Power scaling concepts for fiber lasers

The use of a two-mirror beam shaper to re-format the output from a diode- stack to allow efficient cladding-pumping of fiber lasers is described. In addition, the use of a helical-core geometry to suppress oscillation on higher-order modes in large-core double-clad fiber lasers is discussed. In preliminary experiments we have obtained ~90W of output in a beam with M2≈5 from a conventional straight-core Yb-doped double-clad fiber with V=11 for ~150W of launched pump power at ~938nm from a beam-shaped diode-stack, and ~ 24.3W of output in a beam with M2≈3 from a Yb-doped helical-core fiber for ~50W of launched pump power. The prospects for further improvement in performance and beam quality are considered.