670 kW nanosecond all-fiber super-irradiation pulsed amplifiers at high repetition rates

We report a high peak power of 670 kW laser output with 4.7 ns pulse duration at a center wavelength of 1064 nm generated by an all-fiber super-irradiation pulsed amplifier (SPA) working at a high repetition frequency of 20 kHz. The SPA consists of four amplifier stages: two preamplifiers, a boost amplifier and a main amplifier. A single-mode pulse signal with 10 nm broadband bandwidth is launched by a super-luminescent diode (SLD) as the seed. In the main amplifier, about 68.5% of optical-optical conversion efficiency is realized from a 92 W pump laser diode working at 976 nm. It is shown that the output pulses have great stability (<2%). The beam quality M² is measured to be better than 1.6 in both orthogonal directions.