Characterization of Yb:YAG active slab media based on a layered structure with different doping

Antonio Lapucci, Marco Ciofini, Laura Esposito, Paolo Ferrara, Leonida A. Gizzi, Jan Hostaša, Luca Labate, Angela Pirri, Guido Toci,Matteo Vannini

Proceedings of SPIE, vol. 8780: HIGH-POWER, HIGH-ENERGY, AND HIGH-INTENSITY LASER TECHNOLOGY; AND RESEARCH USING EXTREME LIGHT: ENTERING NEW FRONTIERS WITH PETAWATT-CLASS LASERS, Article Number: UNSP 87800J, (2013).

Abstract

Slabs with non-uniform doping distribution are studied with the aim of reducing thermal deformations in high-energy high-average-power Yb:YAG slab systems. We present a numerical analysis based on Finite Element Mesh (FEM) methods suitable to model non-uniform devices. The thermal variation of the refractive index, the end-faces deformations and the photo-elastic effect have been calculated in order to estimate the total thermal-lens effect. The stress distributions are also obtained. Some results of this numerical approach are compared to experimental thermal lens measurements in a simple geometry for both uniform and structured samples, in order to validate the numerical procedures. Finally we compare numerical simulations for different single-or double-sided pumping and cooling geometries. They show that structured slabs can reduce thermal gradients with respect to uniformly doped means with comparable absorption and geometry. This means a reduction of thermal lens effect and thus an increase of maximum allowed pump power loading. Previous literature reports some work made with structured slabs where higher doping was located in layers with lower pump radiation levels, in order to get a more uniform absorption. Interestingly our modeling indicates that reduced thermal effects are instead obtained when a higher doping is located close to the cooled surfaces.