Nonlinear acousto-optical diffraction by standing acoustic waves: cascading effects

International audienceThe phenomenon of nonlinear optical diffraction is characterized by diffraction of incident electromagnetic wave (EMW) with frequency ω at the double frequency 2ω on periodically distributed inhomogeneties which modulate quadratic polarization of a medium, if period of modulation is comparable with the wavelength of second harmonic radiation. If modulation is made by standing acoustic wave in crystal with corresponding wavelength, it would be possible to observe effect of nonlinear acousto-optical diffraction (NAOD) at the frequencies (2ω ± Ω) as was shown in our paper. In this paper we analysed direct transformation of two EMWs into diffracted EMW with doubled frequency which was moduated by standing acoustic wave.In present communication we theoretically investigate cascading effects which also can lead to the NAOD. The sheme of this effect can be presented as follows: in a crystalline plate it is necessary to exite a standing acoustic wave with the wavelength compared with the wavelength of incident EMW. After linear acousto-otical diffraction (stage one), the diffracted beams at frequency (ω ± Ω) may ineract with another incident EMW with frequency ω due to the quadratic nonlinearity (stage two). As the result it would be possible to obtain NAOD signals at frequency (2ω ± Ω). We analyse a possibilities to separate contributions of direct and cascading NAOD signals into observed radiation for nonlinear diffraction by both longitudinal and transversal standing acoustic waves