Real-Time Measurements of Atmospheric CO Using a Continuous-Wave Room Temperature Quantum Cascade Laser Spectrometer

A compact mid-infrared laser spectrometer based-on a thermoelectrically (TE) cooled continuous-wave room temperature (RT) quantum cascade laser working at a wavelength of 4.566 μm and TE-cooled detectors has been newly developed to demonstrate the applicability of high precision measurements of atmospheric CO. Wavelength modulation spectroscopy technique combined with a multiple pass absorption cell was employed to achieve high sensitivity. The Allan variance technique analysis indicates a 1-s CO measurement precision of 1.03 ppbv, improving to a minimum of 0.28 ppbv at the optimum integration time of 53 s. Long-term performance of the instrument was examined with alternate measurements of a sample gas with known concentration and ambient air at a typical 1-Hz sampling rate and a 1-hourly calibration cycle. This completely thermoelectrically cooled system shows the capability of long-term, unattended and continuous operation at RT without any complicated cryogenic cooling.