Sub-part-per-billion monitoring of nitric oxide by use of wavelength modulation spectroscopy in combination with a thermoelectrically cooled, continuous-wave quantum cascade laser

We used a thermoelectrically cooled, continuous-wave, quantum cascade laser operating between 1847 and 1854 cm(-1) in combination with wavelength modulation spectroscopy for the detection of nitric oxide (NO) at the sub-part-per-billion by volume (ppbv) level. The laser emission overlaps the P7.5 doublet of NO centered around 1850.18 cm(-1). Using an astigmatic multiple-pass absorption cell with an optical path length of 76 m, we achieved a detection limit of 0.2 ppbv at 10 kPa, with a total acquisition time of 30 s. The corresponding minimal detectable absorption is 8.8 x 10(-9) cm(-1) Hz(-1/2).