Corrosion monitoring with speckle correlation

The changes in the microtopography of a metal surface during a corrosion pr ocess are measured by decorrelation of the scattered speckle fields under c oherent illumination. For that purpose a quantitative relation between the decorrelation of the scattered light fields and the rate of corrosion is es tablished in a theoretical model, based on the statistics of phase and refl ectivity changes of point scatterers at the surface. The speckle fields are recorded by a CCD camera and processed numerically in a computer, yielding the standard deviation of the topography changes with nanometer sensitivit y. From the analysis of a series of images taken at equal time intervals du ring the corrosion process, the degree of interrelation among subsequent to pography changes is calculated. (C) 1999 Optical Society of America.