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．     

基于Mie散射理论的C@H_2O复合粒子散射特性研究

大气中大量存在的复合粒子会对激光传输效率产生很大影响。由于空气中水蒸气含量较高,以C作为凝结核外层包裹以水的核壳结构微粒对光传输具有明显的散射效应。本文应用Mie散射理论对C@H_2O核壳结构微粒的散射特性进行了理论分析和数值计算,首先给出了不同入射波长、核粒子半径以及水膜厚度条件下散射强度分布变化曲线;其次给出了不同入射波长、核粒子半径以及水膜厚度条件下偏振变化情况;最后讨论了光学截面与粒子半径之间的关系。结果表明各参数对前向散射强度影响较大,入射波长越大散射强度越弱,C核半径增大粒子的前向散射增强,水膜厚度增大粒子的前向散射增强,而后向散射无明显影响;入射波长较大时,粒子在多个角度出现线偏振光,入射波长增大、碳核半径变大、水膜厚度增大,偏振度峰值都会增多;随着入射波长的增大,散射截面最大峰值位置向着半径增大的方向移动,并伴随一定的振荡现象,散射和消光截面在碳核半径为0.1μm左右达到最大值。     

复合金属粒子散射强度分布的计算与分析

根据Mie散射理论,对金银复合粒子的散射强度和偏振度进行了数值计算与理论分析,得到了散射强度、偏振度与散射角、入射波长及核壳大小之间的关系。结果表明,入射波长越大,前向散射越强,易出现线偏振光;而核壳半径越大,背向散射越弱,易出现退偏振现象。该结论对金银复合材料光学特性方面的开发和应用提供理论参考。     

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。     

水中气泡上的体散射函数的模拟与计算

基于几何光学的基本原理,推导出一种可以计算水中大尺度气泡上光散射角度与强度的关系式。推导中避免引入衰减因子G,较Davis模型更为简单。该模型可应用于光在水中单个气泡上散射的数值计算。最后,模拟计算了平行光束入射水中气泡的体散射函数曲线,发现水中气泡的前向散射远大于后向散射;当气泡半径在远大于光波波长的前提下变化时,气泡上散射光强分布规律与气泡半径无关;而介质相对折射率的增大会削弱前向散射而增强后向散射光强。     

基于Mie散射理论的MgF_2颗粒散射特性研究

本文应用Mie散射理论对微球体颗粒光散射的性质进行了理论分析与数值计算,得到了吸收截面与波长,散射强度与散射角以及散射强度与参数x的关系。结果表明,入射波长在300~4800 nm,粒子的吸收截面都为零;当λ>4800 nm,吸收截面随着粒子半径的增大而增大。     

基于几何光学的泡沫滴/水滴光散射计算模型

为深入研究舰船泡沫 水两用幕的光衰减机理,建立了基于几何光学的泡沫滴/水滴光散射强度分布计算模型。利用该模型对液相折射率m2为1.20至1.50范围内、气泡相对半径r为0至0.99的球状泡沫滴和水滴、散射角为1至10内的光散射强度进行了数值计算。结果表明,泡沫滴/水滴对可见光具有强烈的散射作用,内的散射强度与入射光强度之比T随的增大而提高,最高可增加2个数量级;随m2的增大而降低,m2从1.30至1.40变化,T降幅最高达11.6%;随r的增加先下降而后提高,达到最低0和最高80.8%;T最低值对应的最优气泡半径ro随m2的降低和的增大而提高,从0.1最多增至0.4。该结论可为舰船泡沫 水两用幕技术的发展提供必要的理论基础。     

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.     

基于MATLAB与LabVIEW的 Mie散射参数分析系统

针对激光散射法测量0.1 m~10 m微小球形颗粒过程中,Mie散射理论各参数的分析、计算、最优化选取比较复杂和繁琐,通过收敛速度、折射率和尺度参数测量范围、叠加次数的比较,采用球形粒子Mie散射参量的MATLAB改进算法, 结合MATLAB较强的计算能力和LabVIEW良好的图形化界面,进行LabVIEW和MATLAB混合编程。设计了Mie散射理论参数分析系统,系统实现散射系数的计算,并分别对散射系数与颗粒直径关系曲线、散射强度分布曲线、入射光波长与散射光强关系曲线、颗粒直径与散射光强关系曲线、入射光偏振角与散射光强关系曲线进行分析。通过实验结果和结论对比验证系统可行,且散射系数、消光系数和散射光强的计算结果可精确到小数点后17位,从而达到减少大量计算和编程工作的目的。     

沙尘气溶胶粒子群的散射和偏振特性

根据Mie散射理论,以对数正态分布函数描述沙尘气溶胶粒子群的粒径尺度分布,计算了沙尘气溶胶粒子群在0.2～40μm波段间对太阳短波辐射和地球大气长波辐射的单次散射反照率、散射相矩阵函数,揭示了不同相对湿度时,沙尘粒子群对入射辐射的散射和偏振的特征。结果表明,沙尘粒子群的单次散射反照率随着入射波长的增加有较大起伏,不同相对湿度条件下,变化趋势基本一致;在可见光、近红外波段单次散射反照率随湿度增加而变大,湿度95%时非常接近于1;大于10μm的热红外波段单次散射反照率随相对湿度增加而减小,具有较强的吸收辐射能力。散射辐射强度受湿度影响较小,随散射角的增加呈现先减小后增大的趋势,且增大的趋势随着波长的增加而减弱;不同波段上,线偏振和圆偏振随散射角和相对湿度变化存在差异;在前向和后向仅对入射辐射为圆偏振辐射产生圆偏振散射;散射光的偏振特性及其湿度差异主要表现在后向散射区,多以拱形形式体现。拱顶峰值散射角位置存在差异,且峰值散射角随相对湿度的降低向后向漂移。     

非球形椭球粒子参数变化对光偏振特性的影响

针对自然界中多数沙尘、烟煤粒子的非球形问题, 在球形粒子偏振特性的基础上, 进一步研究非球形椭球粒子的折射率、有效半径、粒子形状等参数变化对光偏振特性的影响, 采用基于T矩阵的非球形粒子仿真方法, 模拟非偏振光经椭球粒子传输后光的偏振特性及其与球形粒子间的差异, 并以实际沙尘、海洋、烟煤三种气溶胶粒子为例说明结果的正确性. 结果表明: 当折射率实部越小, 虚部越大时, 球形粒子与非球形粒子的偏振差异越不明显; 当粒子有效半径增加时, 球形粒子偏振度的变化比非球形粒子更为明显, 且最大值分别出现在散射角为150°和120°的位置; 当粒子形状不同时, 不同形状椭球及球形粒子的差异在散射角小于60° 时并不明显, 且当椭球粒子纵横比互为倒数时, 两种粒子的偏振特性近似相同. 通过以上分析可知, 在光传输过程中, 椭球粒子多数情况下无法被近似为球形粒子进行计算.     

Effect of electric field on light scattering by aqueous colloids of diamond and graphite

We present the results of our experimental investigation of light scattering by polydisperse colloids of diamond and graphite. The scattering is studied at a random orientation of particles and in an external radiofrequency electric field, which orients particles along the strength. The average dimensions of particles in both colloids are close to each other and comparable with the wavelength of the incident light. The shape of particles and the optical and electrooptical properties of diamond and graphite colloids are significantly different. We analyze the polarization components of scattered light energy when the light incident on the colloids is linearly polarized. We show that the quadrupole light scattering by isotropic diamond particles has the main effect on angular dependences of depolarization of scattered light. For light scattering by anisotropic graphite particles, the depolarization of scattered light is mainly determined by a particular feature of the dipole scattering of particles. It is shown that, in both colloids, the orientational order of particles considerably reduces the depolarization of light scattered by particles. We show that relative changes in the intensity and depolarization of scattered light, which depend on the scattering angle and polarization direction of light, as well as on the parameters of particles, can be used as a measure of electrooptical effects observed in colloids.     

手性薄膜表面二次谐波圆二向色性的研究

给出了螺旋型手性分子薄膜表面反射方向的圆二向色性的谐波强度表示式,分析了谐波的强度与手性分子的取向,分子的螺距和半径等结构参数的关系,给出了数值模拟结果,发现在入射光强一定的情况下,谐波强度在螺距和半径的取值范围内分别存在着最大值,以及螺距与半径之间满足的关系式随分子取向角的变化而不同。     

Study of the sensitivity of size-averaged scattering matrix elements of nonspherical particles to changes in shape, porosity and refractive index

Studies of the physical parameters that influence the single scattering properties of a size distribution of small particles in random orientation are fundamental in understanding the origin of the observed dependence of the scattering matrix elements on the scattering angle. We present results of extensive calculations of the single scattering matrices of small nonspherical particles performed by a computational model based on the Discrete-Dipole Approximation. We have particularly studied the sensitivity of the size-averaged scattering properties at visible wavelengths of nonspherical, randomly oriented absorbing particles considering changes in shape, porosity and refractive index. These studies have importance regarding the inversion of physical properties of small particles as measured in the laboratory and the dust properties in various astrophysical and atmospherical environments. We have found that size distributions of randomly oriented irregular particles of different shape, including large aspect ratio particles, show similar scattering matrix elements as a function of the scattering angle, in contrast with the pattern found for regularly shaped particles of varying axis ratios, for which the scattering matrix elements as a function of the scattering angle show much larger differences among them. Regarding porosity, we have found a very different pattern in the scattering matrix elements for an ensemble of compact and porous particles. In particular, the linear polarization for incident unpolarized light produced by compact and absorbing particles of large size parameter tend to mimic the pattern found for large absorbing spheres. For porous particles, however, the linear polarization for incident unpolarized light tends to decrease as the size of the particle grows, with the maximum being displaced towards smaller and smaller scattering angles.     

The effect of a layer of varying density on spatial correlation of sea-bottom backscattering signal

The research is about the effect of a layer of varying density of sea-bottom sediments on spatial correlation of sea-bottom backscattering.The relationship between scattering cross section and spatial correlation is that backscattering cross section decreases quickly and the spatial correlation becomes stronger as the incident angle increases.Therefore,the densitydepth profile is introduced into sea-bottom high-frequency backscattering echo model,which is used to simulate sea-bottom backscattering and calculate the function of spatial correlation.The influence of the density gradient on spatial correlation of sea-bottom backscattering is investigated by analyzing the relations between vertical gradient of density and the scattering cross section.As can be seen from the simulation results,the impact of the density gradient on the spatial correlation is found more significant.While the density gradient increases,the scattering cross-section and the radius of the spatial correlation broaden,the spatial correlation becomes stronger.At the same time,the scattering cross-section decreases more quickly as the incident angle increases.     

1.053μm激光打靶产生的二次谐波

测量了基频激光打靶条件下不同角度的二次谐波光谱,得到了谐波光强随发射角度的变化关系以及能量转换效率随激光强度变化的曲线.实验现象可能与参量衰变级联造成的Langmuir湍流有关 关键词： 二次谐波发射 激光等离子体 共振吸收 离子声衰变不稳定性     

具有复折射率微粒的Mie散射光学特性研究

利用Mie散射理论,对大气溶胶中烟灰颗粒的Mie散射、消光和吸收截面以及散射场进行了计算,同时给出了Mie散射的散射场强度随散射角的变化以及内部场强随粒子半径的变化。     

Electron-spin-dependent 4He+ ion scattering on Bi surfaces

We studied low-energy (～ 1.55 keV) electron-spin-polarized ⁴He⁺ ion scattering on a Bi(111) ultrathin film epitaxially grown on a Si(111) substrate. We observed that the scattered ion intensity differed between the incident He⁺ ions with up and down spins even though Bi is a non-magnetic element. To analyze the origin of this spin-dependent ion scattering (the spin asymmetry), we investigated the detailed relationship between the spin asymmetry and the incident angle, the azimuthal angle, the scattering angle, and the incident energy. All the data indicate that the spin asymmetry originates from the scattering cross section owing to the non-central force in the He⁺–Bi atom binary collision. The non-central force is most likely attributed to the spin–orbit coupling that acts transiently on the He⁺ 1s electron spin in the binary collision.     

海底密度梯度对底回波信号空间相关特性的影响研究

研究了海底表层沉积物的垂直密度梯度对底回波空间相关特性强度的影响。底回波散射截面与空间相关特性间的关系为:随入射角的增大,回波散射截面下降得越快,底回波空间相关特性越强。因此,将密度-深度模型引入海底高频回波模型进行回波仿真,计算回波的空间相关函数,通过分析密度梯度对底回波散射截面大小的影响,考察其对底回波空间相关特性强度的影响。从仿真分析结果可以看出,海底表层沉积物密度梯度对空间相关特性的影响较为显著,随着密度梯度的增大,回波散射截面变大且随入射角的增大下降趋势变快,空间相关半径变长,空间相关特性变强。      

超衍射极限相干反斯托克斯拉曼散射显微成像技术中空心光束的形成

空心光束的质量是超衍射极限相干反斯托克斯拉曼散射显微成像技术中决定成像质量的一个至关重要的因素. 本文基于菲涅耳衍射理论,分析了螺旋相位片法产生空心光束的物理机理,并且模拟了不同的入射条件对产生的空心光束的影响. 模拟结果表明:波长与相位片中心波长匹配且光强呈圆对称分布的高斯光垂直入射到相位片上,当高斯光束中心与相位片中心完全对准时,可获得较理想的空心光束;入射光光强分布的圆对称性以及入射光中心与相位片中心的对准程度都会影响产生的空心光束的强度分布;同时,高斯光束小角度倾斜入射时,空心光的强度分布仍呈圆对称,却在观察面发生一定的位移;此外,入射光中心波长偏离相位片中心波长不大时,对产生的空心光束的强度分布几乎没有影响. 上述分析结果对用于超衍射相干反斯托克斯拉曼散射显微成像技术中理想空心光束的获取具有重要的指导意义. 关键词： 空心光束 超衍射极限 相干反斯托克斯拉曼散射 螺旋相位片