Phase-shifting point diffraction interferometers with high repeatability

As the accuracy of a Phase-shift Point Diffraction Interferometer(PSPDI) is mainly limited by calibration procedure, and its repeatability is principally influenced by the quality of composed devices and the measuring environments. This paper introduces the composition of the PSPDI and working principles and analyses the error sources which damage the measurement repeatability. Then, a point diffraction interferometer with phase-shifting technique is developed to measure optical surface figures. A spheric concave mirror is tested with this interferometer. Vibration isolation and a special phase reversion algorithm are applied to the measurement. The measuring results show that the measurement repeatability has been better than 0.2 nm RMS. Finally, it points out that further calibration process is necessary to improve the measuring accuracy.