Interference inspection procedure - compares specimen shape with master by superposition of interference patterns

摘要

The method for checking the shape of a specimen against that of a master uses optical interference effects, and produces very sharply defined interference patterns. Light from a source, preferably a divergent beam laser is spread by a lens and passed through a diffraction grating. The interference pattern falls on the specimen and generates a pattern of contour lines which is imaged by a lens on to a photographic plate or other recording device. Superimposition of the resulting image with that obtained in similar fashion from the master shows deviations in the form of Moire fringe patterns.