[摘要]：We report on high-energy femtosecond pulse generation from an ytterbium-doped rod-type fiber oscillator emitting around 976 nm. Self-starting and stable single-pulse operation are demonstrated with 4.2 W of average output power at a repetition rate of 8.4 MHz. The resulting energy level reaches 0.5 mu J. Because of the all-normal dispersion of the laser cavity, output pulses are naturally chirped with a duration of 14 ps. External compression using diffraction gratings shortens the pulse duration down to 460 fs. (C) 2011 Optical Society of America
