INTERFEROMETRIC TESTING OF PLANE AND CYLINDRICAL WORKPIECES WITH COMPUTER-GENERATED HOLOGRAMS

Increasing demands for accuracy and speed in manufacturing and interna tional standards of quality control require faster and more precise me asurement techniques. Surface inspection and shape control of technica l workpieces is commonly done by tactile profilometers. A faster alter native to this mechanical tool can be realized interferometrically. Gr azing incidence of laser light onto the technical surface reduces spec kle noise significantly. In our setup computer-generated holograms (CG Hs) are used both as references for the technical surfaces to be teste d and as beamsplitter or recombining element. Each class of workpieces requires specific CGHs, e.g., phase gratings for plane surfaces or di ffractive axicons for cylindrical and conical surfaces. An ideally sha ped workpiece will result in a zero fringe field. Deviations from the ideal shape will be indicated by interference fringes and fringe disto rtions. The sensitivity of the interferometer can be adapted to techni cal needs. The surface deviations of the workpiece are superimposed by adjustment aberrations which can be described mathematically with suf ficient accuracy and eliminated by a least squares fit. This measureme nt technique is demonstrated with workpieces of different shape. (C) 1 998 Society of Photo-Optical Instrumentation Engineers.