OPTICAL-DAMAGE-RESISTANT IMPURITIES IN LITHIUM-NIOBATE

We analyzed the properties of damage-resistant LiNbO3 crystals doped w ith Mg, Zn, or In. Damage resistance is due to an essential increase i n the photoconductivity sigma(p). In the first two compounds the incre ase in sigma(p) is most pronounced at concentrations exceeding certain threshold (5.5 mol.% MgO or 7 mol. % ZnO in the congruent melt), wher eas in In-doped crystals it occurs at any In concentration. The increa se in sigma(p) is directly related to the reduction of the intrinsic d efects Nb(Li) because of their substitution by damage-resistant impuri ties. If an iron impurity is present, then an abrupt decrease in the c apture cross section of Fe3+ acceptors at Mg or Zn concentrations high er than the threshold is responsible for the observed increase in sigm a(p).