Influence Analysis And Experimental Study Of Laser Longitudinal Mode On Performance Detection Using High-spectral-resolution Lidar

Aerosol is one of the important factors affecting the stable state and spatial distribution of atmospheric environment, thus it is very important to observe the spatial and temporal distribution ofaerosols with high accuracy.High-spectral-resolution lidar(HSRL) is an important remote sensing tool for fine detection of atmospheric aerosol optical characteristics. HRL can be divided into single-longitudinal-mode HSRL and multi-longitudinal-mode HSRL according to the selection of the spectrum of laser transmitter.Single-longitudinal-mode HSRL selects the seeder injection technology of single frequency pulsed laser as the excitation light source, and atomic/molecular absorption filters or interferometric optical filters as the spectral discriminator for fine separation of aerosols Mie scattering and molecular Rayleigh scattering excited by the single longitudinal mode laser; Multi-longitudinal-mode HSRL directly uses the multi-longitudinal-mode high power pulsed laser as the excitation light source,and can only choose the interferometric optical filter with periodic transmittance function as the spectral discriminator for fine separation aerosols Mie scattering and molecular Rayleigh scattering signal excited by the multi-longitudinal-mode laser. Both techniques can realize the accurate detection of aeroso optical parameters.Based on the similarities and differences between single-longitudinal mode HSRL and multi-longitudinal-mode HSRL, the thesis focuses on the analysis and comparison ofthe spectral discriminators used in the HSRL The Mach-Zehnder interferometer (or Michelsor interferometer) based on dual-beam interference and Fabry-Perot interferometer based on multi-beam interference can be selected as the spectral discriminator ofHSRL. which has the different system structure, and the different discrimination performance with advantages and disadvantages, Based on the parameters for evaluating the spectral discrimination performance,including atmospheric molecular effective transmittance,aerosol effective transmittance,spectral discrimination ratio and performance evaluation function,the thesis discusses the optimal design parameters of Fabry-Perot interferometer and Mach-Zehnder interferometer in the application of the single-longitudinal-mode HSRL and the multi-longitudinal-mode HSRL in detail.Moreover,the influences of frequency locking error,reference optical path error and incident angle error on the spectral discrimination performance of these two optical interferometers are investigated.The results show that Fabry-Perot interferometer and Mach-Zehnder interferometer have their representative advantages as the spectral discriminator in the single-longitudinal-mode HSRL system,while Mach-Zehnder interferometer has more advantages as the spectral discriminator in the multi-longitudinal-mode HSRL system.In the thesis,the experimental observations of single-longitudinal-mode HSRL and multi-longitudinal-mode HSRL using Mach-Zehnder interferometer as the spectral discriminator are carried out respectively.The comparison of laser energy between single-longitudinal-mode pulsed laser and multi-longitudinal-mode pulsed laser shows that the output energy of multi-longitudinal-mode pulsed laser is about 140m J higher than that of single-longitudinal-mode pulsed laser under the same setting of laser parameters.When the Mach-Zehnder interferometer has the same setting of optical path difference(OPD=1000mm),the detection range(SNR≥100)by the multi-longitudinal-mode HSRL is about 1km higher than that by the single-longitudinal-mode HSRL.Under the optimal setting of optical path difference of Mach-Zehnder interferometer,the single-longitudinal-mode HSRL using the Mach-Zehnder interferometer with the optical path difference of 130mm can detect atmospheric aerosol optical characteristics to the height of 3km under sunny and cloudy conditions.While the multi-longitudinal-mode HSRL using Mach-Zehnder interferometer with the optical path difference of 1000mm can detect atmospheric aerosol optical characteristics up to 5km under sunny(fogless)and cloudy conditions.The results show that the multi-longitudinal mode HSRL can obtain higher SNR and detect longer distance.