Measurement of aspheric optical surface by quantitative shadow method model developing with image-processing techniques

This article introduces a new method based on knife-edge test to quantitatively characterize local surface deformations of aspheric surface. A set-up of image processing under computer controlling is placed behind of traditional shadow measure device for recording and analyzing the images. Through picking up the characteristics of images, the relationship is determined between illumination levels changing and deformations of surface based on the Fourier Optics principle, and the aspheric surface under test can be reconstructed. The simulation date indicate that the RMS accuracy can reach about 1λ□λ=632.8nm□in one dimension for one parabolic surface under manufacture, therefore this method is efficient and economic for measuring and reconstructing surface in pre-polishing state.