Performance criteria in Low Coherence Speckle Interferometry (LCSI)

Electronic Speckle Pattern Interferometry with a light source of short coherence length allows depth-resolved deformation analysis below the surface of light-scattering objects (Low Coherence Speckle Interferometry - LCSI). Interference is tuned to a thin layer - called the coherence layer - by appropriate adjustment of the length of the reference path. The quality of the results is degraded by background light from outside the coherence layer and by de-correlations due to the passage of the useful light through regions that have been altered by the overall deformation field. Basic experimental studies are conducted on a simple two-interface object (two roughened surfaces of glass slides) to determine the effects that one interface (and its deformation) exerts on the quality of the deformation measurement in the other interface. Analytical theoretical calculations of speckle de-correlation on the basis of Fresnel diffraction provide comparative data.