Sub-ppbv nitric oxide concentration measurements using cw thermoelectrically cooled quantum cascade laser-based integrated cavity output spectroscopy

A nitric oxide (NO) gas sensor based on a thermoelectrically cooled, continuous-wave, distributed feedback quantum cascade laser operating at 5.45 μm (1835 cm-1) and off-axis integrated cavity output spectroscopy combined with a wavelength-modulation technique was developed to determine NO concentrations at the sub-ppbv levels that are essential for a number of applications, such as medical diagnostics, environmental monitoring, and industrial process control. The sensor employs a 50-cm-long high-finesse optical cavity that provides an effective path length of ∼700 m. A noise equivalent (SNR=1) minimum detection limit of 0.7 ppbv with a 1-s observation time was achieved.