Reconstruction of surface profiles from their diffraction spectra

A possible method for reconstruction of two-dimensional, periodic surface profiles, from their diffraction spectra is outlined. Formulas for the distribution of diffracted power, based on physical optics, are summarized and computed by approximating real profiles by piecewise linear functions. The profiles are reconstructed from measured spectra by a steepest descent method. A computer program searches for profiles whose spectra fit as close as possible to the measured spectra. For experimental demonstration a low-power CO(2) laser is used as radiation source, and the roughness profiles of a turned metal cylinder are reconstructed and compared with traced profile curves.