| Diode-pumped alkali vapor laser(DPAL)achieves near-infrared laser output by using a diode to pump alkali-vapors such as potassium(K),rubidium(Rb),and cesium(Cs).It has the advantages of high quantum efficiency,large absorption cross-section,small refractive index disturbance of gas medium,and scaleable amplification.Compared with the traditional solid-state laser,DPAL can reduce the thermal effect by circulating alkali metal vapor flow and has high heat dissipation performance.It has the advantages of high power,high efficiency,and high laser beam quality,and can be applied to national defense,medical treatment,laser processing,and other fields.Cs-vapor DPAL(Cs-DPAL)has the advantages of low threshold,high gain,high pump absorption efficiency and easy fluorescence suppression,which has broad application prospects.This dissertation carries out theoretical research on flowing-gas circulation Cs-DPAL,establishes the theoretical model of flowing-gas circulation Cs-DPAL,simulates and analyzes the influence of pump coupling,gas flow mode and various laser parameters on the temperature distribution and output characteristics of flowing-gas circulation Cs-DPAL and optimize them,as to provide a theoretical basis for the experimental study of high power circulating flow Cs-DPAL.The main contents of this dissertation are introduced below:1.In terms of the theoretical model,the beam propagation equation is introduced into the flowing-gas circulation Cs-DPAL theoretical model firstly,and the flowing-gas circulation Cs-DPAL theoretical model is constructed by combining the rate equation,fluid mechanics equation,and heat balance equation with the beam propagation equation.Firstly,the density distribution of the Cs atom of each energy level in the vapor cell is solved by the rate equation,and then the absorption coefficient of the pump light and the gain coefficient of the laser are calculated.Then,the absorption coefficient and the gain coefficient are substituted into the beam propagation equation to solve the propagation process of the pump light and the Gaussian laser in the resonant cavity,and the three-dimensional amplitude distribution of the pump light and the laser is obtained.Then,the three-dimensional temperature distribution in the vapor cell is obtained by solving the hydrodynamic and thermal equilibrium equations,and the parameters in the rate equation are modified.Repeat the above process until the temperature and laser power stabilize,and finally the three-dimensional distribution of flowing-gas circulation Cs-DPAL laser and temperature in steady-state can be obtained.2.In terms of the selection of pump and gas flow patterns,the theoretical models of end-pumped and side-pumped are compared.The calculation results show that the maximum temperature in the end-pumped Cs-DPAL vapor cell is lower than that in the side-pumped Cs-DPAL vapor cell,and the corresponding laser output power is higher than that in the side-pumped Cs-DPAL vapor cell when the gas flow rate is low under the k W-level pump.When the gas flow rate is high enough,the maximum temperature in the end-pumped and side-pumped Cs-DPAL vapor cell is close,and the output power is almost the same.However,the beam quality of end-pumped Cs-DPAL is better,and the dual-end-pumped Cs-DPAL is easier to inject high-power pump light.Therefore,in the case of the k W-level pump,the dual-end pump is the best pump coupling mode.In this dissertation,the simulation results of dual-end pump Cs-DPAL are compared with the experimental results.The laser output of 966.3W is obtained under a 2 k W pump,and the optical efficiency is 48.3%.The simulation results are very close to the experimental results,which proves the accuracy of the model.The working gas transverse flow Cs-DPAL and axial flow Cs-DPAL are compared.The results show that under the same conditions,the transverse flow Cs-DPAL can take more heat than the axial flow Cs-DPAL,and better reduce the thermal effect in the vapor cell.The laser power corresponding to the transverse flow Cs-DPAL is significantly higher than the axial flow Cs-DPAL at the same flow rate.Therefore,gas transverse flow is a better way of gas flow,and the simulation results are consistent with the research results.3.The parameters of Cs-DPAL with dual-end pump transverse flow are optimized.The effects of pump center wavelength and line width,pump beam waist radius,sidewall temperature of vapor cell,length of vapor cell and resonant cavity,window transmittance of vapor cell and reflectivity of output mirror,buffer gas ratio,pressure and gas flow rate on the temperature and power of dual-end pump transverse flow Cs-DPAL are analyzed,and the above parameters are optimized.The simulation results show that under the condition of a 1 k W pump,when the gas flow rate is 50m/s,the maximum temperature in the optimized vapor cell is 419.9 K,the laser output power is 813.1 W,and the optical and optical efficiency is more than 80%. |
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