Application of a broadband blue laser diode to trace NO_2 detection using off-beam quartz-enhanced photoacoustic spectroscopy

We applied for the first time, to our knowledge, broadband off-beam quartz-enhanced photoacoustic spectroscopy (BB-OB-QEPAS) to trace NO_2 detection using a broadband blue laser diode centered at 450?nm. A detection limit of 18?ppbv (parts in 10^9 by volume) for NO_2 in N_2 at atmospheric pressure was achieved with an average laser power of 7?mW at a 1?s integration time, which corresponds to a 1?σ normalized noise equivalent absorption coefficient of 4.1×10^−9?cm^−1?W/Hz^1/2. An Allan variance analysis was performed to investigate the long-term stability of the BB-OB-QEPAS-based NO_2 sensor.