Scattering matrices for horizontally oriented ice crystals

Scattering matrices for horizontally oriented ice crystals are calculated with a code based on the geometric optics. The main physical regularities inherent to the scattering matrices are discussed. Degree of polarization of the scattered light is shown to be a qualitative criterion of number of photon trajectories that contribute effectively to the scattered light. The inverse scattering problem of retrieving aspect ratios of the horizontally oriented hexagonal ice plates from polarization of the scattered light in the bistatic sounding scheme has been proposed and discussed.     

Random lasing in porous scattering medium

The spectrum behavior evolution and the threshold of random lasing depending on the way of photon walk randomization in an active random medium were investigated. The following three ways of photon walk randomization were implemented: multiple light scattering by corundum and silica particles embedded into a solid polymer solution of dye (astrafloxin), multiple light reflection at sub-millimeter extensive air pores (mean diameter 200 μm) produced in the medium, and the combined action of both these effects. The most effective lasing is observed in the case of an active medium with air pores and scattering particles in the interpore space. Such a combined porous scattering medium acts as a network of dielectric waveguides transmitting effectively the random light. This spatial structure of the random active medium significantly increases the photon path in the medium, thereby promoting photon multiplication due to stimulated emission. In this combined medium the random lasing reveals the narrowest spectrum, the lowest threshold, and the highest density of spectral energy in the spectrum maximum.     

Lasing with guided modes in ZnO nanorods and nanowires

A vertically arranged nearly parallel array of ZnO nanorods and randomly oriented nanowires has been grown by low pressure chemical vapor deposition (CVD) on silica substrates and on stainless steel gauze woven from a wire with a diameter of 40 μm, respectively. The quality of the produced material is high enough to act as a gain medium for stimulated emission in the ultraviolet spectral region. Multiple sharp lasing peaks were realized from single hexagonal nanorods and arrays of hexagonal ZnO nanorods. The lasing peaks display successive onset and saturation with increasing excitation power density and fit well the expected resonance spectrum of guided modes in hexagonal nanorods. The behavior of lasing spectra from shot to shot of pumping in randomly oriented nanowires along with the independence of the lasing threshold on the excitation spot area suggest that the emission spectrum results from the superposition of lasing modes in individual nanowires, rather than from random lasing due to photon coherent scattering.     

非共振条件下单壁碳纳米管拉曼散射强度的计算

利用非共振情况下的键极化模型理论，对单壁碳纳米管的拉曼光谱强度进行了研究.考察了碳纳米管结构、入射光和散射光的偏振方向以及管轴的取向对散射光强度的影响.计算结果表明，光的偏振方向对拉曼散射强度影响较大，而手性对拉曼光谱的影响较小.针对碳管样品的实际情况，给出了无规取向碳管的拉曼散射光谱. 关键词： 碳纳米管 拉曼散射 声子 键极化     

Photoemission of spin-polarized electrons from negative electron affinity GaAsP

GaAs_0.62P_0.38 activated to negative electron affinity and irradiated with circularly polarized light of a wavelength shorter than approximately 680 nm emits electrons whose spins are mainly oriented antiparallel to the photon spins. At 650 nm a degree of electron spin polarization around 40% is observed. The spectrum of spin polarization of the photoelectrons is similar to that known from GaAs cathodes but is shifted to shorter wavelengths. 25 μA current of spin-polarized electrons were achieved with a 5 mW He-Ne laser.     

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.     

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.     

光子偏振度受大气散射影响的分析

采用矩阵形式描述光子的偏振态和大气散射理论, 分析了“BB84协议”中四个不同偏振光子经单次散射后光子的偏振度与前向散射角的关系。发现单次散射不改变偏振光子的总偏振度, 但改变偏振光子的线偏振度与圆偏振度, 尤其对垂直偏振光子的线偏振度与圆偏振度改变明显; 当前向散射角小于0.25 rad时, 四个不同偏振光子的线偏振度基本保持不变, 量子信息仍然保持; 同时分析了大气散射对不同波长的垂直偏振光子线偏振度的影响, 发现长波光子偏振度保持度高。     

V型高双折射光子晶体光纤超连续谱产生的实验研究

高非线性高双折射光子晶体光纤是超连续谱产生的最有效介质之一, 因此本文选取V型光子晶体光纤作为研究对象. 通过多极理论数值模拟的结果, 确定V型光纤具有高双折射、高非线性等特性. 通过实验手段, 发现入射光中心波长和光纤的双折射效应对产生的超连续谱有很大的影响: 当入射光波长处于光子晶体光纤大的反常色散区时, 脉冲相对展得比较宽, 长轴要比短轴方向的超连续谱更宽, 频谱成分更加丰富. 在同一波长下光偏振方向越接近45°时, 超连续谱谱宽范围越大. 随着入射脉冲功率的增加, 超连续谱展得越宽, 但是当功率比较大时会达到功率饱和. 关键词： 光子晶体光纤 高双折射 多极理论 超连续谱     

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。     

Manifestation of spin-orbital interaction of a photon

The review of the effects which can be considered as manifestation of spin-orbital interaction of a photon (mutual influence of light polarization and propagation) has been presented. The effect of polarization influence on propagation and the effect of the propagation influence on polarization under light propagation through locally isotropic inhomogeneous medium have been described. The notion of spin and angular momentum of a photon and their conversion into mechanical momentum have been discussed. The experimental conditions which are suitable for investigation of spin-orbital interaction under light propagation through optical fiber have been described.     

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。     

Dependence of the circular polarization of backscattered light in random media on anisotropy of scatterers

The scattering of linearly or circularly polarized light from a semi-infinite randomly inhomogeneous medium is considered. Using the Monte Carlo method, it is shown that, in the case of a wide front of incident and scattered optical radiation and irrespective of the degree of scattering anisotropy, the copolarized component of backscattered light dominates the cross-polarized component for the linear polarization and the cross-polarized component dominates the copolarized component for the circular polarization. If the beams of incident and scattered radiation are spatially separated and the size of scatterers exceeds the wavelength, the circular copolarized component dominates the cross-polarized one. A similar effect of the change in direction of the rotation of the plane of polarization in relation to the size of scatterers is revealed for pulsed radiation.     

Manipulating light–matter interaction in a gold nanorod assembly by plasmonic coupling

The interaction of light with a single gold nanorod (GNR) depends strongly on the polarization and wavelength of the light. For isolated GNRs, the maximum of the polarization (wavelength)‐dependent linear and nonlinear absorption appear at the same excitation polarization (wavelength). Here, it is demonstrated that these relationships can be manipulated in a GNR assembly composed of randomly distributed and oriented GNRs by controlling the plasmonic coupling strength between GNRs. It is revealed that the strongly localized modes resulting from the plasmonic coupling of GNRs play a crucial role in determining these relationships. For a GNR tetramer, it is shown by numerical simulation that the maximum two‐photon absorption achieved at a particular polarization can be switched to the minimum absorption and vice versa by controlling the coupling strength. More importantly, it is demonstrated both numerically and experimentally that the two‐photon‐absorption peak of a GNR assembly can be made to be different from its single‐photon‐absorption peak by increasing the coupling strength. Both properties are distinct from previous experimental observations. Our findings provide a useful guideline for engineering the interaction of light with complex plasmonic systems.

     

Scattering response of a bianisotropic cylinder with electrically small cross-section

EM scattering response of an infinitely long bianisotropic cylinder with electrically small cross-section suspended in free space is presented. Formulation of this problem is based on the coupled integral equation method with the long wavelength approximation. Reduced expressions for the scattering of plane waves, both E-wave and H-wave types, are obtained. It is revealed that for certain polarization matrices determined by the constitutive parameters of the scatterer, cross-polarization and/or co-polarization phenomena may occur, respectively.     

On propagation of high-energy photon in a medium in presence of an external field

The polarization tensor is calculated which originates from interaction of a photon with the electron–positron field. The effects of multiple scattering of electrons and positrons in a medium side by side with external fields are included. The corresponding general representation of polarization tensor is found in the form of two-dimensional integral. The both effects may be essential for propagation of high-energy photons in oriented single crystals.     

Polarization entanglement generation at 1.5 μm based on walk-off effect due to fiber birefringence

In this Letter, a linear scheme to generate polarization entanglement at 1.5 μm based on commercial polarization maintained dispersion shifted fiber (PM-DSF) is proposed. The birefringent walk-off effect of the pulsed pump light in the PM-DSF provides an effective way to suppress the vector scattering processes of spontaneous four-wave mixing. A 90 deg offset of fiber polarization axes is introduced at the midpoint of the fiber to realize the quantum superposition of the two correlated photon states generated by the two scalar processes on different fiber polarization axes, leading to polarization entanglement generation. Experiments of the indistinguishable property on single-side and two-photon interference in two nonorthogonal polarization bases are demonstrated. A two-photon interference fringe visibility of 89±3% is achieved without subtracting the background counts, demonstrating its great potential in developing highly a efficient and stable fiber based polarization-entangled quantum light source at the optical communication band.     

Scattering and absorption of particles by a black hole involving a global monopole

Under the conditions that the wavelength of a particle is much larger than its radius of central mass, and the Schwarzschild field is weak, the scattering of a particle has been studied by many researchers. They obtained that scalar and vector particles abide by Rutherford’s angle distribution by using the low level perturbation method and the scattered field’s approximation in a weak field. The scattering cross section of a photon coincides with the section in Newton’s field of point mass. We can obtain the photon’s polarization effect by calculating the second-order perturbation in the linear Schwarzschild field. This article discusses the scattering and absorption of a particle by a black hole involving a global monopole by using the aforesaid method.     

Interference effects in backscattering of light by a layer of a discrete random medium

Multiple backscattering of light by a layer of a discrete random medium is considered. A brief derivation of equations for describing the coherent and incoherent components of scattered light is presented. These equations are solved numerically in the approximation of doubled scattering of light by a semi-infinite medium of spherical scatterers having a size comparable with the wavelength in order to study the effect of the properties of particles on the angular dependence of interference effects. Calculations show that the half-width of the interference peak decreases upon an increase in lateral scattering by particles and that the degree of polarization has a complex angular dependence on the properties of the particles. For an optically thin layer of the medium, the relations defining the interference peak half-width and the scattering angle upon extreme linear polarization as functions of the effective refractive index are given.     

高斯光束在双层云中传输的蒙特卡罗模拟

基于辐射传输理论, 利用蒙特卡罗方法模拟了无限窄(冲击函数)准直光束入射到典型水云以及冰水双层云时的后向散射特性, 进而将得到的冲击响应与高斯光束卷积, 得到高斯光束在云层中传输的多次散射特性. 文中给出了两种波束入射时水云以及冰水双层云的反射函数随径向r和天顶角α的变化关系, 并给出了光强在云层内部的二维分布图. 计算结果表明, 高斯光束入射时, 云层反射函数的特点与无限窄准直光束入射时有较大区别. 因此在利用激光雷达进行云层探测时需要考虑激光的散斑, 文中的方法可以为此提供理论依据.