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70-W Graphene-Oxide Passively Q-Switched Thulium-Doped Double-Clad Fiber Laser

We report on a graphene-oxide (GO) passively Q-switched thulium-doped double-clad fiber laser with two-stage amplifiers that can deliver >70 W average power at ~1950.27 nm wavelength. The achieved highest average power is ~73 W, corresponding to ~1.5 μs pulse duration, ~0.877 mJ pulse energy, and ~585 W peak power. To our best knowledge, this is the first high-power pulsed output by using passive method to generate Q-switched pulses, especially by using GO as the saturable absorber, paving the way toward practical application of GOSA in high power pulsed double-clad fiber laser system.