Thermal Management Technology Of A Liquid Cooling Thin-Disk Oscillator

High average power and high beam quality solid-state laser is one of the research focuses in the field of laser technology currently. However, the temperature gradient is formed within laser gain medium with the coactions of pumped field and cooling medium, and then the thermal effects such as thermal lens, thermal stress birefringence and so on are emerged. Thermal-induced problems seriously restrict the development of high average power and high beam quality solid-state laser. In the paper, a structure of liquid cooling thin-disk laser is designed and the thermal management technology will be mainly studied for solving the thermal effect of solid-state laser. In order to reduce the offset of the output spot and improve the uniformity of laser output, The laser gain medium which is placed in Brewster Angle fully immersed in the coolant. Liquid can take out the heat from the gain area by flowing avoiding heat accumulation, so as to realize high-efficiency thermal management.This paper first discusses the development of high energy laser system and the latest scientific research in the field of laser technology at home and abroad. The four level energy structure of Nd:YAG is simply introduced. The advantage and disadvantage of traditional solid-state laser, liquid laser and laser containing a distributed gain media are introduced detailed in the aspect of thermal management. The solving steps of the computational fluid dynamics are elaborated in detail; control equations and three kinds of numerical simulation calculation method are introduced, the three-dimensional physical modeling and meshing were conducted, the high quality grid is got. Based on the principle of computational fluid dynamics, the thermal-flow-solid coupling model is established. Through the simulation analysis method, the distribution characteristics of temperature field and velocity field are researched. The wave-front aberration of the laser passing the gain region is simulated under the condition of liquid cooling. The PV value of total optical difference in the gain medium and coolant is 1.09λ and the result shows that wave-front aberration has a little influence of beam quality.The dispersion curve and temperature refractive coefficient of the cooling liquid are measured. The thin-disk oriented at Brewster Angle relative to the laser emission direction immersed in coolant liquid is demonstrated. Laser output is obtained with LDA side pumped. The coupling efficiency, the slope efficiency and the pulse width of the pumping system is tested; the far-field pattern of the output laser is obtained in the experiment. Under the repeated pumping frequency of 10 Hz, a maximum output energy of 615 mJ was realized. The optical-optical efficiency and the slope efficiency is 23% and 21% respectively. The coefficient of variance of the output energy index of output uniformity is 1.27% which shows good performance of thermal management.