Effective dichroism in forward scattering by inhomogeneous birefringent medium

The Mueller matrix model for inhomogeneous medium characterized by simultaneous linear and circular birefringence for single scattering in the forward direction is derived. We find that the presence of inhomogeneity results in the occurrence of new polarization effects. In particular, forward scattering by inhomogeneous birefringent medium exhibits linear and circular dichroism. We show that in the case of weak depolarization (when Cloude's entropy is less than 0.5), the initial parameters for linear and circular birefringence can be obtained from deterministic Mueller matrix associated with the largest eigenvalue of Cloude's coherency matrix. Sample calculations are given for quartz.     

Influence of the order of the constituent basis matrices on the Mueller matrix decomposition-derived polarization parameters in complex turbid media such as biological tissues

The influence of the multiplication order of the constituent basis matrices on the Mueller matrix decomposition-derived polarization parameters in complex tissue-like turbid media exhibiting simultaneous scattering and polarization effects are investigated. A polarization sensitive Monte Carlo (MC) simulation model was used to generate Mueller matrices from turbid media exhibiting simultaneous linear birefringence, optical activity and multiple scattering effects. Mueller matrix decomposition was performed with different selected multiplication orders of the constituent basis matrices, which were further analyzed to derive quantitative individual polarization medium properties. The results show that for turbid medium having weak diattenuation (differential attenuation of two orthogonal polarization states), the decomposition-derived polarization parameters are independent of the multiplication order. Importantly, the values for the extracted polarization parameters were found to be in excellent agreement with the controlled inputs, showing self-consistency in inverse decomposition analysis and successful decoupling of the individual polarization effects. These results were corroborated further by selected experimental results from phantoms having optical (scattering and polarization) properties similar to those used in the MC model. Results from tissue polarimetry confirm that the magnitude of diattenuation is generally lower compared to other polarization effects, so that the demonstrated self-consistency of the decomposition formalism with respect to the potential ambiguity of ordering of the constituent matrices should hold in biological applications.     

Influence of single scattering and multiple scattering on backscattered Mueller matrix in turbid media

Monte Carlo algorithm and Stokes-Mueller formalism are used to simulate the propagation behavior of polarized light in turbid media. The influence of single scattering and multiple scattering on backscattered Mueller matrix in turbid media is discussed. Single and double scattering photons form the major part of backscattered polarization patterns, while multiple scattering photons present more likely as background. Further quantitative analyses show that single scattering approximation and double scattering approximation are quite accurate when discussing the polarization patterns near the incident point.     

Measurements of structure-induced polarization features in forward scattering from collections of cylindrical fibers

Many applications in remote sensing, material sciences and biomedical field are characterized by a transition domain between single scattering and multiple-scattering regimes. This regime is described by typical polarization features which can be used to retrieve structural information. An electronically agile technique was used for measuring in real time the Stokes vectors of light incident on and emerging from an inhomogeneous medium. Subsequently, the Mueller matrix associated with the scattering medium is determined. We focus our attention on forward scattering from systems consisting of random as well as partially oriented long cylindrical fibers. We discuss the effects of: (1) shape of individual scattering centers, (2) structure parameter, and (3) optical density of the scattering medium. The anisotropic behavior of the structure function at different packing fractions determines nontrivial characteristics of the polarization transfer. The complex effective index of refraction can be polarization dependent as a result of the optical anisotropy due to both the shape of the individual scatterers and the structure characteristics of the scattering system. Some of the Mueller matrix elements are shown to be related to the optical anisotropy of the system for the case of long cylindrical fibers. The polarization efficiency, the structure parameter, and the packing fraction are used to quantify this relationship. We also found that some of the matrix elements are more sensitive to the degree of structural anisotropy and the packing fraction, while other elements are sensitive to structural non-uniformities across the investigated area.     

Calculations of Backscattering Mueller Matrices for Turbid Media with a Sphere Queue Model

A sphere queue model is introduced to calculate Mueller matrices of turbid media. Combined with the single scattering approximation, the backscattering Mueller matrices of turbid media can be computed rapidly by Mie theory. The numerical results agree with the azimuthal dependences of backscattering Mueller matrices＇ patterns from turbid media, which indicates that the major contribution to the Mueller matrices＇ patterns comes from the single scattering of the sphere queue, and the multiple scattering considered as a high-order correction does not change the patterns. The numerical analysis reveals that the contrast of Mueller matrices＇ patterns will decrease with increase of the concentration of media and the distance from the incident point.     

Mueller matrix polarimetry for the characterization of complex random medium like biological tissues

The polarization parameters of light scattered from biological tissues contain wealth of morphological and functional information of potential biomedical importance. But, in optically thick turbid media such as tissues, numerous complexities due to multiple scattering and simultaneous occurrences of many polarization events present formidable challenges, in terms of both accurate measurement and unique interpretation of the individual polarimetry characteristics. We have developed and validated an expanded Mueller matrix decomposition approach to overcome this problem. The approach was validated theoretically with a polarization-sensitive Monte Carlo light propagation model and experimentally by recording Mueller matrices from tissue-like complex random medium. In this paper, we discuss our comprehensive turbid polarimetry platform consisting of the experimental polarimetry system, forward Monte Carlo modelling and inverse polar decomposition analysis. Initial biomedical applications of this novel general method for polarimetry analysis in random media are also presented.     

Measurements of diffuse backscattering Mueller matrices of turbid media

We report on the development of a method that records spatially dependent intensity patterns of polarized light that arise from illuminating a turbid media with a polarized laser beam and being diffusely backscattered. Our technique employs polarized light from a He-Ne laser () which is focused onto the surface of the scattering medium. A surface area of approximately 2×2 cm centered on the light input point is imaged through polarization analysis optics onto a CCD camera. The Mueller matrix is reconstructed by 49 intensity measurements with various orientations of polarizer and analyzer. The measured Mueller matrix of polystyrene spheres was compared with the theory result of incoherent scattering of light by spheres. The experimental and theory results are in excellent agreement. It appears that the azimuthal patterns of the Mueller matrix are determined by the symmetry of the turbid media.     

Revisit to the symmetry relations in diffusely backscattered polarization patterns of turbid media

As there exists an inconsistency in claiming the symmetrical relations in the 16 Mueller matrix elements used to describe a turbid medium, the author restudies the symmetrical relationships between diffusely backscattered polarization patterns in isotropic turbid media and simulates all two-dimensional elements of diffusely backscattered Mueller matrix in both cases of Rayleigh and Mie scatterings using the doublescattering approximation and the Monte Carlo algorithm, respectively. The previous experimental observatious are compared with the numerically determined matrix elements, showing a good agreement in both double-scattering model and Monte Carlo simulation. The symmetrical relations between the Mueller matrix elements are clarified.     

Analysis of forward scattering of diffuse photon-density waves in turbid media: a diffraction tomography approach to an analytic solution

We present a model of the forward problem for diffuse photon-density waves in a turbid medium containing a spherical inhomogeneity, using diffraction tomographic (DT) methods. Recently, by use of DT methods, the forward problem was investigated [Opt. Express 1, 6 (1997); www.osa.org] assuming weak perturbations from the background medium but an arbitrary inhomogeneity structure. We apply DT concepts to a forward problem solution that permits strong perturbations but requires a spherical inhomogeneity. We show that this model is consistent with previous DT results and discuss the application of this new model.     

手性介质中后向散射米勒矩阵特性及其在血糖无创检测中的应用初探

利用斯托克斯-米勒矩阵表述分析偏振光在手性介质中的传输规律,利用瑞利近似下的单次散射模型和基于米氏散射理论的多次散射的蒙特卡罗方法,探讨葡萄糖对后向散射偏振光传输特性的影响,计算了不同葡萄糖浓度下的后向散射米勒矩阵. 结果表明在含有葡萄糖的手性介质中后向散射米勒矩阵的若干矩阵元表现出微弱的旋光效应,旋光度随葡萄糖浓度增大而增大. 为了检测低浓度下微小的旋光变化,定义了函数对含-不含葡萄糖的米勒矩阵元图像进行处理,提取由葡萄糖引入的图像差异. 结合无创血糖检测应用要求,分析了葡萄糖生理浓度下的矩阵元图像,获 关键词： 医用光学与生物技术 偏振光 斯托克斯-米勒表述 蒙特卡罗模拟     

随机介质背散射二维Mueller矩阵的数值模拟与分析

推导了随机介质背散射Mueller矩阵的直接计算公式,并运用矢量Monte Carlo方法进行了数值模拟.结果表明随机介质背散射二维Mueller矩阵方位关系随散射系数的减小而增强,而与微粒大小关系不大;Mueller矩阵元素绝对值的空间分布随径向呈近似指数规律衰减,矩阵元素的方位变化具有周期性.对称系统的二维Mueller矩阵的花样图中仅有7幅独立,其余9幅可通过对称、旋转变换得到.     

含葡萄糖的混浊介质的Mueller矩阵模拟与分析

利用矢量Monte Carlo算法结合葡萄糖的旋光特性模拟了含糖混浊介质的背散射Mueller矩阵.数值模拟表明:含糖混浊介质的背散射Mueller矩阵元素中除Mll、M14、M41、M44外的其它元素花样均发生龙卷风状的不同程度的扭曲,其中M24、M34、M42、M43的扭曲程度更为显著.研究发现M24、M34、M4...     

Theoretical analysis of backscattered polarization patterns of turbid media containing glucose

Single scattering model and Stokes-Mueller formalism are introduced to investigate the influence of glucose on backscattered polarization patterns in turbid media. Glucose molecules rotate the polarization plane and induce changes in backscattered Mueller matrix patterns. Some Mueller matrix elements present higher optical rotation as the concentration of glucose augments. Using image subtraction and integration,linear relationship between low glucose concentration in the physiological range and optical rotation degree can be derived.     

Iterative approach of high-order scattering solution for vector radiative transfer of inhomogeneous random media

By stratifying a random scatter media into multiple thin layers in the vertical z direction, the first-order scattering solution of each thin layer is employed to derive high-order scattering solution of whole random media. Using the Fourier transform and Mueller matrices in discrete ordinates, an iterative approach to solve high-order scattering solution of vector radiative transfer (VRT) equation is newly developed. Numerical results are well compared with the Mueller matrix solutions of the first order for a single layer medium, second order for a half-space, and the results of the discrete ordinate and eigen analysis method. It demonstrates our approach as feasible, effective and especially applicable to high-order solution of VRT for both bistatic scattering and thermal emission of inhomogeneous non-spherical scatter media.     

混浊介质二维后向漫散射穆勒矩阵的测量

研制了一套实验系统用于测量混浊介质的后向漫散射穆勒矩阵.在系统中，激光被调制成所需偏振态，聚焦于混浊介质表面.利用CCD相机配合相应的偏振元件，测量入射点周围区域的后向散射光中特定偏振态的能量空间分布，并由测量值计算出介质的后向漫散射穆勒矩阵.描述了系统的组成、测量原理以及方法，分别测量了消偏振分光棱镜的反射穆勒矩阵和浓度1.5％的脂肪乳溶液的后向漫散射穆勒矩阵.实验证明:该系统能够完全消除样品表面镜面反射光的干扰，精确的测量混浊介质的后向漫散射穆勒矩阵；并可望用于生物组织的研究中.     

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.     

Measurement and calculation of the two-dimensional backscattering Mueller matrix of a turbid medium

We present both experimental and Monte Carlo-based simulation results for the diffusely backscattered intensity patterns that arise from illumination of a turbid medium with a polarized laser beam. A numerical method that allows the calculation of all 16 elements of the two-dimensional Muller matrix is used; moreover, it is shown that only seven matrix elements are independent. To validate our method, we compared our simulations with experimental measurements, using a turbid medium consisting of 2.02-microm -diameter polystyrene spheres suspended in deionized water. By varying the incident polarization and the analyzer optics for the experimental measurements, we obtained the diffuse backscattering Mueller matrix elements. The experimental and the numerical results are in good agreement.     

模拟气泡幕激光近轴前向散射照度分布

从Mie散射理论出发,利用单气泡散射理论模型研究了激光前向散射特性以及激光前向散射光轴周围激光照度分布状态。选用波长为632.8 nm的激光,在不同介质和不同压强下测量并分析了气泡幕的散射光照度。研究表明,激光前向散射光主要分布在离光轴0.588的范围内,其沿激光光轴呈轴对称分布,并且沿光轴方向截面分布为高斯分布;在考虑水体自身散射时,0.006 MPa、0.008 MPa和0.010 MPa下,各个散射角被散射掉的光大概占激光前向散射照度的35%、45%和55%,可得到无论考虑水体自身散射与否,激光前向散射光与压强皆成反比。     

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.     

New technique to simulate angular patterns of polarized signals from multiply scattering media in MFOV and CCD lidars

We present a semi-analytical approach to determine angular patterns of a polarized intensity that form lidar signals from multiply scattering media registered by a monostatic multiple-field-of-view receiver or CCD camera for any polarization state of incident light and any analyzer state at a receiver. Multiply scattering media with a highly forward elongated phase functions are considered. The model of lidar signal formation includes the single near-backscattering and small-angle multiple scattering of light. The developed approach allows computation and analysis of polarized images, including the Mueller matrix images, formed by the laser light backscattered by multiply scattering media, for example, from atmospheric clouds, ocean waters, tissue, etc.