R. G. Krämer et al., "Femtosecond written fiber Bragg gratings in Ytterbium-doped fibers for fiber lasers in the kilowatt regime," Opt. Lett. 44, 723 (2019).
We investigate the high-power durability of fiber Bragg gratings written directly into an ytterbium-doped large mode area fiber using ultrashort laser pulses. The gratings were successfully integrated as a high reflector into an oscillator setup reaching up to 1.9 kW signal output power with an efficiency of 87%. Defect states induced during the inscription process could be drastically reduced by a self-annealing process resulting in a stable laser performance.