Ytterbium-doped large-core fibre laser with 610 W of near diffraction-limited output power

A cladding-pumped ytterbium-doped fibre laser, generating up to 610 W of continuouswave output power at 1.1 (mu)m with slope efficiency of 80% and near diffractionlimited beam quality (M/sup 2/=1.3) is reported. No undesirable roll-over was observed in output power with increasing pump power.