Surface measurement and evaluation of large-aperture continuous phase plates

Based on the stitching method using global least squares and the image fusion method, the sub-aperture stitching interferometry method for continuous phase plates(CPPs) is established. The residual surface error calculated by correlative matching is used to evaluate the CPPs fabrication quality. Moreover, the measurement system is built using high precision dynamic interferometer. The numerical simulation and measurement are carried into execution for a CPP with 430 mm430 mm aperture. The results show that the root mean square(RMS) of residual surface error obtained by numerical simulation is only 0.005 nm and the experimental RMS of residual surface error is less than 5 nm. So these parameters can meet the demands of surface measurement and evaluation of large-aperture continuous phase plates, and the correctness and feasibility of this method are verified.