Single-bubble sonoluminescence in microgravity

Abstract

A recent experiment involving single-bubble sonoluminescence aboard NASA’s parabolic research aircraft will be described. Measurements of the intensity of the light emission were performed during periods of microgravity (near 0 g) and hypergravity (near 2 g). Gravitational effects on the luminescence and extinction pressure thresholds were examined. In addition, the light emission was monitored under constant drive conditions as the gravitational acceleration varied during the parabolas. Measurements show some variability in the sonoluminescence intensity for both thresholds. However, during otherwise constant conditions in which the drive pressure amplitude did not change, the intensity from stable single-bubble sonoluminescence was observed to increase during periods of microgravity. There was an initial increase in intensity that occurred simultaneous with the decrease in the gravitational acceleration, followed by a slow increase in intensity that appeared to level off near the end of the microgravity period. The longer time scales over which the intensity changed during the microgravity period may be indicative of gas diffusion occurring as the bubble attains a new equilibrium condition. [Research supported by NSF and NASA.]