The effect of multiple scattering in disperse media on polarization characteristics of scattered light

The effect of scattering of different multiplicity on polarization characteristics of scattered light is studied by the Monte Carlo computer simulation technique. The scattering multiplicity distribution versus the direction of scattering and dimensions of the scattering system is obtained for monodisperse systems of spherical particles of different size. The angular dependences of the elements of the light-scattering matrix (LSM) are calculated. It is shown that in a system of spherical particles, specific features of the LSM structure associated with multiple scattering have much in common with similar features of the LSM in systems of nonspherical particles under conditions of single scattering. The angular dependences of the degree of depolarization of the scattered light are studied.     

Self-focusing and multiple filamentation of laser light in disperse media

We present the results of a computer simulation of the initiation and formation of filaments under conditions of high-power laser pulse scattering on atmospheric aerosols. We demonstrate that the femtosecond filament is robust to the perturbations induced by a disperse medium and can transport a high-fluence energy for long distances. At sufficient pulse power, the intensity perturbations, caused by the interference of light scattered on particles, initiate the generation of filaments and result in multiple filamentation. The results were obtained using the stratified-medium approach of coherent light scattering on an ensemble of aerosol particles.     

Rotation of the polarization ellipse under multiple light scattering in disordered media

A study is performed of the multiple small-angle scattering of circularly polarized waves in random media with large-size transparent inhomogeneities that are less dense than the surrounding medium. In these conditions, a new effect is observed—rotation of the polarization ellipse of the multiply scattered light.     

高散射媒质中的光程可分割动态光散射研究

为研究散射光强度随光子在散射媒质中散射光程的变化,基于单散射理论与扩散波光谱理论,采用了低相干动态光散射装置对不同粒径大小的聚苯乙烯悬浮液进行研究。将测量得到的背散射光光场强度谱的线宽与相应的理论计算结果相比较发现,在短光程区域,考虑容器壁附近拖曳效应的影响后,对于不同粒径的颗粒,光程为约5倍粒子平均自由程的区域可看成为单散射区域;对于光程大于225 m的区域可看成为扩散光波区域。实验结果表明低相干动态光散射法可实现高散射媒质从单散射区域到低次散射再到扩散区域的全光程的可分割的光场强度谱测量。     

Diffuse light scattering in dispersed media

Russian Physics Journal -     

Selection of optical radiation in scattering in partially ordered disperse media

Results of theoretical studies of the interaction between optical radiation and partially ordered disperse media are reported. In terms of the amplitude-phase screen model consideration is given to the concentration effects of whitening and darkening in random close-packed systems of optically soft particles. The concentration dependence of transmission of close-packed systems of coarse particles is described with the use of a small-angle solution of the stochastic finite-difference transfer equation. The effects of coherent reirradiation occurring in close-packed monolayers of highly refracting particles are analyzed using a quasicrystalline approximation of the theory of multiple wave scattering and the radial particle distribution function obtained from a solution of the Percus-Yevick equation. This approach extended to multilayer systems is used to describe formation of forbidden photon zones in transmission spectra of one- and three-dimensional disperse systems with a high degree of ordering. Results of quantitative calculations are shown to agree well with experimental data. The possibility of using established regularities for optimization of spectral characteristics of selective elements based on spatially ordered disperse systems with different structural organization is discussed. Institute of Molecular and Atomic Physics of the National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 5, pp. 721–733, September–October, 1998.     

IMAGING: Focusing light in scattering media

Combining ultrasonic modulation and optical phase conjugation allows light to be tightly focused in a scattering medium, providing benefits for studies of photophysical, photochemical and photobiological processes.     

Multiple scattering of light in superdiffusive media

Light transport in superdiffusive media of finite size is studied theoretically. The intensity Green's function for a slab geometry is found by discretizing the fractional diffusion equation and employing the eigenfunction expansion method. Truncated step length distributions and complex boundary conditions are considered. The profile of a coherent backscattering cone is calculated in the superdiffusion approximation.     

Attenuation of collimated light beams in scattering media

The effect of singly side-scattered light on the attenuation of collimated light beams in turbid media is investigated. Correction formulas for the exponential attenuation law are derived for the case where the viewing angles of the receiving system and radiation source are equal. The ranges in which the corrections are important in the propagation of light beams in haze, fog, and rain are indicated. It is shown that the range of solid angles in which the angular dependence of the scattered light can be neglected is defined by the inequality 1.1, where p is the Mie parameter; the solid angle determines the divergence of the light beam, which is equal in this case to the viewing angle of the receiving system.     

Propagation and scattering of light in stratified media

The propagation and scattering of light in stratified media are considered. Based on the Maxwell equations, the present approaches to the solution of these problems are formulated in a unified way. The particular features of the wave propagation in stratified media are discussed. Scalar and vector fields are considered. Media with small-and large-scale regular inhomogeneities are examined. The construction of the Green’s function of the wave equation in a spatially homogeneous medium is discussed. Stratified isotropic and anisotropic media are analyzed. The scattering of light in a stratified medium is studied with emphasis on the Kirchhoff method, as this makes it possible to obtain calculation formulas in a form convenient for comparing the theory with the experiment. The propagation of waves in photonic crystals and the formation of forbidden zones in such objects are briefly considered.     

Monte-Carlo simulation of light scattering in fractal porous media

Monte-Carlo simulation of light propagation in a porous medium with a mass fractal morphology was carried out. It was shown that the simulation results can be used to analyze experimental data on light scattering and to study the porous medium structure. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 2, pp. 193–196, March–April, 2008.     

Anomalous polarization effects during light scattering in random media

The dependence of the intensity of light backscattered from a layer of a randomly inhomogeneous medium on the polarization of incident light and the size of scatterers has been investigated. The results of numerical simulation have demonstrated that the direction of rotation of the plane of polarization is different in systems with small- and large-scale inhomogeneities. It is shown for the first time that the dependence of the sign of the residual circular polarization on the size of scatterers can be observed in systems described by the Henyey-Greenstein phase function used in simulating biological tissues. A similar anomalous polarization effect, which consists in changing the direction of rotation of the plane of polarization of backscattered light with an increase in the scattering angle, is revealed in studying the coherent backscattering component. These polarization effects are observed in light backscattering from optically active media.     

Cross photoelastic and thermorefractive light scattering in continuous media

Two additional types of light scattering in continuous media are considered. One is the cross photoelastic scattering from density fluctuations caused by thermodynamic temperature fluctuations and the other is the cross thermorefractive scattering from temperature fluctuations caused by density fluctuations, which manifest themselves in propagation of elastic sound waves. Expressions for the light scattering coefficients for these two types of scattering are obtained. The integral intensities of scattered light are shown to be comparable with the well-known integral intensities of light scattering by fluctuations of density (pressure) and temperature (entropy) for some substances.     

Focusing coherent light through opaque strongly scattering media

We report focusing of coherent light through opaque scattering materials by control of the incident wavefront. The multiply scattered light forms a focus with a brightness that is up to a factor of 1000 higher than the brightness of the normal diffuse transmission.     

一种基于多重散射的光学Hash函数

本文提出了一种基于光与多重散射介质相互作用的光学Hash函数构造方法.该方法创新性地利用多重散射介质对相干调制光的天然随机散射作用,实现了对调制光的"混淆"和"扩散",从而满足了Hash函数的核心功能要求:高安全强度的单向编码/加密.所设计的光电混合系统能有效地模拟Hash函数中的"压缩函数",结合具有特征提取功能的S...     

Simulation of multiple light scattering in a bounded nematic

The multiple-scattering problem is formulated for a single-constant model of a nematic liquid crystal with allowance for the dependence on the orienting external magnetic field. Based on the Bethe-Salpeter equation, an original Monte Carlo procedure in a birefringent medium is developed with allowance for the long-range action of dielectric permittivity fluctuations and backward and forward scatterings are calculated. The dependence of multiple scattering in a nematic on the distance between the incident and scattered rays is quantitatively studied for the first time and a nonmonotonic dependence on the external magnetic field is discovered. We numerically have established that the light-diffusion anisotropy noticeably weakens as compared to the extinction length anisotropy; this is shown to be caused by the weak anisotropy of the transport length.     

Coherent effects in multiple scattering of linearly polarized light

Comparing the stochastic Monte Carlo technique with the iteration procedure for solving the Bethe-Salpeter equation in the framework of numerical simulation, the time correlation function and the interference component of the coherent backscattering of a linearly polarized light wave in a multiply scattering medium are calculated. The results of the simulation agree well with theoretical results obtained by generalizing the Milne solution, as well as with experimental data.     

Codalike multiple scattering of elastic waves in dense granular media

We study the multiple scattering of short-wavelength ultrasound through the force networks in dry and wet glass bead packings under stress. Over long distance scales, the diffusion approximation is shown to describe adequately the transport of elastic waves dominated by shear waves. The recovered transport mean path reveals a short-range correlation of the force chains. Also we observe the drastic effect of wetting liquids on the energy dissipation in the granular medium. The relevance of these experimental findings for the seismological applications is discussed.