Nonlinear first sound response of liquid helium at 1, 3 and 10 MHz

The first sound response of liquid helium at 1, 3 and 10 MHz is studied using piezoelectric ceramic transducers. Above specific threshold displacement amplitudes, subharmonic frequencies (f0/2, f0/3,...) and ultraharmonic frequencies (3f0/2, 5f0/2,...) appear in the response spectrum. The magnitude of the threshold displacement amplitudes for the production of subharmonics suggests that vapor microbubble oscillation appears not to be the primary generation mechanism. (Auth.)