Comparison between interferometric and piezoelectric readout of tuning fork vibrations in quartz-enhanced photoacoustic spectroscopy

We report on a comparison between the piezoelectric and interferometric readouts of vibrations in quartz tuning forks (QTFs) when employed as sound wave transducers in quartz-enhanced photoacoustic trace gas sensors. We demonstrate the possibility to properly design the QTF geometry to enhance interferometric readout signal with respect to the piezoelectric one and vice versa. When resonator tubes are acoustically coupled with the QTFs, signal-to-noise ratio enhancements are observed for both readout approaches. These results open the way to the implementation of optical readout of QTF vibrations in applications where external electromagnetic field could distort the piezoelectric signal