Development of DIAL for CO_2 and CH_4 in the atmosphere

摘要

Development of a mid-infrared differential absorption LIDAR system around 2.0 and 2.3 μm wavelength is proposed for remote sensing of greenhouse-effect gases, such as CO_2 and CH_4. A model calculation shows that the 1.6 to 2 μm wavelength region is also suitable for the CO_2 measurements. A widely tunable self-injection seeded Ti~(3+): sapphire laser in combination with a Raman shifter is used for a tunable mid-infrared laser source. This combination could allow a wide tuning range between 1.6 and 2.3 μm. The spectral width of the Ti~(3+): sapphire laser was measured around 0.04 cm~(-1) and stability of the laser source was also studied by a Fabry-Perot interferometer in order to determine the accuracy of the DIAL measurement. Currently, output energy is limited to only a few mJ limiting the detection sensitivity. Nevertheless improved output characteristics should meet the requirements satisfactorily to monitor CO_2 and CH_4 gases in the atmosphere.