Photorefractive grating formation with very short pulses: the bulk photovoltaic effect

Abstract

We investigated the role of the photovoltaic effect on the photorefractive grating formation under illumination of weak ultrashort light pulses whose duration is much shorter than the time constants of the carrier and compared it with the cw case. In our experiments using mode-locked picosecond and cw Nd:YAG lasers, the bulk photovoltaic current in an iron- doped lithium niobate crystal were confirmed to be in the same order of magnitude for both light sources. The evolution of photorefractive gratings was also essentially the same. The Glass expression for the bulk photovoltaic effect is not compatible with the scheme of the band transport model for a very fast response. Therefore we developed a model in which the bulk photovoltaic current was implemented as a spatial shift in the initial carrier distribution. The resultant expression agreed with that of the quasi-cw approximation in the limit of a small spatial shift.