We report on a 2.3 m long air-clad ytterbium-doped large-modearea photonic crystal fiber laser generating up to 80 W output power with a slope efficiency of 78%. Single transverse mode operation is achieved with a mode-field area of 350 microm2. No thermo-optical limitations are observed at the extracted ~35W/m, therefore such fibers allow scaling to even higher powers.

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We numerically demonstrate the existence of a discrete family of robust dissipative soliton bound state solutions ͑soliton molecules͒ in a mode-locked fiber laser with an instantaneous saturable absorber in the normal dispersion domain. For a certain domain of the small-signal gain, we obtain a robust first-level bound state with almost constant separation where the phase of the two pulses evolves independently. Moreover, their phase difference can evolve either periodically or chaotically depending on the small-signal gain. Interestingly, higher level bound states exhibit a fundamentally different dynamics. They represent oscillating solutions with a phase difference alternating between zero and. We identify the crucial role of the linear gain saturation for the existence of these robust molecules independently of their level.