Transient core structural dynamics at the solid-to-plasma transition of the cluster*

We have conducted an x-ray/x-ray pump/probe experiment to study transient nuclear dynamics upon strong electronic excitation in nanoclusters with Angstrom resolution. We employed two-color hard x-ray scattering with well separated energies and well characterized arrival-times at the SACLA free-electron laser. The first x-ray pulse is used to characterize the size and orientation of the van-der-Walls nanocrystals as well as to induce the x-ray ionization and expansion processes in a nanoparticle. The second pulse is used to probe the nuclear dynamics following the strong ionization. Using the exact same Bragg reflection from two different color x-ray pulses yields unprecedented information about the nanoparticle lattice response upon ionization, not accessible in previous experiments [K. Ferguson et al, Sci. Adv. 2, 1500837 (2016)].