Detection of nitric oxide in air with a 5.2 μm distributed-feedback quantum cascade laser using quartz-enhanced photoacoustic spectroscopy.

We demonstrate the detection of nitric oxide in both air and nitrogen atmospheres with a 5.2 μm distributed-feedback quantum cascade laser in a quartz-enhanced photoacoustic spectroscopy system. The photoacoustic signal generated by nitric oxide is shown to be several times larger in air than in nitrogen due to the faster vibrational-translational energy relaxation process induced by the presence of oxygen. A sensitivity of 2.5 parts-per-million by volume is achieved in air at atmospheric pressure.