Research On 2μm Q-switched Pulsed Laser Based On The Doping Concentration Gradient Tm:YAG Crystal

Thulium-doped lasers have advantages such as long fluorescence lifetime,high quantum efficiency,making them an ideal laser source for obtaining 2μm lasers.Solid-state lasers in the 2μm band have been widely used in various fields such as laser radar,laser ranging,and meteorological observation,due to their strong penetration,high sensitivity,and high resolution.However,the severe thermal effect caused by the quasi-three-level structure of the 2.01μm transition of Thulium ions(Tm³⁺)and the small emission cross-section of Tm³⁺prevent the realization of high-performance 2μm laser output.Recent research has found that using the step-like doping concentration technology to process the crystal can effectively alleviate the thermal effect problem.This article conducts thermal field simulation analysis on Tm:YAG crystal and designs two different parameters of step-like doping concentration Tm:YAG crystals to study the output characteristics of step-like doping concentration Tm:YAG continuous and Q-switched pulse lasers.The main research contents are as follows:Theoretical content includes:1.By analyzing the energy level transition of Tm³⁺ions,the continuous and Q-switched rate equation models of quasi-three-level Tm:YAG are established and solved.The output characteristics of the step-like doping concentration Tm:YAG crystal in continuous lasers and the laws of the number of particles in each energy level and oscillating photons in the cavity during the Q-switching process are simulated,and the optimal length and concentration range of Tm:YAG crystal is discussed in combination with the output performance.2.The thermal model of the step-like doping concentration Tm:YAG crystal is established.The internal optical field,temperature field,and stress field of the step-like doping concentration Tm:YAG crystal are simulated and studied using software.The theoretical proof shows that the step-like doping concentration of Thulium ions effectively alleviates the thermal effect of Tm:YAG crystal.Based on the simulation results and the optimal concentration and length range,two step-like doping concentration Tm:YAG crystals are designed as the laser working material.An optically and thermally stable resonant cavity is designed using the ABCD optical transmission matrix,laying the foundation for later experiments.Experimental content includes:1.A step-like doping concentration Tm:YAG laser system is built,and comparative experiments of LD end-pumped single-end bonding/type I step-like doping/type II step-like doping Tm:YAG laser output performance are conducted.The slope efficiencies of the LD end-pumped step-like doping Tm:YAG continuous laser are measured to be 35.44%,39.51%,and 41.25%,respectively.The beam quality factors M²are 1.69,1.54,and 1.51,respectively.The output wavelengths are 2013.65nm, 2013.48nm,and 2013.43nm,respectively.The experimental results prove that step-like doping technology can significantly reduce the thermal effect of the laser.2.A step-like doping concentration Tm:YAG Q-switched pulse laser system is built,and comparative experiments of LD end-pumped single-end bonding/type I step-like doping/type II step-like doping Tm:YAG Q-switched pulse laser system are conducted. At a repetition frequency of 300 Hz,the slope efficiency of 10.28%,10.52%,and 12.47%can be achieved,and the maximum single-pulse energy is 4.01m J,4.22m J,and 5.03m J,respectively.The pulse width at maximum single-pulse energy is 159.40ns、154.10ns和145.60ns,and the beam quality factors M²were 1.69,1.54,and 1.51respectively.From the experimental results,it can be seen that the step- concentration technology can effectively alleviate the thermal effect of Tm:YAG crystal.