Shot-noise-limited measurement of sub–parts-per-trillion birefringence phase shift in a high-finesse cavity

Abstract

We report on a promising approach to high-sensitivity anisotropy measurements using a high-finesse cavity locked by optical feedback to a diode laser. We provide a simple and effective way to decouple the weak anisotropy of interest from the inherent mirror's birefringence whose drift may be identified as the key limiting parameter in cavity-based techniques. We demonstrate a shot-noise-limited phase shift resolution previously inaccessible in an optical cavity, readily achieving the state-of-the-art level of $3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}$ rad.