Absolute surface figure measurement of aspherical surfaces with diffracted wavefronts as reference waves emitted from two optical fibers

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In this year, we have concentrated on to prevent unwanted interference fringes which occurs in phase-shifting interferometry of PS/PDI system. The interference fringes used in PS/PDI are projected on FOP (Fiber Optic Plate). The FOP is used to transfer the interference fringes from its front surface to rear surface. The FOP consists of a large number of optical fibers bundled together. Coherency of the transferred interference fringes decreased at the rear surface of FOP. Therefore CCD image of the fringes did not contain the unwanted fringes or patterns caused by end reflection of optics. Source of vibration was removed by using (1) CCD camera with electronic shutter, and (2) redesigning of shifting program for PZT stage. As a result, repeatability of concave mirror (diameter:200mm, ROC: 1500mm) measurement was estimated to be 0.38nm rms.With the results described above, we have tried to estimate measurement error of the PS/PDI system by phase shifting interferometry between two diffr … More acted waves emitted from optical fibers. As a result, b y removing (1) specifically-patterned error caused by FOP, and (2) fringe error caused by mechanical vibration of experimental environment, the measurement error of the PS/PDI was estimated to be 0.35nm rms. This value may not decrease until we protect an emergent mechanical vibration during the measurement procedure.In principle, the PS/PDI does not give us absolute surface figure directly in the measurement of aspherical surfaces because of a huge distortion of the diagnostic wavefront. Therefore we have tried to reconstruct the absolute surface figure using the PS/PDI result. We have made an original phase diagnostic program based on Helmholtz-Kirchhoff integral theorem. This program reconstructs very spherical surface figure using the result of PS/PDI and an intensity distribution of diagnostic spherical wavefront which reflected on the sample mirror. In the near future, an effectiveness of the program will be checked in the measurement of actual surface such as parabolic reflector. Less