Light-induced thermo-elastic effect in quartz tuning forks exploited as a photodetector in gas absorption spectroscopy

We report on a study of light-induced thermo-elastic effects occurring in quartz tuning forks (QTFs) when exploited as near-infrared light detectors in a tunable diode laser absorption spectroscopy sensor setup. Our analysis showed that when the residual laser beam transmitted by the absorption cell is focused on the QTF surface area where the maximum strain field occurs, the QTF signal-to-noise ratio (SNR) is proportional to the strain itself and to the QTF accumulation time. The SNR was also evaluated when the pressure surrounding the QTF was lowered from 700 Torr to 5 Torr, resulting in an enhancement factor of v4 at the lowest pressure. At 5 torr, the QTF employed as light detector showed an SNR v6.5 times higher than that obtained by using a commercially available amplified photodetector.