Study Of Pr: YLF Double Pulse Laser Based On Double Step Acousto-optic Q-switching

Nowadays,the visible band double pulse laser is widely used in laser clinical medicine treatment,laser beauty,production of precision parts and other fields.In this paper,the research of 639nm double pulse laser with double step acousto-optic Q-switching technology is carried out by combining the characteristics of the acousto-optic Q-switched technology with the characteristics of Pr³⁺:YLF laser.The theoretical and experimental results are mainly reflected in the following points:1.Based on the four level rate differential equation of Pr³⁺:YLF laser,the output theoretical model of CW laser is established.The transmittance of the output mirror is optimized,and the output characteristics such as threshold power and absorption power are simulated.The propagation law of laser in the cavity is analyzed theoretically by using ABCD matrix,the beam waist size and position in the cavity are simulated.2.Combining the four level rate equation of Pr³⁺:YLF laser with the theory of double step Q-switching,introducing the step loss function into the rate equation,the theoretical model of double pulse laser output of visible laser is established.The Runge Kutta method is used to simulate the rate equation of double pulse laser,and the variation law of the inversion particle number and photon number is obtained when the double pulse laser is output,It provides a theoretical basis for the follow-up experiments.3.The experimental study of double pulse visible light laser is carried out based on the above theoretical simulation results:Firstly,the continuous experiment of Pr³⁺:YLF laser is carried out.The stable output of 639 nm red light with average output power of829mw is realized with the maximum injection pump power of 7.2 W,which lays a good foundation for the subsequent pulse experiment.Secondly,the pulse experiment of Pr³⁺:YLF laser was carried out by putting the acousto-optic Q-switched medium into the laser cavity.The single pulse output with repetition frequency of 10k Hz and pulse width of83.60 ns is obtained under the condition of maximum injection pump power to 7.2 W.The average output power is 109 mw and pulse energy is 6.91μJ.Finally,the double pulse experiment of Pr³⁺:YLF laser is carried out.The duration of the first step of the signal generator is set to 40μs and the duration of the second step is 20μs,under the high repetition rate of 10 k Hz,a group of double pulse sequence with equal amplitude and time interval of 20μs is obtained.The pulse widths of the first pulse and the second pulse are108 ns and 152.9 ns respectively,the average output power of the double pulse is 144 mw and the pulse energy is 7.1μJ.By setting the step time of the signal generator and fine adjustment of high and low voltage amplitude,the equal amplitude double pulse output with time interval of 30μs and 15μs is obtained.