Subaperture stitching interferometry based on detection of marker center

The stitching interferometer systems with larger relative movement will show a significantly lower positioning accuracy of subapertures. As a consequence a stitching method based on detection of artificial circular mark center to find the necessary translation between two neighborly subapertures is implemented. Firstly,we take coordinates of mark centers as the marks' coordinates by which the translation is computed. Then all the subaperture data are unified into the same reference by homogeneous coordinate transformation and the full aperture phase are stitched by using mechanical system error compensation algorithm. A subaperture stitching process for a 468 mm flat mirror was carried out including surface accuracy tests during the polishing. In this process,subaperture stitching test offered the surface data precisely for polishing,which ensured the surfaceerror converged quickly to a final RMS of 35 nm. The experimental results show that the method relaxes the precision requirement for subaperture location and can get the full aperture phase for large optical element correctly.