The paper gives us info like sensor, cascade laser, and electronic. Inside this paper you can get description like laser sensor, and detection.
Lots of discussion around laser, and cascade laser sensor are explained inside the paper. These are grabbed from the paper:
We have demonstrated a high-sensitivity, room-temperature quantum cascade laser sensor for detection of SO2 and SO3 in conditions relevant to aircraft test combustor exhaust. Two QC lasers probe infrared absorption features at 7.50 and 7.16 µm for SO2 and SO3, respectively, with a common dual-beam detection system. We inferred a noise-equivalent absorbance of ~1 × 10-4 Hz-1/2. We have demonstrated detection limits for both SO2 and SO3 of (1 to 2) ppmv-m/Hz1/2 for 300 torr, elevated temperature, and path lengths near 1 m.
In addition, this paper explains more such as combustor, and quantum cascade laser.