Efficient laser performance of Yb:Y3Al5O12/Cr4+:Y3Al5O12 composite crystals

National Natural Science Foundation of China [61275143]; Program for New Century Excellent Talents in University [NCET-09-0669]; Fundamental Research Funds for the Central Universities [2010121058]; PhD Programs Foundation of the Ministry of Education of China [20100121120019]Highly efficient passively Q-switched lasers of Yb:Y3Al5O12/Cr4+:Y3Al5O12 (Yb:YAG/Cr4+:YAG) composite crystals have been demonstrated with an optical-to-optical efficiency of 36%. A slope efficiency of 44% was achieved with respect to the absorbed pump power. An average output power of over 1.75 W was obtained at an absorbed pump power of 4.8 W. Laser pulses with a pulse energy of over 180 mu J, a pulse width of 3 ns and a peak power of 60 kW were achieved. Near-diffraction-limited laser beams with M-2 less than 1.3 were obtained. The effects of the absorbed pump power and the transmission of the output coupler on the laser performance of Yb: YAG/Cr4+ : YAG composite crystals were addressed