Abstract

We investigate high brightness pumping of a multi-kW Yb fiber amplifier in a bi-directional pumping configuration. Each pump outputs 2 kW in a 200 µm, 0.2 NA multi-mode fiber. Gold-coated specialty gain fibers, with 17 µm MFD and 5-dB/meter pump absorption, 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.

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