EC-QCL based photoacoustic spectroscopy for detection of SF6 decomposition components

The detection of multiple SF6 decomposition gases based on photoacoustic spectroscopy (PAS) has been a research hotspot in recent years. A highly sensitive sensor for the detection of sulfuryl fluoride (SO2F2), carbon tetrafluoride (CF4), and sulfur dioxide (SO2) in sulfur hexafluoride (SF6) was demonstrated by using PAS. The PA sensor is composed of an external cavity quantum cascade laser (EC-QCL) emitting between 1278 and 1360 cm−1, a Helmholtz differential resonant PA cell isolating the target gas from the surrounding environment, and an acousto-optic modulator (AOM) modulating the laser intensity. When the noise level was evaluated based on the PA signal noise of pure SF6 gas, minimum detection limits of 510 ppb, 9 ppb, and 69 ppb with 1 s integration time for SO2F2, CF4, and SO2 in SF6 were achieved at the characteristic absorption wavenumbers of 1282.8 cm−1, 1283.0 cm−1, and 1348.4 cm−1, respectively. Further, if the integration time was increased to the optimal integration time determined via Allan-Werle deviation analysis, the minimum detection limits were further improved to 70 ppb, 1.5 ppb, and 7 ppb for SO2F2, CF4, and SO2, respectively. The multilinear regression (MLR) statistical algorithm based on the least square method was utilized for discrimination of three-gas spectra and retrieving of three-gas concentrations from a three-gas mixture in SF6 despite the significant overlap between their absorption features. •A PA detection apparatus based on an EC-QCL was developed for detection of SF6 decomposition components.•Minimum detection limits at ppb levels of SO2, CF4 and SO2F2 in SF6 were achieved with the developed PA apparatus.•Multilinear regression was utilized to determine the gas concentrations of a three-gas mixture in SF6.