Research On The Influence Of Air Thermal Effect On The Output Beam Of Thin-disk Laser

Thermal effect is the main factor restricting the improvement of high beam quality and power of solid-state lasers.As a solid-state laser with a special structure,due to the advantages of the larger area-to-volume ratio of the gain medium and the heat dissipation of the end face,thin-disk laser effectively dissipates the heat accumulated in the crystal,which significantly reduces the influence of the thermal effect on the output laser.Then with the improvement of the output power level of thin-disk laser and the improvement of the beam quality,the temperature rising of thin-disk laser crystal itself causes the thermal effect of the surrounding air to cause the uneven refractive index distribution of the air,which causes the wave-front of the beam to be distorted to affect the output beam of thin-disc laser.Based on a comprehensive analysis of the influence of the thermal effect of the disc crystal on the surrounding air,this paper reveals the essential reason for the influence of the air thermal effect on the laser oscillation in the disc laser cavity,and suppresses and compensates the influence of the air thermal effect from the aspects of gas flow and cavity design.To further reduce the influence of the air thermal effect on thin-disk laser,the relevant research results and research contents are as follows:First,establish a finite element model for simulation based on the multi-physics model of the temperature rise of the disk crystal and the heat convection generated by the gas on the surface of the disk crystal.The temperature field distribution of the gas is obtained by simulation,and then the refractive index field distribution is calculated.Simplify the refractive index field and consider the asymmetric wedge-shaped refractive index field in the vertical direction and the symmetric refractive index field in the horizontal direction.Then the one-dimensional optical path difference of the vertical section and the horizontal section are calculated from the refractive index distribution.The essential reason for the influence of the air thermal effect on the oscillating laser beam: the "air lens" effect and the "air wedge" effect.By modifying the physical model,such as gas type,pump spot size,power density and other parameters,compare the strength of the air thermal effect under different conditions.Secondly,based on the results of the theoretical analysis,the "air lens" effect and the thermal lens of the disk crystal are combined and discussed as a variable lens that is related to the optical power and the pump power.The influence of the "air wedge" effect on the oscillating beam in the resonator is simplified as position misalignment and angle misalignment.By substituting the misalignment matrix into the transfer matrix,the relationship between the output beam position and the "air wedge" effect is calculated.Then the resonant cavity is designed to suppress the jitter of the output beam caused by the air wedge effect.Finally,design and experiment to verify the conclusions of simulation and the designed resonant cavity to suppress the output beam jitter.The thermal effect of the disc laser is quantitatively described through experimental measurements,that is,the optical power of the disc thermal lens,the optical power of the air thermal lens and the inclination angle introduced by the air wedge.Experiments prove that the designed cavity can obviously suppress the jitter of the output beam caused by the air heating effect.