Modeling and Design of a Semi-Integrated QEPAS Sensor

Quartz enhanced photo acoustic spectroscopy (QEPAS) has gained a growing interest in recent years for gas sensing technology because of the high sensitivity provided by sharp resonant tuning forks (QTFs) exploited as piezoelectric sound wave detectors; and the modularity, compactness, and robustness of the sensors. The currently used experimental configurations of the QEPAS sensors still rely on free space optics, which are potentially subject to misalignment and require a relatively high space occupation. Here we propose the modelling and the design of a QEPAS sensor with the laser source and optical components for beam delivery bonded together and semi-integrated with the tuning fork. In particular, we propose a configuration in which an optical resonator placed between the prongs of the QTF is coupled with the laser source through a waveguide (OMRSI-QEPAS). For this setup design, COMSOL simulations provided pressure values of the acoustic wavefront comparable with the standard on-beam configuration employing acoustic resonator tubes. Therefore, the design here proposed aims to package the opto-acoustic core of a QEPAS sensor in a single module of few cubic centimeters to definitively address the misalignment issues and pave the way to a further level of miniaturization, integration and deployment for application like mobile and on-drone sensing.