Ionization dynamics in expanding clusters studied by XUV pumpprobe spectroscopy

M. Krikunova, M. Adolph, T. Gorkhover, D. Rupp, S. Schorb, C. Bostedt, S. Roling, B. Siemer, R. Mitzner, H. Zacharias, T. Möller

Zusammenfassung

The expansion and disintegration dynamics of xenon clusters initiated by the ionization with femtosecond soft x-ray extreme ultraviolet (XUV) pulses were studied with pumpprobe spectroscopy using the autocorrelator setup of the Free-Electron LASer in Hamburg (FLASH) facility. The ionization by the first XUV pulse of 92eV photon energy (8 × 10 12 W cm 2) leads to the generation of a large number of quasi-free electrons trapped by the space charge of the cluster ions. A temporally delayed, more intense probe (4 × 10 13 W cm 2) pulse substantially increases a population of nanoplasma electrons providing a way of probing plasma states in the expanding cluster by tracing the average charge of fragment ions. The results of the study reveal a timescale for cluster expansion and disintegration, which depends essentially on the initial cluster size. The average charge state of fragment ions, and thus the cluster plasma changes significantly on a timescale of 13 ps. © 2012 IOP Publishing Ltd.