Spherical optical surface defects digitizing evaluation system

Abstract

This paper introduces a spherical optical surface defects evaluation system (SSDES) based on the dark-field microscopic scattering imaging (DFMSI) method. The specially designed annular illuminant with variable aperture angles ensures the condition of DFMSI for spherical optical components with variable surface shapes and radii of curvature. On account of the small imaging field of view (FOV) of the SSDES relative to the large spherical optical component under test, the scanning path for subaperture images is planned along longitudes and latitudes of the spherical surface to detect the whole surface. Besides, for avoiding the misplaced subaperture images stitching due to the decenter error, a centering system is utilized to perform the alignment of the optical axis of the spherical optics in relation to the reference axis before capturing subaperture images. Then we propose a defect evaluation method, primarily involving the threedimensional (3D) image reconstruction and global coordinate transformation, the projective stitching of 3D subaperture images, and the quantitative evaluation of defects, to process the captured spherical subaperture images. Experiments results are shown in good accordance with the OLYMPUS microscope for the relative error within 5%, and validate the SSDES to the micrometer resolution.