Video investigation of the effects of gravity on single-bubble sonoluminescence

Abstract

Using NASA’s KC-135 aircraft flying parabolic trajectories, we can observe SBSL as the effective gravity changes from near 0 g to about 1.8 g. A spherical resonator operated at 32.5 kHz is suspended in a constant ambient pressure chamber. Then, a photomultiplier measures light emission while a strobed CCD camera obtains images of the bubble collapse. In normal gravity, buoyancy displaces the bubble from the velocity node of the sound field so that water is flowing past the bubble at the time of collapse. Other gravitational effects include the variation in ambient pressure. During intervals of negligible drift of the SBSL intensity, there can be a rapid intensity rise of between 4% and 20% as the effective gravity decreases. The CCD images are then used to calculate the bubble radius. These measurements were fit to the Rayleigh–Plesset equation to infer the size and pressure conditions by assuming spherical bubble oscillations. These conditions were found to be similar to those reported by other groups for measurements in normal gravity. There are also indications that changes in the effective gravity are accompanied by small changes in the maximum bubble radius. [Work supported by NASA.]