An application of speckle correlation to dynamical surfaces

Abstract

A theoretical model describing speckle correlation as a decreasing quadratic exponential function of roughness changes was published in a previous paper. In this work, the theoretical model in a real situation is analyzed: paint drying over rough surfaces with a roughness larger than the wavelength of the He-Ne laser beam used to illuminate it. Speckle correlation of the scattered light is applied to study changes in the system surface-drying paint. A digital algorithm is used to evaluate the correlation of speckles taken while the paint dries. The speckle patterns are captured at different moments of the process, i.e., a first set of pictures when the paint is fresh (first 30 minutes) and another set in a period of several hours. The speckle patterns in the early group were stored every one or two minutes. The speckle correlation is evaluated between the first picture and the others. A graph of correlation vs. time is analyzed using the model and considering that the solvent evaporation follows a decreasing exponential function. The other group is formed by speckle patterns stored every twenty minutes. The speckle patterns are studied as mentioned above and the correlation between one picture and the next is performed as well. That is, the speckle correlation is now evaluated between consecutive patterns. These experimental changes are compared with the theoretical model. Good agreement between the theoretical and experimental results is found.