Cavity-enhanced optical frequency comb spectroscopy in the mid-infrared - application to trace detection of H2O2

TL;DR

This paper presents the first use of cavity-enhanced optical frequency comb spectroscopy in the mid-infrared for sensitive, real-time trace detection of hydrogen peroxide amidst water, achieving ppb-level detection limits.

Contribution

The study introduces a novel mid-infrared cavity-enhanced frequency comb spectroscopy setup with high sensitivity and stability for trace gas detection.

Findings

Achieved a detection sensitivity of 8 ppb for hydrogen peroxide.

Demonstrated stable, real-time detection with a noise reduction factor of 300.

Successfully detected other gases like acetylene, methane, and nitrous oxide.

Abstract

We demonstrate the first cavity-enhanced optical frequency comb spectroscopy in the mid-infrared wavelength region and report the sensitive real-time trace detection of hydrogen peroxide in the presence of a large amount of water. The experimental apparatus is based on a mid-infrared optical parametric oscillator synchronously pumped by a high power Yb:fiber laser, a high finesse broadband cavity, and a fast-scanning Fourier transform spectrometer with autobalancing detection. The comb spectrum with a bandwidth of 200 nm centered around 3.75 {\mu}m is simultaneously coupled to the cavity and both degrees of freedom of the comb, i.e., the repetition rate and carrier envelope offset frequency, are locked to the cavity to ensure stable transmission. The autobalancing detection scheme reduces the intensity noise by a factor of 300, and a sensitivity of 5.4 {\times} 10^-9 cm^-1 Hz^-1/2 with a resolution of 800 MHz is achieved (corresponding to 6.9 {\times} 10^-11 cm^-1 Hz^-1/2 per spectral element for 6000 resolved elements). This yields a noise equivalent detection limit for hydrogen peroxide of 8 parts-per-billion (ppb); in the presence of 2.8% of water the detection limit is 130 ppb. Spectra of acetylene, methane and nitrous oxide at atmospheric pressure are also presented, and a line shape model is developed to simulate the experimental data.