Parametric mixing of surface acoustic waves

A simple approximate theory for the explanation of the parametric mixing of collinear surface acoustic waves (SAW) is proposed. The proposed theory considers only the transverse elastic displacement of the waves and neglects piezoelectricity. The effect of the quasiexponential wave profiles on the interaction is described by two factors of form, one for the up, F312, and one for the down, F412, conversion. Using an optical method, the nonlinear coupling coefficients for the up and down conversions have been measured as a function of the fundamental-frequency ratio f2/f1. This was performed for YZ LiNbO3 in the 20–100-MHz range of frequencies. The observed variations of the magnitudes of the coupling coefficients were found to be in good agreement with those predicted theoretically. Notably, the magnitude of the coupling coefficient for the up conversion was found to be nearly constant and twice as large as that of second-harmonic generation, whereas that of the down conversion decays almost linearly with f2/f1 according to ∼ (1−f2/f1).