Aspheric surfaces can provide significant benefits to optical systems, but manufacturing high-precision aspheric surfaces is often limited by the availability of surface metrology. The lack of 3D surface data required to drive aspheric manufacturing equipment can create risk and unwanted variation in the manufacturing process. One typical approach to gathering this 3D data is using dedicated null correction optics in addition to the interferometer itself. However, the cost, lead time, inflexibility, and calibration difficulty of such null optics makes interferometric aspheric testing a far less attractive solution than the relatively simple spherical test. Subaperture stitching interferometry was originally developed to allow for the full-aperture 3D measurement of large-aperture spheres and flats using commercially available interferometers and transmission elements^{1, 2, 3} The method was then extended to the measurement of mild aspheric surfaces, by exploiting the local best-fitting and magnification of the high density fringe patterns associated with nonnull interferometry.⁴ Subaperture stitching interferometry was then extended by an order of magnitude through the use of a Variable Optical Null (VON) that allowed the measurement of high-departure aspheres. The automated VON has an optical system with a range of motion control that generates an optical wavefront that closely matches the surface of the asphere for each subaperture. The residual wavefront error is measured with a standard interferometer, and the fullaperture surface profile of the asphere is reconstructed using advanced stitching algorithms. This method allows for the accurate measurement of aspheres with more than 1000 waves of departure from best-fit sphere, without the use of dedicated null lenses.

Date Published: 16 October 2012
PDF: 5 pages
Proc. SPIE 8416, 6th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Advanced Optical Manufacturing Technologies, 841604 (16 October 2012); doi: 10.1117/12.2009289

Published in SPIE Proceedings Vol. 8416:
6th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Advanced Optical Manufacturing Technologies
Li Yang; Eric Ruch; Shengyi Li, Editor(s)