|Controlling X-ray Induced Explosion Dynamics in Mixed Solid/Superfluid Clusters with X-ray Double Pulses|
|Full Author List||Michael Ziemkiewicz, Camila Bacellar, Adam Chatterley, Thomas Möller, Andrey Vilesov, Christoph Bostedt, and Oliver Gessner|
Lawrence Berkeley National Lab
Intense x-ray induced fragmentation dynamics of Xe nanostructures embedded in large superfluid helium nanodroplets are studied by femtosecond time - resolved ion mass spectrometry. The dopant and host clusters contain ~ 10 6 and ~ 10 9 atoms , respecti vely . The clusters are photoionized by a pair of intense 860 eV x-ray FEL pulses, resulting in fragmentation and ejection of charged species with kinetic energies up to several keV. The resulting ion mass spectra are monitored as a function of the delay between the x-ray pulses and the pulse intensity interacting with the clusters. The production of He ++ cations is of particular interest as this species 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 time delay between the x-ray pulses. In particular, it exhibits a marked increase of higher kinetic energy contributions at an intermediate time delay of 200 fs compared with delays of 0 fs and 800 fs. This suggests that x-ray absorption and/or ionization mechanisms in the sample upon arrival of the second pulse are sensitive to the stage of ionization and disintegration induced by the first pulse in a nontrivial fashion. Existing models describing similar results for experiments using intense infrared laser pulses fail here due to the difference in absorption mechanisms. Possible phenomena underlying the observed trends are discussed.