Light scattering by diamond and graphite nanodisperse systems with their particles orientationally ordered in an electric field

We have presented the results of our investigations of relative changes in the intensity of light scattered by nanodisperse systems that are exposed to the action of an electric field. To orient particles of the systems under study, sinusoidal fields of variable amplitude and frequency from the radiofrequency range were used. We have examined aqueous polydisperse suspensions of diamond and graphite particles. The average sizes of particles in the two suspensions are close to each other and are comparable with the wavelength of the incident light. Graphite particles had the shape of disks, while polycrystalline diamond particles did not have a clearly pronounced shape. Investigations have been conducted not only in the regime of a stationary orientational order of particles in the field, but also in the course of forced and free relaxation of this order. For the graphite nanodisperse system, the normalized-in-amplitude dependences of observed electrooptical effects on the field strength almost do not depend on the scattering angle, whereas, for the diamond nanodisperse system, they considerably vary as this angle changes. Upon relaxation of the orientational order of particles, the time dependences of these effects in both systems change with varying scattering angle. We have compared field and time dependences of scattering-induced effects with analogous dependences of field-induced dichroism.     

Electrooptical properties of aqueous suspensions of nickel hydrosilicate nanotubes

We present the results of our investigations of electrooptical effects that occur as a result of light scattering by an aqueous polydisperse system the disperse phase of which consists of nickel hydrosilicate nanotubes with a chrysotile structure. Multilayer nanotubes were synthesized by the hydrothermal method and had the composition Ni₃Si₂O₅. The dimensions of nanotubes were as follows: the length was 0.1–1 μm or more, the outer diameter was 10–15 nm, and the inner diameter was 3 nm. We have studied relative changes in the intensities of light transmitted and scattered by the suspension that were caused by the orientation of nanotubes in an external electric field. Experiments have been performed at different directions of the linear polarization of the incident and scattered light, different scattering angles, and different degrees of orientation of nanotubes along the field. These measurements allowed us to determine the magnitude of electrooptical effects, such as the conservative dichroism, the light scattering, and the influence of the orientation of nanotubes in the field on the intensity and degree of depolarization of light scattered by them. Curves of free relaxation of electrooptical effects and their field dependences allowed us to determine the distributions of nanotubes and their aggregates in the colloid over lengths and polarizability anisotropy values. The dependences of the degree of depolarization of the scattered radiation on the scattering angle and the relaxation dependences of electrooptical effects allowed us to characterize the aggregation stability of nanotubes in water.     

Specific features of the electrooptical effect and light scattering of water dispersed system of carbon nanotubes

Results of an electrooptical study of a water solution of carbon nanotubes obtained using the catalytic method are presented. It is shown that nanotubes, which anisotropically absorb light, are oriented in an electric field and create a pronounced linear electric dichroism due to light absorption, rather than light scattering (as in the case of colloids with particles with sizes close to that of nanotubes). An analysis of the relaxation dependences of the electric dichroism shows that nanotubes deform, which are oriented in the electric field; in this case, the deformation sublinearly depends on the field amplitude and reaches a limiting value. The relaxation dependence of the field-induced dichroism agrees with the autocorrelation function of depolarized light scattered perpendicular to the incident light flux.     

非球形粒子散射光的去偏振特性研究

目标对入射偏振光的散射特性反映了目标的属性信息。在Rayleigh散射理论的基础上，通过单层非球形粒子对入射偏振光的散射数学模型，应用矢量传输方程来计算非球形粒子散射的Mueller矩阵元，求解散射介质的偏振度，讨论在不同介质层厚度、粒子半径和探测角的条件下，非球形粒子散射光去偏振度的变化特性，给出了模拟仿真结果。该方法为研究目标的内部结构、厚度和粗糙度等特征以及目标的探测和识别提供了一种新的途径。     

基于色散偏振度的乳化油光谱检测系统研究

以色散偏振光谱检测技术为背景,着重研究了乳化油颗粒的偏振光学特性及米散射物理模型,构建了色散偏振度光谱检测系统。在400～700 nm波长范围内,分别对四种样品进行了301个波段的光谱反射率采集。结合贝塞尔函数和汉克尔函数,推导出了入射光波长与散射光偏振振幅矢量的关系,提取了一个新的特征参数：色散偏振度（DODP）。在暗室条件下,对乳化油样品ND18和ND75进行测量,利用色散偏振公式计算出了样品在各测量波长处的偏振度值,验证了基于DODP值检测乳化油的可行性。研究发现,虽然米散射的解是由单个球体的衍射推导而来,但是只要它们的直径和组成相同,且彼此之间的距离比波长大,也同样可以用于任意数量的球的衍射。在这种情况下,被不同球体散射的光之间没有相干的相位关系,总散射能量等于被一个球体散射的能量乘以它们的整数。当观测平面与入射波电矢量振动方向之间的夹角Φ=0或者Φ=π／2时,散射光分量E(s)_θ或者E(s)_Φ消失。由于ND18的粒径比ND75的粒径小,所以ND18的前向散射波瓣较大,前向散射与后向散射的比值较小。在相同光照条件下,ND75的多次散射现象要比ND18严重。根据路径相关矩阵的理论,多次散射容易引起退偏振,二次辐射波会在角域内扩散和分布。因此,被测乳化油表面产生的散射次数与入射光能的阻尼能力成正比。由于乳化油表面入射光的能量耗散存在差异,因此能量耗散率与入射波矢量方向的前向散射振幅的分量成正比,且乳化油的偏振散射程度不同于入射光的偏振散射程度。实验结果表明,DODP可以反映出乳化油由多次色散引起的去偏振能力。由于模拟光源是自然光,所以计算散射光的偏振参数非常方便,可以大大缩短数据处理时间,减小实验误差。DODP不仅能够识别海水中的乳化油,而且能够区分不同浓度的污染物,准确识别出乳化油的边缘扩散。     

Light scattering by coated Gaussian and aggregate particles

Light scattering by nonspherical and inhomogeneous small particles is studied by varying particle shapes, sizes, and compositions. We introduce an efficient tool for deforming particle shape and composition by adding a coating on an initial particle. This concave-hull transformation is applied to wavelength-scale Gaussian and aggregate particles, and the differences in the optical properties of the coated particles are compared to those of the uncoated geometries. The light-scattering computations are performed using the discrete-dipole approximation method which allows for internal inhomogeneity and irregular particle shapes. The results are analyzed concentrating on the intensity of the scattered light, the degree of linear polarization for unpolarized incident light, and the depolarization ratio. Polarization results yield the most significant differences and, moreover, coated aggregates are observed to produce net positive polarization, whereas it is negative for the Gaussian particles, also resembling the polarization of a spherical particle. As for the depolarization ratio, an intriguing double-lobe feature is observed near the backscattering direction for both particle geometries regardless of size, shape, and composition. The double-lobe maxima and minima generally coincide with those of the intensity and polarization.     

动态光散射实验中散射光偏振状态的研究

颗粒散射光的偏振状态对提高动态光散射实验系统空间相干性和测量结果正确性有着重要影响,因此研究散射光的偏振状态具有重要现实意义的。本文利用米散射理论分析了入射光与散射光偏振状态之间的关系,在此基础上揭示了在动态光散射中使用垂直偏振光作为入射光的理论依据,并在实验中验证了上述理论的正确性。     

Polarized light-scattering measurements of dielectric spheres upon a silicon surface

The polarization of light scattered into directions out of the plane of incidence by polystyrene latex spheres upon a silicon substrate was measured for p -polarized incident light. The experimental data show good agreement with theoretical predictions for three sizes of spheres. These results demonstrate that the polarization of light scattered by particles can be used to determine the size of particulate contaminants on silicon wafers. Theoretical models, based on successive degrees of approximation, indicate that the mean distance of a particle from the surface is the primary determinant of the scattered light polarization for small out-of-plane scattering angles.     

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。     

聚合物分散液晶光栅的衍射特性的研究

报道了一种由聚合物分散液晶膜与具有周期性条状电极结构板结合的新型光栅器件，借助于聚合物分散液晶膜的电光特性，这种栅对入射光的散射或衍射取决于对其施加的电压，即它是电场可调的，实验结果显示出当驱动电压超过器件器件阈值电压时，衍射光的强度和衍射斑的可见级次被电场调制，而且它能入射光的线性偏振态变为椭圆偏振态。     

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。     

The effect of multiple scattering in disperse media on polarization characteristics of scattered light

The effect of scattering of different multiplicity on polarization characteristics of scattered light is studied by the Monte Carlo computer simulation technique. The scattering multiplicity distribution versus the direction of scattering and dimensions of the scattering system is obtained for monodisperse systems of spherical particles of different size. The angular dependences of the elements of the light-scattering matrix (LSM) are calculated. It is shown that in a system of spherical particles, specific features of the LSM structure associated with multiple scattering have much in common with similar features of the LSM in systems of nonspherical particles under conditions of single scattering. The angular dependences of the degree of depolarization of the scattered light are studied.     

喇曼散射光极值法定金刚石结构薄层的晶向

本文提出了一个测定任意取向的金刚石结构薄层晶向的方法——喇曼散射光极值法。文中推导了任意取向的金刚石结构薄层的喇曼散射光强与薄层晶向及入射光偏振方向间的函数关系,并利用此函数的极值定出晶向。利用本文方法所得硅单晶定向结果与X射线衍射法定向结果进行了比较。 关键词：     

Polarization of light backscattered by small particles

We study scattering of light by wavelength-scale spherical, cubic, and spheroidal particles as well as clusters of spherical particles for equal-volume-sphere size parameters 4≤x≤10 and refractive indices 1.1≤m≤2.0. Such particles exhibit three specific features in the regime of backscattering: first, the intensity shows a backscattering peak; second, the degree of linear polarization for unpolarized incident light is negative; and, third, the depolarization ratio is double-lobed. We find that the overall characteristics of the scattering-matrix elements can be explained by an internal field composed of waves propagating in opposite directions near the particle perimeter and forming standing waves, as well as a wave propagating forward with the wavelength of the internal medium. When moving from the central axis of the particle toward its perimeter, the internal field changes from a forward-propagating wave with a wavelength dictated by the particle refractive index toward a standing wave with an apparent wavelength of the surrounding medium. The mapping of the internal field to the scattered far field is like an interference dial where rotation of the dial by a quarter of a wavelength on the particle perimeter results in a change from a destructive to constructive interference feature in the angular patterns (or vice versa). The dial is a manifestation of a well-known rule of thumb: the number of maxima or minima in the scattering-matrix elements is given by the size parameter. We explain the backscattering peak as deriving from the backward-propagating internal wave near the particle perimeter. Negative polarization follows from the spatial asymmetry of the internal fields: inside the particle, the fields are amplified near the central plane perpendicular to the polarization state of incident light, resulting in more pronounced interference effects for the perpendicular polarization than for the parallel polarization. The double-lobe feature in the depolarization results from the same internal-field structure with leading cross-polarized fields located slightly different from the copolarized fields. We discuss practical implications of these findings for the retrieval of particle sizes, shapes, and refractive indices from observations and laboratory experiments.     

Imaging and multiple scattering through media containing optically active particles

This paper examines the behaviour of polarized light scattered by a medium containing small chiral spheroidal particles. We show that for single scattering the observed phenomena of optical activity may be interpreted in terms of an averaged Mueller matrix and describe how the degree of polarization is affected by such a medium. The polarization properties of multiply scattered light by chiral particles are considered through the use of Monte Carlo simulations. It is shown that the effects of chirality under multiple scattering can be interpreted as an order-preserving influence in a disordered system and that this influence can, in principle, be exploited for the purposes of imaging.     

聚合物分散液晶(PDLC)光栅的制备及其光衍射特性

聚合物分散液晶（ＰＤＬＣ）光栅的制备及其光衍射特性任洪文黄锡珉王宗凯马凯（中国科学院长春物理研究所北方液晶研究开发中心长春１３００２１）ＦａｂｒｉｃａｔｉｏｎｏｆＰＤＬＣＧｒａｔｉｎｇａｎｄＩｔｓＯｐｔｉｃａｌＤｉｆｒａｃｔｉｖｅＰｒｏｐｅｒｔｉｅｓ...     

颗粒溶液颗粒尺寸及浓度的差分偏振弹性散射光谱在线分析方法

偏振弹性散射光谱技术的基本原理为在偏振光入射条件下,根据出射光的偏振特性不同可以筛选出浅表层组织的单次散射光信息和深层组织的漫散射光信息。该研究的创新点在于将这种方法应用于颗粒溶液检测,目的是在颗粒溶液原始状态下实现对颗粒尺寸及浓度的同时检测。设计了一个共轴笼式光学系统,测量了聚苯乙烯微球颗粒溶液某一角度的背向散射信号,通过控制入射端和收集端偏振片的偏振方向获得了颗粒溶液的偏振平行光谱与偏振垂直光谱,两者之差即偏振差分光谱对应颗粒的单次散射信息,将该单次散射信息与Mie散射数据库进行比对获得颗粒的尺寸,然后在颗粒尺寸作为已知的条件下进一步分析偏振垂直光谱,将该垂直光谱对应的颗粒溶液的漫散射信息代入光漫散射下的近似表达式拟合得到颗粒的浓度信息。将实验结果与样品提供值进行了比对,并进一步分析了在获取颗粒数浓度时,颗粒直径的方差分布对结果的影响,最终验证了该实验方法的可行性。该方法的潜在应用包括对标准颗粒制造厂商的产品在线检测以及对牛奶制品中脂肪和蛋白质的浓度检测研究。     

切比雪夫雾霾粒子的紫外光散射偏振特性研究

雾霾天气已严重影响人们的日常生活,通过检测雾霾粒子的紫外光散射偏振特性可以有效分析雾霾成因。矿物粒子、灰尘粒子等雾霾颗粒均有小规模表面粗糙度的形态学特征,因此可用切比雪夫粒子作为模型分析。“日盲”紫外光与切比雪夫雾霾粒子相互作用发生散射,散射光偏振特性可反演切比雪夫雾霾颗粒物理性质(如粒子尺寸参数、复杂折射率、粒子形变、波纹参数)。采用紫外光单次散射模型和T矩阵方法,仿真分析切比雪夫雾霾粒子物理参数与散射光偏振特性(Stokes矢量和偏振度)之间的关系,结果表明：粒径对散射光Stokes矢量Is和Qs随散射角的变化趋势影响很大,粒子的粒径和复杂折射率虚部的变化会造成散射光偏振度随散射角的变化趋势的改变;具体分析散射角度为10°时,得到粒径对Is和Qs的数值影响最大,当粒径r<1 μm时,Is随粒径呈现抛物线趋势;切比雪夫粒子形变的增大,Is呈现先增大后减小的趋势。     

Imaging and multiple scattering through media containing optically active particles

Abstract

This paper examines the behaviour of polarized light scattered by a medium containing small chiral spheroidal particles. We show that for single scattering the observed phenomena of optical activity may be interpreted in terms of an averaged Mueller matrix and describe how the degree of polarization is affected by such a medium. The polarization properties of multiply scattered light by chiral particles are considered through the use of Monte Carlo simulations. It is shown that the effects of chirality under multiple scattering can be interpreted as an order-preserving influence in a disordered system and that this influence can, in principle, be exploited for the purposes of imaging.     

On neutron depolarization in magnetized media

The neutron depolarization in magnetized samples is considered as a result of scattering in the case of arbitrary orientations between the incident polariztion, the sample field and the direction of polarization analysis. It is shown that the depolarization is determined by the small-angle magnetic scattering within the angular beam width and by an additional contribution arising from the spin-dependent scattering outside the passing beam. The latter follows from the consideration of the interference between the scattered and the transmitted beams. Special attention is paid to the analysis of several measuring regimes for the depolarization and its dependence on neutron wavelength. The depolarization in multidomain ferromagnets is considered.