Abstract

A retrosphere (either a convex ball or a concave mirror) is a convenient element to use in the interferometric optical test of an objective. However, under some conditions the retrosphere can cause ambiguities in the interferogram due to the effects of Fresnel diffraction. This paper provides diffracted beam propagation analysis and results showing the magnitude of these effects for a range of system f-numbers and retrosphere radii. The paper also presents an alternative retroreflector design concept that avoids the ambiguities.

© 2010 OSA, SPIE