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Recent development of intense EUV and XUV light sources (FEL or high-harmonics of infrared lasers) made multiphoton few-electron reactions in this energy range experimentally accessible. Here we report on a series of experimental studies on few-photon-induced double and multiple ionization of rare gas atoms, and on dissociation and Coulomb explosion of simple molecules (N2, O2, D2) irradiated by intense free-electron laser pulses. Employing cold-target recoil ion and coincident electron momentum spectroscopy, we demonstrate the signatures of sequential and direct ('non-sequential') pathways for two- or three-photon double ionization, and discuss the possible role of intermediate resonant transitions. For molecules measurements of the kinetic energy release from few-photon-induced Coulomb explosion suggest a method to map the time delay between the absorption of individual photons. Finally, we discuss possible schemes of time-resolved measurements with FEL pulses, and report on the first steps towards pump-probe experiments. |
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