External cavity quantum cascade laser based gas sensor for sulfur hexafluoride detection

Abstract

Abstract External cavity quantum cascade laser (ECQCL) is a ideal mid-infrared (MIR) spectral light source, which provides ultra wide wavelength tuning range for multiple trace gases sensing simultaneously. In this paper, a gas sensor system was developed by using a broadband tunable ECQCL and a direct absorption spectroscopy detection scheme with a short path absorption cell of 29.6 cm. For spectral signal detection, a cheap and miniaturized quartz crystal tuning fork (QCTF) based light detector was used for laser signal detection. The characteristics of the QCTF detector was theoretically simulated and experimentally observed. To demonstrate this sensing technique, sulfur hexafluoride (SF6) was selected as the analyte, which can be used as an effective indicator to identify fault types of gas insulated electrical equipments. Preliminary result indicated that a good agreement was obtained between experimentally observed data and reference spectra by according to NIST database and previous publication, and the gas sensor system shows a good linear response to SF6 gas concentration. Finally, Allan deviation analysis indicates that detection limits of 1.889 ppm for SF6 was obtained with a 1 s integration time, which can be further improved to ~ 0.384 ppm by averaging up to 131 s, respectively.