9 - Optical Testing

Abstract

One of the major applications of interferometry is in testing optical components and optical systems. This chapter discusses optical testing through interferometry and the various types of interferometers. The first one is the Fizeau interferometer, which is used to check the faces of a transparent plate for parallelism and checking slabs of optical glass for homogeneity. The second is Twyman–Green interferometer, which is basically a Michelson interferometer illuminated with collimated light, so that fringes of equal thickness are obtained. The chapter also explores the laser unequal-path interferometers and the point-diffraction interferometer. A brief analysis of wavefront aberrations is also presented in this chapter. A wide variety of shearing interferometers is also discussed. Shearing interferometers have the advantage that no reference surface is required and a very simple and compact optical system can be used to test large surfaces. However, shearing interferometers have the disadvantage that numerical analysis of the interferogram is necessary to obtain the wavefront errors. The chapter discusses the grazing-incidence interferometry. Ground surfaces can be tested at grazing incidence by using a longer wavelength.