Tunable multi-mode diode laser absorption spectroscopy for methane detection

•Low cost methane on-line monitoring system was present by using tunable multi-mode diode laser absorption spectroscopy.•The single absorption signal superposed of several absorption signals increase the detection sensitivity.•High linearity between the peak value of WMS-2f signals and concentrations was obtained.•The sensitivity and accuracy of this system were evaluated.

Tunable multi-mode diode laser absorption spectroscopy for methane detection was demonstrated. The exclusive dependence of the 1318 nm laser modes distribution on the input current and temperature was justified. Stable absorption signals related to the methane concentrations were obtained based on second-harmonic detection technique. A real-time data recording and analyzing software program was developed to realize the on-line gas concentration monitoring. A measurement sensitivity of 25 ppm m and an accuracy of 0.27% of this system were achieved.