混浊介质后向漫散射穆勒矩阵的测量

发布时间：2018-04-22 20:38

本文选题：后向漫散射穆勒矩阵 + 偏振成像　；参考：《华中科技大学》2005年硕士论文

【摘要】：当把一束准直的偏振光束聚焦,垂直入射到介质表面时,测量入射点周围区域的后向漫散射光偏振态和强度的空间分布模式,分析区域内每点的位置与该点的后向漫散射光偏振态、强度的函数关系,就可以确定介质的约化散射系数和吸收系数等光学特性参量。进一步分析,还可以获得介质的各向异性因子和散射粒子平均大小等信息。当入射光的偏振态不同时,混浊介质的后向漫散射光的强度空间分布模式也不同。因此引入穆勒矩阵形式可以全面的描述混浊介质的后向漫散射特性,通过穆勒矩阵可以计算出任意偏振态入射光情况下,混浊介质的后向漫散射光的斯托克斯矢量。本文对混浊介质的后向漫散射穆勒矩阵的测量进行研究,主要内容包括: 借用斯托克斯矢量-穆勒矩阵这种数学形式来描述偏振光束和混浊介质的后向散射特性,并结合庞加球阐述了这种形式的物理意义。通过穆勒矩阵运算推导出任意光束的斯托克斯矢量测量方法,然后在光的斯托克斯矢量测量的基础上,完成穆勒矩阵的测量原理的推导。基于推导出的测量原理设计并实现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。然后利用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。从光路、光源和CCD 相机三个方面对系统的各部分性能进行了详尽的分析,并利用系统分别对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进行了测量。实验证明,本系统不仅能够有效地分离混浊介质的漫后向散射光和表面镜面反射光,排除镜面反射光的干扰,而且测量得到图像中所有点均由介质的漫后向散射光所成像得到,不存在无效像素。在消除测量中散斑的负面影响时,延长CCD 相机曝光时间地办法也被实践证明是非常有效的。因此利用本实验系统能够准确地测量混浊介质的后向漫散射穆勒矩阵,且能够用于生物组织的偏振特性的研究。
[Abstract]:When a collimated polarized beam is focused on the surface of the medium, the polarization state and the spatial distribution of the intensity of the diffuse scattering light in the region around the incident point are measured. By analyzing the function relationship between the position of each point in the region and the polarization state and intensity of the backscattered light, the optical characteristic parameters such as the reduced scattering coefficient and the absorption coefficient of the medium can be determined. Further analysis, the anisotropy factor and the average size of scattering particles can be obtained. When the polarization state of the incident light is different, the spatial distribution mode of the diffuse backscattering light in the turbid medium is also different. Therefore, the Muller matrix form can be used to describe the diffuse backscattering characteristics of turbid media. By using Muller matrix, the Stokes vector of diffuse backscattering light can be calculated for arbitrary polarized incident light. The measurement of diffuse backscattering Muller matrix in turbid media is studied in this paper. The main contents are as follows: The Stokes vector-Muller matrix is used to describe the backscattering characteristics of polarized light beams and turbid media, and the physical meaning of this form is explained with the Poincare sphere. The Stokes vector measurement method of arbitrary beam is derived by using Muller matrix operation, and then the principle of Moeller matrix measurement is deduced on the basis of Stokes vector measurement of light. Based on the derived measurement principle, a set of experimental system is designed and implemented to measure the diffuse backscattering Muller matrix in turbid media. In the system, the laser is modulated to the desired polarization state and focused on the surface of the turbid medium. Then the energy spatial distribution of the specific polarization states in the backscattering region around the incident point is measured by using the CCD camera and the corresponding polarizing elements. The diffuse scattering Muller matrix of the medium is calculated from the measured values. The performance of each part of the system is analyzed in detail from three aspects: optical path, light source and CCD camera. The reflectance Muller matrix of depolarization splitter prism and the backscatter Muller matrix of 1.5% fat emulsion solution were measured by the system. Experimental results show that the system can not only effectively separate diffuse scattering light from surface reflection light and eliminate the interference of mirror reflection light, but also measure all points in the image by the diffuse scattering light of the medium. There are no invalid pixels. The method of prolonging the exposure time of CCD camera has also been proved to be very effective in eliminating the negative effect of speckle in measurement. Therefore, this experimental system can accurately measure the diffuse backscattering Muller matrix of turbid media and can be used to study the polarization characteristics of biological tissues.
【学位授予单位】：华中科技大学
【学位级别】：硕士
【学位授予年份】：2005
【分类号】：R311

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