Alignment error model of subaperture stitching interferometry for aspheric surface based on wavefront aberrations

Abstract

We present a novel strategies and a prototype for large optical surfaces test with subaperture stitching. The kinematics model with six degrees of freedom is built to determine the initial configuration of each subaperture, according to the records of nulling motion. An alignment error model based on wavefront aberrations is established for compensation and error separation. Subapertures are primarily stitched by homogeneous coordinate transformation, least square method and Zernike polynomial fitting. Then an error-separation matrix of stitching model is developed to analysis the characteristics and effects of alignment error on test results. The expressions of the alignment errors for aspheric surface testing are built based on motion structure and wavefront aberrations theory. So the alignment errors can be separated and compensated efficiently. Subapertures are then simultaneously stitched by minimizing deviations among the overlapping region, as well as deviations from the nominal surface. As a result, precise prior knowledge of the nulling and alignment motion, which is of six degrees of freedom, is no longer required. Simulations and experiments are given to verify the validity and precision of the proposed algorithm. The result shows that the proposed method with alignment compensation is quite efficient.