>1.5kW narrow linewidth CW diffraction-limited fiber amplifier with 40nm bandwidth

Operation from 1030nm to 1070nm in single narrow linewidth fiber amplifier with >1.5kW output power is presented. The fiber amplifier has up to 3m output cable for <15GHz linewidth. The fiber amplifier in the ruggedized compact modular package has 40% wall-plug efficiency. The spectral dependence of higher order mode instability threshold is described.