Diffusion processes in lightguide materials. The diffusion of OH in silica glass at high temperatures

The OH diffusion in silica glass is investigated between 1500 and 2300°C. Specimens are prepared by deposition of silica glass layers on the inner surface of tubes made of silica glass with different OH content. The diffusion from the tube and from the gas phase within the tube, respectively, into the layers during annealing is studied by measuring the laser beam absorption at 2.73 (J.m wavelength with a high spatial resolution. By fitting the measured radial OH profiles to calculated diffusion distributions, first values of diffusion coefficients at temperatures above 1300°C can be determined. Die OH-Diffusion in Kieselglas wird zwischen 1500 und 2300°C untersucht. Die Praparation der Untersuchungsproben erfolgt durch Abscheidung von Quarzglasschichten auf der Innenoberflache von Quarzglasrohren mit unterschiedlichem OH-Gehalt. Zum Studium der Diffusion vom Rohr bzw. von der Innenrohr-Gasphase in die Schichten beim Tempern der Proben wird die Laser-strahl-Absorption bei 2,73 μm Wellenlange mit hoher Ortlicher Auflosung gemessen. Durch Vergleich der so bestimmten radialen OH-Konzentrationsprofile mit berechneten Diffusionsver-teilungen konnten erstmalig Werte fur den Diffusionskoeffizienten oberhalb von 1300°C ermittelt werden.

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