Ambient detection of CH4 and N2O by Quantum Cascade Laser

Quantum Cascade Lasers (QCL's) have been successfully used to monitor atmospheric pollutants in the mid-infrared (mid-IR) region. However, their use for multiple gases in ambient conditions is less familiar. This paper explores the performance of a novel field deployable open path system based on a chirped single distributed-feedback QCL. In particular, we report both laboratory and open path measurements for simultaneous detection of two greenhouse gases (GHG) methane (CH4) and nitrous oxide. (N2O). We focused on CH4 and N2O because they are long-lived greenhouse gases in the atmosphere with significant global warming effects. Gas spectra were recorded by tuning the QC laser wavelength using a thermal down chirp technique over 1297-1300 cm(-1) optimal spectral window with 0.008 cm(-1) spectral resolution. Based on careful optimization of the spectral window for absorption features of CH4 and N2O, a dual-species, cost-effective, robust and rapid response open-path laser based monitor has been developed for ambient trace gas monitoring. Theoretical signal to noise ratio (SNR) analysis of the system based on an ideal system is briefly discussed in the paper but our main focus is on actual system performance, long term stability and systemic errors. Finally, preliminary results of the open path system are reported