The scaling of solid state lasers, in size and average power, is limited by the thermal dissipation of the unused input pump power. In order to remove the waste heat, the host material must be cooled, which induces thermal gradients and stress in the active medium. If the rod geometry is used, the thermal gradients quickly gives rise to deleterious optical effects. In the slab geometry,1 however, the thermal gradients only affect the optical beam in second order. Therefore, substantially higher average powers, with good beam quality, are possible.