EXCITATION OF SPACE-CHARGE WAVES IN PIEZOELECTRIC PHOTOREFRACTIVE CRYSTALS BY 2 COUNTER-PROPAGATING ACOUSTIC-WAVES

The three-wave interaction between two oppositely propagating acoustic waves and a wave of bound space charge is studied in a uniformly illu minated piezoelectric and photorefractive crystal. A nonlinear partial differential equation describing the space charge field is derived ta king into account the piezoelectric effect. The steady stale solution is found in the approximation of undepleted acoustic waves. It is show n that the efficient resonant excitation of the space charge wave is p ossible if the detuning between the acoustic waves is equal to its eig en-frequency. The acoustic nonlinearity caused by the interaction with the space charge wave is compared with the nonlinearity caused by the ordinary acousto-electronic interaction. Amplitudes of optical gratin gs produced by the space charge wave and the acoustic wave are also co mpared. (C) 1997 Elsevier Science Ltd.