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.     

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.     

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.     

Polarization characteristics of backscattering of turbid media based on Mueller matrix

Mueller matrix is one approach to characterizing optical polarization of the turbid media. We have simulated the two-dimensional images of Mueller matrix based on single-scattering approximation model and implemented experiments to verify the simulations. By comparing the experimental results to the theoretical simulations, we have obtained some conclusions. When the particle size is smaller than the wavelength, the linearly polarized light propagating through the turbid media of Rayleigh scatterers has better polarization-maintaining ability. Whereas when the particle size is larger than the wavelength, the circularly polarized light propagating through the turbid media of Mie scatterers has better polarization-maintaining ability. Moreover, the radial dependence of the element patterns becomes weak as the transport mean free path decreases. This study can help us understand to the fundamental principle of optical polarization.     

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.     

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     

Numerical study of the characterization of forward scattering Mueller matrix patterns of turbid media with triple forward scattering assumption

We propose a triple forward scattering model to numerically investigate the forward scattering Mueller matrix of a turbid medium. The calculated results show that the Mueller matrix based on the triple scattering model can completely describe the basic symmetries and azimuthal structures of the forward scattering Mueller matrix of a turbid medium. The results show that the forward scattering Mueller matrix is characterized with special symmetric structure compared with backscattering Mueller matrix patterns. The method will extend the investigation to light scattering mechanism from cells and to diagnosis of diabetes and other blood related diseases.     

Extended calculation of polarization and intensity of fractal aggregates based on rigorous method for light scattering simulations with numerical orientation averaging

The intensity and polarization of fractal aggregates have been investigated using both rigorous and approximate methods for light scattering simulations. However, previous studies using the analytical orientation averaging version of the rigorous method were generally limited to a few hundred monomers when the monomer size parameter was around 1.7. In this study, we propose using numerical orientation averaging instead of analytical orientation averaging. The numerical averaging is performed together with a fixed orientation version of the rigorous T-matrix method for clusters of spheres. This approach enables increasing the number of monomers by a factor of 2-7 or the size of monomers by a factor of 8-10 compared to the analytical orientation averaging version.We investigated the influence of monomer size and the number of monomers on the light scattering of silicate aggregates (refractive index m=1.68+0.03i) for incident light with a wavelength of . We considered ballistic particle-cluster aggregates (BPCA) and ballistic cluster-cluster aggregates (BCCA) composed of 128, 256, 512, and 1024 monomers with radii between 0.11 and .Our results show that the size of monomers plays an important role in reproducing the negative polarization branch for all the BPCA and BCCA. Silicate aggregates with the monomer radius of less than contribute to reproducing the negative polarization branch, while aggregates with monomers larger than do not have the negative polarization branch. Polarization oscillation with scattering angle occurs for larger monomers (i.e., monomer radius ).The maximum polarization decreases for increasing monomer radius between 0.11 and . However, the negative polarization branch is generally enhanced for monomer radii up to around , and reduced for further increase of monomer size.The number of monomers also has a large influence on the negative polarization branch in the case of BPCA. The increase in the number of monomers from 128 to 1024 shifts the scattering angle of minimum polarization to larger angles for BPCA. In addition, the increase in the number of monomers reduces the values of negative polarization for BPCA while the variation with the number of monomers for BCCA is small and is not monotonic.     

Attenuation and depolarization of millimeter waves due to incoherent scattering in tropical rainfall

The radiative transfer equation has been applied to investigate the effects of multiple scattering on communication at the millimeter wavelength in tropical rain. Horizontal linearly polarized incident waves are assumed. The scattering characteristics are calculated using the Mie theory at frequencies of 16, 34.8, 82, 140 and and at rainfall rates of 12.5, 50 and . Some results of the directional patterns of the incoherent intensities at various points in the rain medium are presented. The frequency dependence of the propagation distance, attenuation coefficient and the variation of incoherent specific intensities in tropical rainfall are investigated. The incoherent power at the receiver relative to the coherent power, which is important in assessing the quality of signal in the receiver, is also investigated. It is observed that the maximum incoherent copolarized received power is about in tropical rainfall at rainfall rate. Also the difference between the copolarized incoherent power in tropical and temperate rainfall is about at frequencies higher than , and about for the cross-polarized incoherent power components. It may therefore be safely said that multiple scattering may not result in serious degradation of the coherent wave component even in the most intense tropical precipitation. It also appears that it is independent of regional rainfall climatology.     

Dependence on average atomic number of coherent/incoherent scattering intensity ratios in compounds

We have investigated the dependence on average atomic number of coherent/incoherent scattering intensity ratios in molecules. A Am-241 source is used to provide γ-rays. Several compounds having different average atomic numbers were used as scatterers. Scattering γ-rays were counted by a Si(Li) detector (FWHM at ). We observed an increase in the coherent/incoherent scattering intensity ratios with increasing average atomic number.     

Polarized neutron scattering studies of the kagomé lattice antiferromagnet

We report polarized neutron scattering studies of spin-wave excitations and spin fluctuations in the lattice antiferromagnet KFe₃(OH)₆(SO₄)₂ (jarosite). Inelastic polarized neutron scattering measurements at 10 K on a single crystal sample reveal two spin gaps, associated with in-plane and out-of-plane excitations. The polarization analysis of quasi-elastic scattering at 67 K shows in-plane spin fluctuations with XY symmetry, consistent with the disappearance of the in-plane gap above the Néel temperature . Our results suggest that jarosite is a promising candidate for studying the 2D XY universality class in magnetic systems.     

Evaluation of micro-bubble size and gas hold-up in two-phase gas-liquid columns via scattered light measurements

In this paper, potential use of an elliptically polarized light scattering (EPLS) method to monitor both bubble size and gas hold-up in a bubble-laden medium is explored. It is shown that with the use of the new EPLS system, normalized scattering matrix elements (M_ij's) measured at different side and back-scattering angles can be used to obtain the desired correlations between the bubble sizes and input flow parameters for a gas-liquid (GL) column, including gas flow rate and surfactant concentrations. The bubble size distributions were first evaluated experimentally using a digital image processing system for different gas flows and surfactant concentrations. These images showed that the bubbles were not necessarily spherical. We investigated the possibility of modeling the bubbles as effective spheres. The scattering matrix elements were calculated using the Lorenz-Mie theory and the results were compared against the experimentally determined values. It was observed that the change in the bubble size yields significant changes in M₁₁, M₃₃, M₄₄, and M₃₄ profiles. An optimum single measurement angle of θ=120^° was determined for a gas velocity range of 0.04-0.35 cm/s (). The choice of the optimum angle depends on frit pore size, column diameter, gas pressure, and surfactant concentration. These results suggest that a simplified version of the present EPLS system can effectively be used as a two-phase flow sensor to monitor bubble size and liquid hold-up in industrial systems.     

Influences of diffusive reflection intensity and pulse shaping of ultrashort lasers on turbid media

The influences of the absorption μ_a, the scattering μ_s, and the anisotropy coefficient g on the optical properties of ultrashort pulse in turbid media has been simulated based on the diffusive approximation theory. The laser pulse intensity will be attenuated and the diffusive scattering pulse shape will be widened in the turbid media. Various medium parameters have different influences on the reflection of the laser pulse. The intensity loss of the diffusive reflection light is obtained when μ_a and μ_s are increased in turbid media. The pulse width of the diffusive reflection pulse is rapidly increased far away from the incident point and at the same time the pulse times that are delayed have been numerical simulated in the boundary conditions of semi-infinite homogenous media.     

Fast weighting functions for retrievals from limb scattering measurements

The satellite-borne UV-visible-NIR spectrometers SCIAMACHY and OSIRIS perform operational measurements of the Earth's limb radiance with global coverage. The vertically resolved atmospheric composition is retrieved from the measurements. We have computed synthetic limb measurements and weighting functions (WFs) with several orders of scattering and surface reflection. Comparisons reveal the wavelength-dependent contributions of single scattering and the second orders of scattering and surface reflection. We have also performed test retrievals of the and profiles with the program package SCIARAYS. They prove that the single scattering approximation is sufficient for the calculation of the WFs during the retrieval process. We conclude that algorithms for the analysis of limb scattering measurements can be accelerated by neglecting higher orders of scattering in the WF calculations.     

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.     

Formation of multiple nanoscale twin boundaries that emit intense light in indirect-gap AlGaAs epilayers

Parallel twin boundaries arranged at similar intervals of nanometer length, that emitted an intense monochromatic light polarized parallel to the boundaries, were self-organized in an indirect-gap AlGaAs epilayer; the epilayer was grown on a rough As-deficient surface of an AlGaAs(0 0 1) substrate with any lattice constant, by conventional metal-organic chemical-vapor deposition. Most boundaries were of -type on B, and they extended from the interface between the epilayer and the substrate. There existed no compositional fluctuation around the boundaries. The formation mechanism was discussed.