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Transparent alumina |
Transparent alumina is a transparent form of aluminium oxide, Al2O3. In bulk, solid form, alumina is a colorless, transparent solid. Rubies and sapphires are two forms, containing different impurities, which occur naturally. Rubies and sapphires can also be manufactured synthetically, and synthetic rubies are important in making lasers that emit red light. Synthetic rubies contain an impurity of chromium, which is what gives them their color and laser properties.
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As a powder or solid formed by sintering (welding together small particles), alumina is opaque or translucent. Recently, a method of sintering very small particles of alumina has been developed by researchers at the Fraunhofer Institute for Ceramic Technologies and Sintered Materials. This sintered alumina is very hard, nearly transparent, and has a very high melting point (2303 Kelvin), yet like other sintered materials it can be produced at temperatures much lower than its melting point.
In 2004, Anatoly Rosenflanz and colleagues at 3M in Minnesota used a "flame-spray" technique to alloy alumina (aluminium oxide) with rare-earth metal oxides to produce strong glass with good optical properties. The method avoids many of the problems encountered in conventional glass forming and may be extensible to other oxides.
The first working laser was made by Theodore H. Maiman in 19601 at Hughes Research Laboratories in Malibu, California, beating several research teams including those of Charles H. Townes at Columbia University, Arthur Schawlow at Bell Labs,2 and Gould at a company called TRG (Technical Research Group). Maiman used a solid-state light-pumped synthetic ruby to produce red laser light at a wavelength of 694 nanometers (nm). Synthethic ruby lasers are still in use.
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