Reflective grating interferometer in a noncollimated configuration

A third-order aberration analysis for a reflective grating interferometer ( RGI) is developed for a noncollimated configuration. In such a configuratio n the RGI is still a folded and reversing interferometer that is sensitive only to coma aberration, as it is in the collimated configuration. However, for an unaberrated input beam converging on a plane grating, the reflectiv e grating of the interferometer introduces self-aberrations. Consequently, a nonnull fringe pattern is obtained. Nevertheless, a RGI in the noncollima ted configuration has the potential to be applied for isolating and measuri ng coma, and a possible configuration for this application is proposed. As an example of the application, the coma of a large mirror could be isolated and measured by use of a converged configuration to avoid the main limitat ion in using the RGI in a configuration with a nearly collimated beam. (C) 2000 Optical Society of America.