X-ray Imaging of Cavitation Dynamics with Free-Electron Laser Pulses

Cavitation dynamics are fast non-equilibrium hydrodynamic processes involving matter at extreme states. A first relevant mechanism is the light-matter interaction during (ultrafast) laser-induced optical breakdown and plasma formation. The following bubble formation, or similarly, the collapse of cavitation bubbles involves violent dynamics and the generation of shock waves. Finally, the energy-focusing during the compression of matter in a collapsing bubble can lead to the emission of light, i.e. sonoluminescence. In current research, the spatial and temporal scales of interest have often reached the limits of common experimental techniques. In the present work, we have explored time-resolved phase-contrast holography with single hard X-ray Free-Electron Laser pulses as a novel and versatile method to study cavitation dynamics. Enabled by highly brilliant XFEL radiation, this technique allows a unique view on fast (hydrodynamic) processes. Outstanding features are a high spatial resolution, no distortion by curved phase-boundaries and a quantitative contrast, based on the electron density of the sample. This thesis focuses on three experiments carried out at the European XFEL, investigating the scenarios of (i) femtosecond laser-induced breakdown and filamentation, (ii) the spherical collapse of a single sonoluminescent cavitation bubble and (iii) collapsing cavitation bubbles close to a solid boundary.