.57μm Active Laser Heterodyne Spectrometer and CO2 Concentration Measurement

CO2 is an important greenhouse gas(GHG) that affects the Earth's atmosphere, and continuous measurement of CO2 helps understand its sources and sinks. The passive laser heterodyne spectrometer(LHS) has been used in meteorology and environmental monitoring recently, especially in the measurement of the radiation properties of the Earth and the densities of atmospheric greenhouse gases. As well known, the passive LHS uses sunlight, the heterodyne efficiency is low, the heterodyne signal processing is complex, and it cannot be measured without sunlight. Therefore, it is difficult for passive LHS to achieve continuous measurement of the GHG of interest. In order to improve the application field of LHS, a 1.57 μm active LHS is investigated and built by using a tunable DFB laser, acoustic-optic frequency shifter and fiber amplifier. It adopts the reflected laser after amplified and frequency shifted as the input light and mixed with seed laser, which possesses the advantage of high coherence efficiency and continuous observation day and night. The CO2 absorption spectrum measurement in the range of 2.2 km is realized, and the signal-to-noise ratio is about 286. The densities of CO2 are 419.15 ~ 424.48ppmv during the experiment. The research will make up for the deficiency of the passive laser heterodyne spectrometer.