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Fukuzawa H.,Tohoku University | Fukuzawa H.,RIKEN | Son S.-K.,German Electron Synchrotron | Motomura K.,Tohoku University | And 31 more authors.
Physical Review Letters | Year: 2013

We have investigated multiphoton multiple ionization dynamics of xenon atoms using a new x-ray free-electron laser facility, SPring-8 Angstrom Compact free electron LAser (SACLA) in Japan, and identified that Xen+ with n up to 26 is produced at a photon energy of 5.5 keV. The observed high charge states (n≥24) are produced via five-photon absorption, evidencing the occurrence of multiphoton absorption involving deep inner shells. A newly developed theoretical model, which shows good agreement with the experiment, elucidates the complex pathways of sequential electronic decay cascades accessible in heavy atoms. The present study of heavy-atom ionization dynamics in high-intensity hard-x-ray pulses makes a step forward towards molecular structure determination with x-ray free-electron lasers. © 2013 American Physical Society.


Singh K.P.,Indian Institute of Science | Rost J.M.,Max Planck Institute for the Physics of Complex Systems | Rost J.M.,Max Planck Advanced Study Group at CFEL
Chemical Physics | Year: 2010

We investigate dynamics of atomic and molecular systems exposed to intense, shaped random fields and a weak femtosecond laser pulse theoretically. As a prototype example, the photoionization of a hydrogen atom is considered in detail. The net photoionization undergoes an optimal enhancement when a broadband random field is added to the weak laser pulse. The enhanced ionization is analyzed using time-resolved wavepacket evolution and the population dynamics of the atomic levels. We elucidate the enhancement produced by spectrally shaped random fields of two different classes, one with a tunable bandwidth and another with a narrow bandwidth centered at the first atomic transition. Motivated by the large bandwidth provided in the high harmonic generation, we also demonstrate the enhancement effect exploiting random fields synthesized from discrete, phase randomized, odd-order and all-order high harmonics of the driving pulse. These findings are generic and can have applications to other atomic and simple molecular systems. © 2010 Elsevier B.V. All rights reserved.


Gnodtke C.,Max Planck Institute for the Physics of Complex Systems | Saalmann U.,Max Planck Institute for the Physics of Complex Systems | Saalmann U.,Max Planck Advanced Study Group at CFEL | Rost J.-M.,Max Planck Institute for the Physics of Complex Systems | Rost J.-M.,Max Planck Advanced Study Group at CFEL
Chemical Physics | Year: 2013

The photo-electron spectrum resulting from multi-photon absorption of an extended target, such as an atomic cluster or a large molecule, from an intense laser pulse with photon energies larger than the ionization potential of the atomic constituents is discussed. We develop an approximate analytical framework and provide simple analytical expressions for the shape of the photo-electron spectrum in the limit of sequential and parallel ionization, realized by long and short pulses, respectively. The width of the spectrum provides valuable information about the absorbed photons of the target in relation to its extension. © 2012 Elsevier B.V. All rights reserved.


Camus N.,Max Planck Institute for Nuclear Physics | Fischer B.,Max Planck Institute for Nuclear Physics | Kremer M.,Max Planck Institute for Nuclear Physics | Sharma V.,Max Planck Institute for Nuclear Physics | And 11 more authors.
Physical Review Letters | Year: 2012

The strong-field induced decay of a doubly excited, transient Coulomb complex Ar **→Ar2 ++2e - is explored by tracing correlated two-electron emission in nonsequential double ionization of Ar as a function of the carrier-envelope phase. Using <6fs pulses, electron emission is essentially confined to one optical cycle. Classical model calculations support that the intermediate Coulomb complex has lost memory of its formation dynamics and allows for a consistent, though model-dependent definition of "emission time," empowering us to trace transition-state two-electron decay dynamics with sub-fs resolution. We find a most likely emission time difference of ∼200±100 as. © 2012 American Physical Society.


Gnodtke C.,Max Planck Institute for the Physics of Complex Systems | Saalmann U.,Max Planck Institute for the Physics of Complex Systems | Saalmann U.,Max Planck Advanced Study Group at CFEL | Rost J.-M.,Max Planck Institute for the Physics of Complex Systems | Rost J.-M.,Max Planck Advanced Study Group at CFEL
Physical Review Letters | Year: 2012

Massively parallel ionization of many atoms in a cluster or biomolecule is identified as a new phenomenon of light-matter interaction which becomes feasible through short and intense FEL pulses. Almost simultaneously emitted from the illuminated target the photo-electrons can have such a high density that they interact substantially even after photoionization. This interaction results in a characteristic electron spectrum which can be interpreted as a convolution of a mean-field electron dynamics and binary electron-electron collisions. We demonstrate that this universal spectrum can be obtained analytically by summing synthetic two-body Coulomb collision events. Moreover, we propose an experiment with hydrogen clusters to observe massively parallel ionization. © 2012 American Physical Society.

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