The anisotropy of optical absorption induced in sapphire by neutron and electron irradiation

Abstract

Measurements have been made of the anisotropy of the optical absorption induced by neutron and electron irradiation. Some of the measurements were made with a six-plate fluorite polarizer, whose efficiency was found to be 65% at 2500 å, and which could be used at shorter wavelengths than a Clan-Thomson prism. In the spectrum induced by neutron irradiation, bands are resolved at −185°c at 1.9, 2.2, 2.8, 3.5, 4.1, 4.8 and 6.1 ev, the latter being measured both with a quartz spectrophotometer and a fluorite vacuum spectrograph. The 6.1 ev band was found to be isotropic but the 2.8, 3.5, 4.1 and 4^.8 ev bands were anisotropic, having parallel to perpendicular ratios greater than 1. The anisotropy measurements reveal the presence of a band of opposite anisotropy at 5.3 ev. In order to account for the complete shape of the spectrum of the anisotropic ratio it is necessary to assume tho presence of other bands having the same anisotropy as the 5.3 ov band. Tho 5.3 ev band did not appear in the electron irradiated specimens, although both the 4.8 (μ∥ < μ_⊥ and 6.1 ev (isotropic) bands were found. Possible models for these two centres are discussed. The rate of decrease of absorption with heat treatment haa been measured for temperatures up to 500°c and is compared with the rate of recovery of the neutron induced expansion studied by Martin (1959).