Subaperture stitching test for large aperture mild acylinders.

Large aperture acylinders are typical optical elements in synchrotron radiation systems and laser shaping devices. The manufacture of such ultra-precision optical elements requires ultra-precision measurement of the surface figure. The use of computer-generated hologram (CGH) customized for the acylindrical surface can only achieve a "one-to-one" test. Limited by the aperture of CGH, it also cannot meet the requirements for large aperture acylinders. In order to realize flexible test of large aperture acylinders with mild aspherical departure, a method of surface figure reconstruction for subaperture measurements under near-null test is proposed. It is based on ray tracing and rigid body transformation. By using a general CGH for cylindrical surface, near-null test for various acylindrical surfaces can be realized. Subaperture stitching test can overcome the problem of the limited CGH aperture which cannot meet the requirement of large aperture acylinders. Finally an elliptical cylindrical mirror with an aperture of 240mm (sagittal) × 350mm (tangential) is measured. And the cross test is realized by using a customized CGH to verify the validity and precision of the proposed method. [ABSTRACT FROM AUTHOR]