This program is developing the science necessary to produce novel Y3Al5O12 and Y2O3 doped with Nd3+, Er3+, and Yb3+ single crystals for high power laser applications by solid state conversion (SSC). The SSC process takes advantage of extensive grain growth (millimeter to centimeter in size) in a ceramic during high temperature processing such that the largest grains are high quality single crystals. By working in the solid state, rather the commonly used liquid growth processes, the crystals produced have exceptional quality and thus significantly improved optical performance for laser applications.
TECHNICAL DETAILS: Under this research program, the SSC method is being developed to produce optical single crystals of Y3Al5O12 and Y2O3 doped with Nd3+, Er3+, and Yb3+. The Penn State University team is investigating the thermodynamics and kinetics of the SSC process and developing a robust, scientific understanding that can be applied to the SSC growth of single crystals of other materials. Optical performance of the new optical crystals is being compared to ceramics of same composition to understand how grain boundaries affect optical behavior. The project is leading to a new suite of solid state optical materials with greater performance and functionality than any material currently available, and these materials will enable future optical technologies with greater efficiency and power than are currently possible. As part of this research program, graduate students are giving lectures and demonstrations to high school students to educate them about materials used in lasers. Special emphasis is placed on highlighting the roles of materials and ceramic research in the future of laser development with the hope of inspiring students to investigate the field of ceramic science as they begin to make their college entrance decisions.
Technical merit - Transparent neodymium (Nd) doped YAG (Y3Al5O12) ceramics have the potential to replace Czochralski grown single crystals in high power laser applications. However, after more than 20 years of development, there has been limited application of these potentially revolutionary materials. To improve the processing and properties of Nd:YAG transparent ceramics and to facilitate increased adoption, this project explored the effects of sintering aids on defects, densification and single crystal conversion (SCC) of Nd:YAG ceramics. Silica (Si4+) is added in small quantities (<1 at%) to ensure transparency with sintering. If too much is added then it results in a second phase and decreased transparency. We determined by TEM and other analytical techniques that silica forms a solid solution by substituting for Al3+ at sintering temperatures > 1600oC. Fine grain size (<5 μm) is an important property for high power applications of transparent YAG ceramics. The average grain size could be controlled (2.8 μm – 18 μm) in highly transparent ceramics using a combination of SiO2 content, sintering temperature, and sintering time. We developed a new additive technique using a combination of B2O3 and SiO2. This additive system induces transient liquid phase sintering, reduces the sintering temperature of Nd:YAG ceramics to 1600oC and results in a grain size of <2 μm. Also, we showed for the first time that highly transparent (84% in-line transmission at 400 nm) Nd:YAG ceramics could be sintered at 1600oC in either vacuum or flowing O2. Broader Impacts The B2O3 plus SiO2 additive systems means that expensive high temperature vacuum furnaces are not required for manufacturing transparent Nd:YAG; this results in an important cost reduction in capital and the ability to sinter transparent ceramics at much larger sizes than possible with single growth techniques. Increasing size is critical laser power scales with size and single crystal growth techiques can not be scaled anymore than they are today - thus the critical need for ceramics. Other findings of the project about how impurities affect light absorption will enable manufacturers to better source the powders needed for manufacturing tranparent rare earth doped YAG ceramics.
