| High power solid-state lasers play an important role in laser radar,photoelectric countermeasure,laser processing and laser diagnosis.Due to the influence of thermal effect under high average power in practical application,it is difficult to achieve the goal of high repetition rate and large single pulse energy simultaneously.The “burst mode” laser with “intermittent” operation has a short working time,which can effectively reduce the impact of thermal effect on the laser,thus solving the problem well.Based on this,the scheme of main oscillator power amplifier(MOPA)is used in this paper to achieve high repetition rate,narrow pulse width and high energy burst mode laser output in 2 ms pumping time.Based on the rate equations,the influence of the population inversion in the electro-optically Q-switched laser on the parameters of pulse output energy and time width is analyzed.The function expressions of the optimum output coupling mirror,output energy,extraction efficiency,pulse width and peak power are derived.Based on the Maxwell-Schrodinger equation,the theoretical model of multi-pass amplifier is established,and the fluence iteration relationship,efficiency,peak fluence,and amplification time of multi-pass amplifier are obtained;the relationship among the amplified pulse,energy gain coefficient and seed light is obtained by the rectangular pulse amplification theory.The thermal effect of laser crystal is analyzed,including the temperature distribution in the laser medium,the change of refractive index,the expression of thermal focal length,and the distribution of pump light in three-direction and five-direction side pump module is simulated.Through simulation results of the thermal effect and the analysis of the oscillating spot in the cavity,the structure of the cavity is designed reasonably.The oscillating stage adopts 808 nm pulsed Laser Diode(LD)side pumping combined with the RTP electro-optically Q-switching technology solution in the cavity to achieve a 10 k Hz 1.06 ?m burst-mode laser output,and the number of pulses is flexibly selected by controlling the pumping time When the Q-switched repetition frequency is 10 k Hz and the maximum pump energy per burst is 1.5 J,the output energy of the laser pulse burst reaches 456 m J,the single pulse energy reaches 24 m J,the peak power reaches 1.85 MW,the pulse width is 13 ns,and the laser pulse variation coefficient is 6.0%,which has excellent performance.In order to further improve the laser pulse energy,the first-stage single-pass amplification experiment of the burst mode laser is studied.By choosing the appropriate expanding and collimating lens group,the seed laser output from the oscillation stage is expanded about 1.5 times,and injected into the amplification module,so that the seed laser is fully amplified.After the first-stage single-pass amplification,the output of 1.06 ?m laser pulses with the burst energy of 836 m J,single pulse energy of 44 m J,peak power of 3.2 MW,pulse width of 13.6 ns and pulse variation coefficient of 2.1% are achieved at the Q-switched repetition rate of 10 k Hz and the maximum pump energy per burst of 3 J.The 1.06 um fundamental frequency burst mode laser can meet the application needs of 10 k Hz laser diagnosis.After the first-stage single-pass amplification,the laser energy of the pulse burst is significantly improved compared with that of the oscillation stage,and the stability of the laser pulse is also greatly improved,which also provides the possibility for further power amplification.Through the theoretical study of the efficiency of energy extraction in the amplification stage,the following two-pass amplification experiment can be continued to obtain higher energy laser pulse and higher efficiency of energy extraction,and the stability of the laser pulse can be further improved while the energy is increased. |
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