The Thermal Effect Of Nd:YAG Ceramics End Pumped By Laser Diode

Since the laser was developed in the 1960s,near infrared band laser has been widely used in the field of industry,military,medical and our daily life.Laser-Diode?LD?Pump Solid State Laser?DPSSL?has many advantages,such as stability,compact structure,high conversion efficiency,long service life and nice beam quality output.With the breakthrough of laser transparent ceramics preparation technology,it becomes a new laser material.It provides a new idea for the development of all solid-state lasers in the direction of higher power.Nd³⁺energy level structure and the characteristics of YAG matrix determine that Nd:YAG ceramics can withstand higher power radiation,and is an ideal choice for high-power and high-efficiency solid-state lasers.However,in the process of the laser and cooling system acting on the ceramic at the same time,the laser interior appears the temperature gradient distribution,the working material expands,causing thermal deformation,and thus generating thermal effects such as thermal lens.Thermal effects will seriously affect the quality of the laser.Therefore,it is necessary to study the thermal effect deeply.The main content of this paper is as follows:1.The Nd:YAG ceramic laser pumped by laser diode is introduced in terms of working principle,internal structure,pumping mode,operation mode and mechanism of thermal effect.2.In the operation mode of LD end pump,for rectangular Nd:YAG ceramics,the heat model in rectangular coordinate system is established based on the heat conduction theory,and the heat conduction equations under continuous and pulse pump conditions are solved by analytical method,and the corresponding analytical expressions of steady state and transient temperature field are obtained respectively.Mathematica software was used to numerically simulate the calculation results of temperature field and thermoform variable.The influence of different parameters such as super-gaussian order,power,beam waist radius and pulse width on the distribution of temperature field was analyzed.When the super-gaussian order increases,the pump power decreases,the beam waist radius increases,and the pulse width increases,the temperature field decreases.Two thermodynamic models of end surface adiabatic and air convection heat transfer for cuboid Nd:YAG ceramics were analyzed separately.The results show that the heat generated by convection between uncooled surface and air is negligible.3.For Nd:YAG ceramics rod,the thermal model of cylindrical coordinate system was established.Combined with the boundary conditions of adiabatic at both ends and constant temperature at the periphery,the steady-state temperature field and transient temperature field under continuous and pulse pump operation modes are solved.Based on Mathematica software,this paper analyzes the temperature field and thermal deformation field,studies the effects of different parameters on the temperature field.It is found that the temperature field calculated by analytical method is approximately equivalent to that calculated by finite difference method and finite element method.The accuracy of this research scheme is proved.However the method is more reasonable and closer to the actuality,and decreased amount of computation,.The research results provide theory reference for the rational selection and design of parameters in practical application of laser,and have important guiding significance for the improvement of the capacity of carrying thermal load and various performance of laser.