Recording of a travelling interference pattern by a two-frequency field in a crystal

Theoretical and experimental investigations were made of hologram recording in a photorefractive $\mathrm{Bi}_{12}\mathrm{TiO}_{20}$ crystal. The application of an electric field of the $E(t)=E_1\cos{\Omega}_1t+E_2\cos{\Omega}_2t$ type makes it possible to record an interference pattern travelling at a velocity ${v} =({\Omega}_1\pm{\Omega}_2)/q$.