High accuracy measurement of aspherical surface by point diffraction interferometry

Point diffraction interferometry (PDI) provides a promising method for measurement of spherical and aspherical surfaces with nanometer or even sub-nanometer (RMS) accuracy. In this paper, an optimal design of PDI system is discussed in detail and experiment systems are established. A 152.4 mm aspheric mirror is measured in our experiment and the test results show a good agreement with Zygo interferometer testing results. Also, a novel method which combining the point diffraction interferometry and annular subaperture stitching technology for high accuracy measurement of large-departure aspherical surface is proposed and the principles are presented.