Polarisation dynamics of a birefringent Fabry-Perot cavity

TL;DR

This paper develops a theory for the polarization state dynamics in birefringent Fabry-Perot cavities and validates it with experimental measurements, highlighting the importance of mirror birefringence in high-precision polarimetry.

Contribution

The paper introduces a new theoretical model for polarization dynamics in birefringent Fabry-Perot cavities and confirms its accuracy through experimental validation.

Findings

Theoretical formulas match experimental data well.

Mirror birefringence significantly affects polarization states.

Birefringence effects must be considered in high-precision polarimeters.

Abstract

Optical Fabry-Perot cavities always show a non-degeneracy of two orthogonal polarisation states. This is due to the unavoidable birefringence of dielectric mirrors whose effects are extremely important in Fabry-Perot based high-accuracy polarimeters. We have developed and present here a theory of the polarisation state dynamics in a birefringent Fabry-Perot resonator, and we validate it through measurements performed with the polarimeter of the PVLAS experiment. The measurements are performed while a laser is frequency-locked to the cavity, and provide values for the finesse of the cavity and for the phase difference between the two orthogonal polarisation components introduced by the combination of the two cavity mirrors (equivalent wave-plate). The theoretical formulas and the experimental data agree well showing that the consequences of the mirror birefringence must be taken into account in this and in any other similar experiment.