A compact mid-infrared dual-gas CH₄/C₂H₆ sensor using a single interband cascade laser and custom electronics

Abstract

A compact mid-infrared (MIR) dual-gas sensor system was demonstrated for simultaneous detection of methane (CH 4) and ethane (C 2 H 6) using a single continuous-wave (CW) interband cascade laser (ICL) based on tunable laser absorption spectroscopy (TDLAS) and wavelength modulation spectroscopy (WMS). Ultracompact custom electronics were developed, including a laser current driver, a temperature controller and a lock-in amplifier. These custom electronics reduce the size and weight of the sensor system as compared with a previous version based on commercial electronics. A multipass gas cell with an effective optical length of 54.6 m was employed to enhance the absorption signal. A 3337 nm ICL was capable of targeting a C 2 H 6 absorption line at 2996.88 cm-1 and a CH 4 line at 2999.06 cm-1. Dual-gas detection was realized by scanning both the CH 4 and C 2 H 6 absorption lines. Based on an Allan deviation analysis, the 1 σ minimum detection limit (MDL) was 17.4 ppbv for CH 4 and 2.4 ppbv for C 2 H 6 with an integration time of 4.3 s. TDLAS based sensor measurements for both indoor and outdoor mixing ratios of CH 4 and C 2 H 6 were conducted. The reported single ICL based dual-gas sensor system has the advantages of reduced size and cost without influencing the midinfrared sensor detection sensitivity, selectivity and reliability.