Application of stitching interferometer to controlling assembly distortion

During the assembly of large plano-optics, astigmatism will be generated when the assembly manner is improper. This astigmatism has the same character in local surface and full-aperture surface. The flat stitching interferometer has the ability to measure both the local surface and the full-aperture surface. Therefore, we employ a flat stitching interferometer to inspect local the surface during assembly, by which the astigmatism is controlled. Experiments show that the local surface precision of the flat stitching interferometer arrives at 50 nm (PV) and the space rate reaches 5 mm-1, enabling intermediate frequency detection. On the other hand, the flat stitching interferometer can measure the full-aperture of optics by scanning. The test uncertainty is 100 nm and the difference relative to large aperture interferometer is less than 0.04（=632.8 nm）.