Study of systematic error on PS/PDI with two optical fibers

Curved distortion on measurement wavefront by using two point light sources

Abstract

A phase-shifting point diffraction interferometer (PS/PDI) with two optical fibers is appropriate for absolute surface figure measurement for large aperture optics. The point light source for the measurement wavefront is set at a position other than the center of curvature of the test mirror. The reflected wavefront by the mirror focuses at another position. The measurement wavefront curves itself owing to difference between the positions of the point light source and the focusing point. Measurement result of the figure of the test mirror contains the curved distortion. The error has been studied using computer simulation. We present the way to eliminate the error.