A New View on the Sonoluminescent Collapse: X-ray Imaging of Cavitation Bubbles with Free Electron Laser Pulses
The strong collapse of acoustically driven bubbles is a peculiar phenomenon where high pressures and temperatures, chemical reactions, and light emissions (sonoluminescence) can occur. Resolving the collapsed bubble state reaching micron size and sub-nanosecond time scales is extremely demanding. Open questions are related, for instance, to the shape of the collapsed bubble and to the formation of interior shock waves. Both can influence the pressures and temperatures reached as well as the light emission. Here we realize and investigate single bubble sonoluminescence in water in a spherical bubble trap driven at 88 kHz.For imaging, we present single shot X-ray holography with free electron laser (FEL) pulses as a novel experimental approach to study cavitation dynamics. X-ray holography probes volumetric structures and provides sub-micrometer spatial resolution along with and a temporal resolution limited by either a pump or the probe pulse length.This is demonstrated by measurements of the expansion phase of laser-induced cavitation events. Further, we present the design of an X-ray FEL experiment especially tailored to investigate the sonoluminescent bubble collapse in a particularly small resonance chamber. This includes a timing scheme developed to synchronize the bubble collapse with the FEL pulses.