Research On Pulsed-laser-diode Intermittently Pumped Dual-pass Gain Tm³⁺-doped 2-?m Q-switched Laser

The 2?m laser is located in the atmospheric window and thermal radiation area,which belongs to the human eye safety wave band,and it can be used in laser medical treatment,laser radar,photoelectric countermeasure,spectroscopy,optical communication and material processing.In particular,the 2?m all-solid-state,high-repetition frequency and high-energy laser can also be used as a high-efficiency pump source for optical parametric oscillators.In this paper,the single-doped thulium garnet oxide is acted as the working substance,and the high repetition frequency and large energy 2?m Q-switched lasers are demonstrated in aspects of theory,design and experiment.The main contents are as follows:In theory,according to quasi-three-level transition characteristics of Tm:YAG,Tm:LuAG and Tm:LuYAG single-doped thulium garnet oxide crystals,the rate equation models of pulsed LD dual-end pump single-doped thulium laser and pulsed LD dual-end pump single-doped thulium Q-switched laser is built,the laser oscillation threshold and the changes of the photon number in cavity with dual-end pumping and dual-end intermittent pumping is solved.Combined with the generation principle of laser,the output performances of conventional laser and dual-gain laser are compared and analyzed,which provides a theoretical basis for the analysis and discussion of subsequent experimental phenomena.The thermal model of single-doped thulium garnet oxide crystal is established based on the pulsed LD dual-end intermittent pump process,the internal thermal distribution and thermal focal length of single-doped thulium garnet oxide crystal are obtained under the fixed boundary condition,the same pump energy and different repetition frequency.The theoretical results show that it is feasible to reduce the thermal effect of single-doped thulium garnet oxide crystal by using pulsed LD dual-end intermittent pumping technique.In design,the pulsed LD dual-end intermittent pump and dual-gain single-doped thulium laser system is optimized.Based on the theoretical analysis results,the requirements of pulsed LD dual-end intermittent pumping technology for electronic servo system are clarified.Under the premise that the radii of the two fundamental mode spots at the center of the working material have good pattern matching,the dual-gain cavity is designed based on the dual-end gain structure.The mode matching between the pump light and the oscillating light can be achieved by combining the optimized pump spot size,the dual-end pump and dual-gain cavity with good optical and thermal stability and the position of the Q switch,so as to obtain the laser output with high efficiency and high beam quality.In experiment,the experiments of pulsed LD dual-end pump single-doped thulium Q-switched laser,pulsed LD dual-end intermittent pump single-doped thulium Q-switched laser with same repetition frequency,pulsed LD dual-end intermittent pump single-doped thulium Q-switched laser with multiplex repetition frequency,and pulsed LD dual-end intermittent pump and dual-gain single-doped thulium Q-switched laser with double repetition frequency are carried out.Among them,the experimental research of pulsed LD dual-end intermittent pump and dual-gain single-doped thulium Q-switched laser with multiplex repetition frequency combines the intermittent pumping technology and the dual-gain technology.Under the repetition frequency of 200Hz,the parameters of Tm:YAG,Tm:LuAG and Tm:LuAYG lasers are as follows:The output central wavelengths are 2014.66 nm,2023.11 nm and 2029.48 nm,respectively.The maximum single pulse energies are 9.98 mJ,8.6 mJ and 9.62 mJ,respectively.The pulse width are 100.8ns,131.6nsand 120.8ns,respectively.The beam qualities are M_x~2=1.39,M_y~2=1.38,M_x~2=1.37,M_y~2=1.42 and M_x~2=1.38,M_y~2=1.36,respectively.The maximum single pulse energies are 55%,68%and 74.3%higher than those of the pulsed LD dual-ended pumping,respectively.The experimental results show that the intermittent pumping and dual-gain techniques are feasible for improving the output performance of the quasi three-level single-doped thulium laser.In addition,the combination of intermittent pumping technique and dual-gain technique can delay the gain saturation.