Wavelength scanning Q-switched fiber-ring laser intra-cavity QEPAS using a standard 32.76 kHz quartz tuning fork for acetylene detection

Abstract

A novel fiber-ring laser intra-cavity quartz-enhanced photoacoustic spectroscopy (FLI-QEPAS) gas sensor utilizing wavelength scanning Q-switched technique is reported for acetylene detection. The system uses erbium-doped fiber as the gain medium for laser generation and a custom-made fiber Bragg grating attached to a piezoelectric transducer for wavelength scanning to cover the C2H2 absorption line at 1531.58 nm. A standard quartz tuning fork (QTF) operating at 32.76 kHz is placed inside the fiber-ring cavity to fully utilize intra-cavity optical power, realizing an ultra-short absorption path of 10 mm. Acousto-optic Q-switched working mode is employed to enable the fiber-ring laser working in high frequency enough for standard QTF excitation, up to ≃3 W intra-cavity peak power is achieved with 650 mW pump power at 980 nm. In acetylene detection experiments, the system realizes a noise equivalent concentration of 26 ppbv at 50 ms integration time, and Allan deviation shows the minimum detection limit can be improved to 2.8 ppbv at 51 s integration time. A linear dynamic range up to 10,000 ppmv is validated and the stability performance is also analyzed.