title: Collective autoionization in multiply-excited systems: a novel ionization process observed in helium nanodroplets.
abstract: Free electron lasers (FELs) offer the unprecedented capability to study reaction dynamics and image the structure of complex systems. When multiple photons are absorbed in complex systems, a plasma-like state is formed where many atoms are ionized on a femtosecond timescale. If multiphoton absorption is resonantly-enhanced, the system becomes electronically-excited prior to plasma formation, with subsequent decay paths which have been scarcely investigated to date. Here, we show using helium nanodroplets as an example that these systems can decay by a new type of process, named collective autoionization. In addition, we show that this process is surprisingly efficient, leading to ion abundances much greater than that of direct single-photon ionization. This novel collective ionization process is expected to be important in many other complex systems, e.g. macromolecules and nanoparticles, exposed to high intensity radiation fields.
authors.affiliation: Universität Freiburg, Germany.
authors.forename: A C
authors.initials: AC
authors.lastname: LaForge
authors.affiliation: EPFL Lausanne, Switzerland.
authors.forename: M
authors.initials: M
authors.lastname: Drabbels
authors.affiliation: EPFL Lausanne, Switzerland.
authors.forename: N B
authors.initials: NB
authors.lastname: Brauer
authors.affiliation: CNR-IMIP Rome, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Coreno
authors.affiliation: Università degli Studi di Milano, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Devetta
authors.affiliation: University of Trieste, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Di Fraia
authors.affiliation: Elettra-Sincrotrone Trieste, Trieste, Italy.
authors.forename: P
authors.initials: P
authors.lastname: Finetti
authors.affiliation: Elettra-Sincrotrone Trieste, Trieste, Italy.
authors.forename: C
authors.initials: C
authors.lastname: Grazioli
authors.affiliation: Universität Freiburg, Germany.
authors.forename: R
authors.initials: R
authors.lastname: Katzy
authors.affiliation: Universität Freiburg, Germany.
authors.forename: V
authors.initials: V
authors.lastname: Lyamayev
authors.affiliation: European XFEL GmbH, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Mazza
authors.affiliation: Universität Freiburg, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Mudrich
authors.affiliation: CNR-IMIP Rome, Italy.
authors.forename: P
authors.initials: P
authors.lastname: O'Keeffe
authors.affiliation: Technische Universität Berlin, Germany.
authors.forename: Y
authors.initials: Y
authors.lastname: Ovcharenko
authors.affiliation: Università degli Studi di Milano, Italy.
authors.forename: P
authors.initials: P
authors.lastname: Piseri
authors.affiliation: Elettra-Sincrotrone Trieste, Trieste, Italy.
authors.forename: O
authors.initials: O
authors.lastname: Plekan
authors.affiliation: Elettra-Sincrotrone Trieste, Trieste, Italy.
authors.forename: K C
authors.initials: KC
authors.lastname: Prince
authors.affiliation: Elettra-Sincrotrone Trieste, Trieste, Italy.
authors.forename: R
authors.initials: R
authors.lastname: Richter
authors.affiliation: University of Rome "La Sapienza", Italy.
authors.forename: S
authors.initials: S
authors.lastname: Stranges
authors.affiliation: Elettra-Sincrotrone Trieste, Trieste, Italy.
authors.forename: C
authors.initials: C
authors.lastname: Callegari
authors.affiliation: Technische Universität Berlin, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Möller
authors.affiliation: Universität Freiburg, Germany.
authors.forename: F
authors.initials: F
authors.lastname: Stienkemeier