Light Source Design Of Differential Absorption Lidar Based On The Principle Of Stimulated Raman Scattering

As one of the important trace gases in the atmosphere,ozone plays an important role in regulating climate and maintaining the radiation balance of the earth.The monitoring of ozone concentration,especially the detection of vertical profile of ozone concentration,has important scientific significance and application prospect for atmospheric pollution control and climate change research.At present,differential absorption lidar is the main detection method for atmospheric ozone profile detection,and stimulated Raman scattering effect is also an effective method to expand laser light source because of its multi-wavelength and high-intensity coherent radiation.Based on the differential absorption lidar detection technology and the principle of stimulated Raman scattering,the design of differential absorption lidar light source system based on the principle of stimulated Raman scattering is carried out in this thesis.The specific research work is as follows:Firstly,based on the principle of Raman scattering and differential absorption measurement,deuterium gas is selected as the Raman medium,which generates the first stokes light and the second stokes light with the central wavelength at 289nm and 316nm as the differential wavelength pairs of the light source system.According to the strong absorption characteristics of atmospheric ozone in ultraviolet band,the requirements of the emission energy of differential absorption lidar light source system are put forward through the simulation analysis of atmospheric transmittance and channel detection signal-to-noise ratio.In order to realize the detection of atmospheric ozone concentration above 8km in Xi’an area,the emission energy of differential absorption wavelength at 289nm and 316nm should reach more than 20mJ and 15mJ.Furthermore,the design of light source system with Raman cell as the core device is carried out.According to the principle of stimulated Raman scattering,the characteristics of the first order steady-state gain coefficient,the first order transient gain coefficient and the Stokes optical conversion efficiency are simulated and analyzed,and the design length of the Raman cell is 1 m and the upper limit of compression resistance is 30atm.The optical structure of Raman cell is designed based on Zemax.By comparing the output performance of multi-path optical structure Raman cell and single-path optical structure Raman cell,the single-path Raman cell with 2%energy loss is selected,and the mechanical structure is designed based on SolidWorks,and the compression analysis of Raman cell is carried out by ANSYS finite element analysis method.Finally,the experimental test system is built to complete the test and analysis of the performance parameters of the light source system.The stimulated Raman scattering spectrum was obtained at a distance of 1.4m from the exit spot of the Raman cell by using a prism as a spectroscopy.The relationship between the output energy of the light source and the pump input energy,and the relationship between the output energy of the light source and the pressure in the Raman cell were analyzed,and the stability of the output energy was tested.The experimental results show that the conversion efficiency of Stokes light is improved with the increase of laser energy.When the laser energy of 266nm wavelength is 100mJ and the pressure of deuterium in the cell is 3atm,the conversion efficiency of the first Stokes light and the second Stokes light can reach 30%.At the same time,the energy fluctuation of the first order Stokes light S1 is 3.7%,and the energy fluctuation of the second order Stokes light S2 is 4.1%.The energy of the two output beams is stable,which meets the design requirements of the differential absorption lidar source system.