Measurement of Carbon Dioxide by Near-infrared Cavity Ring-down Spectroscopy

A compact continuous-wave (cw) cavity ring-down spectroscopy (CRDS) sensor was developed for measurement of carbon dioxide (CO2) in atmospheric greenhouse gases. A 1573nm cw distributed feedback (DFB) laser was employed for a strong CO2 absorption line in the near-infrared band. We characterized the effects of plano-convex lens and incident high reflective mirror on fundamental mode matching of the cavity and calibrated the CRDS with several CO2 standard gases. The experimental results showed that the sensor had a good inverse proportional relationship between the ring down time and the concentrations of CO2 standard gases in the range of Oppm to 500ppm, and an optimum detection limit of 6.6ppm could be achieved for carbon dioxide with a 2s integration time. The proposed CRDS sensor has numerous potential applications in atmospheric greenhouse gases and ambient air quality monitoring.