An interference method for determining the degree of parallelism of (laser) surfaces.

A method for measuring the angle between two nearly parallel surfaces is presented. Convenient to use, the method has ample brightness and sensitivity for use in aligning the various surfaces often found in laser cavities. A cw laser is focused to provide a point source of light which illuminates the two surfaces in question. The reflected light beams form an interference pattern from which the angle between the surfaces can be easily measured. A simple equation is given relating the fringe position to angular separation.