Comb-locked cavity ring-down spectroscopy of CO2 at 2-micron wavelength

TL;DR

This paper introduces a highly precise, SI-traceable cavity ring-down spectrometer for CO2 detection at 2 microns, utilizing a comb-locked system with advanced spectral analysis for accurate gas measurements.

Contribution

The development of a comb-locked cavity ring-down spectrometer with refined spectral analysis for high-precision CO2 measurement at 2 microns.

Findings

High-precision CO2 absorption spectra recorded

Line center frequencies and pressure coefficients determined

CO2 mole fractions measured with subpromille uncertainty

Abstract

We report on a comb-locked cavity ring-down spectrometer developed for high-precision, SI-traceable, molecular spectroscopy of air-broadened CO2 gas samples. The experimental setup relies on the use of a singly-resonant optical parametric oscillator that acts as an intermediate link between a 2 micron external-cavity diode laser and an optical frequency comb stabilized against a GPS-disciplined Rb-clock. Absorption spectra of the R(50) ro-vibrational component of the CO2 20012-00001 band have been recorded with high precision and fidelity. As a result of a refined spectral analysis, based on the implementation of the modified Hartmann-Tran profile, line center frequencies, pressure broadening and pressure shifting coefficients have been determined. Finally, we demonstrate the measurement of CO2 mole fractions with a subpromille statistical uncertainty