Millijoule-class Yb-doped pulsed fiber laser operating at 977 nm

We report what we believe to be the first millijoule-class ytterbium-doped fiber laser system operating on the zero-phonon line at 977 nm. An actively Q-switched master fiber oscillator delivers nanosecond pulses (FWHM 12-32 ns) at adjustable multiples of 10 kHz repetition rates that are further amplified in an ultralarge core photonic crystal fiber amplifier. At the highest available pumping level, a maximal average power of 78 W was obtained for 32 ns pulses at a repetition rate of 190 kHz, whereas the millijoule energy level was reached for 12 ns pulses at the lower repetition rate of 10 kHz.