OPTICAL-DAMAGE RESISTANCE AND CRYSTAL QUALITY OF LINBO3 SINGLE-CRYSTALS WITH VARIOUS [LI] [NB] RATIOS

Lithium niobate single crystals with various [Li]/[Nb] ratios were grown by the Czochralski method from melts having compositions varying between 45.5-58 mol % Li2O. Their optical damage resistance was characterized by measurement of the photoinduced birefringence change. Their crystal quality was characterized by x-ray topography and x-ray rocking curves. The photoinduced birefringence change increased with an increase in the Li content of the crystal. The Li-poor crystals, which were richer in Nb content than the crystal with the congruent composition, showed the smallest birefringence change, in spite of the fact that the x-ray rocking curve width of these Li-poor crystals was much wider than the congruent crystal. It is concluded that the optical damage resistance of undoped LiNbO3 is increased with an increase in the Nb content of the crystal, and that the crystal quality, as represented by x-ray rocking curve peak width, has no correlation with the optical damage resistance.