Analysis of the local defects of a concave spherical surface using three measurement techniques

摘要

When an optical surface has local deformations, it is not always practical to measure the entire surface at one time, because an average of the entire surface is obtained and the local deformations are smoothed. In a previous work we used the principle of the Chalmers test described by Martin , for analyzing just local defects of an optical surface, the technique uses a reflective spatial light modulator (RSLM), which allows the screen to remain at a fixed position, and only two apertures are used at a time. Our proposed method measures the local or zonal defects in the wavefront. The use of an RSLM provides a very flexible way of selecting a particular zone to be tested. The advantage of the proposed dynamic Chalmers test is that using an RSLM it is possible to select a pair of holes in real time, for any zone, and with different sizes and orientation of the holes. In this work, we compare the results obtained previously, with three different techniques: the first one is the traditional analysis of fringes used in Chalmers experiment. The deviations of the interference fringes from a straight line were calculate, according to the equation of Guenther. The second is an analysis by computer, where we developed a computer program to analyze an interferogram produced by a commercial interferometer (ZYGO™), with the computer program it is possible to know the position of the dark fringes. The ideal separation the dark fringes is obtained by analyzing an area of the interferogram that has no deformations. Finally we analyze the profile of the interference fringes corresponding to the local areas using the commercial program "Durango Interferometry Software".