Georgia Institute of Technology Materials Science and Engineering

Committee Members:

Prof. Robert Speyer, Advisor, MSE

Prof. Naresh Thadhani, MSE

Prof. Rosario Gerhardt, MSE

Prof. Arun Gokhale, MSE

Prof. Wenshan Cai, ECE/MSE

“Advances in Processing of Transparent Lutetia-Based Ceramics for High Power Laser Applications”

Abstract:

Since the development of the first ceramic Nd:YAG laser by Ikesue in 1995, transparent polycrystalline materials as laser gain media have been of great interest. They are often more cost-effective than single crystals for large-scale manufacturing, allow for the production of near net shape parts, and accommodate greater dopant concentrations.

Rare-earth sesquioxides (RE2O3) are an appealing class of potential laser host materials, in part due to their high thermal conductivity, mitigating some of the deleterious effects from high thermal loads (e.g., birefringence from thermal lensing). However, once these materials are doped, many exhibit a significant drop in thermal conductivity. One promising candidate, however, is lutetium oxide (Lu2O3, lutetia), which shows a minor decrease in thermal conductivity when doped with ytterbium (Yb3+), due to their similar atomic masses and ionic radii.

While much work has been done on the development of optical-grade, transparent, lutetia-based ceramics, these processes often rely on the chemical co-precipitation of the doped ceramic powders and/or the use of sintering equipment that may be prohibitively expensive to commercially scale. The primary goal of this research is to characterize and develop methods of producing theoretically transparent undoped and Yb3+-doped lutetia ceramics, using standard thermal/pressure processing equipment, and commercially available powders without chemical reprocessing.

In the bulk of the initial work, highly transparent, undoped Lu2O3 ceramics were developed by optimizing various green body conditions (i.e., binder systems, consolidation methods, and organics removal). Pressureless (vacuum) sintering—with the use of lithium fluoride (LiF) vapor as a sintering aid—was performed and schedules optimized to obtain samples in the closed porosity state with relative densities of 97-98% and micrometer-sized grains. Samples were post-HIPed at or below sintering temperatures to obtain theoretically dense (>99%) ceramics. This work was then translated to the development of Yb3+-doped lutetia ceramics. The preliminary results from 4- and 8-mol% Yb3+:Lu2O3 studies show much promise with further processing optimizations.

Further work proposed here aims to determine optimal schedules for sinter and post-HIP processes to improve the optical quality of the doped ceramics. Further work extending the dopant concentrations to 12- and 16-mol% and characterization of the transmittance and photoluminescence of these samples are planned.