Knowledge Bank

We demonstrate the absolute measurement of optical rotation using a four-mirror cavity-ring-down polarimetric setup. A four-mirror bow-tie cavity allows counter-propagating laser beams, for which symmetry is broken with a longitudinal magnetic field acting upon an intracavity magneto-optic window (producing a Faraday rotation $\theta F$). A chiral sample is introduced in one arm of the cavity, producing a chiral rotation . The different symmetry of the two rotations produces a total rotation of () for one laser beam, and () for the counter-propagating beam. These rotations produce a polarization beating in the cavity ring-down, of frequency and for the clockwise and counter-clockwise beams, respectively. Analysis of the difference () yields the chiral rotation angle , where the sign of the angle is determined by the sign of the applied magnetic field. Therefore, subtracting the signals using +$ecB$ and ?$ecB$ yields , allowing the absolute determination of , without needing to remove the sample [1]. We demonstrate these absolute optical rotation measurements for chiral gases ($\alpha$-pinene) and chiral liquids. This work is a proof-of-principle demonstration of the experimental setup proposed for the measurement of parity non-conserving optical rotation in atomic systems [1]. [1] L. Bougas, G. E. Katsoprinakis, W. von Klitzing, J. Sapirstein, and T. P. Rakitzis, Phys. Rev. Lett {\bf 108}, 210801 (2012).