NON-LINEAR 1ST SOUND RESPONSE OF LIQUID-HELIUM AT 1-MHZ, 3-MHZ 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 ( f{hook}0 2, f{hook}0 3,...) and ultraharmonic frequencies ( 3f{hook}0 2, 5f{hook}0 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. © 1979.