Polarization properties of single metallic nano-spheroid using 3-D boundary element method

The polarization properties of an individual metallic nano-spheroid illuminated by the linearly polarized light are studied based on 3-D boundary element method. The scattering cross sections and the local field enhancements are investigated in detail when the incident lights are with different polarization directions and wavelengths. The numerical results show that the polarization direction of the incident light can strongly influence the scattering spectrum and the enhanced field distribution of the metallic nano-spheroid. The incident light with polarization direction parallel or perpendicular to the major axis can inspire longitudinal or transversal local surface plasmons resonance modes, respectively. The electric field enhancement and distribution around the nano-spheroid can be conveniently tuned by carefully selecting the polarization direction and wavelength of the incident light.     

Multiple scattering of elliptically polarized light in two-dimensional medium with large inhomogeneities

For elliptically polarized light incident on a two-dimensional medium with large inhomogeneities, the Stokes parameters of scattered waves are calculated. Multiple scattering is assumed to be sharply anisotropic. The degree of polarization of scattered radiation is shown to be a nonmonotonic function of depth when the incident wave is circularly polarized or its polarization vector is not parallel to the symmetry axis of the inhomogeneities.     

Residual polarization of non-coherently backscattered linearly polarized light: the influence of the anisotropy parameter of the scattering medium

The effect of preservation of the residual polarization of backscattered light in the case of multiply scattered disordered media illumination by a linearly polarized plane wave is examined using the path-integral approach and Monte Carlo simulation. Disordered ensembles of non-interacting dielectric particles are considered as the model of scattering media. The influence of the anisotropy parameter of the scattering system on the degree of residual polarization is analysed. Experimental results obtained for various scattering systems at different wavelengths of illuminating light are in satisfactory agreement with the results of theoretical analysis and Monte Carlo simulation. The dependence of statistical properties of the polarization states of backscattered field partial components, such as probability distributions of ellipticity, on the anisotropy parameter is studied.     

Self-diffraction of light waves by a nonlocal photorefractive grating in a crystal with the \bar 43m symmetry

A frequency-degenerate steady-state two-wave interaction on a dynamic transmitting phase grating formed in a cubic crystal of the $\bar 43m$ symmetry group with a nonlocal photorefractive response is considered in the paraxial approximation. The conservation laws for the nonlinear system of equations of coupled waves, derived for an arbitrary orientation of interaction relative to the crystallographic axes and the polarization of incident light waves, indicate that the contribution to energy exchange between the interacting waves may come from fluxes in different directions. The possibility of nonunidirectional energy pumping from one wave to the other upon a change in their polarization state due to the interaction is demonstrated. For the transverse configuration of the interaction and linear polarization of incident waves, explicit analytic expressions for the scalar amplitudes of the orthogonal components of the light field are derived in the linear approximation in the coefficient of modulation of the interference pattern of light. The possibility of rotation of the polarization planes of light waves without a change in their intensity is demonstrated. For three particular configurations, the dependence of the efficiency of interaction of linearly polarized waves on the reduced length, orientation of the polarization vectors of the incident light waves, and the ratio of their intensities are analyzed.     

局域体全息光栅的衍射特性

基于三维耦合波理论，研究了两束有限宽度的任意偏振平面波干涉产生的局域体全息光栅的衍射问题。以单位均匀振幅的任意偏振平面波为例，给出了透射波和衍射波振幅的主分量和交叉分量的解析表达式，讨论了记录过程和再现过程中入射的参考光波的偏振角对透射波和衍射波振幅的影响。计算结果表明，记录过程中的偏振角越小，形成的光栅内的耦合越强，衍射效率越高，但光束质量越差；再现过程中不同的偏振角，由于入射波和衍射波的电矢量的不同方向的耦合强弱不同，透射波和衍射波振幅的主分量和交叉分量的振幅变化行为不同。     

长柱状气溶胶粒子的光散射特性

以中纬度卷云中常见的长柱状冰晶为例,利用长柱状粒子光散射理论,探讨了入射光为线偏振时,电矢量平行和垂直于入射面情况下,单个长柱状粒子的散射光强度分布和偏振特性随入射角、尺度参数与偏振态的转化关系:随着入射角的增大,散射强度、偏振总体趋于对称且数值振荡频率降低,散射强度总体减小,偏振的改变程度总体增大;随着尺度参数的增大,散射强度、偏振的数值振荡频率增大,散射强度数值振荡峰的幅度整体减小,电矢量平行于粒子长轴时主偏振的数量、强度和位置皆有变迁,电矢量垂直于粒子长轴时前后主偏振位置相对固定;随着偏振度的减小,散射强度、偏振趋向于一致,两者的数值改变程度减小,当偏振度减小到0时,散射强度、偏振变得完全相同。选取火山尘埃和烟灰与冰晶对比,阐述了粒子散射光的强度分布和偏振特性随折射率的变化规律:折射率虚部不改变散射强度的整体趋势,但使散射强度和偏振的振荡峰幅度增大,当其数值较大时,使得偏振的数值振荡峰覆盖范围拓宽。     

Scattering of on-axis polarized Gaussian light beam by spheroidal water coating aerosol particle

Small particle light scattering can produce light with polarization characteristics different from those of the incident beam. An analytical solution to the scattering by a spheroid with inclusion for an on-axis polarized Gaussian beam incidence is provided within the generalized Lorenz-Mie theory framework. The shapes of the inclusion can be spherical, confocal spheroid, or non-confocal spheroid. The Muller scattering matrix elements are computed for plane wave incidence or Gaussian light beam incidence. The effect of the size and shape of the inclusion or the coating on the polarized Oaussian light scattering characteristics by a spheroidal water coating aerosol Darticle are commlted and a,nalvzed.     

Propagation of polarized light in opals: Amplitude and phase anisotropy

The interaction of linearly polarized light with photonic crystals based on bulk and thin-film synthetic opals is studied. Experimental transmission spectra and spectra showing the polarization state of light transmitted through opals are discussed. A change in polarization is found for waves experiencing Bragg diffraction from systems of crystallographic planes of the opal lattice. It is shown that the polarization plane of the incident linearly polarized wave at the exit from photonic crystals can be considerably rotated. In addition, incident linearly polarized light can be transformed to elliptically polarized light with the turned major axis of the polarization ellipse. Analysis of polarization states of transmitted light by using the transfer-matrix theory and homogenization theory revealed good agreement between calculated and experimental spectra.     

Tunable resonant radiation force exerted on semiconductor quantum well nanostructures: Nonlocal effects

Resonant radiation force exerted on a semiconductor quantum well nanostructure(QWNS) from intersubband transition of electrons is investigated by taking the nonlocal coupling between the polarizability of electrons and applied optical fields into account for two kinds of polarized states. The numerical results show the spatial nonlocality of optical response can induce the spectral peak position of the exerted force to have a blueshift, which is sensitively dependent on the polarized state and the QWNS width. It is also demonstrated that resonant radiation force is controllable by the polarization and incident directions of applied light waves. This work provides effective methods for controlling optical force and manipulating nano-objects, and observing radiation forces in experiment. This nonlocal interaction mechanism can also be used to probe and predominate internal quantum properties of nanostructures, and to manipulate collective behavior of nano-objects.     

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400～700nm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...     

人工异向介质调控电磁波极化特性的实验与仿真研究

电磁波的极化特性在通信、导航和雷达等方面已逐渐得到应用.为了有效控制电磁波的极化状态, 本文设计了一种基于开口环结构的人工异向介质.该人工异向介质由开口环结构,电介质基底和金属背板组成, 可以将入射的线性极化波完整地转换为圆极化波,椭圆极化波以及和入射波极化方向垂直的线极化波. 本文通过实验和仿真验证了本文的设计,实验结果和仿真结果符合较好.     

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。     

Resonant Processes of Scattering with Allowance for Different Populations of Magnetic Sublevels

The effect of different populations of the magnetic sublevels of the ground state on the propagation of polarized radiation through resonant media is studied theoretically. The nonlinear refractive indices for circularly and linearly polarized waves in media with arbitrary angular momenta j ₁ and j ₂ are found. The influence of the coherence between the magnetic sublevels on multiphoton effects is analyzed. It is shown that, as a result of elastic Rayleigh scattering, energy transfer from one component of the wave polarization to the other takes place. The picture of induced four-photon parametric scattering of a weak wave in the presence of a strong wave also changes.     

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The characteristic of electromagnetic scattering by plasma cylinder is researched in this paper. Scattered fields of the parallel-polarized wave and vertical-polarized wave by plasma cylinder are calculated and analyzed. The calculated results show that the higher the electron density, is the greater the scattering intensity in the outside of the cylinder and the higher the plasma frequency of collision, is the smaller the scattering intensity in the outside of the column. In addition, the electromagnetic wave polarization and frequency of the incident wave also have a significant impact on the scattering intensity of electromagnetic waves, the vertically polarized wave is more likely to be scattered, and the lower frequency of the incident wave is also easier to scattering. These have certain reference value for designing and studying of the plasma antenna.     

Anisotropic gratings recorded from two circularly polarized coherent waves

A constant intensity, rectilinear light vibration, with spatially varying orientation, is obtained from superposition of two orthogonal circularly polarized waves propagating, in slightly different directions. Such an exposure on a photoanisotropic medium, prints a grating characterized only by spatial variations in the orientation of the induced optic axis. The diffraction properties of such a grating are investigated. It behaves as a uniformly transparent isotropic medium when illuminated by the same waves as during the recording process. Illumination by a circular wave, generates a transmitted and a single diffracted beam, while an incident elliptically polarized one would produce, apart from the central order, two diffracted beams with orthogonal circular polarizations.     

Bragg diffraction of light by ultrasonic shear waves in a plane-parallel layer

We have studied anisotropic Bragg diffraction of light by ultrasonic shear waves in an optically isotropic plane-parallel layer. We have established the analytical dependences of the relative intensities and polarization azimuths of reflected and transmitted diffracted waves on the intensity of the ultrasound, the layer thickness, the angle of incidence, and the polarization azimuth of the incident light. We show that rotation of the plane of polarization of the diffracted wave is determined by the different Fresnel reflection of the s and p polarized components of the incident light in the plane-parallel layer. We have determined that in mismatched acousto-optic structures, deep amplitude modulation of transmitted and reflected light is possible which is an order of magnitude greater than the usual modulation in matched structures.     

不同波长的散射介质后向散射光偏振度特性

基于Stockes矢量,通过测量以线偏振光和圆偏振光入射时脂肪乳剂后向散射光的偏振度,研究了532nm、650nm和780nm三个波长的光与散射粒子粒径为325nm的脂肪乳剂溶液作用后,其后向散射光的偏振度特性.研究结果表明,对于入射线偏振光,780nm波长后向散射光中的线偏振光成分多于圆偏振光成分,而532nm波长则相反;对于入射圆偏振光,三个波长后向散射光中的圆偏振光成分均多于线偏振光成分;532nm波长的总偏振度高于650nm和780nm两个波长各自的总偏振度;线偏振光的保偏性优于圆偏振光的保偏性,但偏振光在散射介质中的穿透深度较小.因此,后向散射成像技术适用于物体表层成像,而且选择波长略大于粒径的线偏振光可以提高成像质量.     

利用表面散射光偏振差异的目标识别技术

 分析了不同物体散射场偏振特性的差异,依据消光定理的矢量微扰解方法将物体散射场分为零阶和高阶解,零阶反射光可完全保持入射光的偏振度,高阶散射则会导致偏振度的降低,因而总散射光的偏振度依赖于散射表面的粗糙程度。提出了利用斯托克斯-穆勒体系测量物体消偏特性的方法并通过实验对一些物体作了测量,实验结果表明：光滑表面可以较好地保留入射光偏振度,而粗糙表面则有很强的消偏作用,因此偏振成像方法可有效地提高目标探测和识别效率。     

不同波长的散射介质后向散射光偏振度特性

基于Stockes矢量,通过测量以线偏振光和圆偏振光入射时脂肪乳剂后向散射光的偏振度,研究了532 nm、650 nm和780 nm三个波长的光与散射粒子粒径为325 nm的脂肪乳剂溶液作用后,其后向散射光的偏振度特性.研究结果表明,对于入射线偏振光,780 nm波长后向散射光中的线偏振光成分多于圆偏振光成分,而532 nm波长则相反;对于入射圆偏振光,三个波长后向散射光中的圆偏振光成分均多于线偏振光成分;532 nm波长的总偏振度高于650 nm和780 nm两个波长各自的总偏振度;线偏振光的保偏性优于圆偏振光的保偏性,但偏振光在散射介质中的穿透深度较小.因此,后向散射成像技术适用于物体表层成像,而且选择波长略大于粒径的线偏振光可以提高成像质量.     

Unidirectional transmission realized by two nonparallel gratings made of isotropic media

We realize a unidirectional transmission by cascading two nonparallel gratings (NPGs) made of isotropic, lossless, and linear media. For a pair of orthogonal linear polarizations, one of the gratings is designed as a polarizer, which is a reflector for one polarization and a transmitter for the other; another grating is designed as a polarization converter, which converts most of one polarized incident wave into another polarized transmitted wave. It is demonstrated by numerical calculation that more than 85% of the incident light energy can be transmitted with less than 1% transmission in the opposite direction for linearly polarized light at normal incidence, and the relative bandwidth of the unidirectional transmission is nearly 9%. The maximum transmission contrast ratio between the two directions is 62 dB. Unlike one-way diffraction grating, the transmitted light of the NPGs is collinear with the incident light, but their polarizations are orthogonal.