Tunable double-mode sensor for multi-gas detection based on the external-cavity diode laser

An optoelectronic sensor system based on a thermoelectrically cooled (TEC) continuous-wave (CW) double-mode external-cavity diode laser (ECDL) is demonstrated for a multi-gas analysis in this paper. An ECDL that can simultaneously emit at two different wavelengths in the range from 1275 to 1340 nm was utilized as the excitation source for molecule absorption. Each wavelength can be independently tuned. The ECDL was combined with an off-axis cavity-enhanced absorption spectroscopy (OA-CEAS) cell to perform multi-gas sensing. It was shown that the sensor system can be used for detection of multiple trace gases (H₂O, CO₂, and CH₄). The advantages of the reported sensor system are that a single laser and detector system are utilized and that there is no overlapping between the two modes on the mirror surfaces because of the single fiber output from the ECDL.