微纳粒子光学散射分析

为实现利用光学方式对微纳尺度粒子性质的研究,探讨了亚微米线及亚微米球对光电磁波的散射效应.微纳米尺度粒子的光学散射,散射粒子尺寸与入射光波长尺寸可满足米氏(Mie)散射条件.利用Matlab数值模拟的方式,将分析结果以模拟图的形式清晰地展现出来.满足尺寸条件的层状粒子以及任意多个散射粒子存在时对电磁波的散射都可采用Mie散射分析方法,并且针对多粒子散射,分析了散射体位于不同位置时对散射造成的影响.通过分析光学散射光场相关的微分散射截面及近场散射电磁场分布,可得出散射光场随散射角度的变化趋势,以及散射光场受各类因素的影响,包括入射光偏振态、散射粒子尺寸、散射粒子结构及粒子构成层数、散射粒子数量等的影响,也包括一些隐含因素对散射光场的影响,如散射粒子与周围介质的相对折射率.本文的科学意义体现在:与入射光波长尺寸可比的亚微米尺度的粒子,可用作传感器,对于其位移的探测可通过光学方式来实现,而由于粒子本身特性对散射光的影响具有一定的参考价值,从而使通过光学方式对机械位移的读出具有更高准确度.研究结果对于光学方式探测亚微米线机械振动具有指导意义.     

气溶胶凝聚粒子散射特性的数值计算

利用Cluster-cluster aggregation (CCA)模型,模拟了由相同数目球形原始微粒凝聚而成的四种随机取向气溶胶凝聚粒子．根据物质的电结构,将气溶胶凝聚粒子离散为一系列偶极子,结合离散偶极子近似方法,在获得每一个偶极子的电偶极矩之后,数值计算了气溶胶凝聚粒子散射强度的角分布,并分析了散射强度随入射光入射角度和气溶胶凝聚粒子尺寸参数变化的规律．结果显示：当散射角较小时,气溶胶凝聚粒子取向和入射光的入射角度对散射强度影响不大,当散射角增大时,散射强度则明显依赖于气溶胶凝聚粒子取向和入射光的入射角度;对于不同尺寸参数的气溶胶凝聚粒子,在同一角度入射情况下,随尺寸参数的增加,气溶胶凝聚粒子的散射主要集中于前向散射．     

Light scattering by slightly nonspherical particles on surfaces

We investigate the shape dependence of the scattering by dielectric and metallic particles on surfaces by considering particles whose free-space scattering properties are nearly identical. The scattering by metallic particles is strongly dependent on the shape of the particle in the region near where the particle touches the surface. The scattering by dielectric particles displays a weaker, but nonetheless significant, dependence on particle shape. These results have a significant effect on the use of light scattering to size and identify particles on surfaces.     

Scattering matrices and reflectance spectra of forsterite particles with different size distributions

We present measurements of the complete scattering matrix as a function of the scattering angle of three different samples of forsterite particles in random orientation at a wavelength of 632.8 nm. The three samples were prepared so that three different size distributions were obtained. The composition and reflection spectra of the three samples have been experimentally determined. The results indicate that the elements of the scattering matrix are affected in a different way by the size differences. Since light scattering by comets is probably caused by particles similar to our forsterite particles, the results potentially contain information on the size of the cometary particles.     

Optical equivalence of isotropic ensembles of ellipsoidal particles in the Rayleigh-Gans-Debye and anomalous diffraction approximations and its consequences

Light scattering by isotropic ensembles of ellipsoidal particles is considered in the Rayleigh-Gans-Debye approximation. It is proved that randomly oriented ellipsoidal particles are optically equivalent to polydisperse randomly oriented spheroidal particles and polydisperse spherical particles. Density functions of the shape and size distributions for equivalent ensembles of spheroidal and spherical particles are presented. In the anomalous diffraction approximation, equivalent ensembles of particles are shown to also have equal extinction, scattering, and absorption coefficients. Consequences of optical equivalence are considered. The results are illustrated by numerical calculations of the angular dependence of the scattering phase function using the T-matrix method and the Mie theory.     

微小颗粒的光散射数值模拟

简单介绍了以经典Mie理论为基础的光散射测量技术在颗粒直径和颗粒浓度测量中广泛的应用。分别以Mie理论和离散偶极子近似理论(DDA)为基础, 用数值计算方法分析了球型颗粒的光散射特性，给出了微小颗粒对平行入射光散射的强度函数和散射偏振度的数值计算方法。得到了强度函数和偏振度随相关物理参量变化的三维图，为微小颗粒散射研究提供了一种三维视图。计算结果表明：当尺度参量x＜4时，2种方法所得结果差异不大；随尺度参量增大，2种方法所得结果出现较大差异。与经典Mie理论相比，由于离散偶极子近似理论可以解决各种形状的颗粒散射问题，其应用前景更广泛。     

Monte Carlo simulation of light scattering from size distributed sub-micron spherical CdS particles in a volume element

Simulation of polarized light scattering by spherical particles having modal radius of 180 nm is presented in this paper. A Monte Carlo method which is based on the Stokes-Mueller formalism developed in ANSI Standard C-language is used for simulation. Single scattering is considered in our program with monodispersed sub-micron sized spherical CdS particles. We have considered only θ dependent scattering as described by Mie theory for spherical CdS particles. The experiments for studying light scattering properties of these particles were conducted in a designed and developed laser based light scattering studies setup. The simulation results were compared with experimental results and theoretical results obtained purely from Mie theory. The closeness of agreement or disagreement between these results is discussed in this paper.     

Polarization properties of light multiply scattered by non-spherical Rayleigh particles

Abstract

Multiple scattering of incoherent polarized light propagating through a random medium comprised of spheroidal Rayleigh particles is studied using Monte Carlo simulations. Two approaches are taken for the implementation of the simulation: the first uses individual realizations of particle orientation and the second, an accelerated method, averages over the particle orientation. These different methods produce results that are indistinguishable within statistical errors. The depolarization of light is examined in both transmission and backscatter for media comprised of spheroids of different polarizability ratios. In media containing spheroidal particles the depolarization is greater than that for spherical particles. Media containing prolate spheroids are more depolarizing than media comprising oblate particles of the same polarizability ratio. The extra depolarization due to asphericity is much less pronounced in the multiple scattering regime than for single scattering.     

Computer programs for light scattering by particles with inclusions

We present a comparison of computational results from light scattering by spherical particles with inclusions. The different simulation methods like the T-matrix method, multiple multipole method and the method of separation of variables are presented shortly. Exemplary numerical simulations involve scattering by particles with one or two spherical inclusions and scattering by particles with non-spherical inclusions.     

A review of the numerical investigation on the scattering of Gaussian beam by complex particles

The study of light scattering by various particles is an active and important subject of research with myriad practical applications. During the years the scattering of plane wave by various particles has been investigated extensively. In recent years, with the development of laser sources and the tremendous expansion of their application, there has been a growing interest in the study of light scattering by various particles illuminated by a focused Gaussian beam. Since the analytical methods are only suitable for the analysis of Gaussian beam scattering by some regular particles, for complex particles with arbitrary shape and structure, one has to resort to the numerical methods. In this article, we review the recent numerical investigation on the scattering of Gaussian beam by systems of complex particles, including arbitrarily shaped conducting particles, dielectric particles, composite particles with inclusions, as well as random discrete particles and fractal soot aggregates. The essential formulations of the proposed numerical methods are outlined and the numerical results for some complex particles are also presented. This review is expected to provide useful help for the study of the interaction between the laser beams and the complex particles.     

Inelastic surface scattering of non-penetrating particles

This paper is an extension of the authors' earlier work to include a treatment of onephonon inelastic scattering of particles which do not penetrate appreciably into the crystal. A full quantum-mechanical treatment of the lattice vibrations is used throughout, and the results are not restricted to small scattered intensities. Calculations are presented for the scattering of helium atoms by a simplified model of the crystal surface.     

相对论粒子的散射与低速粒子的散射

研究了相对论粒子间散射的规律,推导了相对论粒子间散射的洛伦兹因子公式.结果发现:如果两个粒子的静止质量相同,则粒子在高速时的碰撞规律和低速时的碰撞规律相同,即两个正碰粒子互换速度;如果两个粒子的静止质量不同,则粒子在高速时的碰撞规律和低速时的碰撞规律不同,高速正碰时重粒子将损失大部分能量,轻粒子的速度将接近光速,而不等于重粒子速度的2倍.     

椭圆截面非球形颗粒群的多重光散射

尽管非球形下一些特殊形状颗粒的单散射已被得到,球形多颗粒系（颗粒群）的多重散射也被研究,但至今仍未得到非球形颗粒群的多重散射.文中建立了一类椭圆截面非球形颗粒模型,求得其散射相位函数,借助于辐射传播方程,考虑形状及大小分布,得到了该类颗粒群的多重光散射.在两种特例情况下的结果能与已有的结果符合较好,说明了方法的可靠性.计算分析表明：非球形颗粒群的多重散射光强角分布要比球形颗粒平坦.椭圆截面颗粒的粒度或形状参数越大,多重散射光越集中于小的散射角;粒度分布或形状分布越宽,多重散射光强的角分布越平坦.随着光学厚 关键词： 多重光散射 颗粒 非球形 椭圆截面     

Characteristics of light scattering by smoke particles based on spheroid models

Light scattering models of smoke particles play an important role on the development of photoelectric smoke detection. Aiming at the influence of morphology of smoke particles, spheroid models are introduced to analyze the Stokes scattering matrix of smoke particles, which are lognormal size distributions. Under the condition of random orientations, the effects of refractive indexes and mean size of smoke particles are considered. The results show that after averaging of the orientation and size, the nonsphericity of smoke particles has a considerable effect on their light scattering. Additionally, the nonsphericity of gray smoke particles generated from smoldering fires is more important than soot from flaming fires for analyzing the light scattering.     

Geometrical optics approximation for light scattering by absorbing spherical particles

By means of geometrical optics, an approximation method is presented to compute the light scattering intensity of absorbing spherical particles illuminated by a plane wave. For absorbing particles, the effective refractive index and the effective refractive angle are related to the complex refractive index and incident angle. The formulas for calculation of the break of phases of reflection and refraction, which are different from the case of transparent particles, are exactly derived. Verification of the geometrical optics approximation (GOA) was performed by case studies and comparison of the present results with the Mie scattering. It is found that agreement between the GOA and the Mie theory is excellent in forward directions for weakly/moderately absorbing particles. Differently, for strongly absorbing particles, good agreement between the calculation methods is in the forward directions and large scattering angles. The agreement between the GOA and the Mie theory is better for larger particles.     

Light scattering in a layer of correlatively arranged optically soft particles

The light scattering by an ensemble of monodisperse spatially correlated optically soft spherical particles is studied in the interference approximation. A model of the interaction of particles is proposed in which the spatial correlation between particles is determined by a radius R _c exceeding the particle radius R _p. The radial distribution function is calculated in the Percus-Yevick approximation for hard spheres of the radius R _c. To simulate the radiation scattering from an individual particle of the radius R _p, the Mie equations are used. It is shown that, in a medium of correlated small nonabsorbing particles of the radius R _c > R _p, an abnormal wavelength dependence of the refractive index is possible at a low volume concentration of particles. The results obtained explain some experimentally observed features of the scattering in sodium borosilicate glasses with a small concentration of scattering centers.     

Optical properties of single mixed-phase aerosol particles

We examine the light scattering from wet aerosol particles whose core morphology is a random Gaussian sphere coated by different amounts of water. We compare the results with those calculated from a concentric-sphere particle and from a homogeneous-sphere particle whose refractive index is determined from the Bruggeman mixing rule. In nearly all cases the differences between those of the Gaussian-core and the concentric-sphere particles are small. The most significant differences are seen in calculations of the asymmetry parameters and the intensity and polarization phase functions. The results of the homogeneous-sphere particles vary significantly from those of the Gaussian-core particles, typically an order of magnitude greater than for the concentric-sphere particles. It is not uncommon to see differences of 10% in the efficiencies of large, homogeneous-sphere particles; whereas, in the intensity and polarization phase functions, differences of several tens of percent are not uncommon.     

Size quantification of sub-micron ZnSe semiconductor particles by laboratory scattering methods

A novel route has been developed to synthesize sub-micron Zinc Selenide semiconductor particles through elemental solvothermal process. Transparent polyvinyl alcohol matrix was chosen as host material for embedding these ZnSe particles in order to stop agglomeration of the particles as well as to facilitate optical characterization. Structural and morphological characterizations were carried out through high resolution electron microscopy and UV-vis spectroscopy. In order to understand light scattering phenomena of these particles, they were investigated by a custom made set up which uses a He-Ne laser of wavelength 632.8nm and an array of Silicon photodetectors. An attempt was made to experimentally determine the most significant element of the Mueller scattering matrix. Novel computational technique, involving single scattering for spherical particles using T-matrix theory was applied. The analysis of the experimental data was done by the method of comparison with theoretically generated data. The theoretical prediction was found to agree well qualitatively with the experimental data. Our results validitate that within an acceptable margin of error of the experimental results, the combination of experimental setup and associated computational method is an efficient and reliable in-situ system for size quantification of sub- micron semiconductor particles in the laboratory.     

Scattering of particles with internal degrees of freedom

The scattering of particles with a small number of internal degrees of freedom is considered. Billiard formalism is used to study the scattering of two such structurally complex particles. The main scattering characteristics are found. Various types of scattering modes are revealed. In particular, a mode is detected when the velocity of motion of such particles away from each other is higher than their approach velocity before the collision. The scattering of such particles is shown to occur after a finite number of collisions. A generalized Newton law is proposed for the collision of particles with a small number of degrees of freedom, and the form of the effective coefficient of restitution is found.     

光散射聚集速率测定中T矩阵方法的应用

聚集速率是评估胶体体系特性及稳定性的关键参数, 静态光散射和动态光散射则是测量聚集速率的两个重要方法. 然而, 用静态光散射和动态光散射测量聚集速率时, 需要知道有关单粒子和双粒子聚集体光散射特性的数据. 为此, 通常需要把动、静两种方法结合, 才能消去这个数据. 以前各种近似理论曾用来解决这个问题, 但因粒子尺寸和形状的限制, 结果并不理想. 而T矩阵方法可以不受粒子大小和形状的限制计算其光散射特性. 本工作用T矩阵方法直接计算静态光散射和动态光散射所必须的粒子散射特性, 并将该法得到的聚集速率与动静态光散射结合法得到的聚集速率进行了比较, 两者结果很接近. 本工作为简化静态光散射和动态光散射测量聚集速率, 扩展其应用范围开辟了新途径. 关键词： T矩阵')" href="#">T矩阵 光散射法 聚集速率