Light scattering by optically heterogeneous materials: Structural aspects of dichromatic laser speckle patterns

Abstract

An analysis is given of dichromatic speckle patterns formed by small‐angle scattered light in the illumination of optically heterogeneous systems with light of two nearby wavelengths. The existence of the radial‐fibrillar appearance of the speckle patterns is explained; it is shown that the occurrence of the radial‐fibrillar “structure” corresponds to the measurable correlation of dichromatic speckle patterns as specified by the spectral spatial cross‐correlation function of intensity fluctuations. A measurement of speckle‐pattern correlation to determine σz (the standard deviation of optical path fluctuations due to the passage of coherent light through a layer of heterogeneous material) is described, and the relations between σz and the structural parameters for two simple types of heterogeneous materials are discussed. Experimental results obtained with a series of samples of polyethylene filled with CaCO3 are in comparatively good agreement with theoretical values.

Application of interactive image analysis to light scattering patterns of some polymer systems

“…The correlation of dichromatic speckle patterns is proportional to the refractive index fluctuations and is determined from the contrast (visibility) of interference fringes [16].…”