Incoherent enhancement of the photorefractive response in Bi(12)SiO(20) by subharmonic interaction

A new mechanism for enhancing the photorefractive grating amplitude in Bi(12)SiO(20) is presented. We show experimentally that, by recording two photorefractive running gratings induced by two pairs of mutually incoherent laser beams, it is possible for the two gratings to transfer energy from one to the other. As might be expected, maximum energy transfer is obtained when the phase velocities of the two gratings are equal.