Diffraction analysis of rough reflective surfaces.

For ground metallic samples illuminated at various angles of incidence, optical transform patterns are determined theoretically and then verified both experimentally and using computer simulations. Surface roughness in the range from 0.025 to 3.2 microm is studied and means for categorizing surface roughness automatically are established. A noncontact optical method which provides a real-time display of Fourier transforms is compared to a computer-aided technique that models the optical system using profilometer data as an input. Also, the Fourier transforms for a periodic phase-reflection surface are presented at three angles of illumination to illustrate the effective increase in grating frequency and apparent decrease in roughness as the illumination angle is increased. Excellent results are obtained in accurately measuring roughened flat metallic surfaces remotely.