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Autoionization dynamics of helium nanodroplets resonantly excited by intense XUV laser pulses

Ovcharenko, Y.; LaForge, A. C.; Langbehn, B.; Plekan, O.; Cucini, R.; Finetti, P.; O’Keeffe, P.; Iablonskyi, D.; Nishiyama, T.; Ueda, K.; Piseri, P.; Di Fraia, M.; Richter, R.; Coreno, M.; Callegari, C.; Prince, K. C.; Stienkemeier, F.; Möller, T.; Mudrich, M.

The ionization dynamics of helium droplets irradiated by intense, femtosecond extreme ultraviolet (XUV) pulses is investigated in detail by photoelectron spectroscopy. Helium droplets are resonantly excited to atomic-like 2p states with a photon energy of 21.5 eV and autoionize by interatomic Coulombic decay (ICD). A complex evolution of the electron spectra as a function of droplet size (250 to 106 He atoms per droplet) and XUV intensity (109–1012 W cm−2) is observed, ranging from narrow atomic-like peaks that are due to binary autoionization, to an unstructured feature characteristic of electron emission from a nanoplasma. The experimental results are analyzed and interpreted with the help of a numerical simulation based on rate equations taking into account all relevant processes—multi-step ionization, electronic relaxation, ICD, secondary inelastic collisions, desorption of electronically excited atoms, and collective autoionization (CAI).
Published in: New Journal of Physics, 10.1088/1367-2630/ab9554, IOP