Abstract
A tunable diode laser absorption spectroscopy (TDLAS)-based methane sensor, employing a miniature dense-pattern multi-pass gas cell (MPGC) and a continuous wave, room temperature interband cascade laser (ICL), is reported. The optical integration based on an advanced folded optical path design and an efficient ICL control system with appropriate electrical power management results in a methane sensor with a small footprint (32 x 20 x 17 cm(3)) and low-power consumption (6W). The direct absorption measurement strategy allows absolute quantitative assessments without any calibration. Polynomial and least-squares fit algorithms are employed to remove the baseline of the spectral scan and retrieve CH4 concentrations, respectively. An Allan-Werle deviation analysis shows that the measurement precision can reach 1.4 ppb for a 60 s averaging time. Continuous measurements lasting seven days were performed to demonstrate the stability and robustness of the reported methane sensor.