Sub-millisecond photorefractive two-wave coupling in Bi12TiO20 at 633 nm

Abstract The unusually fast response of the two-wave mixing process in fibre-like Bi12TiO20 crystals on transient change of the external electric field was experimentally observed. Pulses of the amplification of the signal wave with a rise time of 0.2 ms and a width of 0.5 ms at a total input intensity of 6 mW mm−2 are obtained when applying a rising or decreasing front of an external electric field to the crystal. The two-wave coupling without external field has a response time of 200 ms. A simple calculation based on the bandtransport model qualitatively explains the fast transient amplification but fails to explain the slow response without the electric field.