Study on the Multiple Scattering Phenomena of Coherent Light by High Concentration Media

该项目的目的是揭示高度无序介质中相干光多重散射的统计特性，并开发提取多重散射物体结构和运动信息的新技术。(1)光的增强后向散射：从理论上和实验上研究了入射光的空间相干性、介质中悬浮粒子的大小以及散射光的偏振方向对增强后向散射峰的影响。这些参数都对增强的形状和峰值有较大的影响。对粒子布朗运动引起的散射光的时间涨落进行了分析，发现了光完全反向散射的特征行为。(2)分形介质的多重散射：质量分形随机介质散射的光表现出不同于均匀随机介质的特性。进一步表明，分形介质特有的后向散射峰形状是由光子在介质中特有的散射自由程分布形成的。该特性可用于测量多个散射物体的分形维数。弹道光的强度也提供了分形结构的信息。(3)强多重散射新现象：利用计算机模拟研究了强散射介质中散射波在散射点相互干扰的光散射的时空特性。揭示了前向散射光强的对比度增强和后向散射光的负空间强度相关等新现象，并利用光子路径轨迹的交叉概率解释了这些现象的物理根源。(4)流体测速的光谱相关法：利用集中流动的微球进行布朗运动，测量不同波长散射光强度的相互关系。结果表明，谱相关法测量的相关时间不受布朗运动的影响，其倒数与散射介质的流速成正比。提出了一种适用于致密胶体介质的速度测量新技术。少

The aim of the project is to reveal the statistical properties of coherent light multiply scattered by highly disordered media and to develop new techniques for extracting information about the structure and motion of multiple scattering objects.(1) Enhanced backscattering of light : The effects of the spatial coherence of incident light, the size of particles suspended in the medium, and the polarization direction of scatteredlight, on the enhanced backscattering peak were investigated theoretically and experimentally. All these parameters were found to influence strongly the shape and peak value of the enhancement. The temporal fluctuations of scattered light due to Brownian motion of particles were also evaluated, and a characteristic behavior was found for the light scattered exactly in the backward direction.(2) Multiple scattering from fractal media : Light scattered by mass-fractal random media exhibits properties that are different from those of homogeneous random media. It was … More shown that the shape of the backscattering peak peculiar to the fractal medium is formed by its characteristic scattering free-path distribution of photons inthe medium. This feature can be utilized to measure the fractal dimension of multiple scattering objects. The intensity of ballistic light was also found to provide information about the fractal structure.(3) New phenomena on strong multiple scattering : Computer simulations were performed to investigate the spatiotemporal properties of light scattered from strong scattering media in Which the waves in the medium interferewith each other at scattering points. Some new phenomena, such as contrast enhancement of the forward-scattered light intensity and negative spatial intensity correlation of the backscattered light, were revealed and their physical origins were elucidated using the crossing probability of photon path trajectories .(4) Spectral correlation methodfor fluid velocimetry : The cross-correlations of scattered light intensities with different wavelengths were measured using concentrated flowing microspheres undergoing Brownian motion. It was shown that the correlation time measured by the spectral correlation method is unaffected by the Brownian motion, its reciprocal values being proportional to the flowing velocity of the scattering medium. A new technique for velocity measurement was proposed which is applicable to dense colloidal media. Less