High-Power Highly Linear-Polarized Nanosecond All-Fiber MOPA at 2040 nm

We demonstrate a nanosecond all-fiber master oscillator power amplifier with linear-polarized output at 2040 nm, seeded by an in-band-pumped gain-switched thulium-doped fiber laser, which can directly output tens-of-microjoules pulses with designable pulse duration and Gaussian-like pulse profile. After only two stages of amplification, we achieve an average power of 70 W at a pulse width of 114 ns and a repetition rate of 10 kHz, corresponding to a pulse energy of 7 mJ and a peak power of 53.8 kW. Benefit from the on-site polarization control technique we proposed, a polarization extinction ratio (PER) of 25 dB at the highest output is also obtained. To the best of our knowledge, this is the highest power nanosecond all-fiber laser reported at 2-μm waveband and the PER is also a record among high-power fiber lasers.