Analyses and applications of singular intensity variations in Gaussian scattering fields of laser light

最近，在高斯散斑的框架下发现了具有奇异性质的随机场。本研究旨在通过理论、实验和模拟的方法分析这种随机场的统计特性和产生条件。结构散斑的产生机理研究发现，当扩散器被环形狭缝小孔照射时，会出现结构散斑(簇状散斑)。散斑聚集的各向同性是由于环形缝隙的圆形对称性造成的。通过计算机模拟，揭示了散斑聚集的起源。利用小粗糙度散射器实验揭示了部分发展的簇状散斑的发展过程。轴向长空间相关性与无衍射光束特性的关系，从理论上证明了环形狭缝照明产生的簇状散斑在轴向上具有很长的空间相关性。实验结果得到了验证。实验表明，随机分维散射体和普通散射体的双重散射过程可以在二次散射体的傅里叶变换面上产生具有分形性的散斑强度分布。这验证了之前给出的理论预测。还考察了散斑的三维相关特性。菲涅耳衍射区和像面上的分维散斑研究表明，采用适当的结构，在菲涅耳衍射区和普通漫射体的像面上也可以产生具有分维性质的散斑强度分布。

Recently, random fields with singular properties were found in the framework of Gaussian speckles. The present study aims at analyzing statistical properties and generation conditions of such random fields through theoretical, experimental and simulation approaches.1. Generating mechanism of structured specklesStructured speckles (clustered speckles) are found to appear when a diffuser is illuminated by a thin ring-slit aperture. An isotropy of the speckle clustering was shown to be due to circular symmetry of the ring slit. An origin of speckle clustering was shown by means of computer simulations. Developing process of partially-developed clustered speckles are revealed experimentally by using small-roughness diffusers.2. Axially long spatial correlationWith relation to properties of a non-diffracting beam, it was shown theoretically that the clustered speckles produced by the ring-slit illumination have very long spatial correlations in the axial direction. The results were verified by experiments.3. Generation of fractal specklesIt was shown experimentally that a double scattering process using a random fractal diffuser and an ordinary diffuser can produce speckle intensity distributions with a fractal property in a Fourier transform plane of the second diffuser. This verified a theoretical prediction given previously. A 3D correlation properties of the speckles were also examined.4. Fractal speckles in Fresnel and image regionsIt was shown that speckle intensity distributions with fractal properties can also be generated in the Fresnel diffraction regions and in the image plane of the ordinary diffuser by using suitable configurations.