AStudy of anisotropic speckle patterns by rough cylindrical surfaces

The statistical properties of the speckle image from slightly rough cylindrical surfaces in the Fresnel diffraction field are researched. The relation between the correlation function of intensity fluctuations and cylindrical curvature and surface roughness parameter is derived. According to the discretization definition of its intensity fluctuations, the correlation function is obtained in theory and experiment when there is structure difference in radial and axial direction of the cylinder. It is shown that the light speckles are elongated in the direction normal to the cylinder axis for C1,C2, and that the fluctuation of correlation function intensity are differed in the directions parallel and perpendicular to cylindrical axis; the scattering characteristics of the two directions are basically the same for C3,C4. Further experiments show the dimensions of light speckles depend on both the surface roughness and the surface curvature. The result can be used in machinery manufacturing quality control such as column type pipelines, bearing etc.