Simultaneous multi-gas detection between 3 and 4 μm based on a 2.5-m multipass cell and a tunable Fabry-Pérot filter detector

We demonstrated a versatile and innovative gas sensing system based on a Fabry-Pérot (FP) filter detector, which operates in the spectral range from 3.1 to 4.4 μm (3226–2273 cm−1) with a spectral resolution of 20 nm. The developed sensor system can be used to record the entire spectrum by means of a one-time scan or, alternatively, to access selected spectral regions by using the tunable FP filter detector. A multipass cell with an effective path length of 2.5 m was implemented to improve the detection sensitivity. The spectra of methane, formaldehyde and carbon dioxide were simultaneously measured, with detection limits of 200 ppm, 900 ppm and 20 ppm, respectively. A seven-day continuous measurement for indoor carbon dioxide gas was carried out demonstrating the stability and robustness of the reported sensor system.