Abstract

Metrology of spherical surfaces for form error at the <λ/20 level requires reference surfaces which exceed this surface quality. To certify optics and references in this regime, some type of absolute testing is required. Absolute testing of spheres by interferometry has appeared several times in the technical literature. The procedure was originally proposed for the Twyman-Green interferometer and later applied to Fizeau interferometers.^1,2,3 It requires three measurements of the part: two at the confocal position, rotating the part 180° between measurements and one measurement at the cat's-eye (point focus) position(see Figure 1).

© 1994 Optical Society of America