摘要： A laser master oscillator power ampli?er (MOPA) system consisting of a ?ber ampli?er and a two-stage Yb:YAG single crystal ?ber (SCF) is experimentally studied. The nonlinear stimulated Raman scattering (SRS) is avoided by limiting the output power of the ?ber preampli?er to 600 mW. Due to the bene?t from the low nonlinearity and high ampli?cation gain of the SCF, a laser pulse duration of 16.95 ps and a high average power of 41.7 W at a repetition rate of 250 kHz are obtained by using a two-stage polarization controlled double-pass ampli?cation of Yb:YAG SCF, corresponding to an output energy of 166.8 μJ and a peak power of 9.84 MW, respectively. The polarization controlled SCF ampli?cation scheme achieved a gain as high as more than 69 times. During the ampli?cation, the spectra gain narrowing e?ect and the polarization controlled four-pass ampli?cation setup are also studied. The laser spectrum is narrowed from over 10 nm to less than 3 nm, and the pulse width is also compressed to hundreds of femtosecond by dechirping the laser pulse. This compact-sized, cost-e?ective laser source can be used in laser micromachining, or as the seeder source for generating much higher power and energy laser for scienti?c research. For some applications which need femtosecond laser, this laser source can also be compressed to femtosecond regime.