Transparent Yb-doped YAG ceramics for laser applications

Yttrium aluminium garnet (Y3Al5O12, YAG) doped with rare earth ions is one of the most widely used transparent solid state laser materials. Due to significant advantages regarding materials preparation, or economic and production aspects, transparent ceramics have recently drawn considerable attention as a substitute for YAG single crystals. Yb:YAG ceramics are interesting IR laser materials, which allow significantly higher doping (one order of magnitude) compared to the generally more frequently used Nd:YAG. That is particularly useful for high-power lasers. This work presents the preparation of transparent polycrystalline Yb:YAG ceramics for laser applications via vacuum sintering. Samples with Yb doping from 0 up to 20 at. % have been prepared by solid state sintering of cold isostatically pressed mixtures of pure oxide powders with tetraethyl orthosilicate as a sintering aid. Various sintering conditions were tested and related to the microstructure and optical quality of the sintered materials. The effect of Yb on the microstructure and material properties was studied: the microstructure was characterised by optical and electron microscopy (both SEM and TEM), optical transmittance was measured on finely polished samples by an UV/VIS spectrophotometer and thermal and mechanical properties were measured at room temperature and at elevated temperatures. Samples with optical transmittance higher than 80 % were prepared and their laser performance was examined. Slope efficiency more than 70 % was obtained in the case of 10 at. % Yb doped ceramics. The advantages of ceramic processing were used for the preparation of layered composite materials which allow better thermal management and are promising for example for the production of thin disk lasers. Ecers