arXiv:1002.3812v1 [quant-ph] 19 Feb 2010 Bailly RScI 2009 Highly sensitive frequency metrology for optical anisotropy measurements Gilles Bailly, Rapha¨ el Thon, and C´ ecile Robilliard ∗ IRSAMC; F-31062 Toulouse, France. CNRS, UMR 5589; F-31062 Toulouse, France. (Dated: November 11, 2018) Universit´e de Toulouse-UPS; Laboratoire Collisions Agr´egats R´eactivit´e, In this paper we present a novel apparatus aimed at measuring very small birefringences and anisotropies, based on frequency metrology and not on polarimetry as usual. In our experiment, a very high finesse resonant cavity is used to convert the phase difference into a resonance frequency difference, which can then be measured with very high accuracy. We describe the set-up and present the results of experimental tests which exhibited a sensitivity δn ≃ 2 × 10 − $^{18}$, allowing for the measurement of long-predicted magneto-electro-optical effects in gases. Since the shot- noise limited sensitivity of our apparatus lies well below the state-of-the-art sensitivity, frequency metrology appears as a promising technique for small birefringence measurements. PACS numbers: 33.57.+c, 42.25.Lc, 42.62.Eh, 06.30.Ft Abstract ∗ Electronic address: cecile.robilliard@irsamc.ups-tlse.fr 1