Chapter 8 - Optical Testing

Abstract

This chapter discusses several types of interferometers and techniques used in testing optical components and optical systems. The Fizeau interferometer allows absolute measurements of deviations from flatness by using a liquid surface as a reference flat surface. Alternately, three series can be tested in a series of combination to evaluate their individual errors. One common application of the Fizeau interferometer is to check the parallelism of the faces of a transparent plate. With a laser source, problems of coherence are eliminated and quite thick plates can be tested. This chapter also describes Fizeau interferometer— which uses convergent or divergent light to test curved surfaces, the Twyman-Green interferometer, which uses collimated light; unequal-path interferometers, which can be used to test large concave mirrors; the scatter-plate interferometer, which also makes use of diffraction but gives a fringe pattern that can be interpreted directly; and grating interferometers, which make use of a very stable arrangement, instead of thin-film beamsplitters.