Open-Air, Broad-Bandwidth Trace-Gas Sensing with a Mid-Infrared Optical Frequency Comb

TL;DR

This paper demonstrates a mid-infrared optical frequency comb for broad-bandwidth, open-air trace-gas sensing, enabling rapid and precise measurement of methane and water vapor concentrations over a 26-meter outdoor path.

Contribution

It introduces a novel mid-infrared frequency comb source combined with VIPA spectrometer for real-time, broadband atmospheric trace-gas detection in open air.

Findings

Successful detection of CH4 and H2O absorption lines

Quantitative concentration measurements in indoor and outdoor environments

Millisecond acquisition time for spectral measurements

Abstract

A mid-Infrared frequency comb is produced via an optical parametric oscillator (OPO) pumped by an amplified 100 MHz Yb:fiber mode-locked laser. We use this source to make measurements of the concentration of the atmospherically-relevant species of CH4 and H2O over a bandwidth of 100 nm centered at 3.25 um. Multiple absorption lines for each species are detected with millisecond acquisition time using a virtually-imaged phased array (VIPA) spectrometer. The measured wavelength-dependent absorption profile is compared to and fitted by a model, yielding quantitative values of the atmospheric concentration of both CH4 and H2O in a controlled indoor environment, as well as over a 26 m open air outdoor path.