0.5 µJ femtosecond pulses from a giant-chirp ytterbium fiber oscillator

Pulse energy scaling of mode-locked femtosecond fiber oscillators is important for applications in material processing and nonlinear optics. To date the highest output pulse energies have been obtained from all-normal dispersion fiber oscillators operating in the dissipative soliton regime. The energies of these dissipative solitons are limited by the total nonlinear phase-shift accumulated over one resonator round-trip. To increase the pulse energy the peak intensities inside the fiber section of the oscillator must be reduced. This can be achieved either by increase of the mode-field diameter of the fibers or the pulse duration. The mode-field diameter can be increased up to approximately 25 μm in standard large-mode-area (LMA) fibers. Long pulse durations can be obtained in the giant-chirp regime of all-normal dispersion fiber oscillators with large total resonator dispersion. We combined both power-scaling methods to obtain 0.5 μJ pulses from a ytterbium step-index fiber oscillator.