Abstract

The absolute measurement of spherical surfaces is important with optics specified to be less than 1/20 of a wavelength peak-to-valley. A number of techniques have been described in the literature.¹-⁵ A technique widely used with phase-measuring interferometry was first described by Jensen,² and then further discussed by Bruning,³ Truax,⁴ and Elssner et al.⁵ This technique has the advantage of giving the absolute shape of the sphere under test independent of the reference surface and diverger optics as long as the test surface is aligned correctly. The main disadvantage of this technique is the requirement that the test surface be aligned so that it can be rotated and keep the fringe pattern unchanged. A simpler technique has been developed which does not require this precise alignment and requires only two measurements. The result is not exactly an absolute measurement, but as long as the test surface has even symmetry, the test can be absolute. This paper will discuss this new technique and compare it to Jensen's technique.

© 1990 Optical Society of America