A near-infrared methane detection system using a 1.654 μm wavelength-modulated diode laser

By adopting a distributed feedback laser（DFBL） centered at 1.654 μm, a near-infrared（NIR） methane（CH4） detection system based on tunable diode laser absorption spectroscopy（TDLAS） is experimentally demonstrated. A laser temperature control as well as wavelength modulation module is developed to control the laser＇s operation temperature. The laser＇s temperature fluctuation can be limited within the range of-0.02-0.02 °C, and the laser＇s emitting wavelength varies linearly with the temperature and injection current. An open reflective gas sensing probe is realized to double the absorption optical path length from 0.2 m to 0.4 m. Within the detection range of 0-0.01, gas detection experiments were conducted to derive the relation between harmonic amplitude and gas concentration. Based on the Allan deviation at an integral time of 1 s, the limit of detection（Lo D） is decided to be 2.952×10-（-5） with a path length of 0.4 m, indicating a minimum detectable column density of -1.2×10-（-5） m. Compared with our previously reported NIR CH_4 detection system, this system exhibits some improvement in both optical and electrical structures, including the analogue temperature controller with less software consumption, simple and reliable open reflective sensing probe.