Low-Coherence Photothermal Interferometry for Precision Spectroscopic Gas Sensing

Abstract

Laser spectroscopy has shown great potential as a cost-effective method for trace gas detection with high sensitivity and specificity. However, it still falls short in applications such as the measurement of stable isotope ratios, which require high precision and stability. Here, ultrasensitive gas detection with remarkable precision and stability as well as better immunity to isobaric interference is demonstrated by use of low-coherence photothermal interferometry. With a 10 cm long hollow-core fiber, acetylene detection is achieved with a noise-equivalent concentration of 0.7 part-per-billion and measurement precision of 0.025%. The instability of the detection over a period of 3 h is ±0.038%, 10 times better than the state-of-the-art photothermal spectroscopy. The measurement of the 13C/12C isotope ratio of acetylene is demonstrated with measurement precision of ≈0.01%. This study highlights the potential of low-coherence photothermal interferometry as an alternative to mass spectrometers, offering reliable gas detection in a compact form.