2mJ pulse energy, 420kW peak power, all-fiber amplifier with diffraction-limited beam quality

We demonstrate record high energy of 2 mJ, with four nanosecond pulses a peak power of ⪆420 kW and average power of 660 W, in a fiber amplifier using a novel 26 μm mode-field diameter Yb-doped gain fiber. The TMI threshold for this fiber was measured to be 1kW. This is achieved at a diffraction limited beam quality of M²=1.14.