Optical freeform surfaces have been widely used in optical systems owing to their design degrees of freedom, which cansimplify the structure and improve the performance of optical systems. High accuracy testing for freeform surface isneeded due to the improvement of machining accuracy. However, it is still a challenge to achieve high measuringaccuracy because freeform surfaces lack rotational symmetry. In this paper, an off-axis catadioptric partial compensator(OACPC) design for non-null interferometric method is proposed to measure freeform surface. The design of OACPCconsists of two parts: constructing initial structure and optimizing. The initial structure is obtained by the vectoraberration theory and PW method. Based on the initial structure, the OACPC is generated by modelling and optimizingin the optical design software. In order to verify the feasibility, universality and effectiveness, a design example is given.Theoretical analysis and simulation results demonstrate that the design can realize the measurement of freeform surfaces.
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