Unambiguous measurement of surface profile using a Sagnac interferometer with phase feedback

摘要

The fringe prgfiles from a two beam intefferometer with phase feedback are almost unambiguous over a range of 2π or more. This allows phase and therefore surface profile to be determined directly from output intensity of an interferometer. In this paper we describe how feedback can be applied to a polarisation Sagnac common path interferometer using a parallel aligned nematic liquid crystal spatial light modulator. Initial experiments have shown that the device is capable of measuring profiles to accuracies grater than one tenth of a wavelength.