Impossibility of Stokes decomposition for a class of light beams

Decomposition throughout all space of a typical light beam into the sum of a completely polarized and a completely unpolarized beam (Stokes decomposition) seems to be rather the exception than the rule. However, it is known that such decomposition can often be made across a certain plane, although it may lose validity upon propagation. Then, one may guess that, for any light beam, there exists at least one plane where the Stokes decomposition can be performed. Without adopting any particular model for polarized and unpolarized beams, we present a class of beams for which no such plane can exist.     

Experimental determination of two-point Stokes parameters for a partially coherent broadband light beam

The generalized Stokes parameters, which are two-point extensions of conventional Stokes parameters, are determined for a pair of points in the cross-section of a partially coherent broadband light beam. For this purpose, using a two-mirror and two-beam-splitter assembly, unpolarized, linearly polarized and partially polarized electromagnetic beams are generated. This simple experimental method for determining generalized Stokes parameters establishes an analogy with the experimental scheme of determining conventional Stokes parameters, which in succession contributes to appreciable reduction in uncertainty in the measurements.     

基于自适应无下采样提升框架的Stokes图像获取方法

根据成像偏振探测中stokes参数图像获取的原理和方法，分析了传统求取stokes参数图像方法在保留图像细节信息和处理输入图像微小平移等方面的不足，在此基础上提出了基于自适应平移不变小波分解的stokes参数图像求取方法，并用无下采样的提升框架来执行平移不变小波分解以提高算法的灵活性和计算速度.针对不同的stokes参数图像求取方法，用均值、方差、熵、边界能量对融合结果进行评价和分析.通过仿真，表明本文方法提高了stokes参数图像的质量并改善了stokes参数图像计算方法对输入图像平移的敏感性.     

Image quality assessment using the singular value decomposition theorem

In objective image quality metrics, one of the most important factors is the correlation of their results with the perceived quality measurements. In this paper, a new method is presented based on comparing between the structural properties of the two compared images. Based on the mathematical concept of the singular value decomposition (SVD) theorem, each matrix can be factorized to the products of three matrices, one of them related to the luminance value while the two others show the structural content information of the image. A new method to quantify the quality of images is proposed based on the projected coefficients and the left singular vector matrix of the disturbed image based on the right singular vector matrix of the original image. To evaluate this performance, many tests have been done using a widespread subjective study involving 779 images of the Live Image Quality Assessment Database, Release 2005. The objective results show a high rate of correlation with subjective quality measurements.     

Orthogonal decomposition of elliptically polarized light through resonators composed of magnetic film

In order to control and analyze light polarization, we design a magnetic resonator and study its transmission properties by the 4×4 transfer matrix method. Through the magnetic resonator an incidence of elliptically polarized light results in two resonance wavelengths. At the two resonance wavelengths, the elliptically polarized light is orthogonally decomposed into left-handed circular polarization and right-handed circular polarization. One of the two circular polarizations is transmitted and the other is reflected.     

基于旋转波片的斯托克斯参量检测与精度分析

用于偏振光学遥感器定标的参考光源,其偏振态的检测精度会直接影响偏振光学遥感器的定标精度,进而影响目标特性的反演水平。选用870 nm波段的水平线偏振光作为被测试的定标参考光源,通过旋转1/4波片(quarter-wave plate, QWP)对其光强进行调制。调制光强可表达为波片快轴旋转角度的傅里叶级数,采用傅里叶变换法反演出级数的系数,根据该系数即可计算出被测试光源的Stokes参量。给出10次测量各参量及偏振度的平均值、标准偏差、合成不确定度以及测量平均值与理论值的相对偏差。为提高测试精度,通过对波片快轴初始定位角度偏差Δα、延迟量偏差Δδ与检偏器透光轴角度偏差Δβ进行分析,提出了偏差修正模型。该模型通过Stokes参量检测偏差随Δδ和Δβ的变化趋势及实际偏差值,确定Δδ和Δβ的大小。结合模拟出的波片快轴初始定位角度偏差Δα,对实验装置加以调整,再次对光源的偏振态进行检测。结果表明,基于该修正模型测得光源的各Stokes参量与理论值最大偏差从未经修正的3.77%降低至1.41%。证实了基于本实验的原理、装置、测量方法及所提出的偏差修正模型可有效提高定标参考光源偏振态检测的精度。     

三层流体界面内波的二阶Stokes解

以小振幅波理论为基础，利用摄动方法研究了三层密度成层状态下的界面内波，求得了三层成层状态下各层速度势的二阶渐近解及界面内波波面位移的二阶Stokes解.结果表明：一阶解为正弦波解，与传统线性理论的结果相一致；二阶解描述了界面波的二阶非线性修正及两界面波之间的非线性相互作用；一阶解及二阶解都依赖于各层流体的厚度及密度.Umeyama导出的理论结果为本文的特殊情形. 关键词： 三层密度成层流体 内波 二阶Stokes解 小振幅波理论     

Stokes vector for small rough particles: Regression analysis

The Stokes parameters and the linear polarization P_l of small rough particles composed of ice and silicate are studied with statistical methods. The probability density function of P_l and a regression analysis for the first two Stokes parameter I_s² and Q_s² are presented for three typical scattering angles θ_s=60°, 90° and 150°. The width of the probability density function of P_l given by its standard deviation increases with the roughness of the particles. A linear relationship between I_s² and Q_s² is found by the regression analysis. The slope of the linear model reflects the correlation between I_s² and Q_s² that, for a specific composition of the particles, depends on the roughness of the particles and the scattering angles. The value of the constant of the linear regression is characteristic of the composition of the particles and is not sensitive to the roughness of the particles and the scattering angles. The scattering angle θ_s=150° is the most appropriate angle for a study of rough particles of different composition.     

Suppression of Stokes heating processes and improved optomechanical cooling with frequency modulation

Ground-state cooling of mesoscopic mechanical objects is still a major challenge in the unresolved-sideband regime. We present a frequency modulation (FM) scheme to achieve cooling of the mechanical resonator to its ground-state in a double-cavity optomechanical system containing a mechanical resonator. The mean phonon number is determined by numerically solving a set of differential equations derived from the quantum master equations. Due to efficient suppression of Stokes heating processes in the presence of FM, the ground-state cooling, indicated by numerical calculations, is significantly achievable, regardless of whether in the resolved-sideband regime or the unresolved-sideband regime. Furthermore, by choosing parameters reasonably, the improvement of the quantum cooling limit is found to be capable of being positively correlated with the modulation frequency. This method provides new insight into quantum manipulation and creates more possibilities for applications of quantum devices.     

基于多角度多光谱Stokes参数Q和U测量反演气溶胶偏振相函数

偏振相函数是气溶胶重要的光学参数之一,它对气溶胶复折射指数、粒子尺度和形状都十分敏感。多角度多光谱偏振遥感可以有效获取气溶胶偏振相函数信息。新一代CIMEL太阳-天空偏振辐射计CE318-DP作为高精度地基气溶胶偏振遥感仪器已被引入全球气溶胶自动观测网AERONET(AErosol RObotic NETwork),并作为扩展多波长偏振测量的太阳-天空辐射计观测网SONET(Sun/sky-radiometer Observation NETwork)的主要仪器,已在不同类型气溶胶观测站点积累了多年的偏振数据。但目前偏振反演仅能利用线偏振度或偏振辐亮度。与线偏振度和偏振辐亮度相比,Stokes参数Q和U不仅包含天空光线偏振强度信息还包含偏振方向信息。利用CE318-DP多光谱多角度测量的天空光Stokes参数Q和U反演气溶胶偏振相函数的方法。针对CE318-DP标准主平面偏振观测模式PPP(Polarized Principal Plane)下Stokes参数U对气溶胶特性变化不敏感、信息难以利用的不足,测试了新的平纬圈偏振扫描模式ALMP(ALMucantar Polarization)获取Stokes参数Q和U,并成功应用于偏振相函数的反演。系统分析了340～1 640 nm多光谱通道上典型生物质燃烧型气溶胶和水溶性气溶胶的-P₁₂/P₁₁反演结果并测试了反演方法在晴朗和灰霾不同大气条件下的适用性。无论在主平面还是平纬圈观测几何下,反演结果在可见光和近红外通道上均与真实值具有较好的一致性。进一步讨论了模型中基于气溶胶参数初始值和大气气溶胶参数真实值计算的“大气单次散射/大气散射”的比值近似相等的假设条件在短波通道不能很好地满足是造成紫外波段反演结果偏差较大的原因之一。后续有待进一步提高反演模型在短波通道的适用性,为利用不同光谱通道上-P₁₂/P₁₁的变化特征改进气溶胶微物理参数反演奠定了基础。     

The Dissipative Scale of the Stochastics Navier–Stokes Equation: Regularization and Analyticity

We prove spatial analyticity for solutions of the stochastically forced Navier–Stokes equation, provided that the forcing is sufficiently smooth spatially. We also give estimates, which extend to the stationary regime, providing strong control of both of the expected rate of dissipation and fluctuations about this mean. Surprisingly, we could not obtain non-random estimates of the exponential decay rate of the spatial Fourier spectra.     

有流存在时三层流体界面波的二阶Stokes波解

以小振幅波理论为基础，利用摄动方法研究了有背景流场存在时密度三层成层状态下的界面内波，得到了各层流体速度势的二阶渐近解及界面内波波面位移的二阶Stokes波解，并讨论了界面波的Kelvin-Helmholtz不稳定性.结果表明：有流存在的情况下三层密度成层流体界面内波的一阶渐近解(线性波解)、频散关系及二阶渐近解不仅依赖于各层流体的厚度和密度，也依赖于各层流体的背景流场；界面内波波面位移的二阶Stokes波解不仅描述了界面波之间的二阶非线性相互作用，也描述了背景流与界面波之间的二阶非线性相互作用；当每层流 关键词： 界面波 均匀流 二阶Stokes波解 Kelvin-Helmholtz不稳定性     

三层密度分层流体毛细重力波二阶Stokes波解

以小振幅波理论为基础,利用摄动方法研究了三层密度分层流体的毛细重力波,给出了三层成层状态下各层流体速度势的二阶渐近解及毛细重力波波面位移的二阶Stokes波解.结果表明:一阶解及二阶解除了依赖于各层流体的厚度及密度,与表面张力也有很重要的关系.     

Coherence properties of Stokes beams

A Stokes beam is a light beam which is expressible as a superposition of a completely polarized and a completely unpolarized beam. In this note we study coherence properties of a wide class of beams of this kind. The behaviors of the degree of coherence of a Stokes beam produced by a circular planar source are expressed in terms of Lommel functions and theoretical results are illustrated by computed examples.     

遥感遥测中偏振信息的研究进展

偏振是光的固有特性之一。地球表面和大气中的任何目标物在与光相互作用的过程中,由于目标物的表面结构、内部结构以及光入射的角度不同,都会产生其自身性质决定的特征偏振。而偏振遥感探测就是以目标物辐射能量的偏振特征作为探测信息,可以在复杂的背景中提取目标的七维信息并很好地分辨目标物上低反射区域和目标轮廓,解决了传统遥感所不能解决的大气探测和伪装识别方面的问题,具有良好的应用前景。文章介绍了偏振遥感遥测的机理,详细阐述了偏振探测的理论模拟、偏振遥感探测仪以及偏振遥感探测技术在大气探测、地球资源探测、海洋表面与水下探测、生物医学、天文探测、军事等领域应用的国内外研究概况、水平和发展趋势,归纳了目前存在的问题,并指出目前国内外偏振探测技术的研究方向,以期为后续的同类研究提供参考。     

Lower Bounds for Eigenvalues of the Stokes Operator

In this paper, we propose a condition that can guarantee the lower bound property of the discrete eigenvalue produced by the finite element method for the Stokes operator. We check and prove this condition for four nonconforming methods and one conforming method. Hence they produce eigenvalues which are smaller than their exact counterparts.     

偏振遥感在伪装目标识别上的应用及对抗措施

 为了研究偏振遥感对伪装目标的识别特点,分别对不同颜色的伪装网进行了偏振参数测量和成像实验。通过数据分析发现,伪装网的散射偏振度受观测条件和材料自身特性（如反射率、折射率和表面粗糙度）影响很大;伪装涂层对入射光的散射作用可以分为面散射和体散射,其中面散射具有起偏振作用而体散射具有消偏振作用;与自然背景相比,伪装目标的偏振特征非常显著,利用偏振遥感可以有效地识别出常规侦察手段所不能发现的伪装目标。通过偏振遥感的侦察原理和特点分析,提出了可以利用表面结构设计和烟雾等方法对抗偏振遥感的侦察。     

油雾浓度对激光偏振度的影响

基于斯托克斯矢量,通过测量偏振度,研究不同入射偏振态的激光分别在不同浓度油雾介质中传输后偏振特性的变化情况.实验采用波长为671nm和532nm的水平、45°、-45°、90°的线偏振光,使它们分别入射到5种不同浓度的油雾介质中,计算四种偏振态偏振光的偏振度变化情况.结果表明,在相同油雾浓度下,对于不同波长的激光,波长越长,线偏振度越高,然而每种波长随浓度的变化趋势是一样的;在相同波长情况下,随着浓度的改变,水平与垂直线偏振光的偏振度变化较大,可达50%,135°与45°线偏振光的偏振度变化较小,约为20%.     

过阻尼布朗棘轮的斯托克斯效率研究

根据随机能量理论解析得到阻尼环境中布朗粒子的概率流和斯托克斯效率,并进一步研究布朗粒子的输运性能.详细讨论了空间的不对称性、外偏置力及外势结构等对棘轮定向输运的影响.研究发现,合适的外偏置力能使棘轮的定向输运达到最强.通过调节外势的不对称性可使棘轮中粒子的运动反向,当选择合适的空间不对称性时布朗粒子的反向输运可获得最强.此外,一定条件下合适的外势高度也能增强棘轮输运,且能使粒子克服黏滞阻力的斯托克斯效率达到最大.所得结论能够启发实验上设计合适的外势及外偏置来优化布朗棘轮的定向输运性能,并为生物纳米器件的研制提供一定的理论参考.     

Stokes-parameters representation in terms of the radial and azimuthal field components: A proposal

A simple characterization of the polarization state of partially polarized beams is proposed on the basis of the Stokes parameters expressed in terms of the radial and azimuthal components of the field at each point of the beam cross-section. The main properties of the proposed Stokes representation are also shown, and its physical meaning is discussed.