Measurement of convex aspheric mirror by non-null testing

Conventional testing methods for convex aspheric surfaces were briefly reviewed, and two novel methods for testing convex asphere by partial compensation method and sub-aperture stitching interferometry (SSI) were proposed. The basic principle and theory of the two methods were investigated. The partial compensator was designed and customized, the system error of the partial compensator was calibrated, and the synthetical optimization stitching model and the effective stitching algorithm were established based on homogeneous coordinate transformation and simultaneous least-squares fitting. The prototype and setup for testing of convex asphere by the non-null testing were developed. A convex SiC asphere with the aperture of 130 mm was tested by the two methods respectively. The results show that the difference of PV and RMS error between SSI and partial compensation is 0.010 and 0.002 respectively, the full aperture surface maps of the two methods are consistent and it provides two non-null testing methods for measuring convex aspheric surfaces.