Recombination-Enhanced Surface Expansion of Clusters in Intense Soft X-Ray Laser Pulses

Rupp Daniela , Flückiger Leonie , Adolph Marcus , Gorkhover Tais , Krikunova Maria , Müller Jan Philippe , Müller Maria , Oelze Tim , Ovcharenko Yevheniy , Röben Benjamin , Sauppe Mario , Schorb Sebastian , Wolter David , Mitzner Rolf , Wöstmann Michael , Roling Sebastian , Harmand Marion , Treusch Rolf , Arbeiter Mathias , Fennel Thomas , Bostedt Christoph and Möller Thomas

Abstract

We studied the nanoplasma formation and explosion dynamics of single large xenon clusters in ultrashort, intense x-ray free-electron laser pulses via ion spectroscopy. The simultaneous measurement of single-shot diffraction images enabled a single-cluster analysis that is free from any averaging over the cluster size and laser intensity distributions. The measured charge state-resolved ion energy spectra show narrow distributions with peak positions that scale linearly with final ion charge state. These two distinct signatures are attributed to highly efficient recombination that eventually leads to the dominant formation of neutral atoms in the cluster. The measured mean ion energies exceed the value expected without recombination by more than an order of magnitude, indicating that the energy release resulting from electron-ion recombination constitutes a previously unnoticed nanoplasma heating process. This conclusion is supported by results from semiclassical molecular dynamics simulations.