7.7 mJ pulses from a large core Yb-doped cladding pumped Q-switched fibre laser

Summary form only given. Double-clad rare-earth doped fibre lasers pumped by high brightness laser diodes are very efficient and compact sources of cw and pulsed radiation. For Q-switching, fibre lasers are limited by the build-up of amplified spontaneous emission (ASE) between pulses. Rayleigh backscattering and fibre facet damage are other important issues that need to be considered. The ASE limit is relaxed if large-core fibres are used, however, at some point the fibre becomes multimoded. This is often undesirable. We have previously studied Q-switching of large-core Yb-doped fibre lasers, including those with special core designs for enhancement of the beam quality (so-called large mode area fibres). We also investigate Q-switching of a large-core cladding-pumped Yb-doped fibre laser, but here, we focus on maximizing the pulse energy and pay less attention to beam quality. We used a fibre with a 60 /spl mu/m core.