Space-invariant achromatic grating interferometers: theory.

A general analysis of an n-grating interferometer under various conditions of illumination is presented, where n = 1,...,4. Conditions for fringe localization and effects of misalignment are given. The lesser known phenomenon of the imaging of a grating by a second grating is described from which the fringe forming capacity of multiple-grating interferometers stems; this can occur regardless of the coherence of the source.