A planar waveguide laser consisting of a 13mm x 12mm x 150μm Yb:YAG core with 1mm high sapphire claddings is
edge pumped using two 450W diode stacks with custom aberration correcting phase-plates. A plano-concave resonator
gives 400W average power in a low-order transverse, multi-longitudinal mode beam with 75% slope efficiency,
comparable to other thin disk and slab lasers. Transverse beam quality is improved through use of novel mode selective
toroidal laser-cut resonator mirrors, whilst lateral beam quality is improved through the use of an unstable resonator.
Uniform gain with an amplification of 3-4 per pass shows promise for amplifier operation.
A waveguide with 150 μm core height of 2% Yb:YAG between sapphire claddings is core-pumped at 480W by diode
bars coupled into the 13 mm long edge-facet. The pump unit has custom correction of collimation errors and lens
aberrations. Using a 6mm width and 7° edge-facet angle, power is limited by competing ASE loss or parasitic oscillation
along TIR-trapped internal paths, giving 40 W output for stable and 25 W for unstable resonators. Ray-tracing shows a
20° facet angle is necessary to successfully out-couple ASE from the core. Preliminary operation at 90W and an
increased threshold for the parasitic oscillation are obtained.