Theoretical Study On Thermal Effect Of All-solid-state End-pumped Pr³⁺:YLF Laser

As strenuous growth of the all-solid-state lasers,the output laser contains infrared,visible and ultraviolet wavelengths,its stable,efficient and tunable beam characteristics are used over a wide area.Take military,scientific research and production for instance.Among them,the all-solid-state Pr³⁺:YLF laser gains strengths in simple structure,high optical conversion efficiency,excellent thermal stability as well as wide emission wave coverage.Both them are located in the visible wavelength,and ultraviolet band laser can be obtained by one frequency doubling,which attracted wide attention from researchers and scholars.However,the formation of laser crystal thermal effects,thermal lensing,and thermogenic diffraction losses in all-solid-state lasers has become the key factor limiting high power laser output and performance index,which is a pivotal element of high-power all-solid-state laser research.The thermal effect of the gain crystal in an all-solid-state laser is determined by the pump light energy and distribution characteristics,the physical and chemical properties of the crystal itself,and the heat dissipation method.In order to investigate the endothermic effect of endopumped Pr³⁺:YLF crystals,we model the heat conduction,Matlab theory was used to study the temperature field distribution inside the crystal under Gaussian beam and flat-top beam pumping conditions.Based on that,the numerical and variation laws of thermal lensing effects produced by temperature gradients,thermal stress birefringence and end-face deformation are calculated by classification theory,provides a basis for the experimental design of a stable and efficient resonant cavity structure.The author made the theoretical calculation of thermal diffraction loss in the resonant cavity of an all-solid-state Pr³⁺:YLF laser,on the basis of thermal spatial rate equation diffraction loss and a four-energy laser system,the effect on the relationship between pump light and oscillating laser at different pump powers,and the relationship between mode crossover ratios were analyzed.provided a theoretical basis for optimizing mode matching,lowering the laser threshold,and improving the optical-optical conversion efficiency to obtain high power laser output.The author simulated thermogenic stresses in end-surface pumped Pr³⁺:YLF crystals and the mechanism of its generation by using ANSYS software,theoretical expectations of the ultimate crushing stress of laser crystals,gained the rational design of laser systems for experiments to prevent crystal damage.The research results of this thesis show that,in the course of high power end-pumped all-solid-state Pr³⁺:YLF laser,because of the characteristics of the physicochemical parameters of Pr³⁺:YLF crystal,compared with crystals as Nd:YAG,titanium gemstone,Nd:YVO₄,the thermal effect of the laser crystal due to the absorption of pumped light is serious,this thermal effect is expressed as a shorter negative thermal lens,but also accompanied by serious thermogenic diffraction loss,and thermogenic damage stress,will have a serious impact on the laser output performance index,unfavorable to the light-optical conversion efficiency and beam quality,which is the design of high power all-solid Pr³⁺:YLF visible laser can not be ignored factors.