Hollow waveguide CO₂ laser sensing system for rapid detection of trace sulfur hexafluoride (SF₆) gas

Sulfur hexafluoride (SF6) has been widely applied in electrical facilities due to its excellent electrical insulation and high-voltage arc extinguishing properties, although it is a potent greenhouse gas. Rapid detection of trace SF6 gas is significant for monitoring the operation safety of high-voltage power grid facilities and greenhouse gas emissions. In this work, a SF6 gas sensing system was proposed and built using a CO2 laser as the light source and a 700 mu m bore Ag/AgI hollow glass waveguide (HGW) as the gas chamber and laser transmission channel. Sensing performances of the SF6 gas HGW sensors with different lengths were investigated. The gas sensing sensitivity and standard deviation (SD) of blank increase as the waveguide length increases. The limit of detection (LOD) decreases with waveguide length increase but the decline becomes less pronounced after the length exceeds 120 cm. The HGW length exhibits minor effect on the response and recovery time of the sensor system. The sensor sensitivity undergoes a slight reduction as the HGW is bent. Optimization of the sensing performance was achieved based on the straight 120 cm-length HGW SF6 gas sensor system. Its sensitivity reaches 0.384 dB/ppm and the LOD is 148 ppb with good cyclic response characteristics (response and recovery time 2-3 s). The present work provides a feasible idea for building up a trace SF6 gas sensing system with simple structure, easy operation and high performances.