Yb:YAG Ceramic Laser Produced by Solid-State Reactive Sintering
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Candidates for Space Observatory Optics: Pyrex and ULE Glasses Withstand Greater Force in Vacuum than Air Imagine delicate glass discs two meters in diameter floating with the ease of soap bubbles gliding in air. The unencumbered vacuum of outer space may provide just the hospitable environment needed to manufacture sensitive optics for a giant space surveillance observatory. T.A. Manning and D.A. Gregory from the University of Alabama in Huntsville in collaboration with D.S. Tucker and K.A. Herren of NASA Marshall Space Flight Center investigated the strength of Pyrex and Ultra Low Expansion (ULE) glasses in vacuum conditions. In the October issue of the Journal of the American Ceramic Society (p. 3318; DOI: 10.1111/ j.1551-2916.2007.01872.x), the researchers report that at room temperature, Pyrex and ULE glass discs showed 54% and 82% greater average strength, respectively, in vacuum over discs tested in 1 atm air pressure. To accomplish the strength tests, the researchers designed and built a strengthtesting device inside a vacuum chamber. During a test, a thin glass disc sample rested flat on three points while a spherical contact applied a downward load to the top disc surface. The researchers attribute part of the observed increase in strength of the materials in vacuum to the absence of subcritical crack growth commonly caused by water vapor. Manning and colleagues also examined the impact of mild heat treatment on glass strength in vacuum. They held 12 samples of both materials at 200°C for 24 h in vacuum and then strength tested samples in vacuum at 50°C. The glass transition temperature of Pyrex is 560°C and of ULE is 1000°C. Heat treatment did not cause a statistically significant change in the strength of either material in vacuum. The researchers look forward to learning whether the theoretical strength of the glasses can be obtained in space. “The logical and more ambitious extension of this experiment would be to actually melt glass under vacuum, shape and cool it to form glass discs, and then measure the strength of those discs in situ,” they stated. ASHLEY PREDITH
Yb:YAG Ceramic Laser Produced by Solid-State Reactive Sintering Recent advances in high-performance InGaAs laser diodes emitting in the 0.9–1.1 μm range have stimulated the interest in developing diode-pumped Yb3+ ceramic lasers. A team of researchers asso994
ciated with the Chinese Academy of Sciences (Y. Wu, J. Li, Y. Pan, and J. Guo from the Shanghai Institute of Ceramics, in collaboration with B. Jiang, Y. Xu, and J. Xu from the Shanghai Institute of Optics and Fine Mechanics) have fabricated fully transparent Yb:YAG ceramics by a simple solid-state reaction, as they reported in the October issue of the Journal of the American Ceramic Society (p. 3334; DOI: 10.1111/ j.1551-2916.2007.01885.x). The researchers used high-purity commercially available α-Al2O3, Y2O3, and Yb2O3 powders that weighed in proportion to the stoichiometry of 1 at.% Yb:YAG. They mixed these reagents by ball milling in anhydrous alcohol for 12 h, adding a binder,
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