“…This is because the targeted gases mentioned above have their absorption features in this area of the electromagnetic field [ 14 , 15 , 16 , 17 , 18 , 19 ], as one can see in Figure 1 . Mid-IR gas sensor types are different in cost and efficiency, depending on their configuration [ 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 ]. Some of the most sensitive systems (sensitivity up to parts-per-trillion concentration), such as the mid-infrared sensor system based on continuous-wave (CW) interband cascade laser (ICL) [ 16 ], or those based on Tuneable Diode Laser Absorption Spectroscopy (TDLAS), Quartz-Enhanced Photoacoustic Spectroscopy (QEPAS) [ 15 ], include laser as emitting sources.…”