Extreme ultraviolet ionization of pure He nanodroplets: Mass-correlated photoelectron imaging, Penning ionization, and electron energy-loss spectra

Buchta, Dominic; Krishnan, S. S.; Bräuer, N.; Drabbels, Marcel; O’Keeffe, Patrick; Devetta, M.; Fraia, Michele Di; Callegari, Carlo; Richter, Robert; Coreno, Marcello; Prince, Kevin C.; Stienkemeier, F.; Ullrich, J.; Moshammer, R.; Mudrich, M.

doi:10.1063/1.4818531

Cited by 47 publications

(29 citation statements)

References 52 publications

(199 reference statements)

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“…1(a). This peak corresponds to a line observed at even lower power density with synchrotron radiation [19]. Since its relative intensity at high power density is rather low [20], we can conclude that this is due to the ICD type decay, as we will show below.…”

Section: Prl 112 073401 (2014) P H Y S I C a L R E V I E W L E T T Ementioning

confidence: 69%

“…In addition, in a small cluster most of the free electrons are created near the surface, which suppresses further inelastic collisions. Based on the 2p photoexcitation and the 2p photoionization cross sections of 25 [19] and 0.02 Mb [27], respectively, we obtain an ionization fraction of 0.6% due to resonant two-photon ionization at the end of PRL 112, 073401 (2014) P…”

Section: Prl 112 073401 (2014) P H Y S I C a L R E V I E W L E T T Ementioning

confidence: 99%

“…Before discussing this aspect in detail we point out that under our experimental conditions (power density of 10 13 W=cm 2 ) a large population of 2p states can be created within a few fs. Using the estimated value of 2p excitation cross section of 25 Mb [19] we expect that ∼50% of the atoms are in 2p excited states within 20 fs. In other words, a very unusual plasma is formed during the duration of the light pulse.…”

Section: Prl 112 073401 (2014) P H Y S I C a L R E V I E W L E T T Ementioning

confidence: 99%

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Novel Collective Autoionization Process Observed in Electron Spectra of He Clusters

et al. 2014

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The ionization dynamics of He nanodroplets irradiated with intense femtosecond extreme ultraviolet pulses of up to 10 13 W=cm 2 power density have been investigated by photoelectron spectroscopy. Helium droplets were resonantly excited to atomiclike 2p states with a photon energy of 21.4 eV, below the ionization potential (I p ), and directly into the ionization continuum with 42.8 eV photons. While electron emission following direct ionization above I p is well explained within a model based on a sequence of direct electron emission events, the resonant excitation provides evidence of a new, collective ionization mechanism involving many excited atomiclike 2p states. With increasing power density the direct photoline due to an interatomic Coulombic decay disappears. It indicates that ionization occurs due to energy exchange between at least three excited atoms proceeding on a femtosecond time scale. In agreement with recent theoretical work the novel ionization process is very efficient and it is expected to be important for many other systems. With the advent of short-wavelength free-electron lasers (FELs) the interaction between intense, high-energy light pulses and matter has become a very active field of research [1][2][3] and one of the most exciting topics in atomic and molecular science. Key questions are related to ionization dynamics on an atomic level, answers to which will help to develop an understanding of processes in more complex systems. In pioneering experiments and theoretical studies, various new phenomena such as absorption enhancement [1,4], bleaching [3,5,6], as well as modification [7] and suppression [8] of electron emission were discovered.At high power densities a nanoscale sample, such as a large molecule or cluster, can absorb a large number of photons and the system undergoes a transition to a highly excited, nonequilibrium state. Ionization in this case is strongly interlinked with correlated electron dynamics, either due to multielectron collisions with energy exchange [7] or by novel types of autoionization processes related to interatomic Coulombic decay (ICD), as predicted recently [9]. According to this work, clusters resonantly irradiated by intense light pulses with photon energies insufficient to ionize the atoms by single photon absorption are efficiently autoionized due to the energy exchange between two excited electrons [ Fig. 1(a)]. As a result, an unusual form of a collectively excited, plasmalike state may be formed which is expected to autoionize on a fs-ps time scale [9]. Initial evidence for such an ionization process in Ne clusters has been reported recently [10,11].In this Letter we report a study of electron emission from He clusters irradiated by intense pulses from the new seeded-FEL FERMI [12] at power densities where such collective autoionization (CAI) processes are expected to occur [13]. He droplets were either resonantly excited to the 2p atomiclike state [14], which is well below the ionization potential (I p ), or excited into the continuum. The elect...

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Section: Prl 112 073401 (2014) P H Y S I C a L R E V I E W L E T T Ementioning

confidence: 69%

Section: Prl 112 073401 (2014) P H Y S I C a L R E V I E W L E T T Ementioning

confidence: 99%

Section: Prl 112 073401 (2014) P H Y S I C a L R E V I E W L E T T Ementioning

confidence: 99%

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Novel Collective Autoionization Process Observed in Electron Spectra of He Clusters

et al. 2014

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“…Instead, the measured He + ions originate from free He atoms that accompany the droplet beam. 30 In contrast, the He The PES feature complex peak structures which have been interpreted using electronic structure calculations. 35,39,40 In contrast, the He droplet PIES are broadened toward low energies and nearly structureless.…”

Section: Resultsmentioning

confidence: 99%

Penning Ionization of Acene Molecules by Helium Nanodroplets

et al. 2018

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Acene molecules (anthracene, tetracene, pentacene) and fullerene (C) are embedded in He nanodroplets (He) and probed by EUV synchrotron radiation. When resonantly exciting the He nanodroplets, the embedded molecules M are efficiently ionized by the Penning reaction He + M → He + M + e. However, the Penning electron spectra are all broad and structureless, largely differing from those measured by binary Penning collisions, as well as from those measured for dopants bound to the He droplet surface. Simulations based on elastic binary electron-He collisions qualitatively reproduce the measured spectra only when assuming unexpectedly large He droplets, indicating that electron spectra of molecules embedded in helium nanodroplets are severely affected by collective electron-helium interactions.

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“…Alternatively, ICD or a process involving a quasi-free nanoplasma electron can take place27. In superfluid He nanodroplets28 autoionization might also be caused by collisions of excited atoms and is referred to as a Penning ionization29. To account for a broad family of electron correlation processes that may take place in clusters, a general term - correlated electronic decay (CED) - was introduced27.…”

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confidence: 99%

Correlated electronic decay in expanding clusters triggered by intense XUV pulses from a Free-Electron-Laser

Oelze

Schütte

Müller

et al. 2017

Sci Rep

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Irradiation of nanoscale clusters and large molecules with intense laser pulses transforms them into highly-excited non- equilibrium states. The dynamics of intense laser-cluster interaction is encoded in electron kinetic energy spectra, which contain signatures of direct photoelectron emission as well as emission of thermalized nanoplasma electrons. In this work we report on a so far not observed spectrally narrow bound state signature in the electron kinetic energy spectra from mixed Xe core - Ar shell clusters ionized by intense extreme-ultraviolet (XUV) pulses from a free-electron-laser. This signature is attributed to the correlated electronic decay (CED) process, in which an excited atom relaxes and the excess energy is used to ionize the same or another excited atom or a nanoplasma electron. By applying the terahertz field streaking principle we demonstrate that CED-electrons are emitted at least a few picoseconds after the ionizing XUV pulse has ended. Following the recent finding of CED in clusters ionized by intense near-infrared laser pulses, our observation of CED in the XUV range suggests that this process is of general relevance for the relaxation dynamics in laser produced nanoplasmas.

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Extreme ultraviolet ionization of pure He nanodroplets: Mass-correlated photoelectron imaging, Penning ionization, and electron energy-loss spectra

Cited by 47 publications

References 52 publications

Novel Collective Autoionization Process Observed in Electron Spectra of He Clusters

Novel Collective Autoionization Process Observed in Electron Spectra of He Clusters

Penning Ionization of Acene Molecules by Helium Nanodroplets

Correlated electronic decay in expanding clusters triggered by intense XUV pulses from a Free-Electron-Laser

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