Propagation in one-dimensionally stratified time-independent scattering media

We calculate the probability density distributions of the power reflection coefficient, and of the various fluxes of the components of an erstwhile plane wave that propagates in a one-dimensionally stratified slab of a time-independent scattering medium. We determine the second- and fourth-order statistics of the power-fluxes, discuss the relevance of this problem to the localization phenomenon, examine the distribution of the emerging power-flux and the limitations on the assumption that it possesses a lognormal distribution, and finally discuss and rationalize the differences between the above and the corresponding characteristics of the radiation propagating in a time-dependent variant of this problem.     

Low-order light scattering in multiple scattering disperse media

Light scattering has been investigated in systems in which both single and higher order scattering occur. The Monte Carlo simulation technique for studying light scattering in randomly inhomogeneous, strongly scattering disperse media was employed. The reliability of the data obtained has been checked by comparing the results of the computer simulation with analytical calculations for the intensity of doubly scattered light. The first several scattering orders have been analyzed for different geometries of the optical experiment. It has been shown, in particular, that, depending on the detector aperture, the contribution of multiple scattering can vary by almost an order of magnitude.

     

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 -     

Three-dimensional problem of inverse scattering in stratified randomly inhomogeneous media

Conclusions The problem with a stratified medium is of immediate interest in acoustics (in particular, marine acoustics), just as it is in radiophysics [8], but its importance consists primarily of the fact that it permits closely fitting a solution of a problem with three-dimensional inhomogeneities.One can isolate the characteristic facts associated with IS in stratified media. In the first place, spatial-temporal scales arise which restrict the region of applicability of the approximate methods. Outside this region the approximate methods do not work due to accumulating effects, and, secondly, fluctuations of the IS intensity increase there. It would be very timely to investigate, in this respect, media with three-dimensional inhomogeneities, which is necessary for problems of probing randomly inhomogeneous media by the IS method.Pacific Ocean Oceanological Institute, Far East Scientific Center, Academy of Sciences of the USSR. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 25, No. 9, pp. 1032–1040, September, 1982.     

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.     

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.     

超短THz脉冲在随机散射介质中的传播

用Monte-Carlo方法模拟了超短THz脉冲在随机散射介质中的传播.根据Mie理论计算出随机散射介质的散射系数和各向异性因子，研究了随机散射颗粒及介质厚度的大小对透射脉冲的影响.结果表明在Mie散射范围内，在相同的浓度下，颗粒尺寸越小，散射介质越厚，THz散射越严重，对透射脉冲的影响越大.散射同时降低了THz脉冲在随机散射介质中的成像分辨率. 关键词： 超短THz脉冲 随机散射介质 Mie理论 Monte-Carlo方法     

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.     

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.     

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.     

Propagation of polarized light in media with large discrete inhomogeneities

An approximate analytical method of solution of the vector radiative-transfer equation for an optically isotropic medium with large-scale inhomogeneities is proposed. The method is based on an assumption about the distinct anisotropy of single scattering. The method was used to calculate the polarization characteristics of light multiply scattered in a monodisperse medium with large spherical particles.     

Propagation of circularly polarized light in media with large-scale inhomogeneities

Small-angle multiple scattering of circularly polarized waves in disordered systems composed of large (larger than the light wavelength) spherical particles is discussed. The equation for Stokes’s fourth parameter V — the difference between the intensities of the left-and right-hand polarized light — is shown to have the form similar to that of the scalar transport equation for intensity I, the only difference being the presence of an additional “non-small-angle” term responsible for depolarization. In the case of small-angle scattering, depolarizing collisions are relatively rare and, in contrast to the scalar case, the problem contains an additional spatial scale, namely the depolarization depth. The polarization degree and helicity of the scattered light are calculated for the case of purely elastic scattering and in the presence of absorption in the medium. For strong absorption, depolarization is shown to follow the transition to the asymptotic regime of wave propagation. The features appearing in strong (non-Born) single scattering are also discussed. Zh. éksp. Teor. Fiz. 115, 769–790 (March 1999)     

Propagation of light through a forbidden zone in chiral media

The particular features of the propagation of light in uniaxial chiral liquid crystals with a large pitch of the spiral are considered. There exist forbidden zones in these systems for fairly large angles of incidence of an extraordinary ray. On the one hand, this results in an efficient reflection of the wave from the zone boundary, and, on the other hand, this causes the wave to decay inside the zone. A case of narrow forbidden zones is studied, and it is shown that optical effects that arise upon propagation of rays near turning points are equivalent to the tunnel and over-barrier reflection effects. The angular dependences of the intensities of rays that were refracted in a forbidden zone and transmitted through it are calculated. The percolation effect is experimentally studied in a mixture of a nematic liquid crystal with a chiral addition. The intensity of a transmitted extraordinary ray is studied as a function of the angle of incidence, which determines the width of the forbidden zone. Both the over-barrier reflection and the percolation effects are observed. The calculation results are shown to agree with experiment.     

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.