Cavity ringdown spectroscopy at 2 ${\mu}$m wavelength assisted by a comb-locked optical parametric oscillator

TL;DR

This paper presents a high-precision cavity ring-down spectrometer at 2 μm wavelength, utilizing a comb-locked optical parametric oscillator and frequency comb stabilization for accurate molecular spectroscopy.

Contribution

It introduces a novel comb-locked cavity ring-down spectrometer with sub-MHz frequency accuracy, enabling the observation of previously unmeasured N₂O transitions.

Findings

Achieved 108 kHz uncertainty in frequency measurements.

Observed a new N₂O transition not previously recorded.

Demonstrated high-precision spectroscopy at 2 μm wavelength.

Abstract

We report on a comb-locked cavity ring-down spectrometer developed for high-precision molecular spectroscopy at 2 ${\mu}$m. It is based on the use of an external-cavity diode laser that is offset-frequency locked to the signal output of a singly-resonant optical parametric oscillator. This latter acts as reference laser, being locked to a self-referenced optical frequency comb, which in turn is stabilized against a GPS-disciplined Rb-clock. The performance of the spectrometer is investigated by probing a pair of N$_2$O transitions belonging to hot vibrational bands. One of these, never observed before, is included in the N$_2$O line list of the ExoMol database. Absolute center frequencies are retrieved with a 1-${\sigma}$ global uncertainty of 108 kHz.