1. Introduction
Gas sensors based on absorption spectroscopy are attractinggreat interest in a variety of applications related to the detectionand control of exhaust gases originating from combustion and otherindustrial devices [1–5]. The ability of these sensors to simulta-neously monitor multiple species is of utmost importance. In manycases, the concentration ratio is more informative than the absoluteconcentrations of individual components. This is due to the depend-ence of the latter on possible dilution by other gases at the point ofmeasurement. For instance, the ratio of CO2to CO is a well-knownindicator of the completeness of combustion, so measurement ofboth gases is often required in technical combustion equipmentor its exhaust gases. Accurate and simultaneous measurement ofthese gases, along with a precise temperature determination, iscrucial to evaluating the environmental and performance aspectsof combustion and gas-reforming devices.