Parametric interaction of gravity-capillary wave triads under radiation pressure of ultrasound.

Nonlinear parametric coupling of gravity-capillary waves (GCW) by ultrasound wave impinging on a liquid surface is studied experimentally. Modulation of the plane wave radiation pressure by dynamically curved surface of the liquid is considered as a mechanism of the coupling. The standing GCW modes are excited near antinodes by ultrasound beam of carrier frequency 1.030 MHz and coupled parametrically by a plane ultrasound wave with a frequency 1.035 MHz. The beam was modulated at resonance frequencies of GCW overtones f=5.265 Hz and f=7.873 Hz while intensity of the plane wave was modulated at frequency f=2.657 Hz that corresponds to the nonlinear parametric resonance f=2f-f. The amplitudes of the parametric interaction of GCW triads are measured and compared with critical condition for GCWs explosive instability.