FERROELECTRIC PHENOMENA IN HOLOGRAPHIC PROPERTIES OF STRONTIUM-BARIUMNIOBATE CRYSTALS DOPED WITH RARE-EARTH ELEMENTS

We report on a relation between the two-beam coupling gain factor Gamm a in Sr0.61Ba0.39Nb2O6 (SBN:0.6) crystals and their ferroelectric prop erties. In SBN:0.6 doped with rare-earth-metal impurities Ce and Tm we found a hysteresis dependence of Gamma versus the external de-field E applied after recording which is due to the ferroelectric P-E hystere sis. Particularly, Gamma-E hysteresis manifests itself in an alteratio n of the sign of Gamma, i.e., of the direction of the energy transfer between the coupling beams, under applying of E reversing Ps. The valu e of Gamma at room temperature essentially increases with impurity con centrations. It is caused by an increase of the dielectric permittivit y, which in its turn is due to a significant lowering of the phase-tra nsition temperature T-c produced by a rare-earth doping.