25 research outputs found
Ionization heating in rare-gas clusters under intense XUV laser pulses
The interaction of intense extreme ultraviolet (XUV) laser pulses
(, \,W/cm) with small rare-gas clusters
(Ar) is studied by quasi-classical molecular dynamics simulations. Our
analysis supports a very general picture of the charging and heating dynamics
in finite samples under short-wavelength radiation that is of relevance for
several applications of free-electron lasers. First, up to a certain photon
flux, ionization proceeds as a series of direct photoemission events producing
a jellium-like cluster potential and a characteristic plateau in the
photoelectron spectrum as observed in [Bostedt {\it et al.}, Phys. Rev. Lett.
{\bf 100}, 013401 (2008)]. Second, beyond the onset of photoelectron trapping,
nanoplasma formation leads to evaporative electron emission with a
characteristic thermal tail in the electron spectrum. A detailed analysis of
this transition is presented. Third, in contrast to the behavior in the
infrared or low vacuum ultraviolet range, the nanoplasma energy capture
proceeds via {\it ionization heating}, i.e., inner photoionization of localized
electrons, whereas collisional heating of conduction electrons is negligible up
to high laser intensities. A direct consequence of the latter is a surprising
evolution of the mean energy of emitted electrons as function of laser
intensity.Comment: figure problems resolve
Ionization avalanching in clusters ignited by extreme-ultraviolet driven seed electrons
We study the ionization dynamics of Ar clusters exposed to ultrashort
near-infrared (NIR) laser pulses for intensities well below the threshold at
which tunnel ionization ignites nanoplasma formation. We find that the emission
of highly charged ions up to Ar can be switched on with unit contrast by
generating only a few seed electrons with an ultrashort extreme ultraviolet
(XUV) pulse prior to the NIR field. Molecular dynamics simulations can explain
the experimental observations and predict a generic scenario where efficient
heating via inverse bremsstrahlung and NIR avalanching are followed by resonant
collective nanoplasma heating. The temporally and spatially well-controlled
injection of the XUV seed electrons opens new routes for controlling
avalanching and heating phenomena in nanostructures and solids, with
implications for both fundamental and applied laser-matter science.Comment: 5 pages, 4 figure
Mikroskopische Beschreibung der ultraschnellen Anregungs- und Relaxationsdynamik von Edelgasclustern in intensiven VUV-, XUV- und Röntgenlaserpulsen
Ultrakurze intensive Röntgenlaserpulse ermöglichen Beugungsexperimente zur Strukturanalyse von Nanoobjekten mit atomarer Auflösung. Sie erzeugen aber simultan auch ein heiĂes dichtes Plasma aus Elektronen und Ionen. Um dieses bei der Rekonstruktion zu berĂŒcksichtigen, ist und ein grundlegendes VerstĂ€ndnis der Laser-Materie-Wechselwirkung erforderlich. Mithilfe semiklassischer Molekular-Dynamik-Simulationen wurde fĂŒr Edelgascluster der Einfluss des Nanoplasmas auf die Elektronenemission, die Clusterexpansion und die Elektron-Ion-Rekombination untersucht und mit experimentellen Daten verglichen.Ultrashort intense X-ray laser pulses enable the structural analysis of individual nanoparticles via single-shot diffractive imaging. They also lead to the generation of a dense plasma of hot electrons and highly charged ions. A fundamental understanding of the laser-matter interaction is indispensable to retrace these effects in the reconstruction process. By employing semi-classical molecular dynamics to atomic clusters, the impact of the nanoplasma evolution on the electron emission, the cluster expansion, and the electron-ion-recombination is investigated and compared to experimental data
Observation of correlated electronic decay in expanding clusters triggered by near-infrared fields
When an excited atom is embedded into an environment, novel relaxation
pathways can emerge that are absent for isolated atoms. A well-known example
is interatomic Coulombic decay, where an excited atom relaxes by transferring
its excess energy to another atom in the environment, leading to its
ionization. Such processes have been observed in clusters ionized by extreme-
ultraviolet and X-ray lasers. Here, we report on a correlated electronic decay
process that occurs following nanoplasma formation and Rydberg atom generation
in the ionization of clusters by intense, non-resonant infrared laser fields.
Relaxation of the Rydberg states and transfer of the available electronic
energy to adjacent electrons in Rydberg states or quasifree electrons in the
expanding nanoplasma leaves a distinct signature in the electron kinetic
energy spectrum. These so far unobserved electron-correlation-driven energy
transfer processes may play a significant role in the response of any nano-
scale system to intense laser light
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Recombination dynamics of clusters in intense extreme-ultraviolet and near-infrared fields
We investigate electron-ion recombination processes in clusters exposed to intense extreme-ultraviolet (XUV) or near-infrared (NIR) pulses. Using the technique of reionization of excited atoms from recombination (REAR), recently introduced in SchĂŒtte et al (2014 Phys. Rev. Lett. 112 253401), a large population of excited atoms, which are formed in the nanoplasma during cluster expansion, is identified under both ionization conditions. For intense XUV ionization of clusters, we find that the significance of recombination increases for increasing cluster sizes. In addition, larger fragments are strongly affected by recombination as well, as shown for the case of dimers. We demonstrate that for mixed ArâXe clusters exposed to intense NIR pulses, excited atoms and ions are preferentially formed in the Xe core. As a result of electron-ion recombination, higher charge states of Xe are efficiently suppressed, leading to an overall reduced expansion speed of the cluster core in comparison to the shell
Recombination dynamics of clusters in intense extreme-ultraviolet and near- infrared fields
We investigate electron-ion recombination processes in clusters exposed to
intense extreme-ultraviolet (XUV) or near-infrared (NIR) pulses. Using the
technique of reionization of excited atoms from recombination (REAR), recently
introduced in SchĂŒtte et al (2014 Phys. Rev. Lett. 112 253401), a large
population of excited atoms, which are formed in the nanoplasma during cluster
expansion, is identified under both ionization conditions. For intense XUV
ionization of clusters, we find that the significance of recombination
increases for increasing cluster sizes. In addition, larger fragments are
strongly affected by recombination as well, as shown for the case of dimers.
We demonstrate that for mixed ArâXe clusters exposed to intense NIR pulses,
excited atoms and ions are preferentially formed in the Xe core. As a result
of electron-ion recombination, higher charge states of Xe are efficiently
suppressed, leading to an overall reduced expansion speed of the cluster core
in comparison to the shell
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Correlated electronic decay following intense near-infrared ionization of clusters
We report on a novel correlated electronic decay process following extensive Rydberg atom formation in clusters ionized by intense near-infrared fields. A peak close to the atomic ionization potential is found in the electron kinetic energy spectrum. This new contribution is attributed to an energy transfer between two electrons, where one electron decays from a Rydberg state to the ground state and transfers its excess energy to a weakly bound cluster electron in the environment that can escape from the cluster. The process is a result of nanoplasma formation and is therefore expected to be important, whenever intense laser pulses interact with nanometer-sized particles
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Intracluster Coulombic decay following intense NIR ionization of clusters
We report on the observation of a novel intracluster Coulombic decay process following Rydberg atom formation in clusters ionized by intense near-infrared fields. A new decay channel emerges, in which a Rydberg atom relaxes to the ground state by transferring its excess energy to a weakly bound electron in the environment that is emitted from the cluster. We find evidence for this process in the electron spectra, where a peak close to the corresponding atomic ionization potential is observed. For Ar clusters, a decay time of 87 ps is measured, which is significantly longer than in previous time-resolved studies of interatomic Coulombic decay
Recombination dynamics of clusters in intense extreme-ultraviolet and near-infrared fields
We investigate electron-ion recombination processes in clusters exposed to intense extreme-ultraviolet (XUV) or near-infrared (NIR) pulses. Using the technique of reionization of excited atoms from recombination (REAR), recently introduced in SchĂŒtte et al (2014 Phys. Rev. Lett. 112 253401), a large population of excited atoms, which are formed in the nanoplasma during cluster expansion, is identified under both ionization conditions. For intense XUV ionization of clusters, we find that the significance of recombination increases for increasing cluster sizes. In addition, larger fragments are strongly affected by recombination as well, as shown for the case of dimers. We demonstrate that for mixed ArâXe clusters exposed to intense NIR pulses, excited atoms and ions are preferentially formed in the Xe core. As a result of electron-ion recombination, higher charge states of Xe are efficiently suppressed, leading to an overall reduced expansion speed of the cluster core in comparison to the shell