Precise optical rotation measurements play an important role in the analysis of chiral molecules in various fields, especially in biological chemistry and pharmacology. In this paper, we demonstrate a new variant of continuous-wave cavity-enhanced polarimetry for detecting the optical activity of two enantiomers of a chiral molecule at 730 nm. It is based on a signal-reversing technique for which the chiral specific rotation is directly determined by the cavity ring-down signal from two counter-propagating beams in a bow-tie cavity. In particular, we ensure reproducible excitation of both modes by broadening the linewidth of a diode laser source by application of a radio frequency perturbation to its injection current. The performance of the polarimeter is demonstrated for the specific rotation of (+)- and (−)-α-pinene in different environments, including the pure vapor, open air, and the liquid phase; the detection precision ranges between 10–5 and 10–4 degrees per cavity pass depending on the environment. The apparatus is a robust and practical tool for quantifying chirality and can be developed for the entire visible and near-infrared spectral regions.
