Measurement of parallelism of the surfaces of a transparent sample using two-beam nonlocalized fringes produced by a laser.

A detailed analysis of an interference technique for measuring the parallelism of the two surfaces of a transparent sample is presented. The technique utilizes the displacement of the center of a set of two-beam, high-visibility, nonlocalized circular fringes, which are produced when divergent laser light is incident on the sample, to give a direct measure of the wedge angle between the two surfaces of the sample. A simple equation is given relating the displacement of the center of the circular fringe system to the wedge angle. The technique is simple and lends itself to use under shop conditions.