Abstract

Diffraction by rough reflective surfaces is studied in theory and experiment. Specifically, the diffraction caused by one-dimensionally grooved metallic surfaces is analyzed for roughness between 0.025- and 3.2-µm rms height. A noncontact optical method which provides a real-time display of Fourier transforms for each of the sample surfaces is compared to a computer-aided technique that models the noncontact optical system. To model the optical system, the phase perturbation to a wave front reflected by the rough surfaces is derived and a fast Fourier transform routine is implemented. These surfaces are categorized by the standard deviation of the transform intensity distributions. Good agreement is found between the optical system and the computer model; as the surface roughness increases, the standard deviation of the transform intensity distribution decreases. Also, the Fourier transforms of a phase reflection grating, frequency 10 mm⁻¹, and a metallic grinding surface with rms roughness equal to 0.1 µm, are presented for three angles of illumination—0, 10, and 30°—to illustrate the effective increase in grating frequency and apparent decrease in roughness as illumination angle is increased.

© 1985 Optical Society of America