High performance continuous-wave laser cavity enhanced polarimetry using RF-induced linewidth broadening

Area of Science:

• Analytical Chemistry
• Physical Chemistry
• Spectroscopy

Background:

• Optical rotation is a fundamental property of chiral molecules.
• Accurate measurement of optical rotation is crucial for enantiomeric identification and quantification.
• Existing methods for gaseous samples can be limited in precision and sensitivity.

Purpose of the Study:

• To develop and demonstrate a highly precise method for measuring optical rotation of gaseous chiral samples.
• To quantify the specific rotation of α-pinene and limonene enantiomers.
• To assess the utility of the technique for analyzing non-racemic mixtures.

Main Methods:

• Utilized near-infrared continuous-wave cavity-enhanced polarimetry.
• Employed counter-propagating beams and a magneto-optic crystal to measure polarization rotation.
• Optimized the polarimeter using broadband RF noise for laser linewidth control and quantified linewidth via self-heterodyne detection.

Main Results:

• Achieved an optimum detection precision of 10 µdeg per cavity pass.
• Determined specific rotation of (+)-α-pinene and (-)-α-pinene at 730 nm with an uncertainty of ~0.1 deg dm⁻¹ (g/ml)⁻¹.
• Presented measurements for R-(+)-limonene and a non-racemic limonene mixture, showcasing the technique's applicability.

Conclusions:

• The developed cavity-enhanced polarimetry technique offers high precision for gaseous chiral sample analysis.
• The method provides accurate specific rotation values for enantiomers.
• This technique is valuable for characterizing enantiomeric composition in various chiral compounds.