Vertex radius of curvature fabrication error measurement of aspheric surface based on aberration analysis in partial compensation interferometry

Vertex radius of curvature (VROC) is one of the most important shape parameters to determine the properties of an optical conicoid surface. Precisely measuring the VROC error is critical for manufacturing and aligning optical conicoid. In general, the VROC error is measured directly by curvature fitting from profile measurement data from contact or noncontact testing. And to our knowledge there is no effective way to measure VROC error with non-null interferometry. In this paper, partial compensation interferometry (PCI) with aberration analysis is presented for determining the VROC error. PCI is a kind of non-null interferometry proposed by the authors aiming at testing conicoid or generally aspherical surface figure error (SFE). SFE is defined as the irregular difference between the measured and nominal surface. It mainly comes from local manufacture error and can be calculated from interferograms with digital moiré phase-shifting (DMPSI) method. Here we suppose SFE has already been measured with PCI. Then we measure the VROC error with aberration analysis of the residual wavefront at the exit pupil of the interferometer. Simulations are done to verify the method, and the results show that the relative measuring accuracy is less than 0.003%.