Gas-phase optical activity measurements using a compact cavity ringdown polarimeter

Abstract

We present a compact polarimeter, which can perform sensitive measurements of optical rotation in vapor. The operation of the polarimeter is based a Cavity Ring-Down scheme which employs two signal reversals, which increase sensitivity and reduce noise, allowing the realization of sensitive measurements in the presence of spurious birefringence. We describe the operation of the polarimeter, give the basic equations for the signal analysis and retrieval of optical rotation angle, and present measurements that demonstrate a sensitivity of ~80 μdeg/pass.

Assignment-free chirality detection in unknown samples via microwave three-wave mixing

“…Mass spectrometry and Nuclear Magnetic resonance (NMR) rely on chiral derivitization reagents and can be sensitive to contaminants [4][5][6]. For unknown multi-component mixtures, polarimetry can be inconclusive, as the calculation of specific rotation requires knowledge of concentration and it is often referenced to neat samples [7][8][9]. Spectroscopic methods such as vibrational, photoelectron circular dichroism [10][11][12][13][14], and microwave spectroscopy [15][16][17][18][19][20][21][22][23] can be mixture compatible and provide highly accurate information on species identity.…”

Rapid parameter determination of discrete damped sinusoidal oscillations

“…Several different research fields rely on the precise and accurate extraction of the time constants and frequencies of damped sinusoidal signals. Prominent examples include: nuclear magnetic resonance (NMR) [1], where information on the structure and the spin environment of a target molecule is extracted from precise determination of the frequency and decay constant of a damped sinusoidal signal; free-induction-decay (FID) optical magnetometry [2][3][4][5][6][7], where the magnetometric sensitivities depend on the precision of the measurement of the oscillating frequency; and pulsed/continuous-wave cavity ring-down polarimetry (CRDP) [8][9][10][11][12][13][14][15] and ellipsometry (CRDE) [16][17][18][19], where polarization-dependent absorption and refraction/reflection through/by an optical medium is extracted with high sensitivity through the precise measurement of the signal-decay time and its polarization beat frequency.…”

Continuous-Wave Cavity-Enhanced Polarimetry for Optical Rotation Measurement of Chiral Molecules

“…More recently, bow-tie CRDP using pulsed lasers has been developed involving two counter-propagating linearly polarized beams, in which the effects of intracavity birefringence are cancelled by means of a signal-reversing technique and a reference Faraday rotation angle is induced by an intracavity magneto-optic crystal. − In this case, the optical rotation is then deduced from the two cavity ring-down signals without needing to remove the sample from the polarimeter. The pulsed CRDPs utilize lasers that are typically expensive and relatively bulky and have large optical linewidths (∼GHz or more).…”