Controlling explosion dynamics in mixed He/Xe clusters with X-ray double pulses

Intense X-ray induced fragmentation dynamics of hybrid systems consisting of Xe structures embedded in large superfluid helium nanodroplets are studied by femtosecond time-resolved ion mass spectrometry. The clusters are photoionized by a pair of intense X-ray pulses from the Linac Coherent Light Source (LCLS), resulting in fragmentation and ejection of ions with kinetic energies of up to several keV. The production of He$^{\mathrm{++}}$ is of particular interest as this cation is only formed in the mixed system and not upon X-ray illumination of pure He nanodroplets. It is found that the He$^{++}$ product kinetic energy distribution varies sensitively with the relative timing of the X-ray double pulse, exhibiting complex dynamics as a function of pump-probe delay. Existing models describing similar results for experiments using intense infrared laser pulses are not applicable to this study due to the disparate interactions of intense optical and X-ray fields with matter. Possible phenomena underlying the observed trends are discussed.