21 W, 105 μJ regenerative amplifier based on Yb:YAG SCF and NALM fiber oscillator

We present a regenerative amplifier (RA) based on Yb:YAG single-crystal fiber (SCF) and nonlinear amplifying loop mirror (NALM) fiber oscillator. The home-made all-fiber NALM oscillator is constructed with polarization maintaining (PM) fibers for improved environmental stability, delivering a stable pulse train. The seed is directly amplified in a single stage without using CPA technique. 21 W, $105~\mu \text{J}$ , 2.4 ps at 200 kHz repetition rate with beam quality of 1.3 has been achieved. A remarkable optical gain of 57.4 dB is obtained with a seed injection of 190 pJ. Further increase in average power is expected.