  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.
