ROOM-TEMPERATURE OPTICAL-ABSORPTION IN UNDOPED ALPHA-AL2O3

Optical absorption over a large dynamic range obtained by two different experimental techniques is reported for an undoped α-Al2 O 3 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 Al 2 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.