Testing of Aspheric Surfaces with Computer Generated Holograms

Usually, aspheric testing by CGH uses Twyman-Green interferometer setup. Then the accuracy is limited by the reference mirror and optical elements been used. We use the modified Fizeau interferometer setup. A second beam splitter is placed in the focal plane of a diverger lens. The reflection beam by this B.S. is regarded as reference wave. Then the setup will have three merits: (1) The two beams go through almost the same position at each optical element, so the quality of the optical elements such as the diverger lens and the first beam splitter can be neglected. (2) The second beam splitter (now the reference surface) is easily to be made high quality because of the region been used is very small. So we may consider the reference wave as perfect. (3) It is easily to control the diffraction order to obtain the interference pattern. Besides, we describe the real interference pattern by computer based on analytic equations and calculate the exact position of the interference fringes as in the conventional hologram. Therefore, the plot of the CGH is pure interferometric type.