Nonlinear interaction of transverse and longitudinal sound waves in metals

The influence of a strong longitudinally or transversely polarized sound wave on the propagation of weak transverse sound in metals is investigated. It is assumed that the ratio of the wave numbers of the strong and weak waves is equal to an integer or a half-integer. Under nonlinearity conditions, when resonant electrons are trapped by the field of the strong wave, the electromagnetic and deformation coefficients of gain and attenuation of the weak wave are determined. It is shown that the weak sound can be amplified under the conditions w1≲|w1−w|≪1/q1τr,ωr/qc(w/vF)1/2≫1,w1<w, in which case the gain is determined by its deformation part, which is proportional to the parameters ω0τr≫1 (q1, w1 and q, w are the wave numbers and velocities of the weak sound and the strong wave, respectively, ω0 is a typical oscillation frequency of the trapped particles, and τr is the relaxation time). The results of the calculations are compared with experimental data.

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