降雨粒子的无线紫外光散射特性

紫外光与降雨粒子相互作用发生散射,散射光特性改变能够反映降雨粒子的相关物理特性（如粒子尺寸参数、浓度、形态）,因此研究粒子的物理参数对散射光特性的影响对有效提高光谱法定量探测降水的精度有很大意义。由于雨滴在非球形降水粒子中具有代表性,以群雨滴粒子为例,采用T矩阵理论,利用紫外光直视和非直视单次散射模型,分析了入射光波长、群雨滴粒子形态、降雨强度、粒径大小与散射光强之间的关系。并用蒙特卡洛方法仿真分析了非球形群雨滴粒子在不同降雨强度和粒径下散射角与散射光强之间的关系,以及降雨环境中的风切变对紫外光散射特性的影响。通过理论及仿真分析,得到了不同群雨滴粒子形态下的路径损耗,不同降雨强度、风切变率和粒径下的散射光强分布。仿真结果表明：在紫外光直视与非直视通信方式下,降雨环境中的通信质量比晴天条件下的通信质量差,即路径损耗增大。当粒径分布已知时,随着降雨强度的增大,衰减系数增大,路径损耗增加,且直视通信方式的路径损耗比非直视降低7 dB左右。随着降雨强度、风切变率和粒子粒径的增大,散射光强曲线整体呈下降趋势,其中,降雨强度的变化对散射光强分布影响程度最大。相同通信距离时,不同降雨强度下的紫外光散射光强分布均随着散射角的增大而减小,当散射角继续增大到90°时,有效散射体体积逐渐减小,接收到的光子能量减小,暴雨中的散射光强衰减程度最大。相同降雨强度下考虑风切变时,相比较无风时的路径损耗增大5 dB左右。除此之外,还研究了椭球形和切比雪夫形粒子对紫外光散射光强的影响,结果表明当粒子粒径分布相同时,椭球形粒子的散射光强衰减较广义切比雪夫形粒子大。根据散射粒子的散射光强分布以及路径损耗能够区分雨滴粒子是否由相同粒径及形态组成,为粒子测量提供理论基础。分析降水中群雨滴粒子的光散射特性,为提高光谱法评估降水衰减的数值模拟方面提供理论依据,为光学技术在探测识别降水现象等气象领域的广泛应用提供了设计参考。     

The influence of the characteristics of a collection of particles on the scattered spectral density and its applications

The far-zone scattered spectral density of a light wave on the scattering from a collection of particles is investigated, and the relationship between the character of the collection and the distribution of the scattered spectral density is discussed. It is shown that both the number of particles and their locations in the collection play roles in the distribution of the far-zone scattered spectral density. This phenomenon may provide a potential method to reconstruct the structure character of a collection of particles from measurements of the far-zone scattered spectral density.     

光在水中吸附膜层气泡上的散射特性

光在水中大尺度气泡上散射特性的研究多是基于Davis模型.该模型没有考虑到吸附膜层对光在气泡上散射的影响,而海水中的大多数气泡都有膜层附着,这些膜层会影响到气泡的光散射特性.本文从几何光学的角度出发,建立了吸附膜层气泡的体积散射函数简化公式.在此理论基础上,模拟计算了尺度远大于入射光波长的大气泡散射光强分布曲线,得出光照射下气泡上散射光强的远场特性,讨论了影响气泡散射光强分布的主要因素.并与无膜气泡光散射分布曲线比较,讨论了油膜膜厚、折射率等参量对气泡的光散射特性影响.得出结论:吸附膜层气泡的光强分布曲线与无膜气泡相似,但吸附膜层会削弱前向散射光,增强后向散射光.     

关于折射率对散射光场分布影响的研究

根据Mie散射理论,采用理论计算和实验相结合的手法,研究了光散射现象以及散射介质的折射率对散射光场分布的影响.通过对空气中不同折射率的散射介质形成的散射光场光强的实验比较,论证了散射介质折射率的实部变化对散射光强的影响不大,其主要影响是通过对相位的变化来实现的,也即散射介质折射率的虚部变化对光强的影响很大,在实际应用中不可忽略.这一结论对以散射光场的分布为基础的各种研究具有一定的指导意义.     

Polarization visualization of scattering media with CW laser radiation

The method of polarization visualization of a multiply scattering medium containing macroinhomogeneities based on analysis of polarization spatial distribution of a scattered linearly polarized light is discussed. The treatment is based on statistical properties of the effective optical path distribution of scattered field components. The influence of media scattering properties and the geometry of the experiment on the inhomogeneity image contrast obtained with use of polarization degree and of normalized scattered intensity of radiation as visualization parameters are discussed, as well as spatial resolution achieved in these both cases. Using the results of theoretical analysis and of the experimental model, the relationship between the shapes of spatial distributions of polarization degree and the intensity of the scattered light is considered as a function of the position of the visualized object (an absorbing half-plane immersed in a plane layer of the scattering medium). The opportunities for enhancing the quality of the images formed in this way are also discussed.     

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。     

Scattering of scalar light wave from a Gaussianben Schell model medium

The scattering of scalar light wave from a random medium with a correlation function of Gaussian–Schell model distribution is studied. It is shown that the properties of the scattered field, i.e., the spectral density and the spectral degree of coherence of the scattered field, are closely related to the properties of the scattering medium, including the scaled effective radius and the scaled correlation length of the correlation function.     

Signal statistics of laser light scattering

After a brief survey of number fluctuations, a topic of current interest in light scattering research, the theory is developed for a particular case of this type. A laser beam of Gaussian cross section illuminates a volume in which there is a fluctuating number of identical particles. For incoherent detection the scattered intensities are additive. The interest centers on the statistics of the total scattered intensity. Starting from the moment generating function, the distribution function of scattered intensity is computed using two different methods. In an experiment designed to test the computed distributions, agreement between theory and measurement is found if the mean particle number within the scattering volume exceeds 3. The experimental procedure is described and some difficulties are explained which so far did not permit application of the theory for particle numbers much below 3.     

纺织纤维光散射特性的模拟与实验

纺织纤维的光散射特性在纺织材料微观结构、光学性质以及无损检测中至关重要。利用纺织纤维各向异性的结构特点改进现有的角谱展开法,得到纺织纤维对倾斜入射平面波的散射以及表征其光散射特性的Mueller矩阵。采用蒙特卡罗算法模拟了平行棉纤维束对倾斜入射偏振光的多次散射,并对其计算结果进行了实验验证。结果表明理论计算和实验测量的散射光斑在形状特征、光强分布上均一致,从而验证了蒙特卡洛方法模拟纺织纤维光散射的正确性。结果同时也表明蒙特卡罗方法在纺织材料光传播特性的理论研究中具有重要的指导意义。     

Nonlinear scattering in BaTiO3 induced by two orthogonally polarized waves

A new nonlinear scattering effect is described which is induced by the simultaneous action of ordinary and extraordinary waves impigning on a BaTiO₃ crystal in the plane perpendicular to the c-axis. The scattered light of ordinary polarization propagates along a circular cone and the light intensity on this cone is nonuniform. We present a model that describes the experimental observations rather well, including phase matching conditions and the unusual intensity distribution of the scattered light.     

Gas-surface scattering distributions according to the hard-spheroid model

Gas-surface scattering distributions are calculated on the basis of the hard-spheroid model. This new model is related to the hard-cube model but incorporates surface structure by letting the surface atoms have hard spherical caps. Surface structure is found to reduce the maximum scattered intensity and to broaden the scattering distribution. The decrease in the maximum scattered intensity is most pronounced for a light gas. Broadening is asymmetric relative to the direction of maximum scattered intensity in that backscattering towards the surface is favored. Adding surface structure to the hard-cube model improves significantly the agreement between model predictions and experimental results.     

Scattered Light Photometer for On-Line monitoring of size distribution parameters and particle number concentration

A scattered light photometer which monitors the particle number concentration of aerosols is described. The photometer measures the scattered light from illuminated submicron particle clouds with known material properties at certain scattering angles. Intensity ratios in combination with the degree of polarization are used to determine the mean particle diameter and the geometric standard deviation of an assumed log-normal particle size distribution. The determination of the particle size distribution is based on an algorithm which compares the measured and calculated (Mie theory) relative intensity quantities described. Furthermore, the particle number concentration is monitored from a single absolute intensity measurement at one scattering angle. In order to obtain quantitative results a spherical particle shape is required.     

Reflection and scattering from laser-irradiated solid targets at a wavelength of 0.44 μm

Studies of the reflectivity and spectral behaviour of the light scattered from plane solid targets irradiated with the third harmonic of the iodine laser (λ = 0.44 μm) in the intensity range 10¹² to 10¹⁵ W/cm² are reported. The complex spectra of the scattered light observed with normally and obliquely incident laser light provide evidence of stimulated scattering processes. The results are compared with current theories on stimulated Brillouin scattering.     

3D surface topography from the specular lobe of scattered light

Scattered light from a surface contains a huge amount of information including surface slope, roughness, pattern, texture, etc. In this paper, the relationship between the intensity distribution of scattered light from a surface and the 3D surface topography will be investigated. From the geometrical point of view the intensity distribution of scattered light from a surface may be modelled with three components, the specular spike, specular lobe and diffuse lobe. In the situation when light is scattered from a relatively smooth surface whose roughness is much larger than the wavelength of the incident light, the scattered light intensity distribution will consist of only a diffuse lobe and a specular lobe, which are well described by a combination of the Lambertian and Torrance–Sparrow geometrical models. Based on the light scattering phenomenon, in this paper a scanning method capable of measuring the 3D surface topography with 500 mm scanning width, high scanning speed, and micron resolution is presented. The 3D topography measurement is implemented by using a linear photodiode array to measure scattered light intensity distribution at different angles against the surface normal. Then the specular lobe of the scattered light will be extracted at each scanning point to calculate the surface normal distribution. Sequentially, the 3D surface topography is obtained by using gradient integration techniques.     

Scattering of light in an inhomogeneous fluctuating plasma

Scattering of light in an inhomogeneous fluctuating plasma is treated whose mean density distribution is given by a solution of the Korteweg-de Vries equation. The amplitude and phase correlation functions are computed for given mean density and spectral function of the density fluctuations.The non-linear effect of the mean inhomogeneous density distribution on the scattered light leads to beatings in the spectral functions of the amplitude and phase correlations. It is shown that the covariance function for the log-amplitude (which is to first order proportional to the intensity of the scattered light) can be approximated in a large L-region by a power law whose exponent is smaller than in the homogeneous case.     

Fluctuations of the intersubband splitting energy and the potential well shape of two-dimensional electrons in the quantum Hall effect regime

Recombination radiation and inelastic light scattering spectra of 2D electrons are studied simultaneously in structures with a single GaAs quantum well in the quantum Hall effect regime. It is found that the intensity of intersubband inelastic light scattering (the SDE mode) at the filling factor ν = 2 exhibits fluctuations in phase with fluctuations of the photoluminescence intensity of 2D electrons of the ground subband. It is shown that, simultaneously with fluctuations of the scattered light and recombination radiation intensities, the spectral positions of these lines change stepwise by 0.3–0.5 meV. The jumps found in the spectral positions of lines are observed only in narrow intervals of magnetic fields corresponding to the quantum Hall effect and are presumably associated with zero-point fluctuations (Casimir-Lifshits force).     

Angular intensity distribution of scattered light in systems of closely spaced particles

The results of experimental and computational investigations of the dependence of the angular intensity distribution of scattered light on the concentration of scatterers are discussed. It is shown that a high density of small and large scatterers in a three-dimensional system results in a deformation of the scattering indicatrix. The changes in the angular distribution of intensity of the scattered light at large concentrations are explained by the appearance of fields of multiply scattered waves at significantly lower optical thicknesses than for independent scatterers.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 99–103, March, 1976.     

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     

Second-order orientation effects in light scattering by polarized atoms

A compact expression is derived for the part of the cross section for light scattering by axisymmetrically polarized atomic systems proportional to the third-rank state multipole. The effect of the second-order orientation determined by this state multipole on the polarization and angular distribution of the scattered light is studied. The polarization of the incident light can be arbitrary and is specified by the Stokes parameters. A number of orientation effects in the scattering process are shown to be induced precisely by the second-order orientation. In particular, when nonpolarized light is scattered by an oriented atom, the scattering intensity in the perpendicular direction depends on the second-order orientation alone. The second-order orientation also preserves circular dichroism in the linear polarization of the forward-and back-scattered light.     

Characteristics of the crystalline and luminescence properties of a-plane GaN films grown on γ-LiAlO2 （302） substrates

A method of clarifying bioaerosol particles is proposed based on T-matrix. Size and shape characterizations are simultaneously acquired for individual bioaerosol particles by analyzing the spatial distribution of scattered light. The particle size can be determined according to the scattering intensity,while shape information can be obtained through asymmetry factor(AF) . The azimuthal distribution of the scattered light for spherical particles is symmetrical,whereas it is asymmetrical for non-spherical ones,and the asymmetry becomes intense with increasing asphericity. The calculated results denote that the 5 –10 scattering angle is an effective range to classify the bioaerosol particles that we are concerned of. The method is very useful in real-time environmental monitoring of particle sizes and shapes.