Composite Yb:YAG/sapphire thin-disk active elements for high-energy high-average power lasers

Composite active elements (AEs) of thin-disk geometry with an anti-amplified-spontaneous-emission (ASE) cap were created for the first time from dissimilar materials (Yb:YAG and sapphire crystals) using the surface-activated direct bonding method based on etching the surfaces with an Ar ion beam and then bringing them into optical contact. Using a sapphire anti-ASE cap allows the thermal lens optical power and the ${{\rm M}^2}$M^2 factor to be reduced significantly compared with the same AE with a YAG anti-ASE cap, and ${{\rm M}^2}$M^2 compared to standard Yb:YAG disks without an anti-ASE cap. Lasing with 320 W average power and ${\sim}{50}\% $∼50% slope efficiency was obtained.