High-resolution trace gas detection by sub-Doppler noise-immune cavity-enhanced optical heterodyne molecular spectrometry: application to detection of acetylene in human breath

Abstract

A sensitive high resolution sub-Doppler detecting spectrometer, based on noiseimmune 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 2.2 × 10 -13 cm -1 at 60 s, which, for the targeted transition in C2H2, corresponds to a 3σ detection sensitivity of 130 ppt, is demonstrated. It is shown that despite significant spectral interference from CO2 at the targeted transition, which precludes Db detection of C2H2, acetylene could be detected in exhaled breath of healthy smokers.

Comb coherence-transfer and cavity ring-down saturation spectroscopy around 1.65 μm: kHz-accurate frequencies of transitions in the 2ν3 band of 12CH4

“…16 However, only recent advances in laser technology and introduction of high sensitivity detection techniques, such as cavity ring-down spectroscopy (CRDS), make saturation spectroscopy attractive for a wide range of problems in high precision molecular spectroscopy and optical metrology. 6,[17][18][19][20][21][22][23][24][25][26][27] It is important to underline that application of high-finesse optical resonators for saturation spectroscopy demands laser radiation of high spectral purity. A first reason is that Lamb dips are spectrally narrow: Lorentzian widths of less than 500 kHz are typically observed.…”

“…16 However, only recent advances in laser technology and introduction of high sensitivity detection techniques, such as cavity ring-down spectroscopy (CRDS), make saturation spectroscopy attractive for a wide range of problems in high precision molecular spectroscopy and optical metrology. 6,17–27…”

Cavity Ring-Down Spectroscopy: Recent Technological Advancements, Techniques, and Applications

“…On the other hand, the HD molecule whose high-precision measurements enable verification of fundamental theories has also been probed with a high accuracy of 30 kHz . NICE-OHMS has also been utilized for C 2 H 2 sensing in human breath even in the presence of CO 2 overlapping in the 1.534 μm region . Here, C 2 H 2 was determined in the breath of smokers in the ppbv range, and a sensitivity of ∼130 pptv was attained.…”

“…Nevertheless, human exhaled breath is a complex matrix with overlapping spectral features. Axner and co-workers 69 provided an innovative methodology in combination with a NICE-OHMS system for precise detection of a target species in the presence of a significant spectral overlapping from another abundant associated species. They validated the methodology measuring C 2 H 2 with ppt level sensitivity from the exhaled breath of healthy smokers in the presence of strong spectral overlapping from exhaled CO 2 .…”

“…68 NICE-OHMS has also been utilized for C 2 H 2 sensing in human breath even in the presence of CO 2 overlapping in the 1.534 μm region. 69 Here, C 2 H 2 was determined in the breath of smokers in the ppbv range, and a sensitivity of ∼130 pptv was attained. As a laboratory-based technique, NICE-OHMS provides superior performance as compared to many others.…”