Temperature response in participating media with anisotropic scattering caused by pulsed lasers

It is not by isotropic scattering but by anisotropic scattering that radiant energy is redistributed in some materials containing real particles, fibers, or impurities. In some instances, great difference can be caused in transient thermal behavior between isotropic scattering and anisotropic scattering media. Ray tracing method combined with Hottel's zonal method is introduced to deduce thermal radiative source term for various optical boundary conditions induced by collimated incidence passing through translucent boundary. Temperature response caused by laser pulse at non-incident side of participating and anisotropic scattering media is examined. We investigate effects of scattering albedo, scattering phase function, initial temperature of media and thickness of media on temperature response. Results obtained for anisotropic scattering media are compared with those for isotropic scattering one and show that anisotropic scattering must be considered in the simulating measurement of thermophysical properties by the laser flash method for some materials with big scattering albedo which behave anisotropically, or big error will be introduced; forward scattering can increase excess temperature and backward scattering can decrease it at non-incident side of the considered sample irradiated by laser pulse.     

Unified Mie and fractal scattering by biological cells and subcellular structures

Angle-resolved light scattering spectroscopy of biological cells is investigated in the visible wavelength range. A unified Mie and fractal model is shown to provide an accurate global agreement with light scattering spectra from 1.1 degrees to 165 degrees scattering angles. It is found that light scattering in forward directions (<8 degrees ) is dominated by Mie scattering by the bare cell and nucleus, whereas light scattering at large angles (>20 degrees ) is determined by fractal scattering by subcellular structures. The findings are consistent with the results of experimental investigation of the contributions of different cellular components to light scattering by cells.     

Method for solving the problems of multiple scattering by several bodies in a homogeneous unbounded medium

A method is developed for solving problems of multiple scattering by an aggregate of bodies in a homogeneous unbounded medium. For this purpose, the problem on the multiple scattering produced by two bodies in the field of a plane wave is first considered under the assumption that the initial unperturbed scattering amplitudes of both scatterers are known. The solution is constructed by considering plane waves multiply rescattered by the scatterers. Integral equations are obtained that allow one to calculate the resulting scattering amplitude of each scatterer and the combined scattering amplitude of the system of two scatterers. It is shown that knowledge of the solution to this problem is sufficient to solve the problem on the scattering field of a system consisting of an arbitrary number of scatterers. Expressions for the scattering amplitude in the case of an arbitrary primary field are presented. The relationship between the integral equations describing the multiple scattering in a homogeneous space and the multiple scattering by a single scatterer located near an interface is demonstrated. Approximate expressions are given for calculating the scattering amplitude in the case of multiple scattering.     

共振光散射的时间量子理论

本文发展了Ｓｃｈｏｍｍｅｒｓ的时间观点，定义了时间，尤其是表征量子系统光散射的散射时间和共振散射时间。通过散射时间本征态的假定实现了散射时间的量子化，得到了量子化的共振散射时间。对原子的弹性光散射和Ｒａｍａｎ散射的成功应用推出了原子和原子的价电子逐级电离所形成的离子的所有原子能级的普适近似公式。     

Dynamische Theorie der elastischen Elektronenbeugung unter Verwendung komplexer Atomformfaktoren

The two-beam approximation of dynamic electron diffraction in crystals is deduced from successive scattering by two-dimensional gratings. The scattering-amplitude caused by the single grating (phase-grating) is determined by the atomic scattering factors of the single atoms. The use of real atomic scattering factors leads here to the same solutions as the twobeam theory, using the Schroedinger-equation. Anomalous absorptions effects are described in the usual theory by introducing a complex lattice potential into the Schroedinger-equation, taking into account inelastic scattering. A more exact calculation of only elastic scattering by a single atom results in complex atomic scattering factors. Using the complex atomic scattering factors one can describe the anomalous absorption, if recursion-formulae for successive scattering are applied. On the other hand, the transformation to differential equations leads to results, which are not in agreement with experiments. The influence of inelastic scattering for the anomalous absorption can be neglected compared with the complex atomic scattering factors.     

外部加环肋有限长圆柱壳体声散射

为了深入理解双层加肋圆柱壳体的声散射机理,专门研究了两层壳体之间环肋的声散射。仅考虑模型的刚性散射,采用Kirchhoff近似推导了单个环肋的反向散射声场的解析解,并推广到等间距的环肋散射,结合圆柱壳刚性散射得到外部加周期性环肋的圆柱壳体的散射声场近似解。同时,利用图形声学方法(GRACO)对模型的目标强度进行数值计算。理论与实验的结果表明,刚性散射在反向散射声场中起主要作用,周期性环肋引起的Bragg散射对散射声场有重要贡献,同时遮挡效应在实际情况下有较大作用。      

Theoretical analysis and measurements on near specular scattering

In scattering measurement it is important and also difficult to separate instrument scattering from the scattering of a sample. Particularly at angles near the specular reflection, it is believed that the small angle limit for scattering measurement is determined not only by detector proximity to the specular beam, but also by the sample scattering. When the scattering angles are smaller than a certain limit, the total scattering combining the instrument scattering and the sample scattering is lower than the instrument scattering. This prevents us from discriminating the instrument scattering and the sample scattering at angles smaller than this limit. In this paper a data processing method is reported that enables us to distinguish the instrument scattering at angles smaller than this limit. Based on this method, we can measure the scattering at angles restricted only by the performance of the instrument.     

基于Mie光散射理论的尾流气泡前向散射光特性研究

实验中利用CMOS图像传感器代替传统的光电探测器接受前向散射光,由几何光学和图像处理分析得出不同散射角的散射光与采集图像中的光环相对应.通过计算各个光环的所有像素值的总和就可以得到前向散射光光强的相对值,进而可以得出前向散射光光强变化规律.根据米氏（Mie）光散射理论可以计算出气泡各个方向的散射光光强,通过比较实验结果和Mie理论计算结果可以看出,采用CMOS图像传感器探测和图像处理技术可以准确地得出散射光强度的变化规律.     

Spectral power determinations of compressibility and density variations in model media and calf liver using ultrasound

A model of scattering is used to relate average differential scattering cross section and power spectra of scattering medium variations. The model expresses the average differential scattering cross section as a sum of the power spectrum of medium compressibility variations, the power spectrum of density variations weighted by the square of the cosine of the scattering angle, and the cross-power spectrum of compressibility and density variations weighted by twice the cosine of the scattering angle. Known values of the average differential scattering cross section at a minimum of three different scattering angles and temporal frequencies corresponding to the same spatial frequency are used to calculate each of the three power spectra. Since noise and statistical fluctuations are present in actual measurements of average differential scattering cross section, the calculations of power spectra are obtained from an overdetermined set of equations to which a solution is found by using a singular value decomposition. Data derived from a model for scattering from a cloud of correlated particles are employed to show the influence of additive noise. Calculations are also made from measurements of scattering from three suspensions of particles that have a different average radius in each suspension but are similarly modeled by scattering from a cloud. Additionally, the calculations are applied to measurements of average differential scattering cross section of calf liver. The results show that determination of the power spectra of scattering medium variations can be made under practical conditions, and also imply that density variations contribute significantly to scattering by calf liver.     

Brewster's scattering angle in scattered waves from slightly rough metal surfaces

Brewster's scattering angle in electromagnetic wave scattering from slightly random metal surfaces is investigated by means of the stochastic functional approach. While there are dips due to Brewster's scattering angle in scattering profiles from dielectric surfaces, Brewster's scattering angle does not exist in scattering from metal surfaces. However, the dips can exist in scattering from rough metal surfaces with the optically denser medium to convert evanescent wave into radiative wave.     

Multiple small-angle scattering—A review

Small-angle scattering (SAS) is a powerful experimental technique in condensed matter physics for studying structural features of inhomogeneities of colloidal dimensions. So far the technique has been largely exploited to study thin samples for which the single scattering approximation, for the radiation-matrix interaction, holds good. The single scattering approximation is invalid when the thickness of the sample exceeds the scattering mean free path. This situation calls for a guideline to analyse the scattering data having significant contribution from multiple scattering. Since multiple scattering broadens the scattering profile, the beam broadening nature of multiple scattering can also be exploited, by making the sample suitably thick, to study large size inhomogeneities which are otherwise inaccessible to a small-angle scattering set up because of its resolution constraints. The present article presents a review and extension of the theoretical basis for analysing multiple scattering data from the point of view of a recent formalism on multiple small-angle scattering. The formalism is valid for both monodisperse and polydisperse scattering media characterized by the presence of large size inhomogeneities in the matrix. It is shown that multiple scattering from a polydisperse sample can be described by a system of coupled integrodifferential equation. However, multiple scattering from a monodisperse sample can be described by a Fokker-Planck type of equation. These equations have been analysed with an emphasis laid on the nature of the structural information pertaining to the inhomogeneities which is extractable from the multiple scattering profile. When the linear dimension of inhomogeneities becomes comparable to the scattering mean free path of the radiation in the sample, the statistical nature of the medium becomes pronounced. The statistical nature of the medium modulates the scattering profile. The modulation effect could be broadening or narrowing of the profile depending upon the nature of the inhomogeneities and their population distribution. The limiting regimes of validity and the implications of various approximations, frequently used to analyse the scattering data, have been indicated.     

Measurements of bubbles in sea water by nonstationary sound scattering

Methods for the characterization of bubbles in sea water by acoustic scattering are analyzed. Nonstationary linear and nonlinear sound scattering methods are proposed. The transient linear and nonlinear sound scattering allows the scattering by resonant gas bubbles to be distinguished from the scattering by other microinhomogeneities. The application of parametric arrays in oceanic experiments, together with the broadband frequency analysis of the backscattering coefficient, allows information about bubbles in sea water to be obtained. Experimental results on sound scattering and gas bubble distribution functions are presented for different conditions in the ocean.     

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.     

Wave diffraction by rough interfaces in an arbitrary plane-layered medium

Abstract

The problem of electromagnetic wave scattering by a slightly rough interface in an arbitrarily layered medium is solved by a small-perturbation method. The bistatic amplitude of scattering as well as the scattering cross sections for statistically rough surfaces are calculated for linear polarized waves. Along with scattering into up-going waves in a homogeneous medium and scattering cross sections in down-going waves into a layered medium, scattering amplitudes from a rough interface in the arbitrarily layered medium are obtained.     

Determination of some scattering factors for the case of mixed scattering of charge carriers by lattice vibrations and ionized impurities

The principal results concerning the scattering of charge carriers by acoustical and optical lattice vibrations together with the scattering of carriers by ionized impurities are summarized. The methods of determining some scattering factors in the case of mixed scattering are described.     

Theoretical investigation on the pumping effect of stimulated Brillouin scattering on stimulated Raman scattering in water

The pumping effect of stimulated Brillouin scattering on stimulated Raman scattering is investigated theoretically through the coupled wave equations of stimulated Brillouin scattering and stimulated Raman scattering. The numerical simulations are in agreement with the experimental results. They indicate that the backward stimulated Raman scattering is excited and amplified collectively by both pump laser and stimulated Brillouin scattering.     

Effects of Breaking Waves on Composite Backscattering from Ship-Ocean Scene

The existence of the sea surface is bound to affect the electromagnetic(EM) scattering from marine targets. When dealing with the composite scattering from targets over a sea surface by applying high-frequency EM theories,the total scattering field can be decomposed into three parts in low sea states, namely, the direct scattering from the sea surface, the direct scattering from targets and the coupling scattering between the sea surface and targets. With regard to high sea states, breaking waves make the direct scattering from the sea surface and the coupling scattering more complicated. To solve this issue, a scattering model is proposed to analyze the composite scattering from a ship over a rough sea surface under high sea states. To consider the effect of breaking waves,a three dimensional geometric model is adopted together with Ufimtsev's theory of edge waves for the scattering from a breaker. In addition, the coupling scattering between targets and breaking waves is taken into account by considering all possible scattering paths. The simulated results indicate that the influence of breaking waves on the scattering field from the sea surface and on the coupling field is non-negligible, and the numerical results also show the effectiveness of the proposed scattering model.     

Scattering of slow neutrons by bound nuclei

TheT-operator for scattering of slow neutrons by a system of bound nuclei is calculated up to quadratic terms in the scattering length. Binding effects as well as effects of multiple scattering have to be included in order to avoid inconsistencies. For the discussion of binding effects one can adopt methods developed by Dietze and Nowak [1] for treating scattering by an elastically bound nucleus. In particular the case of coherent elastic scattering is discussed: we show how the corrections can be expressed in terms of correlation functions and that binding effects are most important for scattering by light nuclei.     

Electric field modulated Raman scattering in CdS

We have observed electric field modulated Raman scattering by A₁ LO phonons in CdS. The field induced scattering is observed with a geometry in which Raman scattering by A₁ LO phonons is normally allowed. The interference of the field induced and allowed terms in the transition susceptibility leads to a modulated Raman scattering intensity proportional to the applied field. This is contrasted with data previously reported on field induced Raman scattering by E₁ LO phonons in a configuration in which the Raman scattering is normally forbidden and in which there is no interference between linear wavevector dependent and field induced terms in the transition susceptibility. Electric field effects on Raman scattering by TO phonons and by 2 LO phonons is also discussed.     

气溶胶激光散射信号的特征分析

本文应用Mie散射理论对微球体粒子光散射的性质进行了理论分析与数值计算,得出了散射光分布与微球体尺度参数、复折射率之间的关系。结果表明:不同尺度参数的粒子的散射光强的分布相差极大,随着尺度参数的增加散射光强越来越集中于前向;复折射率的变化对散射光强影响不大。并且在边界层大陆乡村型霾的气溶胶模型下对大气气溶胶的体角散射系数进行了分析与数值计算,得出:气溶胶粒子的散射光强主要分布在前向,并且随着散射角的增加有规律的减小。由此提出了利用气溶胶粒子体散射系数的性质,通过测量散射点前向散射光强和延迟时间来实现激光束的近轴定位的方法。