Computer reconstruction of two-dimensional random rough surfaces from scattered light measurement

The profile of a two-dimensional random rough surface is visualized by computer processing. For this purpose the studied surface is scanned by a thin light line (with a width of 30 mu m), for which the surface profile appears one-dimensional. The reference (the field of the laser beam), the scattered and the mixed fields (the field obtained from the mixing of the reference and the scattered fields) are registered for every light line [1]. The surface profile illuminated by every light line is expanded in a Fourier series as a sum of sinusoidal gratings. The surface is reconstructed by subsequent computer processing of the optical fields since the obtained one-dimensional profiles are arranged in the same way as during the scanning. Solutions for the amplitudes of all the harmonics in a Fourier series for every light line are found utilizing the Kirchhoff approximation. The surface is scanned with 100 Lines over a 20 mu m distance. The studied surface is three-dimensionally visualized The statistical parameters such as the mean roughness Ra, root mean square sigma, and correlation length lambda are calculated for every line along with the mean values of these parameters for the whole surface. The obtained Ra and sigma values are in good agreement with those measured by a contact pin method.