MEASURING THE PARALLELISM OF TRANSPARENT AND NONTRANSPARENT PLATES

A technique for measuring the parallelism of the surfaces of transpare nt and nontransparent plates is presented. To obtain a measure of the wedge angle between the two surfaces of the transparent plate, the tec hnique utilizes the displacement of a laser beam that is produced afte r passing through the sample twice. To measure the parallelism in nont ransparent plates a Twyman-Green interferometer is used in conjunction with the apparatus described for measuring transparent plates. In thi s case, the displacement of the laser beam is produced after reflectio n off a single face of the plate. In both cases, the measurements can be made visually with the aid of an electronically generated circular scale stored on a personal computer, or automatically by the same comp uter. The precision of the measurements can be suitably modified by ch anging the setup parameters. (C) 1996 Society of Photo-Optical Instrum entation Engineers.