Tran Dang-Bao-An, Peverall Robert, Rosson Sarah, Manfred Katherine M, Ritchie Grant A D
Opt Express. 2021 Sep 13;29(19):30114-30122. doi: 10.1364/OE.435006.
We present precise optical rotation measurements of gaseous chiral samples using near-IR continuous-wave cavity-enhanced polarimetry. Optical rotation is determined by comparing cavity ring-down signals for two counter-propagating beams of orthogonal polarisation which are subject to polarisation rotation by the presence of both an optically active sample and a magneto-optic crystal. A broadband RF noise source applied to the laser drive current is used to tune the laser linewidth and optimise the polarimeter, and this noise-induced laser linewidth is quantified using self-heterodyne beat-note detection. We demonstrate the optical rotation measurement of gas phase samples of enantiomers of α-pinene and limonene with an optimum detection precision of 10 µdeg per cavity pass and an uncertainty in the specific rotation of ∼0.1 deg dm (g/ml) and determine the specific rotation parameters at 730 nm, for (+)- and (-)-α-pinene to be 32.10 ± 0.13 and -32.21 ± 0.11 deg dm (g/ml), respectively. Measurements of both a pure R-(+)-limonene sample and a non-racemic mixture of limonene of unknown enantiomeric excess are also presented, illustrating the utility of the technique.
我们展示了使用近红外连续波腔增强偏振法对气态手性样品进行的精确旋光测量。旋光通过比较两束反向传播的正交偏振光束的腔衰荡信号来确定，这两束光在存在旋光样品和磁光晶体时会发生偏振旋转。将宽带射频噪声源施加到激光驱动电流上，用于调谐激光线宽并优化偏振仪，并且使用自外差拍频检测对这种由噪声引起的激光线宽进行量化。我们展示了对α-蒎烯和柠檬烯对映体的气相样品的旋光测量，每次腔程的最佳检测精度为10微度，比旋光度的不确定度约为0.1度·分米²/克，并且确定了在730纳米处，(+)-和(-)-α-蒎烯的比旋光参数分别为32.10±0.13和-32.21±0.11度·分米²/克。还展示了对纯R-(+)-柠檬烯样品和对映体过量未知的非外消旋柠檬烯混合物的测量，说明了该技术的实用性。
