Optical fatigue of undoped lithium niobate crystals caused by irreversible photorefractive damage at high-intensity illumination

It has been established by Raman scattering study that the optical damage in nominally pure LiNbO3 crystals presents an irreversible part. This irreversible fraction of the optical damage is induced only by the high-intensity (I ⩾ 25 kW/cm2) exposition for a long time, and it has accumulative character with exposure time. This irreversible effect has been shown to be related to the optical fatigue of the material. The consequent needle-like domain inversion was considered to cause accumulative deterioration of the material, i.e., a fatigue due to the continuous electric field application, relating to the high space-charge field induced by inhomogeneous high-intensity illumination.