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).
Autoionization dynamics of helium nanodroplets resonantly excited by intense XUV laser pulses / Y. Ovcharenko, A.C. Laforge, B. Langbehn, O. Plekan, R. Cucini, P. Finetti, P. O'Keeffe, D. Iablonskyi, T. Nishiyama, K. Ueda, P. Piseri, M. Di Fraia, R. Richter, M. Coreno, C. Callegari, K.C. Prince, F. Stienkemeier, T. Moller, M. Mudrich. - In: NEW JOURNAL OF PHYSICS. - ISSN 1367-2630. - 22:8(2020 Aug 17). [10.1088/1367-2630/ab9554]
Autoionization dynamics of helium nanodroplets resonantly excited by intense XUV laser pulses
P. Piseri;
2020
Abstract
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).
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