Photoacoustic trace gas sensing with mid-IR quantum cascade lasers

We report on the realization of an optoacoustic sensor based on mid-infrared quantum-cascade lasers (QCLs) for the detection of nitric oxide (NO) and formaldehyde (CH
₂
O). A resonant photoacoustic cell equipped with 4 electret microphones was excited in its first longitudinal mode by the modulated laser light. A detection limit of 150 parts in 10
⁹
(ppbv) for NO and CH
₂
O was found, using distributed feedback QCLs operating in pulsed mode at 5.34 mum and 5.62 mum, respectively.