The Influence And Optimized Design Of The Beveled Edge Of Yb:YAG Thin-disk Crystals On The ASE Effect

The thin-disk laser concept is designed for diode-pumped solid-state laser,with large diameter-to-thickness ratio,which allows realization of lasers with high output power,high efficiency,and good beam quality,simultaneously.There is a very broad development prospect about the thin-disk laser.As we know,one way to improve the output power of thin disk laser is to increase the size of pumped area.However,enlarging the pumped area will increase the transmission path of photons generating from spontaneous emission,which means that it will bring more and more severe amplified spontaneous emission(ASE)effect.The ASE photons will compete with the output laser photons.Thus,the ASE effect becomes a major cause of loss of the upper laser level population,and limits the scalability of thin-disk lasers.The beveled disk is an effective way to suppress the ASE effect.The“geometric optics analytical method"and the "Monte Carlo ray-tracing method" are used to establish an analysis model of the beveled disk.The ability to suppress the ASE effect of thin-disk crystals with different beveling angles is analyzed,and the dynamic process of ASE photons propagating in the beveled disk is revealed.Through the optimization analysis,a proper beveling angle is given.This will provide the theoretical support to select the proper beveling angle of thin disk crystal in the real application.The specific research contents are as follows:First,We take the Yb:YAG thin-disk laser as an example.Combining the "Monte Carlo ray-tracing method" with the "geometric optics analytical method",we've built a theoretical model of a beveled disk crystal.By a series of analyses and reasonable approximations,a critical beveling angle,57°,is demonstrated and it's very important for the design of beveled disk crystal.When the beveling angle is less than the critical angle,the ability of the beveled disk suppressing the ASE effect increases gradually.When the beveling angle is equal to the critical angle,the ability of the beveled disk suppressing the ASE effect basically reaches its maximum.Continuing to increase the beveling angle will just decrease the available pumped area of the beveled disk.Then,based on the theoretical model above,the ASE photon flux density model built by Jochen Speiser and the quasi-three-level rate equations of Yb:YAG,the result of the thin-disk laser' s output power of different beveling angles is obtained.Finally,we've used the finite element analysis software COMSOL to analyze the temperature distribution of the thin-disk gain medium with different beveling angles.Combining with the related experiments,we found the main factor that causes the severe heat generation on the edge of the thin disk is the residual metal solder In.By the way,we also design two experimental schemes that can verify the theoretical conclusions of this thesis.Through the research in this thesis,we found that the beveled disk can indeed suppress the ASE effect,and can effectively reduce the heat generation on the side of the thin-disk crystal.When the beveling angle is 57°,the ability of the beveled disk suppressing the ASE effect basically reaches its maximum.