High power passively Q-switched ytterbium fiber laser with Cr(4+):YAG as a saturable absorber.

We report an efficient high-peak-power and high-average-power passively Q-switched ytterbium fiber laser with a Cr(4+):YAG crystal as a saturable absorber in an external-resonator configuration. At an incident pump power of 17.5 W, the passively Q-switched fiber laser produces an average power greater than 6.2 W with a pulse repetition rate of 48 kHz. The output pulses noticeably display a mode-locking phenomenon that leads to the maximum peak power to be higher than 20 kW.