Composite Yb:YAG/sapphire thin-disk active elements produced by thermal diffusion bonding

Thermal diffusion bonding of Yb:YAG and sapphire crystals was successfully implemented for the first time, and composite active elements having a geometry of a thin disk with an undoped cap were fabricated. The composites were tested in a continuous-wave thin-disk laser scheme at up to 400 W output average power, confirming that bonding strength is sufficient to operate at high thermal load. The radiation phase and polarization distortions as well as the small signal gain were studied. It is shown that depolarization is a significant problem in the considered composites; however, a proper choice of the parameters allows minimizing this impact.