Abstract: A method and apparatus for determining the profile of a surface using contactless distance measurement, wherein a light pencil which has been scattered and reflected from the surface is split into two light pencils having substantially the same distribution of intensities in a plane transverse to the direction of propagation. In doing so, the ratio of the intensities of the two partial pencils is dependent on the principal beam direction of the light pencil which was scattered and reflected from the surface. At least one of the partial pencils is then detected by a photodetector and a resulting signal from the photodetector is evaluated as an accurate measure of surface profile or roughness. By providing this method and apparatus, noise from interference phenomena such as "speckles" is significantly reduced, and thus, the evaluated signal(s) from the photodetector(s) become more reliable.

Abstract: The invention relates to a process and a device for the interferometric detection of surface displacements of solids, particularly in test material which is excited with ultrasonic waves, in which an illumination laser 10 radiates the test material surface 2, and a portion of the reflected light, after passing through a differing optical path length, is brought into a state of interference, while the interference is identified by an installed detector 9. In arrangements of this type known to the prior art, a very expensive apparatus and control system is needed to assure that demodulation of the reflected laser light is performed with maximum sensitivity.