Microchip laser operation of Yb-doped gallium garnets

Continuous-wave microchip laser operation and thermal lensing are studied for Yb-doped gallium garnets, Yb:LuGG, Yb:YGG, Yb:CNGG and Yb:CLNGG under diode-pumping at similar to 932 and 969 nm. It is shown that although thermal the conductivity of Ga garnets is lower than that of Yb:YAG, the compromised thermo-optic properties, high absorption in the zero-phonon line and low internal loss make the ordered Yb: YGG and Yb: LuGG crystals to be promising for compact highly efficient microchip lasers. In particular, Yb: LuGG microchip laser generated 8.97 W of output power with a slope efficiency eta = 75% and 9.31 W with eta = 65%, for pumping at 932 and 969 nm, respectively. Multi-watt output in the range 1039-1078 nm is emitted for different transmission of the output coupler. The sensitivity factor of the thermal lens for this crystal is 2.1 m(-1)/W (pumping at 969 nm with a pump waist radius of 100 mu m) and the estimated thermal conductivity is 5.8 +/- 0.5 W/mK. Power scaling of Yb: CNGG and Yb: CLNGG microchip lasers is limited by poor thermo-optic properties and high internal losses. Ordered Ga garnets show good prospects for the development of passively Q-switched microchip lasers with high pulse energies. (C)2015 Optical Society of America