Design of twin computer-generated hologram for absolute testing of aspheric surfaces

Abstract

Testing of aspheric surfaces by means of computer-generated holograms（CGHs）is well known. To perform an absolute test of rotationally symmetric aspheric surfaces, a specially designed computer-generated hologram (CGH) that reconstructs an aspherical wave as well as a spherical auxiliary wave. Since both phase functions have the same symmetry and their pattern is simultaneously encoded, we call this type of multiplex hologram a Twin-CGH. The spherical wave is used for calibration. The design principle of Twin-CGH is introduced in this paper. We mathematically analyze the Twin-CGH constructed by taking the phase corresponding to the linear combination of two weighted phase functions. We show that this Twin-CGH may be written as a new linear combination for the original phase functions with new weights. Then we absolutely test aspheric surfaces by Twin-CGH.