Sub-parts-per-billion level detection of NO2using room-temperature quantum cascade lasers

Abstract
We report the sub-parts-per-billion-level detection of NO2using tunable laser-based photoacoustic spectroscopy where the laser radiation is obtained from a room-temperature continuous-wave high-power quantum cascade laser operating in an external grating cavity configuration. The continuously tunable external grating cavity quantum cascade laser produces maximum single-frequency output of ≈300 mW tunable over ≈350 nm centered at 6.25 μm. We demonstrate minimum detection level of ≈0.5 parts per billion of NO2in the presence of humidified air.