Sonoluminescence from single cavitation bubbles near solid surfaces

Sonoluminescence, the light emission from bubbles undergoing large volume oscillations, has traditionally been associated with near-spherical bubble collapses in free liquid. In contrast, highly asymmetric bubble collapses near solid boundaries are known to cause surface erosion from transient and extreme pressure build ups. While both phenomena are caused from energy focusing during bubble collapse, a connection between erosion and light emission has not been previously reported. Here, we for the first time observe the highly asymmetric toroidal cavitation bubble collapse leading to erosive effects on the nearby boundary emits light, too. Through multi-modal measurements of the bubble dynamics and the associated phenomena near solid surfaces, we find that light emission occurs exclusively at the sites and time of the most intense flow focusing. Yet, we find no correlation between the occurrence of light emission from sonoluminescence and erosion. This findings reveal that the mechanisms governing energy focusing within the bubble and in the liquid are resulting from distinct energy focusing pathways.