Research On Passively Q-switched Burst-pulse 1.06 ?m Nd:YAG Laser With Amplification Technique

High-repetition-rate,high-pulse-energy lasers are widely needed in many fields such as laser radar,laser processing and laser diagnostics.Because of the thermal effect,high repetition rate and large pulse energy restrict each other,wich can be solved by combing pulse-burst laser with master oscillator power amplifier(MOPA)together.By researching on the generation and amplification of laser pulse burst,we obtained laser output with high frequency,short pulse width,large pulse energy during the pump period(~ms).Fristly,we had a brief introduction and compare on different passively Q-switched laser techniques,and showed the advantages of Cr:YAG as the saturable absorber.By sloving the rate equations,the behavior of passively Q-switching with Cr:YAG as the saturable absorber is analyzed.The rate equations of the amplified pulse signal were established and solved.Furthermore,based on general solution of the rate equations,the change of energy gain was discussed with ideal ectangle pulse as the incident signal.Then,the absorption spectra of Nd:YAG crystal was measured.And the experiment of the oscillator was carried on,with YAG/Nd:YAG/Cr:YAG composite crystal as the gain medium and saturable absorber.The output performances with 879 nm Laser Diode(LD)or 885 nm LD as the pump source are compared.When 885 nm LD was used as the pump source,the shortest pulse width was 1.4 ns.With pump energy of 124.6 mJ,burst energy,single pulse energy,pulse width,peak power,and optical-optical conversion efficiency were 20.5 mJ,238.0mJ,2.0 ns,119.0 kW and 16.5%,respectively,with 86 pulses obtained in 1-ms pump duration.By using the knife-edge method,the beam quality factors were estimated to be M_x~2=2.9 and M_y~2=2.8 in horizontal and vertical directions.Besides,the spatial beam distribution was in good symmetry.Finally,the amplifier performance was reseached.After a first stage single-pass amplification,burst energy,single pulse energy,pulse width and peak power reached50.9 mJ,592.0?J,2.0 ns and 296.0 kW,respectively.After a first stage double-pass amplification,burst energy,single pulse energy,pulse width and peak power reached117.0 mJ,1.4 mJ 1.9 ns and 715.8 kW,respectively.Based on the first stage double-pass amplification,a second stage single-pass amplification was carried on,and burst energy,single pulse energy,pulse width and peak power reached 409.4 mJ,4.8 mJ,1.9 ns and2.5 MW,respectively.After amplification pulse width and repetition rate kept almolst the same with the seed laser.Because of gain saturation effect,the stability of laser pulse was improved with the increasing of amplifier stages,and after the two stage amplification,coefficient of variation reached 5.0%,finally.