DICHROISM OF AN LIF CRYSTAL UNDER CONDITI ONS OF IRREVERSIBLE SPATIALLY SELECTIVE BLEACHING OF F-2(-) COLOR-CENTERS BY LAMBDA-SIMILAR-TO-1.06-MU-M RADIATION

An investigation was made of the characteristics of an LIF:F-2(-) crys tal irradiated with strong resonant radiation (lambda approximate to 1 .06 mu m). This irradiation bleached the F-2(-) colour centres of all the orientations except one. The irradiated part of the crystal had th e combined properties of a partial polariser and a phase plate. The pr opagation of weak radiation, which did not saturate the absorption by the colour centres, in the irradiated zone rotated the polarisation ve ctor by 5 degrees. The irradiated zone also acted as a lambda/15 phase plate when either weak or strong (saturating completely the absorptio n by the F-2(-) centres) radiation pro-pagated in the crystal.