Effects of higher-order modes and harmonics in single-bubble sonoluminescence

Abstract

This paper presents the results of a series of experiments that was performed to study the higher-order modes and harmonics that exist within water-filled resonators during single-bubble sonoluminescence [SBSL]. These experiments demonstrated that: (1) the spatial position and the phase of the light flashes of an SBSL bubble relative to the fundamental sound field could be significantly changed by adding higher harmonics, (2) SBSL could be produced in spherical flasks at eigenfrequencies of the higher-order modes and higher harmonics of the spherical Bessel functions, j1, and j2, thus producing noncentered flashing bubbles, and (3) it is possible to produce the SBSL effect at eigenfrequencies at which the eigenmodes are degenerate. These experiments show that a rich, complex mode structure evidently exists within the water-filled resonator. The externally generated higher modes and higher harmonics influence the position, spatial stability, and phase of the light-flash characteristic of single-bubble sonoluminescence. These experiments suggest that any higher-order modes and harmonics, self-generated by the collapsing bubble, may spatially shift their position within the resonator and thus may play a significant role in destabilizing the bubble’s motion.