Speckle from a cascade of two diffusers

Abstract Speckle patterns for single pieces of frosted glass and for pairs with controlled separation have been studied. Intensity versus frequency data are obtained at fixed positions in the Fresnel zone using a tunable dye laser for the illumination. From these intensity data, both the autocorrelation versus frequency and the spectral intensity are computed and shown to be sensitive to the detailed microstructure of the object's surface. Examples of diffuse surfaces adequately characterized by smooth distribution functions and those with glint-like facets requiring δ-function augmentation are presented. For the cascade the autocorrelation function drops initially as controlled by the fine-scale roughness of the separate diffusers, i.e., almost independently of their spacing which is varied from 20 to 110 μm. Its low frequency content is found to be dependent on this spacing.