Ionization and charge migration through strong internal fields in clusters exposed to intense X-ray pulses

A general scenario for electronic charge migration in finite samples illuminated by an intense laser pulse is given. Microscopic calculations for neon clusters under strong short pulses as produced by X-ray free-electron laser sources confirm this scenario and point to the prominent role of field ionization by strong internal fields. The latter leads to the fast formation of a core-shell system with an almost static core of screened ions while the outer shell explodes. Substituting the shell ions with a different material such as helium as a sacrificial layer leads to a substantial improvement of the diffraction image for the embedded cluster thus reducing the consequences of radiation damage for coherent diffractive imaging.