Non-null compensator design method in digital Moiré interferometry for freeform surface measurement

Abstract

High accuracy interferometric testing for freeform optics surface has always been a great challenge because of its arbitrary form. Our group proposed a Digital Moire Interferometric Technique (DMIT) based on partial compensator (PC) for aspheric surface testing since the year 2003. But the PC design method for non-rotational symmetric freeform surface is still a challenge. In this paper, we propose a PC design method for non-null freeform surface measurement. The PC generates non-rotational symmetry aberration by off axis and rotation round axis. Later the design criterion of PC is also analyzed. Finally an off-axis aspheric surface was measured in the simulation experiment, and the error of PV and RMS is 0.0053λ and 0.0498λ theoretically. Experimental results indicate that the designed PC is able to be utilized in freeform surface measurement.