Aspheric and free-form surfaces test with non-null sub-aperture stitching

A free-form surface sub-aperture stitching interferometry (FSSI) is proposed for aspheric and free-form surfaces testing. Different from normal annular and circular sub-aperture stitching method, non-null interferometric configuration and irregular sub-apertures are employed to make the best use of the resolved fringes. Meanwhile, a multi-aperture simultaneous reverse optimizing reconstruction (MSROR) process is proposed for full aperture figure error reconstruction. With the multi-configuration model, full aperture figure error would be extracted in form of Zernike polynomials from sub-apertures wavefront data by the MSROR method. This method concurrently accomplishes sub-aperture retrace error and misalignment correction, requiring neither complex mathematical algorithms, nor sub-aperture overlaps. The experiments show that, the aspheric annular sub-aperture stitching accuracy with the proposed FSSI is more than 1/50 lambda (rms) comparing with the result of ZYGO Verifier Asphere interferometer. The bi-conic surface sector sub-aperture stitching accuracy is about 1/50 lambda (rms) comparing with result of Taylor Hobson contourgraph in longitudinal section contour.