Sub-parts-per-billion level detection of NO2 using room-temperature quantum cascade lasers

We report the sub-parts-per-billion-level detection of NO2 using 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 approximately 300 mW tunable over approximately 350 nm centered at 6.25 microm. We demonstrate minimum detection level of approximately 0.5 parts per billion of NO2 in the presence of humidified air.