Abstract
Human activities, at a personal and at an industrial level, cause the release of numerous molecular species in the atmosphere. Even a very low level of certain molecules can lead to the alteration of the air quality. Gas sensors are therefore required for monitoring the concentration of such molecules and must fulfill various features. They should be able to detect very little quantity of molecules (sensitivity), should respond only to the target species and not to other species (selectivity), have moderate footprint (compactness) and effective cost. However, actual commercial sensors often lack one of these properties. One promising technology to meet these requirements is based on laser spectroscopy and photoacoustic detection, and in particular a technique called QEPAS. The objective of this PhD is to develop a gas sensor for monitoring the air quality based on the QEPAS technique. In order to achieve low limits of detection, quantum cascade lasers are employed as they emit in the mid-infrared region where strong molecular absorption occurs. The QEPAS sensor is optimized, using a specific acoustic characterization setup. It demonstrates good performances for the detection of methane, ethylene and carbon monoxide and is also used for a biomedical application. Eventually, the stability of the sharply resonant mechanical resonator is studied. A setup is developed to measure its resonance and proved to successfully prevent the sensor drift, showing a strong enhancement potential for next QEPAS sensors.