A sensitive method for optical birefringence measurement is presented. To optimize the signal over the noise ratio, the polarization of the laser beam is modulated exceptionally with a high frequency electro-optical modulator. The specially developed optical apparatus exhibits high sensitivity and accuracy, which were checked by measuring the Cotton-Mouton effect in nitrogen as a function of the pressure. It is able to measure the retardance down to 2x10-4 rad. This apparatus will be used with the locked optical cavity. The optical cavity will serve as an optical path multiplier for increasing the sensitivity. This proposed set-up will be able to measure the Cotton-Mouton effect in helium, where the birefringence effect is Δn ≈ 2.4x10-16.
"High sensitive method for optical birefringence measurement", Proc. SPIE 9442, Optics and Measurement Conference 2014, 94420O (7 January 2015); doi: 10.1117/12.2086877; https://doi.org/10.1117/12.2086877