LARGE-APERTURE HIGH-ACCURACY PHASE-SHIFTING DIGITAL FLAT INTERFEROMETER

A large-aperture high-accuracy phase-shifting digital flat interferome ter that is a combination of optics, mechanics, electricity, and algor ithm is described, The aperture size is 250 mm and a liquid surface is used as an absolute flat to eliminate system error. The accuracy is b etter than lambda/50 (lambda=0.6328 mu m, peak-to-valley value). The t ested aperture can be enlarged to 500 mm. This interferometer has been used as an optical flat standard instrument for China. The optical in terferometer, phase shifter, and calibration of precision are describe d. (C) 1996 Society of Photo-Optical Instrumentation Engineers.