Abstract
The optical properties of Yb:YAG ceramic doped with different Yb concentrations are presented. The absorption coefficient at peak absorption wavelength of 940 nm increases linearly with Yb concentration in Yb:YAG ceramics. Low-threshold and highly-efficient continuous-wave (cw) laser-diode end-pumped Yb:YAG microchip ceramic laser with near-diffraction-limited beam quality was demonstrated at room temperature. Slope efficiencies of 79%, 67% and optical-to-optical efficiency of 60%, 53% at 1030 nm and 1049 nm, respectively were achieved for 1-mm-thick Yb:YAG ceramic plate (C Yb = 9.8 at.%) under cw laser-diode pumping. Dual-wavelength operation at 1030 nm and 1049 nm with 5% transmission of the output coupler was achieved by varying pump power intensity. 1049 nm laser operation was automatically obtained by using 5% transmission output coupler when absorbed pump power is higher than 1 W. The lasers operate in multi-longitudinal-mode; the effect of pump power on the laser emission spectra for both wavelengths is addressed. The laser wavelength around 1030 nm shifts to short wavelength at low pump power region and then to red with increase of the absorbed pump power, while the laser wavelength around 1049 nm does not change with the pump power. Excellent laser performance indicates Yb:YAG ceramic laser materials could be potentially used in high-power solid-state lasers operating at 1030 nm, 1049 nm, or both wavelengths simultaneously. Laser-diode pumped lowthreshold and highly-efficient passively Q-switched Yb:YAG ceramic microchip laser with Cr 4+ :YAG ceramic as saturable absorber has also been demonstrated. The slope efficiency is as high as 37%, and the optical-to-optical efficiency is as high as 29% for 89% initial transmission of Cr 4+ :YAG ceramic. The pulse width of 380 ps and peak power of over 82 kW at repetition rate of 12.4 kHz was obtained. Single-longitudinal-mode oscillation and wide-separated multi-longitudinal-mode oscillation due to etalon effect of Cr 4+ :YAG thin plate was achieved depending on the pump power level.
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