Measurement of aspheric surface combining point diffraction interferometry and annular subaperture stitching

Point diffraction interferometry (PDI) combined with annular subaperture stitching is proposed for ultrahigh-accuracy measurements of aspheric surfaces. By adding an axial movement to the test optics in the PDI system, aspheric surfaces with large departures can be measured with high accuracy by stitching the annular measurement data of different axial positions. We examine the principle of PDI-based annular subaperture stitching and the stitching algorithm. Simulations and experiments demonstrate the feasibility and effectiveness of our proposed method. Our method retains the ultra-high accuracy of PDI while extending the vertical dynamic range of the interferometer, enabling nanometer or even subnanometer accuracy measurements of large-departure rotationally symmetric aspheric surfaces.