The Research of the CO_2 Differential Absorption Coherent Lidar Technology

摘要

The CO_2 differential absorption lidar (DIAL) technique have advantages such as high vertical and horizontal resolution, the ability to acquire simultaneous species and aerosol profiles, day and night coverage and no dependence on external radiation. An all solid-state 1.5 μm CO_2 differential absorption coherent lidar was designed in the paper. The key technology of the system such as high precision laser wavelength control, echo correlation detection were solved the tunable-diode-laser (newfocus model 6330) was selected as the laser source. The reference CO_2 gas pool was selected as for absorption calibration. The modulated laser signal was sent through the gas pool and detected by the detector. By observing the frequency of output voltage of the detector, the wavelength of the on-laser was locked. The experiment showed the precision of the laser wavelength control was under 0.1pm which is narrower than the CO_2 absorption band width. The aim of the echo coherent detection is promoting the SNR of the Lidar. By the polarization separating and collecting for the echo and local-oscillator signal, the problem of polarization matching between the echo and seed was solved. The balanced detector was selected to achieve the balanced detection, which remarkably eliminated the affection of the local-oscillator noise. The laboratorial experiment for the lidar was carried out to detect the CO_2 inside the gas pool. The analysis of the experiment data showed the CO_2 detection sensitivity of the system is up to the 25ppm pre kilometer long path.