Diode-pumped Yb:LuAG and Yb:YAG disk laser amplifiers with high pulse energies

Ytterbium-doped garnets are attractive for use in high-energy diode-pumped solid-state lasers due to their spectral and thermal properties. Yb:YAG is one of the most well developed thin-disk laser materials. Recently, Yb:LuAG [1-4] was investigated as a promising candidate for kW thin-disk lasers because of its superior thermal conductivity especially at high doping concentrations compared to Yb:YAG. In this paper we demonstrate high-energy ns-pulse multipass amplification in Yb:YAG and Yb:LuAG. Pulses with a duration of 6 ns at a center wavelength of 1030 nm were generated in a cavity dumped oscillator and amplified to 20 mJ in an Yb:YAG based booster amplifier. The gain medium of a further (main) amplifier was pumped by a stack of micro-lens homogenized laser diodes operating at 940 nm a peak output power of 4kW. The pump light is focussed to a spot size of 4 mm into the disk while the reflected (not absorbed) light was recovered by an imaging system leading to two double-passes through the gain medium. The output of the booster is sent into a semi-stable resonator cavity (mirror based 4-f imaging system around the laser disk) forming a 10-pass amplifier.