Modeling And Simulation Of Flowing-DPAL

Diode Pumped Alkali Vapor Laser(DPAL) has both the advantages of the solid state and gas lasers, including high quantum efficiency, cycling operation and convective cooling of the gain medium, no limitation of single power scaling, all-electricity driven, slight and compact, near infrared laser wavelength and good atmospheric transmission. It has become one of the most promising novel high energy lasers. Under high power pump, DPAL requires a cycling convective cooling system for effective heat management. Although the research groups in the United States and Russia have realized Flowing-DPAL systems(FDPAL), related theories and models have been seldom reported. In order to decide the parameters of the flowing system and study the gas dynamic effects, a relatively complete model is of great significance but still unattainable. This thesis sets up an FDPAL model, based on which investigations on fluid parameters and gas dynamic effects are performed. And these results are supposed to provide a useful tool for a better design of the FDPAL system. Contents of this thesis include:1.A qualitative estimation of the thermal effect in an FDPAL system is studied based on published parameters. The results show that, despite the low quantum defect of alkali atoms, obvious heat density as well as temperature rise could be induced by high pump intensity and spontaneous radiation. To explain this effect, an optical-fluid coupled model is required. For the first time, with the concept of substantial derivative, an optical-fluid coupled 3-dimensional model is set up. This model could describe the main lasing dynamic processes and fluid parameters’ distribution, including gas dynamic equations, rate equations and pump-lasing transmitting equations.2.The model above is simplified to solve an end-pumped longitudinal flow FDPAL model, and a fast convergent iteration numerical solution is proposed. The influences of flow rate on laser performance are studied, such as lasing efficiency, temperature variation and their distribution along flow direction et al. The simulation results show that the flow velocity is in the subsonic range which is easy to realize.3.The end pumped transverse flow configuration is considered, which is much more scalable. Based on the complete model, a combined method is adopted to obtain the light field information by Matlab and fluid information by finite volume method. Pump light absorbed by the alkali atoms are transformed into fluorescence, electron quenching, quantum defect and scattering. This method could obtain the distribution and light-fluid parameters’ variation along flow direction. It is also analyzed how velocity influences the performance of FDPAL system. The result may be useful for the design of a end-pumped transverse flowing system. Based on this method, a conceptual design of a mega-Watt FDPAL is presented.