Research On Key Technologies Of High Power Thin Disk Laser

Thin disk laser(TDL)is becoming an important development direction of high power continuous laser and high energy,high average power,high repetition rate ultrafast laser because of its significant advantages in structure,efficiency and beam quality.It has an important application prospect in industry,science,military and other fields.At present,the key technologies such as multi-passes pumping,high efficiency heat exchange and crystal thermal deformation control and compensation are insufficient,which limit the further development of high power TDLs.Based on the 2kW continuous output high-power TDL,this paper has carried out systematic theoretical and experimental research on the scientific issues related to the key technology of restricting the development of high-power TDL.Firstly,this paper introduces the research status of high-power TDL,and analyzes the key technical issues affecting the further development of high-power disk laser.On this basis,the misalignment rule of the pump spot on the 24 multi-passes pump crystal is simulated and analyzed by using ZEMAX.Based on the cooling technology of porous foam and millimeter channel,the heat transfer process of the technology used in high power TDL heat transfer is studied,and a new efficient heat transfer structure is developed.On the basis of the above technology,the 2 kW Yb: YAG high power disk laser based on unstable cavity is optimized and the experimental research is carried out.The main research contents and academic contributions of this article are as follows:1.Key technology of multi-passes pump.First of all,based on the ray tracing theory,the variation law of the pump spot misalignment sensitivity on the crystal under the multi-pass pump structure is analyzed,the multi-pass pump structure used at high power is determined,and its optical structure is designed.Secondly,based on Lambert's law,in the framework of a multi-passes disk laser,the numerical relationships between the reflectance of the mirror,the crystal thickness,the doping concentration,the angle of incidence,and the number of pump strokes and the absorption efficiency of the pump light are analyzed,carried out theoretical derivation and numerical calculation.Then,based on the threshold pump power per unit volume and the quasi-three-level rate equation,the optimal pump power density on the crystal was determined while maintaining optical-optical efficiency above 50%.Finally,based on the theory of geometrical optics,the generation mechanism of the "stretch" of the crystal Y-axis and the "sharp angle" of the spot when the pump spot is incident at a large angle is analyzed and a solution is given.2.Key technology of efficient heat exchange.For the first time,the porous medium material is introduced into the millimeter channel heat sink structure,and the heat transfer physical model is established based on the momentum equation and energy equation of the porous medium region.The finite element analysis method is used to simulate and optimize the heat sink structure of the porous medium millimeter channel.The simulation calculation and optimization design show that when the thickness of the porous medium is 2mm,the porosity is 40 %,and the inlet water pressure is 4 kg(0.4Mpa),the heat transfer coefficient of the heat sink reaches 1.51×10~5 w / m~2 ? K,and experimental verification is performed.The heat exchange structure has uniform heat exchange.It is more conducive to the realization of high power pump.3.Key technology of thermally induced deformation control and compensation of crystal.A thermal analysis model of the thin disk crystal is established.The analysis shows that: the crystal can be used as a heat source for a uniform pump only when the thickness of the crystal is much smaller than the diameter;increasing the thickness of the crystal cap layer can effectively reduce the magnified spontaneous radiation in the thin disk crystal and give The change law of the crystal strain and the thickness of the cap layer is given;the changes of the optical path difference caused by the photo thermal effect,photo elastic effect,thermal expansion and bending deformation of the crystal under different thickness cap layers are given,and the crystal cap layer is determined When the thickness is 1.5 mm,the ASE effect in the crystal is effectively suppressed,and the change in strain and optical path difference in the crystal is the smallest.4.Experimental research of 2 kW TDL.Based on the research of multi-pass pumping technology,high-efficiency heat transfer technology and crystal-induced thermal deformation control and compensation technology,a 24 multi-passes pumped kilowatt-level TDL system was designed based on the theory of resonant cavity,and continuous light emission experiments were performed The study obtained a continuous laser output of 2011 W and a optical-optical efficiency of 57.7 %.The research work in this paper has laid an important theoretical and experimental basis for the development of continuous 10 kW TDLs and high-power ultrafast laser amplifiers.