Patent ID: 6914683

Claim:
A method for detecting small periodic wave patterns in surfaces, comprising: illuminating a surface using a primary beam of monochromatic coherent light; directing said primary beam onto the surface at a large angle of incidence relative to a normal to the surface of the workpiece, and approximately at right angles to expected periodic wave patterns; generating a diffraction image of the periodic wave patterns produced in secondary light returned by the surface; and evaluating an intensity and spacial distribution of neighboring intensity maxima in the diffraction image; wherein, for separate determination of the wave pattern of a ground surface, in which the wave pattern has finer, steeply indented stochastic ground structures superimposed on it, the ground structures are shadowed by providing an approximately grazing incidence of the primary light beam onto the workpiece surface at a constant angle of incidence within an angular range of approximately 83±2°, whereby a diffraction image solely representing the wave patterns is produced because of an isolated illumination of the wave patterns thereby achieved, with primary light incident on their sides facing towards and away from the light and on respective wave crests.