  Femtosecond laser ablation is a process that bears both fundamental physics
interest and has wide industrial applications. For decades, the lack of probes
on the relevant time and length scales has prevented access to the highly
nonequilibrium phase decomposition processes triggered by laser excitation.
Enabled by the unprecedented intense femtosecond X-ray pulses delivered by an
X-ray free electron laser, we report here results of time-resolved small angle
scattering measurements on the dynamics of nanoscale phase decomposition in
thin gold films upon femtosecond laser-induced ablation. By analyzing the
features imprinted onto the small angle diffraction patterns, the transient
heterogeneous density distributions within the ablation plume as obtained from
molecular dynamics simulations get direct experimental confirmation.
