810 W continuous-wave and single-transverse-mode fibre laser using 20 μm core Yb-doped double-clad fibre

It is shown that continuous-wave kW-power fibre lasers can be built using double-clad fibres with relatively small cores. 810 W in a single-transverse-mode output (M 2 =1.27) is demonstrated experimentally with 20 μm core low-NA (NA=0.06) Yb-doped double-clad fibre. A laser numerical model matches experimental results and predicts scalability of achievable powers into a multi-kW range.