Krikunova, M.; Adolph, M.; Gorkhover, T.; Rupp, D.; Schorb, S.; Bostedt, C.; Roling, S.; Siemer, B.; Mitzner, R.; Zacharias, H.; Moeller, T.: Ionization dynamics in expanding clusters studied by XUV pump-probe spectroscopy. Journal of Physics B 45 (2012), p. 105101/1-6
10.1088/0953-4075/45/10/105101
Open Accesn Version

Abstract:
he expansion and disintegration dynamics of xenon clusters initiated by the ionization with femtosecond soft x-ray extreme ultraviolet (XUV) pulses were studied with pump–probe spectroscopy using the autocorrelator setup of the Free-Electron LASer in Hamburg (FLASH) facility. The ionization by the first XUV pulse of 92 eV photon energy (8 × 1012 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 × 1013 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 1–3 ps.