High-sensitive double incidence multi-pass cell for trace gas detection based on TDLAS

A high-precision gas detection system with a dual-incidence multi-pass cell (D-MPC) based on TDLAS was developed, which can simultaneously measure quadruple component gases. Two Distributed Feedback (DBF) Laser Diodes with central wavelength of 1654 nm and 2004 nm were utilized to measure methane (CH4) and carbon dioxide (CO2) for evaluating the performance of the system. High sensitivity and low frequency drift were accomplished by utilizing the second harmonic signals (WMS-2f) detection and peak-locking technology. A LabVIEW-based control and acquisition program, which could be used for direct absorption and wavelength modulation, was developed. Kalman adaptive filtering, Least Mean Squares (LMS) adaptive filtering and S-G filtering were employed for denoising in direct absorption spectroscopy (DAS), respectively, and optimal denoising technology of S-G filtering was selected. According to Allan deviation analysis, the optimal detection precision for CH4 and CO2 was 12 ppb at an integration time of 36 s and 270 ppb at an integration time of 43 s, respectively. A two-day continuous monitoring of atmospheric CO2 and CH4 was implemented to verify the system stability and can be applied to other trace gases monitoring.