Surface recombination and photorefraction in LiNbO3-Fe Crystals

A spontaneous decrease of photorefraction (quasi-breakdown) has been studied in LiNbO₃−Fe (0.1 wt%) crystals. It is shown that the quasi-breakdown effect depends on the crystal environment (air, argon) and is absent in a liquid dielectric medium. Quasibreakdown can be avoided reducing the diameter of the light beam from a He−Ne laser. The critical value of birefringence change for quasi-breakdown decreases with growing temperature. The quasi-breakdown effect is also observable after illumination, in the dark. It is shown that quasi-breakdown can be explained by the recombination of light-induced space charge carriers at the surface or in the environment (air, argon) near the crystal surface. The erasure of photorefraction with quasi-breakdown is performed under under uniform illumination of the crystal with visible light.