| The 2?m band is located at the atmospheric transmission window and the absorption peak of water molecules,and it is safe for human eyes.Therefore,lasers working in the 2?m band have broad development and application prospects in many fields such as medical surgery,environmental monitoring,lidar,industrial processing,and optoelectronic countermeasures.High peak power 2?m solid-state lasers are ideal pump sources for optical parametric oscillators(OPO)and optical parametric amplifiers(OPA).Laser diode pumping single-doped Tm3+ gain medium is an effective way to obtain 2?m laser.Tm:YAG crystal has the advantages of wide absorption and emission spectra,good mechanical strength and thermal stability.In addition,Tm:YAG is suitable for commercial high-power laser diode pumping.Therefore,Tm:YAG crystal is an ideal medium for solid-state lasers in the 2?m band.Q-switching technology is to obtain high peak power output by modulating the Q value of the resonant cavity.Electro-optic Q-switching has the advantages of short switching time,high control accuracy,and good stability.It is a common technology for obtaining high peak power 2?m lasers.This paper studies the laser diode side-pumped Tm:YAG electro-optic Q-switched laser from both theoretical and experimental aspects,and achieves high peak power pulsed laser output.The theoretical work of this thesis focuses on the study of Tm:YAG electro-optic Q-switched lasers.Analyze the stability of the resonator through the ABCD matrix theory and determine the structural parameters of the resonator;establish the Tm:YAG laser quasi-three-level structure rate equation set,and on this basis,establish the Tm:YAG laser rate equation set during Q-switched operation.Analyzed the change rule of the number of inverted populations and the number of photons in the resonator during the Q-switching process.After deduction,the peak power,output energy,and pulse width of the laser as a function of repetition frequency were derived,and the peak output power,single pulse energy and pulse were simulated The width changes with the repetition frequency;compare the characteristics of different electro-optic crystal materials,select LGS crystal as the electro-optic Q switch according to the requirements,and calculate the driving voltage used in its work through the theory of refractive index ellipsoid equation.The experimental research content mainly includes:Based on the self-made LGS electro-optic Q-switch,a Tm:YAG electro-optic Q-switched laser system pumped by the laser diode side is developed,which achieves a high-energy,narrow pulse width 2?m laser output.A laser diode array with an emission wavelength of 785nm was used as the pump source,and a Tm:YAG crystal with a doping concentration of 3.5at.%was used as the gain medium.The dielectric film polarizer,the white sapphire stack and the Glan prism were respectively used as the polarizing plates.The laser output characteristics of the device.The experimental results found that the damage threshold of the dielectric film polarizer is low,and it is difficult to obtain high energy output;when the white sapphire stack is used as a polarizer,a tail pulse will appear as the pump energy increases,which affects the laser output;Glan prism is used as a polarizer.When the polarizer is used,no tail pulse appears.When the repetition frequency is 10Hz and the pump energy is 7.2J,the maximum single pulse energy is 60 mJ,the pulse width is 63.5 ns,the peak power reaches 0.91 MW,and the slope efficiency reaches 5.4%.Experiments show that the high extinction ratio and high threshold of the Glan prism are beneficial to suppress the generation of tail pulses and help to obtain laser output with high peak power and narrow pulse width.And we also add resistance wire to the water cooling system reduces the instability of output from 11.1%to 1.4%. |
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