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多次散射的相干光的统计特性，并开发提取关于多次散射物体的结构和运动信息的新技术。(1)光的后向散射增强：从理论和实验上研究了入射光的空间相干性、悬浮颗粒的尺寸以及散射光的偏振方向对后向散射增强峰的影响。所有这些参数被发现强烈地影响增强的形状和峰值。由于粒子的布朗运动的散射光的时间波动也进行了评估，并发现一个特征行为的光散射正好在向后的方向。(2)分形介质的多重散射：质量分形随机介质的光散射表现出与均匀随机介质不同的特性。这是 关于我们 指出分形介质所特有的后向散射峰的形状是由其特有的光子在介质中的散射自由程分布所形成的。该特征可用于测量多散射体的分形维数。弹道光的强度也被发现提供有关分形结构的信息。(3)强多次散射的新现象：利用计算机模拟研究了强散射介质中光散射的时空特性，在强散射介质中，波在散射点处相互重叠。利用光子路径轨迹的交叉概率揭示了前向散射光强度对比度增强和后向散射光强度空间负相关等新现象，并阐明了其物理根源。(4)流体速度测量的光谱相关法：利用布朗运动的浓缩流动微球，测量了不同波长散射光强度的相关性。结果表明，用谱相关法测得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。提出了一种适用于稠密胶体介质的速度测量新方法。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