Spectral Absorption Coefficient of Molten Aluminum Oxide from.0.385 to 0.780 μm

Abstract

The spectral extinction coefficient, k λ , and the absorption coefficient, α λ , of liquid aluminum oxide were determined from emission measurements on partially molten single‐crystal sapphire filaments. Measurements were made at wavelengths from 0.385 to 0.780 μm in both argon and oxygen atmospheres and at 0.650 μm in a 10% H 2 ‐90% N 2 mixture. The values of α λ were found to vary with the time for which the specimen had been molten and achieved different steady‐state values in the three processing atmospheres. A decrease in α λ with wavelength (Urbach tail) was observed from 0.385 μm to about 0.420 μm in argon and 0.490 μm in oxygen, and approximately constant values were obtained at longer wavelengths. Steady‐state values of α λ at the optical pyrometer wavelength of 0.650 μm were 9 ± 2 cm −1 in argon, 41 ± 8 cm −1 in oxygen, and 14 ± 2 cm −1 in the 10% hydrogen‐90% nitrogen gas mixture.