Yttrium aluminum garnet (Y3Al5O12, YAG) doped with rare earth ions is one of the most widely used laser gain media in bulk solid state lasers and due its good thermal and mechanical properties in comparison with glasses it is very attractive for applications in high-power laser devices. The main approach used for the production of YAG is single crystal growth but transparent ceramics, polycrystalline materials composed of grains usually microns to tens of microns in size, have proved to be useful and promising in the recent years, thanks to the advantages provided by ceramic technology compared to that of single crystals. The two types of materials have identical chemical and phase composition, and the main difference between them is their microstructure: unlike single crystals transparent ceramics are polycrystalline materials composed of grains usually microns to tens of microns in size. Not only the production process of transparent ceramics requires lower processing temperature and shorter times in comparison to the Czochralski growth, but a further advantage is the possibility to produce materials with near-net shape and with a controlled and well-defined distribution of doping ions to improve the homogeneity of temperature distribution and thus significantly reduce the temperature gradients and the resulting undesired thermal and thermo-mechanical effects (thermal lensing, surface deformation, etc.)[1]. This is particularly important for the production of gain media for high power lasers, where significant amount of heat is generated during the lasing process. Transparent Yb:YAG ceramics with uniform or layered doping distribution were produced from high purity oxide powders via two different shaping methods. The first consists in granulation of a homogeneous stoichiometric mixture of oxide powders and pressing of the granulate into the desired shape at room temperature. In the latter approach, tape casting is used to produce thin sheets from the suspension of oxide powders. The tapes are then stacked and pressed at elevated temperature in order to produce a bulk compact. In both cases the shaping is followed by heat treatment in air at 800 °C and sintering under high vacuum. The microstructure and Yb distribution were analyzed by SEM-EDX, optical quality characterized by measurements of transmittance and transmittance mapping, and the laser efficiency characterized in a laser cavity under quasi-CW and CW pumping. Slope efficiencies higher than 50 % were obtained. Acknowledgements The authors gratefully acknowledge the support from the Italian Ministry of Defence under PNRM, Contract No. 8723 of 19/12/2014 (CeMiLAP). References [1] L. Esposito et al., Multilayered YAG-Yb:YAG ceramics: manufacture and laser performance. J. Mater. Chem. C 2 (2014) 10138-10148.
Production and characterization of transparent yttrium aluminum garnet (YAG) ceramics: materials for laser sources
Jan Hostasa;Valentina Biasini;Guido Toci;Laura Esposito
2016
Abstract
Yttrium aluminum garnet (Y3Al5O12, YAG) doped with rare earth ions is one of the most widely used laser gain media in bulk solid state lasers and due its good thermal and mechanical properties in comparison with glasses it is very attractive for applications in high-power laser devices. The main approach used for the production of YAG is single crystal growth but transparent ceramics, polycrystalline materials composed of grains usually microns to tens of microns in size, have proved to be useful and promising in the recent years, thanks to the advantages provided by ceramic technology compared to that of single crystals. The two types of materials have identical chemical and phase composition, and the main difference between them is their microstructure: unlike single crystals transparent ceramics are polycrystalline materials composed of grains usually microns to tens of microns in size. Not only the production process of transparent ceramics requires lower processing temperature and shorter times in comparison to the Czochralski growth, but a further advantage is the possibility to produce materials with near-net shape and with a controlled and well-defined distribution of doping ions to improve the homogeneity of temperature distribution and thus significantly reduce the temperature gradients and the resulting undesired thermal and thermo-mechanical effects (thermal lensing, surface deformation, etc.)[1]. This is particularly important for the production of gain media for high power lasers, where significant amount of heat is generated during the lasing process. Transparent Yb:YAG ceramics with uniform or layered doping distribution were produced from high purity oxide powders via two different shaping methods. The first consists in granulation of a homogeneous stoichiometric mixture of oxide powders and pressing of the granulate into the desired shape at room temperature. In the latter approach, tape casting is used to produce thin sheets from the suspension of oxide powders. The tapes are then stacked and pressed at elevated temperature in order to produce a bulk compact. In both cases the shaping is followed by heat treatment in air at 800 °C and sintering under high vacuum. The microstructure and Yb distribution were analyzed by SEM-EDX, optical quality characterized by measurements of transmittance and transmittance mapping, and the laser efficiency characterized in a laser cavity under quasi-CW and CW pumping. Slope efficiencies higher than 50 % were obtained. Acknowledgements The authors gratefully acknowledge the support from the Italian Ministry of Defence under PNRM, Contract No. 8723 of 19/12/2014 (CeMiLAP). References [1] L. Esposito et al., Multilayered YAG-Yb:YAG ceramics: manufacture and laser performance. J. Mater. Chem. C 2 (2014) 10138-10148.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
