Changing surfaces—a theoretical and experimental approach

Abstract

This work is concerned with rough surfaces that undergo small random changes in their morphology. These surfaces and their changes are studied by means of the second order statistical properties of the scattered light. Specifically, the speckle correlation method is used. A new theoretical model relating the speckle phenomenon to changes in the surface roughness is studied. A decreasing quadratic exponential relationship of the speckle correlation to the surface variation is found. This model is valid for dielectric or metallic surfaces. However, for the sake of simplicity, a translucent (dielectric) diffuser is studied and some new experimental results are reported. In the experimental work, the transmitted speckle pattern from a translucent rough surface is recorded before and after this surface suffers a change. The correlation between the two speckle patterns is calculated and related to the surface variation. The roughness is varied in a controlled way by immersing it in liquids of different refractive indices. A good agreement between theoretical descriptions and experimental results obtained in quasi-real time is achieved.