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

Abstract

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 (LoD) 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 CH4 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.