Room-temperature optical absorption in undoped α-Al2O3

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Abstract
Optical absorption over a large dynamic range obtained by two different experimental techniques is reported for an undoped α‐Al2 O3 single crystal. Absorption data are presented in two energy ranges: 0.94–3.5 eV and 4.5–8.6 eV. Vacuum ultraviolet (vuv) absorption measurements were performed on three boules of Czochralski‐grown single‐crystal Al2 O3 with differing starting material purities. The initial powder purities were 99.99%, 99.999%, and 99.999999%. In addition to the vuv measurements, calorimetric absorption results obtained in the visible and near‐infrared (ir) are presented. An empirical formula is obtained that provides an estimate of the absorption coefficient from the near‐ir to the vuv for undoped Al2 O3 . Detailed impurity analyses and sample histories are given for the optical‐quality α‐Al2 O3 utilized herein.