Deep Aspheric Testing Based on phase-shift Electronic Moiré Patterns

The resolutions of CCD camera and digital computer are limited by Nyquist frequency when deep aspheric wavefronts are tested using phase-shifting technique. A new powerful technique based on parallel generations of three phase-shift patterns through electronic multiplication with computer- generated graftings and low pass filtering, is proposed for measuring wavefronts with large departures from a reference sphere such as those encountered during testing of steep aspheric surfaces. The phase distribution of aspheric surfaces is obtained using a three-step phase-shifting algorithm.