The changes in the microtopography of a metal surface during a corrosion process are measured by decorrelation of the scattered speckle fields under coherent illumination. For that purpose a quantitative relation between the decorrelation of the scattered light fields and the rate of corrosion is established in a theoretical model, based on the statistics of phase and reflectivity 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 sensitivity. From the analysis of a series of images taken at equal time intervals during the corrosion process, the degree of interrelation among subsequent topography changes is calculated.
© 1999 Optical Society of America
(030.6140) Coherence and statistical optics : Speckle
(100.4550) Image processing : Correlators
(120.6150) Instrumentation, measurement, and metrology : Speckle imaging
(120.6650) Instrumentation, measurement, and metrology : Surface measurements, figure
(290.5880) Scattering : Scattering, rough surfaces
Thomas Fricke-Begemann, Gerd Gülker, Klaus D. Hinsch, and Karen Wolff, "Corrosion Monitoring with Speckle Correlation," Appl. Opt. 38, 5948-5955 (1999)