| Laser-diode pumped passively Q-switched solid-state lasers are compact lasers with high efficiency, short pulse width, high peak power and high repetition rate. They are widely used in laser processing, laser ignition, medical treatment, material processing and so on. Various applications of laser-diode pumped passively Q-switched solid-state lasers are introduced firstly in this thesis. The development of passively passively-Q-switched solid lasers with Yb3+-doped materials as gain media is also reviewed with the consideration of efficiency and effectiveness. The advantages and characteristic of Yb3+-doped materials as laser media and Cr4+-doped materials as saturable absorbers in passively Q-switched lasers are stated. Passively Q-switched rate equations were also modified to establish the laser model for Yb:YAG/Cr,Yb:YAG self-Q-switched microchip lasers in the thesis. And the effects of pumping parameters, material parameters and output coupling on the laser performance of Yb:YAG/Cr,Yb:YAG self-Q-switched microchip lasers were investigated theoretically. The last part of the thesis, performance of enhanced Yb:YAG/Cr,Yb:YAG self-Q-switched microchip lasers are investigated experimentally and theoretically based on the thought that absorption efficiency could be improved by attaching Yb:YAG to Cr,Yb:YAG. The effects of absorbed pump power, output coupler transmission and laser materials on laser characteristics of Yb:YAG/Cr,Yb:YAG microchip solid lasers were investigated in detail.With a940nm fiber-coupled LD as pump source,1.5-mm-thick Yb:YAG ceramic as gain medium,0.5-mm-thick Cr,Yb:YAG crystal as saturable absorber, the enhanced performance of Yb:YAG/Cr,Yb:YAG microchip lasers were studied experimentally. Maximum average output power of0.53W was obtained with TOC=30%at absorbed pump power of7.07W; corresponding optical-to-optical efficiency of7.5%was achieved. With TOC=30%, laser pulses with repetition rate of25kHz, pulse width of3.75ns, pulse energy of20.4μJ were obtained at the absorbed pump power of7.07W, and corresponding peak power of5.44kW was achieved. With a940nm single emitter laser-diode as pump source,1.2-mm-thick Yb:YAG crystal as gain medium,0.5-mm-thick Cr,Yb:YAG crystal as saturable absorber, the best performance of Yb:YAG/Cr,Yb:YAG microchip lasers under high intensity pumping was achieved with TOC=50%. Maximum average output power of0.8W was obtained at absorbed pump power of2.5W, corresponding optical-to-optical efficiency of32%was obtained. With TOC=50%, laser pulses with repetition rate of65kHz, pulse width of1.68ns, pulse energy of12.4μJ were obtained at the absorbed pump power of2.5W, and corresponding peak power of7.4kW was achieved. Theoretical simulations of Yb:YAG/Cr,Yb:YAG self-Q-switched microchip lasers were performed based on the modified rate equations of passively Q-switched solid lasers, and the numerical simulated results were in good agreement with the experimental results.The transmission of the output coupler has great effect on the laser performance of enhanced Yb:YAG/Cr,Yb:YAG self-Q-switched microchip lasers. The best laser performance of Cr,Yb:YAG self-Q-switched microchip lasers by bonding Yb:YAG crystal was achieved with TOC=50%; while the best laser performance of Yb:YAG/Cr,Yb:YAG self-Q-switched microchip lasers by bonding Yb:YAG ceramic was obtained with TOC=30%. Better laser performance of Yb:YAG/Cr,Yb:YAG self-Q-switched microchip lasers was achieved by bonding Yb:YAG crystal. For different output coupling, the laser efficiencies of Cr,Yb:YAG self-Q-switched microchip lasers by bonding Yb:YAG crystal are higher than those by bonding Yb:YAG ceramic. For the same transmission of the output coupler, e.g.TOC=30%, the slope efficiencies of Yb:YAG/Cr,Yb:YAG self-Q-switched microchip lasers by bonding Yb:YAG crystal and ceramic are30%and10%respectively. High repetition rate and narrow pulse width were obtained in Cr,Yb:YAG self-Q-switched microchip lasers by bonding Yb:YAG crystal, while the pulse energy and peak power were slightly decreased owing to the small pump beam area was applied in the experiments. |
PDF Full Text Request