Diode-pumped narrow linewidth multi-kW metalized Yb fiber amplifier

We investigate ultra-high brightness pumping of a multi-kW Yb fiber amplifier. Gold-coated specialty gain fibers have been developed. The maximum fiber amplifier output power is 3.1 kW, limited by multi-mode instability, with 90% O-O efficiency 12 GHz Linewidth and M2 < 1.15.