Surface figure measurement of flat mirrors based on the subaperturestitching interferometry

Large flat mirrors can be characterized using a standard interferometer coupled with stitching the subaperture measurement data. Such systems can measure the global full map of the optical surface by minimizing the inconsistency of data in the adjacent regions. We present a stitching technique that makes use of a commercial phase-shifting Twyman- Green interferometer in combination with an iterative optimized stitching algorithm. The proposed method has been applied to determine the surface errors of planar mirrors with an accuracy of a few nanometers. Moreover, the effect of reference wavefront error is explored. The feasibility and the performance of the proposed system are also demonstrated, along with a detailed error analysis and experimental results.