Freeform surface measurement with non-null interferometry

Abstract

Freeform surfaces have drawn intensive attention in optical imaging and illumination field because of its great flexibility in optical design. However, the fabrication and testing of freeform surfaces remain a great challenge due to the arbitrary shape. Interferometry is among the high-accuracy testing method of optical surfaces. How to generate a non-rotationally symmetric wavefront similar with the surface under test and retrieve the phase from dense interferogram are hotspot issues. In this paper, we introduce two key technologies in non-null interferometry to solve the above-mentioned problems. The first is the design method of an off-axis catadioptric non-null compensator including a deformable mirror. The second is phase retrieval of single dense interferogram with digital moire phase shifting interferogram and wavelet analysis. Simulations demonstrate the feasibility of the proposed method.