A 400W cryogenic Er:YAG laser at 1645 nm

We report on the design and characterization of a cryogenically cooled, resonantly pumped Er:YAG slab laser operating at 1645 nm. The Er:YAG slab is conductively cooled by liquid nitrogen and face-pumped by a 1.4 kW diode array operating at 1452 nm. The slab is transversely extracted in a highly multi-mode oscillator, producing 386 W of cw output power and 420 W of quasi-cw power at 50% duty cycle. We have measured 45% slope efficiency and 39% optical conversion efficiency (relative to incident pump). The laser has also been configured to operate with low-order multi-mode output, producing over 250 W of quasi-cw power at 25% duty cycle, and has been Q-switched at repetition rates as low as 10 kHz.