Null test of an off-axis parabolic mirror. II. Configuration with planar reference wave and spherical return surface

This paper complements our previous study on testing a 25.4 mm diameter diamond-turned 90 masculine off-axis commercial-quality parabolic mirror with a spherical test wave in a phase-shifting Fizeau interferometer (Opt. Express 17, 3196-3210 (2009). In this study I reverse the optical system and use the Fizeau interferometer with a planar reference surface, auxiliary components, and the surface of the transmission sphere as a reflecting spherical return surface. As in the previous paper, I present a description of the necessary steps for alignment and measurement validation. The reversal of the optical system, and associated co-ordinate systems, necessitates some changes of hardware and analysis that provide insight into the underlying symmetries, and may prove useful in a wider context.