High resolution ultra-sensitive trace gas detection by use of cavity-position-modulated sub-Doppler NICE-OHMS - Application to detection of acetylene in human breath

TL;DR

This paper presents a highly sensitive, high-resolution spectrometer based on NICE-OHMS for trace gas detection, capable of detecting acetylene in human breath despite spectral interference, with potential applications in medical diagnostics.

Contribution

The study introduces a novel cavity-position-modulated NICE-OHMS system with balanced detection and dithering to reduce etalons, achieving record sensitivity for trace gas detection in complex biological samples.

Findings

Achieved an Allan deviation of 2.2×10⁻¹³ cm⁻¹ at 60 s.

Demonstrated detection sensitivity of 130 ppt for acetylene.

Successfully detected acetylene in human breath despite interference from CO₂.

Abstract

A sensitive high resolution sub-Doppler detecting spectrometer, based on noise-immune cavity-enhanced optical heterodyne molecular spectrometry (NICE-OHMS), for trace gas detection of species whose transitions have severe spectral overlap with abundant concomitant species is presented. It is designed around a NICE-OHMS instrumentation utilizing balanced detection that provides shot-noise limited Doppler-broadened detection. By synchronous dithering the positions of the two cavity mirrors, the effect of residual etalons between the cavity and other surface in the system could be reduced. An Allan deviation of the absorption coefficient of coefficient of $2.2 \times 10^{-13}$ $\text{cm}^{-1}$ at 60 s, which, for the targeted transition in $\text{C}_{2}\text{H}_{2}$, corresponds to a $3\sigma$ detection sensitivity of 130 ppt, is demonstrated. It is shown that despite significant spectral interference from $\text{CO}_{2}$ at the targeted transition, which precludes Db detection of $\text{C}_{2}\text{H}_{2}$, acetylene could be detected in exhaled breath of healthy smokers.