Abstract

A uniform beam of light will produce a dc electric field inside some photorefractive crystals. This dc field, called the anomalous photovoltaic field, strongly influences the dynamics of photorefractive hologram formation in iron-doped LiNbO₃, for example. In BaTiO₃ the photovoltaic field is weaker but can be determined by measuring the two-wave mixing gain vs the frequency difference between the two beams. MacDonald¹ determined that the photovoltaic field in BaTiO₃ increases with light intensity, reaches a maximum amplitude of ~100 V/cm, and points in the negative c direction (i.e., opposite the direction of the poling electric field). However, direct measuring of the dc field using external electrodes on the same crystal yields a dc field that differs in sign and is an order of magnitude smaller (20 V/cm) than the dc field determined by two-wave mixing. We show that the origin of this anomaly is the presence of a spatially sinusoidal photovoltaic current and that this new current dominates over the dc photovoltaic field during grating formation.

© 1988 Optical Society of America