608 W average power picosecond all fiber polarization-maintained amplifier with narrow-band and near-diffraction-limited beam quality

In this manuscript, we focus on a narrow-band all fiber polarization-maintained (PM) master oscillator power amplifier (MOPA) configuration seeded by a narrow band gain-switched laser diode for near-diffraction-limited average power scaling in sub-nanosecond pulsed regime by controlling detrimental mode instability (MI) effect. The MI free average power scaling abilities of the MOPA system with different pumping wavelengths are explored experimentally. By pumping the main amplifier with 976 nm laser diodes (LDs), experimental results show that near-diffraction-limited average power is just limited to be about 380 W due to the influence of MI effect. However, by selecting a 915 nm pumping wavelength, a mode-instability free average power of 608 W is achieved with pulse width of ∼810 ps, peak power of ∼128 kW and pulse energy of 60.8 μJ. At 608 W average power, the 3 dB line-width of the whole MOPA configuration is measured to be about 0.19 nm. The beam quality (M² factor) and polarization extinction ratio (PER) at maximal output power are measured to be within 1.4 and 13 dB, respectively. (paper)