An analysis of a surface flaw detection method is presented in which oblique illumination is combined with a high pass spatial filter to detect the light scattered from surface flaws. The effects of surface finishes of test samples (meteoric plates) are assessed statistically, and the sensitivity of the system is calculated. Data have been collected on diffraction patterns and surface scratch detection for three stainless steel plates having different surface finishes. The results agree with theoretical considerations and are quite promising.
T. Sawatari, "Surface Flaw Detection Using Oblique Angle Illumination," Appl. Opt. 11, 1337-1344 (1972)