The Malus Fabry-Perot interferometer

We describe a general model for the behaviour of a sensor based on a Fabry- Perot interferometer placed between crossed polarizers. Compared to single- pass polarimeters, the sensitivity for the measurement of intracavity aniso tropies is shown to be enhanced by a factor of the order of the square of t he finesse compared to single-pass polarimeters. Our model, based on a vect orial spatial description of the cavity, predicts the response of the syste m to circular and/or linear intracavity anisotropies. It also gives the ult imate sensitivity and takes into account the spurious backgrounds. Experime ntal illustrations are presented for different types of reciprocal and non- reciprocal anisotropies. Moreover, it is shown that the insertion of an opt ical bias combined with a modulation of the intracavity anisotropies leads to experimental sensitivities limited only by the shot noise level, in agre ement with theoretical predictions. We discuss further improvements and pot ential applications for the polarimeter. (C) 1999 Elsevier Science B.V. All rights reserved.