External cavity widely tunable quantum cascade laser based hollow waveguide gas sensors for multianalyte detection

In the study presented here, quantitative detection of ethyl chloride, dichloromethane, and trichloromethane individually and in mixture has been demonstrated using an external cavity broadly tunable quantum cascade laser (EC-QCL) based hollow waveguide gas sensor. The EC-QCL has been characterized by coupling into a FT-IR spectrometer documenting sufficient optical power output across a frequency tuning range from 1297 cm−1 to 1219 cm−1. Concentrations as low as 4 ppb for ethyl chloride, 7 ppm for dichloromethane, and 11 ppb for trichloromethane were detected during exponential dilution experiments with the EC-QCL precisely tuned to selective absorption frequencies of the Q-branch for each constituent at 1287.25 cm−1, 1262 cm−1, and 1220 cm−1, respectively.