The nonlinear response of a bifrequency excitation is much more significant than the linear response. This can have important consequences in the characterization of acoustic cavitation in water. The nonlinear response to a bifrequency excitation, with respect to the monofrequency one, can give rise to a bubble implosion and to transient cavitation related to a more extended range of bubble radii. A systematic series of experiments has been worked out by a pulse technique which allows to observe the initial stages of the development of the cavitation zone before the saturation phase. Experimental results in distilled water show that the sonoluminescence increases and the transient cavitation threshold is lowered by adding to one soun d field a few percent in power of another field of different frequency. The results appear to confirm some theoretical previsions.
