Analysis for property of CGH on spherical surface used for aspheric surface testing

Two simple approximative analytical expressions for spatial frequency of various diffraction orders of spherical Computer-Generated Hologram (CGH) and minimal aperture of filtering diaphragm are derived through analyzing influence of various elements on wave-front during measuring process for convex aspheric surface. It is demonstrated that measurement of aspheric surface with spherical CGH can reduce the characteristic sizes of CGH, thus redusing the preparation precision of CGH. Suitable phase function of CGH and filtering diaphragm aperture are selected for fully filtering undesirable orders according to the derived expressions, thus full-aperture measurement of convex aspheric surface is realized. The practical design examples and the experimental results show that when select diaphragm with diameter of 0.2mm and CGHs with line width varying in the range of 40~800micron, the full-aperture measurement of convex aspheric surface with an aperture of 110mm, spherical radius of 500mm and aspheric coefficient of 1 is performed. The measurement result is coincident with the analysis result.