Ppb-level photoacoustic sensor system for saturation-free CO detection of SF6 decomposition by use of a 10 W fiber-amplified near-infrared diode laser

A photoacoustic sensor system for the ppb-level CO detection of sulphur hexafluoride (SF6) decomposition was developed by use of a 10 W fiber-amplified near-infrared (NIR) diode laser. A photoacoustic detection module with symmetrical construction was designed to allow a high power laser beam and a large gas flow. A theoretical model was developed to describe the dynamic equilibrium processes of CO molecular activation and deactivation in the presence of gas flow. The 10 W optical excitation power effectively compensates the CO weak absorption line strength in the NIR spectral region and realizes a saturation-free CO detection with the assistance of the gas flow, resulting in a ppb-level CO detection sensitivity, which is comparable with the detection sensitivity obtained using a mid-infrared CO sensor.