Direct Frequency Comb Cavity Ring-Down Spectroscopy Using Vernier Filtering

Tzu-Ling Chen

doi:10.1021/acs.jpca.4c05188

Direct Frequency Comb Cavity Ring-Down Spectroscopy Using Vernier Filtering

2025-01-24

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Łukasz A. Sterczewski

DOI：10.1021/acs.jpca.4c05188

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We present direct frequency comb cavity ring-down spectroscopy with Vernier filtering as a straightforward approach to sensitive and multiplexed trace gas detection. The high finesse cavity acts both to extend the interaction length with the sample and as a spectral filter, alleviating the need for dispersive elements or an interferometer. In this demonstration, a free running interband cascade laser was used to generate a comb centered at 3.3 mu m covering similar to 10 cm-1 (300 GHz), which was coupled into a high-finesse cavity, providing 0.9 km of effective path length. The Vernier configuration transmitted the comb modes in sequence, and ring-down decays could be initiated either with an acousto-optic modulator or by scanning the cavity length beyond the adiabatic limit, with trade-offs between duty cycle and sensitivity. This implementation achieved a figure of merit of 4.3 x 10-8 cm-1 Hz-1/2 per spectral element, and measurements of toluene demonstrated its ability to observe trace concentrations of a continuum absorber. This method does not require anything beyond a conventional single-mode cavity ring-down instrument other than an optical frequency comb, making it readily accessible to a wide range of applications.

Keywords:

FOURIER-TRANSFORM

SPECTROMETER

LASER

Direct Frequency Comb Cavity Ring-Down Spectroscopy Using Vernier Filtering

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