Quartz tuning forks employed as photodetectors in TDLAS sensors

The main limitations of tunable diode laser absorption spectroscopy (TDLAS) sensors are represented by the high cost, limited detection bandwidth and low adaptability of photodetectors to work in harsh environments. In this work we present an extensive study on quartz tuning forks (QTFs) used as photodetectors, exploiting the opto-thermo-elastic energy conversion arising from the laser radiation-QTF interaction. The role of the strain field, accumulation time and working pressure of the quartz resonator in this Light-Induced Thermo-Elastic Spectroscopy (LITES) approach was then evaluated for a whole set of tuning forks. Once identified the most performant resonator, this QTF was implemented in a TDLAS setup and it was combined with laser diodes, interband- and quantum-cascade laser sources emitting from 1 μm to 10.5 μm and targeting different gas spacies. The detection limits achieved for the QTF were comparable or even lower down to one order of magnitude with respect to market-available photodetectors.