Study On Resonant Pumped Thorium - Doped Solid - State

Eye-safe2μm Tm-doped lasers have been widely used in medicine, laser radar and as the pump source to generate3-5μm mid-infrared radiation. Traditionally,～800nm laser diodes were used to pump the Tm-doped lasers. High Tm3+-doping concentration was usually needed to obtain efficient pumping. However, high Tm3+-doping concentration leads to high thermal distribution density, this will not only exacerbate the beam quality but also restrict the improvement of the output power. In this paper, we have theoretically and experimentally studied the in-band pumped Tm3+-doped solid technology and the performance of the laser.The pump source in our experiments was a homemade Er/Yb codoped fiber laser resonantly pumped Er:YAG ceramic laser at1617nm. The emission wavelength of the Er/Yb fiber laser was tuned and wavelength locked by a VBG at1532nm. We have studied the effects of thermal effects and fiber curvature losses on the Er/Yb codoped fiber laser, and the performance of the fiber laser was optimized. Quasi-three-level model was used to analyzed the properties of the Er:YAG ceramic laser, it is viable to obtain1617nm laser operation of Er:YAG laser by using appropriate output coupler.With some approximations of the rate-equation, analytic solutions of the output power and threshold of the Tm-doped solid-state laser were derived. By using the Er:YAG ceramic laser at1617nm as the pump source and the6at.%Tm3+-doped YAG as the gain medium, up to5.6W of output power was obtained under10.6W of incident pump power at1617nm, corresponding to the slope efficiency of60.2%with respect to the incident pump power. Higher slope efficiency can be obtained with optimized crystal parameters and laser design. Moreover, we analyzed and compared the performance of crystal laser and ceramic laser at the same Tm3+doping concentration. It was found that the performance of the Tm:YAG ceramic laser was close to that of Tm:YAG crystal laser.