Testing surface form of precision optics by a point diffraction interferometer with two beams

Abstract

Testing of an X-ray mirror by a point diffraction interferometer (PDI) D7 with two beams is described. Thanks to the two independent test and reference beams, mirrors metrology using the D7 coupled with accessory optics becomes straightforward and reliable. Therefore procedure of systematic error removal and sub-aperture measurements with stitching are simplified. In this paper, we describe the main technique to achieve high accuracy of stitching sub-aperture wavefronts, followed by further perspectives of the described instrument.