Fiber-ring laser intracavity QEPAS gas sensor using a 7.2 kHz quartz tuning fork

A novel trace gas sensor exploiting fiber-ring laser intracavity quartz-enhanced photoacoustic spectroscopy (FLI-QEPAS) is reported. The gas sensor system couples an erbium-doped fiber-ring laser with a custom-designed quartz tuning fork (QTF) operating at 7.2 kHz. The QTF was placed in the fiber cavity to fully utilize intracavity optical power enhancement for the photoacoustic excitation. We obtained a short intracavity absorption length of 1.5 cm, significantly extending the liner dynamic range of the gas sensor to an order of 10^5. As a proof of principle, the fiber laser was tuned to the C2H2 absorption line at 1531.6 nm. Operating at the optimal gas pressure and modulation depth selected for wavelength modulation spectroscopy, a minimum detectable C2H2 concentration of 27 ppbv at the 300-s integration time has been achieved.