硫酸钡微球掺杂聚碳酸酯材料的光散射特性模拟分析

基于多重米氏(Mie)散射理论和蒙特卡罗(Monte Carlo)方法, 对掺杂硫酸钡(BaSO4)微球体的散射型聚碳酸酯(PC)光散射材料进行了数值模拟。研究了BaSO4粒子粒径、浓度及样品厚度等光学参量对PC材料透光率、扩散率、照度角分布等光学性能的影响, 并进行了设计评估。通过比较不同材料参数下光散射材料光学性能的差别, 总结出了获得良好光学性能所需的合适材料参数。模拟结果为高性能光散射材料的实验制备提供了理论参考。     

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     

煤粉颗粒的后向散射特性研究

利用Mie理论研究了单分散煤粉颗粒对光波的散射特性,给出了单次散射相函数、消光效率因子、散射效率因子、不对称因子和单次散射反照率随粒子尺寸的变化关系;当煤粉浓度较大时,需要考虑颗粒系的多次散射特性,根据辐射传输理论,利用蒙特卡洛方法研究了煤粉颗粒的多次散射特性,并给出了其后向散射随观测角度、粒子半径和光学厚度的变化关系,计算结果对煤粉颗粒反演具有一定指导意义。     

浑浊介质中激光侧向散射实验与仿真研究

通过对M ie散射相位函数的累积概率密度插值获得散射角,建立了激光在浑浊介质中传输的蒙特卡罗仿真模型.借助模型研究了激光在均匀单分散聚苯乙烯浑浊介质中的多次散射现象,探究了不同光学厚度和散射相位函数的浑浊介质对激光多次散射的影响.在研究中控制5μm和10μm两种粒径聚苯乙烯颗粒的浓度,改变浑浊介质的光学厚度分别为2、5...     

水雾包裹沙尘颗粒核壳结构的散射特性研究

基于离散偶极子近似法(DDA),对水雾包裹沙尘颗粒的核壳结构光学特性进行研究,计算了长短轴比例为2∶1的椭球形粒子的核壳结构内、外层厚度及散射角度变化对光散射特性的影响。结果表明,内核大小不变,外层厚度由1.2 μm增大到4.8 μm,核壳双层颗粒散射系数和消光系数由3.4和3.43降低到2.543和2.545,且散射相对强度也明显增大。外层厚度不变,内核厚度由0.6 μm增加到2.4 μm,散射系数和消光系数由3.105和3.111变化为2.76和2.9;可见外层厚度对核壳双层颗粒散射特性的影响更大,这是由于散射光主要与外层物质相互作用引起的。散射相对强度随波长的增加而降低,随核壳结构尺度的增加呈现递增的规律。该结果对大气中气溶胶和水雾共同作用时的散射特性,激光在其中的传输特性等研究有参考价值。     

椭球模型下通过雾场的多重光散射谱

由于雾滴的非球形、多重散射特性以及几何光学效应,光通过实际雾场的散射问题成为一个研究难点. 建立了近于实际的椭球雾滴模型,考虑光的衍射、透射及反射特性后,利用辐射传播方程得到了在不同的雾滴大小分布 及不同的雾滴形状分布下通过雾场的多重散射光强公式.在两种特例下与已有的结果较为相符,说明了方法的可靠性. 计算表明:与随机取向的非球形颗粒场的散射谱呈圆形特征不同,通过椭球形雾滴场的散射谱呈椭圆特征, 不同方位角的散射光强角分布有所差异,雾滴的形状因子越接近于1,差异越小;与单散射不同, 散射谱中的条纹随光学厚度增大逐步消失;对于不同大小分布及不同形状分布的雾滴场, 在不同方位角及不同观察角的散射光强随光学厚度τ的增加总是先增大再减小,光强的极大值位置在τ = 1.0---3.0 范围内.计算同时还表明,由于多数情况下实际雾场的雾滴大小偏差较大, 因而通过雾场的散射谱将呈现以中央亮斑为中心向四周弥散的图样.     

金纳米球壳光学吸收的Mie理论分析

基于Mie散射理论研究了金壳厚度变化、内核尺寸变化及内核介质变化下金纳米球壳的吸收光谱.研究发现,随着金壳厚度的增加,颗粒光学吸收增加到最大值后逐渐降低;随着内核尺寸逐渐增加,金壳颗粒的光学吸收最大值逐渐减小.此外,还发现随着内核介电常数的增大,颗粒的光学吸收逐渐减弱,当内核为空心时,吸收最强.利用等离激元杂化理论及自由电子和振荡电子变化的竞争机制对上述现象进行了理论分析. 关键词： 金纳米球壳 等离激元共振 吸收光谱     

基于气溶胶光学厚度反演大气气溶胶尺度分布

介绍一种基于气溶胶光学厚度测量反演大气气溶胶尺度分布的新方法. 从实测气溶胶光学厚度出发，依据严格的Mie散射理论，将气溶胶尺度分布函数离散，采用线性回归法确定气溶胶尺度分布. 还通过对多重共线性的讨论，确定了用于反演气溶胶尺度分布的光谱波段.     

激光气象雷达多次后向散射信号特性分析

利用小角近似方法，分别给出了单次和多次后向散射激光雷达方程.通过引入的多次散射评价参量，分析了接收视场角和光学厚度等因素对多次后向散射信号的影响.理论研究表明:多次后向散射主要与接收视场角和光学厚度密切相关，当接收视场角比发射视场角大10倍，光学厚度超过3时, 多次后向散射信号逐渐增大并占主要优势，当接收视场角比发射视场角大100倍时，光学厚度超过1时，多次后向散射信号开始明显增强.     

散射模型和有效粒子半径对卷云光学厚度反演的影响

为研究不同散射模型和有效粒子半径对卷云光学厚度反演的影响,计算了不同光学厚度下,一般种类混合模型(GHM)、实心柱状模型(SC)和聚合物实心柱状模型(ASC)取不同有效粒子半径时的反射率。理论分析了不同散射模型及其不同有效粒子半径对卷云光学厚度反演结果的影响。使用基于倍加累加法的矢量辐射传输模型RT3计算3种模型卷云光学厚度查找表,基于POLDER数据,采用查找表法进行卷云光学厚度反演实验,实验结果与理论分析一致。结果可知:采用不同散射模型反演得到的卷云光学厚度存在较大差异,相比GHM和SC模型,ASC模型卷云光学厚度反演结果更接近POLDER产品;有效粒子半径越大,光学厚度反演结果越大,GHM和SC的增幅较大,而ASC增幅很小。因此,在不具备有效粒子半径反演能力时,建议采用ASC模型反演卷云光学厚度,以减小有效粒子半径变化对反演结果的影响。上述研究对我国GF-5卫星的卷云光学厚度反演的散射模型选取及反演结果评价具有参考价值。     

The influence of anisotropic scattering on the radiative intensity in a gray, plane-parallel medium calculated by the DRESOR method

Even though there have been many ways to treat complex anisotropic scattering problems, in most of the cases only the radiation flux or its dimensionless data were provided, and radiative intensity with high directional resolution could merely be seen. In this paper, a comprehensive formulation for the DRESOR method was proposed to deal with the anisotropic scattering, emitting, absorbing, plane-parallel media with different boundary conditions. The method was validated by the data from literature and the integral formulation of RTE. The DRESOR value plays an important role in the DRESOR method, and how it is determined by the anisotropic scattering was demonstrated by some typical results. The intensities with high directional resolution at any point can be given by the present method. It was found that the scattering phase function has little effect on the intensity for thin optical thickness, for example, 0.1. And there is the largest boundary intensity for the medium with the largest forward scattering capability, and the smallest one with the largest backward scattering capability. An attractive phenomenon was observed that the scattering of the medium makes the intensity at boundary can not reach the blackbody emission capability with the same temperature, even if the optical thickness tends to very large. It was also revealed that the scattering of the medium does not mean it cannot alter the magnitude of the energy; actually, stronger scattering causes the energy to have more chance to be absorbed by the medium, and indirectly changes the energy magnitude in the medium. Finally, it is easy to deduce all the associated quantities such as the radiation flux, the incident radiation and the heat source from the intensity, just as done in literature.     

沙尘天气下激光信号的传输特性

以小角度近似为条件,利用逐级递归的方法推导了激光信号在沙尘天气下的辐射传输方程,得到了多次散射下的光强分布函数,以及波长和不对称因子对光强的影响。同时,通过比较不同散射相位函数及沙尘粒子的散射特性,采用了修正的TTHG(Two Term Henyey-Greenstein)散射相位函数,更加全面地反映了沙粒散射后光强的变化规律。研究结果表明,随着光学厚度的增加,散射光强呈现出先增大后减小的趋势,且多次散射的比重相比于单次散射而言逐渐增大。当散射次数超过3次以上时,接收光强的变化可以忽略不计。相对于Mie理论下的结果而言,采用小角度近似理论,从辐射传输的角度分析沙粒的散射特性误差更小,实现了准确描述沙尘天气下激光信号传输特性的目的。     

取向比对椭球气溶胶粒子散射特性的影响

利用T矩阵和离散坐标法研究了取向比对椭球粒子散射特性的影响, 计算了小尺度范围内椭球粒子的散射特征参量, 包括消光效率因子、不对称因子、单次散射反照率、散射相矩阵及双向反射函数(BRDF). 结果表明, 椭球粒子的散射特性与取向比密切相关, 粒子取向比会影响散射参量的振荡频率和振幅, 与球形粒子散射参量的相对差异也呈周期振荡趋势. 研究还发现, 某些特殊粒子尺寸的散射参量与粒子取向比基本无关. 在多次散射条件下, 分析不同取向比粒子群的BRDF随反射角和光学厚度的变化特性. 结果显示: 不同取向比粒子群的BRDF随反射角的变化趋势基本一致, 球形粒子群比非球形粒子群的BRDF曲线波动振幅更大; 球形-非球形粒子的BRDF相对差异随光学厚度和取向比的增大而减小, 随入射角的增大而增大.     

Multiple scattering and the structure of a finite thickness of scatterer

The transport equation is solved for a scattering medium of finite thickness. A method is given for approximate derivation of the size distribution for the particles on the basis of multiple scattering. An appendix deals with the particular case of particles that are small in relation to the wavelength.     

How to measure the optical thickness of scattering particles from the phase delay of scattered waves: application to turbid samples

We present a method based on the optical theorem that yields absolute, calibration free estimates of the optical thickness of scattering particles. The thickness is determined from the phase delay of the zero angle scattered wave. It uses a heterodyne scattering scheme operating in the Raman-Nath approximation. The phase is determined by the position of Talbot-like modulations in the two dimensional power spectrum S(qx, qy) of the transmitted beam intensity distribution. The method is quite insensitive to multiple scattering. It is successfully tested to provide quantitative verification of the optical theorem. Exploratory tests on soft matter samples are reported to suggest its wide applicability to turbid samples.     

Probability density function of the intensity scattered by Rayleigh-particle aggregates. Evolution with optical properties

We study the probability density function of the statistical fluctuations of the intensity scattered by an aggregate freely floating in space and constituted by Rayleigh particles under the dipole approximation. Its evolution as a function of the optical properties of the particles (polarizability) and their separation distance is analyzed. Aggregate geometries with two and three particles will be considered. The influence of the multiple scattering effect on the statistics of the scattered intensity is especially studied.     

Similarity effects in multiple scattering of coherent radiation: Phenomenology and experiments

Based on phenomenological concepts of statistics of effective optical paths for multiple scattering of coherent radiation, an analysis is carried out of similarity effects observed for the dependences of statistical moments of the scattered field on the relaxation parameters with a dimension of reciprocal length. Within the framework of the diffusion approximation, expressions are obtained that describe the autocorrelation function of fluctuations of the scattered-field amplitude, the degree of polarization, and the normalized intensity of scattered light for media with a finite absorption length in the case of forward scattering of coherent radiation in a plane layer of an isotropic scattering medium. The results of the analysis show the similarity of the dependences of these quantities on the corresponding spatial scales. Experiments with model scattering media (aqueous suspensions of polystyrene spherical particles) supported the existence of similarity effects in multiple scattering. An experimental study was made of the relation between the characteristic depolarization length and the transport length for multiple scattering of coherent radiation in a plane layer. The effective value of the radiation diffusion coefficient providing the best agreement between the experimental and the calculated values of parameters of the scattered field is shown to be independent of the absorption coefficient of a medium.