等描述吸收晶体性质和光传播性质的物理量的表达式,推导出透明晶体的相应公式.数值计算表明,由该法得到的晶体表面的反射和透射系数与用复折射率表示法得到的结论一致.     

Self-action of Bessel wave packets in a system of coupled light guides and formation of light bullets

The self-action of two-dimensional and three-dimensional Bessel wave packets in a system of coupled light guides is considered using the discrete nonlinear Schrödinger equation. The features of the self-action of such wave fields are related to their initial strong spatial inhomogeneity. The numerical simulation shows that for the field amplitude exceeding a critical value, the development of an instability typical of a medium with the cubic nonlinearity is observed. Various regimes are studied: the self-channeling of a wave beam in one light guide at powers not strongly exceeding a critical value, the formation of the “kaleidoscopic” picture of a wave packet during the propagation of higher-power radiation along a stratified medium, the formation of light bullets during competition between self-focusing and modulation instabilities in the case of three-dimensional wave packets, etc. In the problem of laser pulse shortening, the situation is considered when the wave-field stratification in the transverse direction dominates. This process is accompanied by the self-compression of laser pulses in well enough separated light guides. The efficiency of conversion of the initial Bessel field distribution to two flying parallel light bullets is about 50%.     

Controlling single-photon Fock-state propagation through opaque scattering media

The control of light scattering is essential in many quantum optical experiments. Wavefront shaping is a technique used for ultimate control over wave propagation through multiple-scattering media by adaptive manipulation of incident waves. We control the propagation of single-photon Fock states through opaque scattering media by spatial phase modulation of the incident wavefront. We enhance the probability that a single photon arrives in a target output mode with a factor 30. Our proof-of-principle experiment shows that the propagation of quantum light through multiple-scattering media can be controlled, with prospective applications in quantum communication and quantum cryptography.     

Composition of propagated,reflected and transmitted waves in arbitrary and continuously stratified environments

First, a solution is presented for a canonical problem in wave propagation. Second, illustrations and applications of the results are carried out to study cases which are relevant to the propagation problem in the ocean and atmosphere.The canonical problem consists of a plane wave incident on an arbitrary and continuously stratified region with planar boundaries. The explicit composition of the reflected, transmitted and propagated waves are derived. The solution is systematic and allows for (i) discontinuities in the acoustic properties at boundaries and arbitrary variation within, (ii) attenuation, (iii) all angles of incidence. The general expressions are obtained by using an alternate procedure to one recently devised [1]. The present approach is straightforward and plainly amenable to physical interpretation of its auxiliary mathematical constants. The discontinuities at the boundaries are satisfied at the outset. The reflected and transmitted waves are directly and explicitly specified. Comparison to widely used techniques in both analytical and numerical works is made to demonstrate the viability of the present approach.A series of cases relevant to the problem at hand are considered. These cases illustrate the mechanics involved in use of the method, and expand its application to problems that appear to be at variance with the formulation of the canonical problem. The illustrations include attenuation in the medium, effect on the solution of different acoustic discontinuities at the boundaries, and use of an inhomogeneous background profile with known independent solutions. The expanded applications treat formally three types of problems: (i) the exact solution for plane waves in continuously stratified media where the well-used ray theory or W-K-B approximation serves only as a first approximation in a correct iterative solution; (ii) the scattering of a plane wave by non-planar boundaries, i.e., spherical or cylindrical acoustic lens with the stratification along the radial direction; (iii) the field due to a point source in a continuously stratified wave guide, like the ocean or atmosphere.     

Multiple Scattering Solution of Millimeter Wave Propagation in Strong Sandstorm

As the operating frequencies of communication systems more higher into the millimeter wave range, and the density of particles in medium is more denser, the effects of multiple scattering in sandstorm become more significant. This paper treats the problems of electromagnetic multiple scattering in strong sandstorm by the Monte Carlo method. Based on the analytical theory of multiple scattering, the millimeter wave propagation and scattering in discrete random media are investigated by means of the particle-tracking technique. The millimeter wave is regarded as a Markov chain of wave particle collisions in a medium in which it is scattered and absorbed. Considering the effect of multiple scattering, millimeter wave attenuation induced by strong sandstorm is simulated numerically. The values of theoretical calculation are in good agreement with the measured results of simulated experiment at 34 and 93 GHz.     

Sound propagation and scattering in media with random inhomogeneities of sound speed, density and medium velocity

This review presents both classical and new results of the theory of sound propagation in media with random inhomogeneities of sound speed, density and medium velocity (mainly in the atmosphere and ocean). An equation for a sound wave in a moving inhomogeneous medium is presented, which has a wider range of applicability than those used before. Starting from this equation, the statistical characteristics of the sound field in a moving random medium are calculated using Born-approximation, ray, Rytov and parabolic-equation methods, and the theory of multiple scattering. The results obtained show, in particular, that certain equations previously widely used in the theory of sound propagation in moving random media must now be revised. The theory presented can be used not only to calculate the statistical characteristics of sound waves in the turbulent atmosphere or ocean but also to solve inverse problems and develop new remote-sensing methods. A number of practical problems of sound propagation in moving random media are listed and the further development of this field of acoustics is considered.     

Rain induced attenuation for 3mm wave band and its measurement system

In this paper, the effect of rain induced attenuation for millimeter wave is discussed. The theory of multiple scattering is used to obtain the solution for the plane wave propagation through a plane parallel medium of thickness L containing randomly distributed nonspherial particles. The coherent field and the total field are studied, respectively. The numerical results are good agreement with experimental data and the multiple scattering effects must be included. A 3mm wave propagation measurement system was made on a 0.8km terrestrial link.     

Reflection–refraction of attenuated waves at the interface between a thermo-poroelastic medium and a thermoelastic medium

Phenomenon of reflection and refraction is considered at the plane interface between a thermoelastic medium and thermo-poroelastic medium. Both the media are isotropic and behave dissipative to wave propagation. Incident wave in thermo-poroelastic medium is considered inhomogeneous with deviation allowed between the directions of propagation and maximum attenuation. For this incidence, four attenuated waves reflect back in thermo-poroelastic medium and three waves refract to the continuing thermoelastic medium. Each of these reflected/refracted waves is inhomogeneous and propagates with a phase shift. The propagation characteristics (velocity, attenuation, inhomogeneity, phase shift, amplitude, energy) of reflected and refracted waves are calculated as functions of propagation direction and inhomogeneity of the incident wave. Variations in these propagation characteristics with the incident direction are illustrated through a numerical example.     

激光在不均匀随机媒质中的传播——多重散射的m-n阶矩方程的解

本文给出了受到多重散射的激光,在波传播方向上的物理参数的涨落是不均匀的、而垂直于传播方向上的物理参数的涨落又是均匀的随机媒质中传播时,当波受到前向小角度散射时,具有不同波数不同位置的场的矩方程的解析解.同时讨论了方程的解在激光传播研究中的一些应用.     

Simulation of color shift in fluorescent LED cap

Computer investigation and design of light propagation in fluorescent scattering media is considered. Suggested solution provides efficient and physically accurate model of light propagation in the media that allows simulating Stokes color shift effect and design of white LED. Based on the suggested solution the program package of simulation and design of optical devices with fluorescent scattering media was implemented and trial design of white LED was fulfilled.     

Causality and the velocity of acoustic signals in bubbly liquids

Several versions of the dispersion formula governing the acoustic propagation in bubbly liquids are shown to exhibit acausal behavior. The cause of this behavior is due to the inappropriate application of a low frequency approximation in the determination of the extinction of the signal from radiative scattering. Using a corrected causal formula, several principles of wave propagation in bubbly media consistent with the general theory of wave propagation in dispersive media are demonstrated: There exist two precursors to any finite signal. Both propagate without regard to the source characteristics at velocities, frequencies, and amplitudes dependent wholly upon the characteristics of the medium supporting the wave motion. The first travels at the infinite frequency phase velocity that is coincident with the infinite frequency limit of the group velocity. That part of a propagating wave oscillating at the source frequency arrives at a time determined by the signal velocity. Analogous to the well known signal velocity of electromagnetic wave propagation in conducting media, the value of the signal velocity depends on the detailed structure of the dispersion formula in the complex frequency plane.     

Fast compressional wave attenuation and dispersion due to conversion scattering into slow shear waves in randomly heterogeneous porous media

Within the viscosity-extended Biot framework of wave propagation in porous media, the existence of a slow shear wave mode with non-vanishing velocity is predicted. It is a highly diffusive shear mode wherein the two constituent phases essentially undergo out-of-phase shear motions (slow shear wave). In order to elucidate the interaction of this wave mode with propagating wave fields in an inhomogeneous medium the process of conversion scattering from fast compressional waves into slow shear waves is analyzed using the method of statistical smoothing in randomly heterogeneous poroelastic media. The result is a complex wave number of a coherent plane compressional wave propagating in a dynamic-equivalent homogeneous medium. Analysis of the results shows that the conversion scattering process draws energy from the propagating wave and therefore leads to attenuation and phase velocity dispersion. Attenuation and dispersion characteristics are typical for a relaxation process, in this case shear stress relaxation. The mechanism of conversion scattering into the slow shear wave is associated with the development of viscous boundary layers in the transition from the viscosity-dominated to inertial regime in a macroscopically homogeneous poroelastic solid.     

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.     

Polarization of light and its use in various problems of optics of scattering media

As light passes through scattering media, certain specific features of the polarization of radiation manifest themselves. The paper presents materials on this problem that were obtained at the Institute of Physics of the National Academy of Sciences of Belarus over recent decades. Results of experimental investigations of media that model real objects are described for the case where the dimensionless optical parameters of media and objects coincide. A method for determining the position of a diffuse light source in the atmosphere via predominant oscillations of the light vector of scattered radiation for two directions of observation is proposed. The structure of aerosol formations (smokes, dust and liquid-droplet and crystalline clouds) is interpreted based on the character of depolarization of laser radiation sounding atmosphere. The polarization of laser radiation passing through a turbid medium and reflected from it is studied. Practical applications are proposed. Fundamentals of an applied vector theory of radiation transfer, which made it possible to considerably expand notions of light scattering in strongly turbid media, are given. Studies of light propagation in encapsulated liquid crystals, which are used for solving of a large number of problems, are described. In these objects, ordinary and extraordinary rays that arise in crystals under electric voltage can give rise to a wave that is attenuated to a different degree and whose phase and polarization characteristics are varying.