Femtosecond written fiber Bragg gratings in ytterbium-doped fibers for fiber lasers in the kilowatt regime.

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.

High power sub-ps pulse generation by compression of a frequency comb obtained by a nonlinear broadened two colored seed.

In this contribution we demonstrate the generation of a frequency comb with sub-picosecond pulses by seeding an amplifier with two narrow linewidth laser diodes separated by 50 GHz. The results are achieved in the normal dispersion regime with parameters where the forming of the comb is dominated by self-phase modulation. A numerical simulation is performed with different nonlinear interaction lengths, whereas the experimental realization is done in a high power Yb-doped fiber amplifier to generate the necessary nonlinearity. An output power of 750 W with compression to sub-picosecond pulse durations is shown. Further perspectives towards higher power levels and larger comb-line spacing are discussed.