Development of field-deployable QCL sensor for simultaneous detection of ambient N2O and CO

We report the development of a field deployable quantum cascade laser (QCL) sensor for simultaneous high sensitivity and high precision detection of the atmospheric trace gases nitrous oxide (N2O) and carbon monoxide (CO). The system relies on a continuous-wave room temperature quantum-cascade laser source emitting at a wavelength of around 4.56 μm, where strong fundamental absorption bands occur for both species. The detection technique is based on second harmonic wavelength modulation spectroscopy and long multi-pass absorption technique. Primary laboratory tests over a 5-day period have been performed to estimate the achievable detection limits and the signal reproducibility levels in view of possible applications for in situ and real time atmospheric measurements. The short-term precision of 1.29 and 1.98 ppbv at 1 Hz under laboratory conditions was demonstrated, corresponding to line centre absorbance of 1.48 × 10−4 and 1.80 × 10−4 for CO and N2O, respectively.