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

Absorption coefficients and scattering losses of TGG, TGP, KTF, FS, and CeF₃ magneto-optic crystals in the visible via cavity ring down spectroscopy

“…Optic crystals play a vital role in various applications in optics and lasers, such as in laser cavities as gain crystals (synthetic ruby, Nd:YAG, Yb:YAG, Ti:sapphire, etc), and in optical modulators ( i.e., electro-optic, acousto-optic, and magneto-optic modulators) [1,2]. In particular, magneto-optic (MO) crystals have significant applications in optical isolators [3], unidirectional ring lasers [4], and sensitive signal-reversing Cavity Ring-Down Polarimetry (CRDP) setups [5][6][7][8][9][10][11][12][13][14]. Such applications, and the development in recent years of high-power diode and fiber lasers which require good optical isolation, pose a requirement for high-quality MO crystals.…”

Absolute optical chiral analysis using cavity-enhanced polarimetry

“…To date, however, all CCP experiments have used pulse-based measurement approaches [i.e., based on the principles of cavity ring-down polarimetry (13,14,16,17)], which are generally susceptible to detection noise and significant technical noise and result in low numbers of collected photons (≪milliwatts) and reduced measurement duty cycles (<1%). These are the primary reasons why recent CCP demonstrations have reached only poor chiral detection limits (~microrads per pass) within relatively long integration times (~minutes) (13)(14)(15)18), conditions that have hindered the extension of CCP to real-time chiral analysis. Maximally benefiting from the sensitivity improvement available in a cavityenhanced approach, as is the case for CCP, becomes feasible in fully continuous-wave measurement schemes.…”

“…S1). Crucially, the placement of an intracavity Faraday rotator, in relation to the symmetry of natural optical activity and the available counterpropagating modes of propagation within the cavity, enables crucial signal-reversal operations that allow for absolute polarimetric measurements not requiring sample removal for a null-sample measurement or instrument calibration (13)(14)(15). To date, however, all CCP experiments have used pulse-based measurement approaches [i.e., based on the principles of cavity ring-down polarimetry (13,14,16,17)], which are generally susceptible to detection noise and significant technical noise and result in low numbers of collected photons (≪milliwatts) and reduced measurement duty cycles (<1%).…”

Absolute optical chiral analysis using cavity-enhanced polarimetry

“…As a result, the application of chiral analysis by ORD and CD measurements has remained limited to the detection of high-concentration samples, in particular liquids. Recently, a polarimetric technique for enhanced ORD and CD measurements was developed, dubbed cavity-enhanced chiral polarimetry (CCP) [14][15][16][17][18] . CCP employs a ring (four-mirror) optical cavity in a bowtie configuration, where the light always passes through the chiral sample from the same direction, to enhance the chiroptical signals (ORD, CD) by the large number of cavity passes (optimally >10 ' ); Fig.…”

“…1. Crucially, the placement of an intracavity Faraday rotator, in relation to the symmetry of natural optical activity and the available counter-propagating modes of propagation within the cavity, enables crucial signal-reversal operations that allow for absolute polarimetric measurements not requiring sample removal for a null-sample measurement or instrument calibration [16][17][18] . To date, however, all CCP experiments have reached only poor chiral detection limits (~μrad/pass) within relatively long integration times (~min) [16][17][18][19] , conditions that have hindered the extension of CCP to real-time chiral analysis.…”