Transparent Yb-doped YAG ceramics for laser applications.

Transparent ceramics are very interesting materials with various applications, e.g. as solid state laser active materials. In this field, where single crystals are traditionally used, ceramics offer higher processing variablity. One of the advantages of ceramic technology over single crystals is the good control over the dopant ions distribution within the material both for the achievement of good homogeneity and structuring. Active laser materials with layered or gradient structure are particularly interesting for high power laser applications, offering better thermal management possibilities with respect to materials with homogeneous doping. However, ceramic processing and microstructure also imply a specific type of light scattering centers - pores. Therefore the elminiation of secondary phases and above all porosity is the major concern in the production of transparent ceramics. The effect of the possible presence of secondary phases or pores on the optical transmittance of YAG ceramics via light scattering will be discussed with reference to known relations, and an approximating approach will be shown, which allows to estimate transmittance with respect to the size and quantity of pores or inclusions. The presented experimental work shows the preparation of transparent YAG ceramics via solid state reaction sintering of oxide powders, where the materials have either homogeneous or varying (controlled) spatial distribution of dopant, and YAG with two dopant ions. XRD measurements were performed to analyze phase composition. In the case of varying dopant content the microstructure of prepared samples was studied with SEM/EDX and the possibility of preparing materials with gradient dopant concentration profile is discussed. The double doping possibility is studied in the case of Yb3+ and Er3+, which act synergically allowing 1.5 µm Er laser emission by pumping in the absorption band of Yb by InGaAs laser diodes. Thermal and optical properties of the prepared materials are presented.