Extreme ultraviolet fluorescence spectroscopy of pure and core-shell rare gas clusters at FLASH

Rare gas clusters exposed to strong laser fields at short wavelength have attracted considerable interest in the last decade. The most common way to study the interaction is by time-of-flight spectroscopy of the resulting charged particles. However, recent imaging experiments give evidence that the measured mass spectra do not reflect the charge states that are initially formed. We present experiments on pure and core-shell Xe and Ar clusters to analyze the initially produced charge states by their extreme ultraviolet fluorescence. The clusters were excited by strong free-electron laser pulses from FLASH at 13 nm. Characteristic fluorescence of multiply charged species reveals detailed information on energy deposition and redistribution as a function of cluster size and FEL intensity. Of particular interest are charge transfer processes as function of the cluster composition in core-shell systems