Observation of space charges in the photorefractive region and surface electric breakdown in LiNbO3-Fe

The space chages formed in the process of photorefraction in LiNbO₃ crystals is visualised by charged powder techniques. The results confirmed the existence of space charge carriers at the periphery of the illuminated region with negative charge carriers in the +z periphery and positive in the –z. The observed patterns on the surface of LiNbO₃-Fe (0.05%) crystal illuminated with higher light intensities presented discharge-like features, namely traces of discharge in the medium at the crystal surface. The correlation between the kinetics curves of birefringence changen(t) and the revealed surface patterns indicated that electric breakdown of the medium at the surfaces was responsible for the periodic reduction ofn(t).