9 kilowatt-level direct-liquid-cooled Nd:YAG multi-module QCW laser.

An average 9 kilowatt-level direct-DO-cooled side-pumped Nd:YAG multi-disk laser resonator at QCW mode with a pulse width of 250μs is presented, in which the straight-through geometry is adopted the oscillating laser propagates through 40 Nd:YAG thin disks and multiple cooling DO flow layers in the Brewster angle. Much attention has been paid on the design of the gain module, including an analysis of the loss of the laser resonator and the design of the Nd:YAG thin disk. Experimentally, laser output with the highest pulse energy of more than 20 J is obtained at a repetition frequency of 10 Hz. At high repetition frequency, the average output power 9.8 kW with η = 26% and 9.1 kW with η = 21.8% are achieved in the stable resonator and unstable resonator, respectively, and in the corresponding beam quality factor β= 14.7 and β= 9.5 respectively. To the best of our knowledge, this is the first demonstration of a 9 kilowatt-level direct-liquid-cooled Nd:YAG thin disk laser resonator.