FRINGE FORMATION IN AN INPLANE DISPLACEMENT MEASUREMENT CONFIGURATIONWITH TWOFOLD INCREASE IN SENSITIVITY - THEORY AND EXPERIMENT

A fringe-formation theory for a dual-beam illumination configuration t hat leads to a twofold increase in sensitivity for the measurement of in-plane displacement is described. Here we have taken into account al l four beams simultaneously that are generated at the image plane owin g to two-beam illumination and their cross-interference terms for frin ge formation. We show that the sensitivity obtainable is the usual int erferometric sensitivity when we take into account all four beams simu ltaneously and doubles only when the retroreflected beams are observed . A detailed theory and an experimental demonstration of the method ar e presented. (C) 1998 Optical Society of America.