Temporal memory effects in photorefractive two-beam coupling: a study comparing n-doped and p-doped BaTiO_3 at 514 nm and 830 nm

Abstract

The photorefractive gain and time response of n-doped and p-doped BaTiO3 were compared in the visible, λ= 514 nm, and in the infrared, λ=830 nm. Two-beam coupling experiments were conducted for beam ratios between 3600:1, 5000:1, and 8000:1. In both infrared and visible it was observed that the measured gains were higher for the p-BaTiO3 by an order of magnitude or more. When the gain was high, a temporal memory effect was observed, suggesting that the time dependence of the space-charge field is determined by the history of the modulation depth. This effect is shown to be consistent with the Kukhtarev equations for a single carrier. Low-gain behavior was observed at all interaction angles for both crystals in the IR. In the visible the high-gain temporal memory effect is reported for the p-BaTiO3.