Mechanisms of Photochromic and Photorefractive Effects in Doubly Doped Lithium Niobate Crystals

The influence of various dopants and their combinations on the photorefractive effect in lithium niobate crystals is investigated and the principal opportunity for controlling the photorefractive parameters by use of combinations of dopants is shown. It is found, that some combinations of impurities cause a photoinduced inverse change of the absorption coefficient (photochromic effect) in lithium niobate crystals. A model of the photochromic effect, based on charge transfer between impurity centres, is suggested. [Russian Text Ignored]