Intracavity trace molecular detection with a broadband mid-IR frequency comb source

TL;DR

This paper demonstrates ultrasensitive intracavity spectroscopy using broadband mid-IR frequency combs generated by optical parametric oscillators, enabling simultaneous detection of multiple gases with high sensitivity.

Contribution

It introduces a novel intracavity spectroscopy method with broadband OPOs operated near degeneracy, achieving high sensitivity and multi-gas detection in the mid-IR range.

Findings

Achieved part-per-billion sensitivity levels.

Detected multiple gases simultaneously.

Observed effective path length enhancement.

Abstract

Ultrasensitive detection of methane, isotopic carbon dioxide, carbon monoxide, formaldehyde, acetylene and ethylene is performed in the spectral range 2.5 - 5 \mu m using intracavity spectroscopy in broadband optical parametric oscillators (OPOs). The OPOs were operated near degeneracy and synchronously pumped either by a mode-locked erbium (1560 nm) or thulium (2050 nm) fiber laser. A large instantaneous bandwidth of up to 800 cm$^{-1}$ allows for simultaneous detection of several gases. We observe an effective path length enhancement due to coherent interaction inside the OPO cavity and achieve part-per-billion sensitivity levels. The measured spectral shapes are in good agreement with a model that takes into account group delay dispersion across the broad OPO frequency band.