| Laser diode pumped passively Q-switched lasers can obtain laser pulses with high beam quality and high peak power,and have wide applications in laser processing,laser range finders,engine ignitions,remote sensing and environmental pollution detection,and so on.Therefore,development of high peak power passively Q-switched microchip lasers has become a highlight in the solid-state laser field.Composite crystals fabricated with thermal diffusion bonding technology have many advantages,such as alleviating the thermal effect and shortening the cavity length,and they have been widely used in constructing compact passively Q-switched miniature lasers with high optical-to-optical efficiency and high peak power.However,there is an interface layer through ion diffusion between the gain medium and the saturable absorber in the composite materials,which has strong effects on laser performance of composite crystals.Up to now,the effect of the interface layer formed in the composite crystal on the laser performance has not been investigated.In this thesis,by using combinations of Yb3+:YAG/Cr,Yb:YAG/Cr4+:YAG laser crystals to simulate a Yb3+:YAG/Cr4+:YAG composite crystal with a Cr,Yb:YAG interface layer,the effect of the Cr,Yb:YAG interface layer on the laser performance of the Yb3+:YAG/Cr4+:YAG composite crystal has been investigated.The experiment results show that the formation of the Cr,Yb:YAG crystal interface layer in the Yb3+:YAG/Cr4+:YAG composite crystal has a negative impact on the average output power,the optical efficiency,as well as the single pulse energy and the pulse peak power.In addition,the Cr,Yb:YAG crystal interface layer in the Yb3+:YAG/Cr4+:YAG composite crystal also leads to a strong mode competition,resulting in the decrease of the longitudinal mode number,the widening of longitudinal mode separations,and the poor stability of laser pulse trains.Besides,in this thesis,rate equations,which are applicable to passively Q-switched lasers structured by composite crystals with codoped interface layers,were estabished by modifying the passively Q-switched rate equations.The analytic solutions of the modified rate equations have been obtained,and the analytic solutions can be used to directly calculate the pulse energy,the peak power,the pulse width,the repetition rate and the average output power of passively Q-switched lasers structured by composite crystals with codoped interface layers.By comparing and analyzing the experiment results and the simulation results,it shows that the simulation results are in good agreement with the experiment results.Afterwards,the effects of the thickness of a codoped interface layer on the passively Q-Switched laser performance of composite crystals were investigated through the simulation method.The simulation results show that the change of the thickness of the codoped layer has little effect on the pulse width,the pulse energy,the peak power and the repetition rate,as well as the average output power.However,the codoped interface layer in a composite crystal has a great influence on the laser longitudinal modes.The single-longitudinal-mode oscillation can be achieved in Yb3+:YAG/Cr4+:YAG composite crystal passively Q-switched microchip laser by adjusting the thickness of the interface layer with proper thermal diffusion bonding parameters.The single-longitudinal mode oscillation in passively Q-switched microchip laser is benefical for stabilizing pulse trains.The results of this study are of theoretical and practical importance to develop novel Yb3+:YAG/Cr4+:YAG composite crystals that could be used to obtain laser pulses with high peak power and high optical efficiency. |
PDF Full Text Request