Beam blocking method for optical characterization of surfaces

A new method for measuring local topography of optical surfaces gives excellent lateral resolution. To obtain one-dimensional image information, the surface is mechanically scanned at a slow rate and vibrated sinusoidally in the direction of the scan. The motion lies in a plane perpendicular to an incident, focused, probing laser beam. The reflected laser beam, angularly modulated by the moving variations in the vibrating surface, is gathered by a lens and directed toward a knife-edge and photodiode combination. One half of the beam is blocked by the knife-edge, the orientation of which is at a right angle with respect to the angular motion of the beam. The detected signal from the photodiode is proportional to the derivative of the local slope convolved with a spread function stemming from the surface vibration and the beam profile. The operational characteristics of the proposed method are superior compared with available methods. © 2001 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 11, 164–169, 2000