A trace CH₄ detection system based on DAS calibrated WMS technique

We report the development of a compact near-infrared (NIR) laser-based trace methane (CH₄) detection system. This detection system relied on a 2334 nm distributed feedback (DFB) fiber laser as the light source. A parallel dense light-spot pattern multipass gas cell (MGC) with 41.5 m effective absorption path length was utilized to improve the system sensitivity. A self-calibration approach based on direct absorption spectroscopy (DAS) calibrated wavelength modulation spectroscopy (WMS) technique was employed to solve the problem of extra concentration calibration requirement in traditional WMS technique, and to improve the accuracy and stability of the system. According to the Allan deviation analysis, 1-s measurement precision of 0.61 ppmv for DAS and 0.16 ppmv for WMS was obtained, which could be further reduced to 0.11 ppmv for DAS and 0.03 ppmv for WMS by averaging up to 80 s and 50 s, respectively. A week-long continuous atmospheric CH₄ concentration measurement was also carried out to demonstrate the long-term performance of our CH₄ detection system. With a fast dynamic response characteristics, high-accuracy and high-sensitivity, the proposed detection system is suitable for CH₄ measurement in many fields such as atmospheric chemistry analyzation, industrial safety monitoring, agricultural information acquisition, etc.