Diode-pumped Continuous-wave And Passively Q-switched Yb:Lu₃Al₅O₁₂ Ceramic Lasers

Laser diode（LD）pumped passively Q-switched lasers in near-infrared have outstanding advantages,such as good stability,high conversion efficiency,good beam quality and compact structure,which are useful for a variety of applications including biomedicine,laser communication,military weapons and scientific research.Yb³⁺-doped laser ceramic materials possess the advantages of Yb³⁺-doped materials and transparent ceramics.They are promising working materials for solid-state lasers at～1μm owing to distinct advantages in energy level structure,upper energy level lifetime,fabrication method and thermo-mechanical properties.In this paper,theoretical and experimental researches on the output performances of diode-pumped continuous-wave and passively Q-switched Yb:Lu₃Al₅O₁₂（Yb:LuAG）ceramic lasers under different coupling output transmittance（T）have been analyzed.In terms of theory,based on the rate equation models,the effects of T on the output performances of continuous-wave and passively Q-switched Yb:LuAG ceramic lasers have been numerically simulated.The relationships between threshold pump power,slope efficiency,output power and light-to-light conversion efficiency with T for 1030 nm and 1047 nm oscillation modes have been numerically simulated by using the quasi-three-level rate equation.The results have showed that,with increasing T,the threshold pump power and slope efficiency increase gradually,the output power and light-to-light conversion efficiency increase firstly and then decrease.Then,based on the passively Q-switched rate equation,the relationships between T and the single pulse energy,peak power,pulse width and repetition frequency of the 1030 nm and 1047 nm oscillation modes have been numerically simulated.The results have demonstrated that,as T increases,the single pulse energy and peak power progressively increase,the pulse width and repetition frequency decrease slowly.In terms of experiment,the performances of diode-pumped continuous-wave and passively Q-switched Yb:LuAG ceramic lasers under different T have been studied.In the continuous-wave regime,the laser wavelength is around 1047 nm for T=1.6%,2.5%,5%,7.5%and 10%.The maximum output power reaches 2.53 W under T=10%.For T=15%,the laser wavelength is around 1031 nm with the maximum output power of 3.11 W.In the passively Q-switched regime,the performances of the passively Q-switched Yb:LuAG ceramic laser with a semiconductor saturable absorption mirror（SESAM）serving as Q switch have been analyzed for T=1.6%and T=7.5%.The laser generates 0.85 W at 1047 nm with the light-to-light conversion efficiency of 9.21%and the slope efficiency of 8.43%for T=1.6%.The laser produces the single pulse energy of 7.81μJ and the peak power of 6.41 W with the pulse width of 1.18μs,while the repetition frequency is 112.63 k Hz.For the case of T=7.5%,the laser wavelength is measured to be about 1031 nm with the highest average output power of 1.47 W.The light-to-light conversion efficiency is 15.85%and the slope efficiency is 19.04%.Under such conditions,the pulse width,repetition frequency,single pulse energy and peak power are 1.10μs,250.50 k Hz,5.98μJ and 5.01 W,respectively.