Mid-infrared dual-gas sensor for simultaneous detection of methane and ethane using a single continuous-wave interband cascade laser.

A continuous-wave (CW) interband cascade laser (ICL) based mid-infrared sensor system was demonstrated for simultaneous detection of atmospheric methane (CH) and ethane (CH). A 3.337 µm CW ICL with an emitting wavenumber range of 2996.0-3001.5 cm was used to simultaneously target two absorption lines, CH at 2996.88 cm and CH at 2999.06 cm, respectively. The sensor performance was first evaluated for single-gas detection by only targeting the absorption line of one gas species. Allan deviations of 11.2 parts per billion in volume (ppbv) for CH and 1.86 ppbv for CH with an averaging time of 3.4 s were achieved for the detection of these two gases. Dual-gas detection was realized by using a long-term scan signal to target both CH and CH lines. The Allan deviations increased slightly to 17.4 ppbv for CH and 2.4 ppbv for CH with an averaging time of 4.6 s due to laser temperature and power drift caused by long-term wavelength scanning. Measurements for both indoor and outdoor concentration changes of CH and CH were conducted. The reported single ICL based dual-gas sensor system has the advantages of reduced size and cost compared to two separate sensor systems.