Analysis of the disturbing diffraction orders of computer-generated holograms used for testing optical aspherics

Aspheric surfaces are increasingly used in the design of high-quality optic al imaging systems. Therefore accurate testing methods for aspherics are al so necessary. One possibility is to use a computer-generated hologram (CGH) as a part of a null lens in an interferometric testing device. However, CG Hs normally have more than one diffraction order, thus causing disturbing a reas in the interferogram. Here a simple approximative analytical expressio n is given for the spatial frequencies of the disturbing light in the inter ferogram coming from the different diffraction orders of the CGH. This expr ession also enables one to calculate the size and the shape of the disturbi ng areas in the interferogram. Some design examples for CGHs are given in a n application of the expression. (C) 2001 Optical Society of America.