UNAMBIGUOUS MEASUREMENT OF SURFACE PROFILE USING A SAGNAC INTERFEROMETER WITH PHASE FEEDBACK

The fringe profiles from a two beam interferometer with phase feedback are almost unambiguous over a range of 2 pi or more. This allows phas e 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 us ing a parallel aligned nematic liquid crystal spatial light modulator. Initial experiments have shown that the device is capable of measurin g profiles to accuracies greater than one tenth of a wavelength. (C) 1 998 Elsevier Science B.V. All rights reserved.