560  W all fiber and polarization-maintaining amplifier with narrow linewidth and near-diffraction-limited beam quality

We present a narrow linewidth, all-fiber polarization-maintained amplifier chain seeded by a phase-modulated single-frequency laser, which is a narrow linewidth. Different from previous phase-modulation techniques, the phase-modulation signal is generated by simply imposing an excited signal to an acoustic-optical driven source. Theoretical simulation results show that this method can suppress stimulated Brillouin scattering (SBS) to a better degree, and the output power can be boosted to about 1.2 kW in terms of the SBS threshold. By amplifying the phase-modulated seed based on master-oscillator power-amplification configuration in experiments, a 560 W output laser is achieved with slope efficiency of 87.2% and linewidth of <5 GHz. Further power scaling is limited by mode instability instead of an SBS effect. At maximal output power, the beam quality (M² factor) and polarization extinction ratio is measured to be within 1.3 and 14 dB, respectively.