Nonlinear Effects in a Focused Acoustic Beam in Pressurized Superfluid ⁴He

Abstract

Sound propagation in superfluid ⁴He can quite easily become highly nonlinear at a moderate sound energy, because its density and sound velocity are both very low. Furthermore, one can change the dispersion relation of phonon in superfluid ⁴He from anomalous to normal by changing the pressure. The propagation properties of the finite amplitude acoustic wave has been investigated on the basis of these aspects⁽¹⁾. Using a high frequency focused pulse, we studied the propagation of acoustic waves which have much higher energy density than used in previous works, and observed new nonlinear effects⁽²⁾.