Three-step shift-rotation absolute measurement of optical surface figure with irregular shaped aperture

The absolute testing technique has been widely employed in sub-nanometer optical surface metrology, we have presented a generalized shift-rotation absolute measurement method for high-numerical-aperture spherical surfaces (Yang et al., 2017). In this paper, a simple and effective three-step shift-rotation absolute testing technique for optical surface figure with irregular shaped aperture is presented. The test surface is tested in an original, a rotational and a shift position. Based on the orthonormal polynomials over irregular shaped aperture, the absolute figure of the test surface is separated from the reference surface errors by the two measurement difference data. Simulation results presented in the paper indicated the validity of the three-step shift-rotation absolute measurement method. The measurement results show a good agreement with the results measured by commercial profiler. The novel three-step shift-rotation absolute testing technique is a promising method to measurement the optical flat and spherical with the irregular shaped aperture.