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- Gryzlova, E. V., et al.
(författare)
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Doubly resonant three-photon double ionization of Ar atoms induced by an EUV free-electron laser
- 2011
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Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 84:6
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Tidskriftsartikel (refereegranskat)abstract
- A mechanism for three-photon double ionization of atoms by extreme-ultraviolet free-electron laser pulses is revealed, where in a sequential process the second ionization step, proceeding via resonant two-photon ionization of ions, is strongly enhanced by the excitation of ionic autoionizing states. In contrast to the conventional model, the mechanism explains the observed relative intensities of photoelectron peaks and their angular dependence in three-photon double ionization of argon.
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2. |
- Kornilov, O., et al.
(författare)
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Coulomb explosion of diatomic molecules in intense XUV fields mapped by partial covariance
- 2013
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 46:16
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Tidskriftsartikel (refereegranskat)abstract
- Single-shot time-of-flight spectra for Coulomb explosion of N-2 and I-2 molecules have been recorded at the Free Electron LASer in Hamburg (FLASH) and have been analysed using a partial covariance mapping technique. The partial covariance analysis unravels a detailed picture of all significant Coulomb explosion pathways, extending up to the N4+-N5+ channel for nitrogen and up to the I8+-I9+ channel for iodine. The observation of the latter channel is unexpected if only sequential ionization processes from the ground state ions are considered. The maximum kinetic energy release extracted from the covariance maps for each dissociation channel shows that Coulomb explosion of nitrogen molecules proceeds much faster than that of the iodine. The N-2 ionization dynamics is modelled using classical trajectory simulations in good agreement with the outcome of the experiments. The results suggest that covariance mapping of the Coulomb explosion can be used to measure the intensity and pulse duration of free-electron lasers.
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3. |
- Mondal, S., et al.
(författare)
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Photoelectron angular distributions for the two-photon sequential double ionization of xenon by ultrashort extreme ultraviolet free electron laser pulses
- 2013
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 46:16
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Tidskriftsartikel (refereegranskat)abstract
- Xenon atoms are double-ionized by sequential two-photon absorption by ultrashort extreme ultraviolet free-electron laser pulses with a photon energy of 23.0 and 24.3 eV, produced by the SPring-8 Compact SASE Source test accelerator. The angular distributions of photoelectrons generated by two-photon double ionization are obtained using velocity map imaging. The results are reproduced reasonably well by the present theoretical calculations within the multi-configurational Dirac-Fock approach.
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6. |
- Ma, R., et al.
(författare)
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Photoelectron angular distributions for the two-photon ionization of helium by ultrashort extreme ultraviolet free-electron laser pulses
- 2013
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 46:16
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Tidskriftsartikel (refereegranskat)abstract
- The two-photon ionization of helium atoms by ultrashort extreme-ultraviolet free-electron laser pulses, produced by the SPring-8 Compact SASE Source test accelerator, was investigated at photon energies of 20.3, 21.3, 23.0 and 24.3 eV. The angular distribution of photoelectrons generated by two-photon ionization is obtained using a velocity map imaging spectrometer. The phase-shift differences and amplitude ratios of the outgoing s and d continuum wave packets are extracted from the photoelectron angular distributions. The obtained values of the phase-shift differences are distinct from scattering phase-shift differences when the photon energy is tuned to a resonance with an excited level or Rydberg manifold. The difference stems from the co-presence of resonant and non-resonant path contributions in the two-photon ionization by femtosecond pulses. Since the relative contribution of both paths can be controlled in principle by the pulse shape, these results illustrate a new way to tailor the continuum wave packet.
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7. |
- Rolles, D., et al.
(författare)
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Femtosecond x-ray photoelectron diffraction on gas-phase dibromobenzene molecules
- 2014
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 47:12
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Tidskriftsartikel (refereegranskat)abstract
- We present time-resolved femtosecond photoelectron momentum images and angular distributions of dissociating, laser-aligned 1,4-dibromobenzene (C6H4Br2) molecules measured in a near-infrared pump, soft-x-ray probe experiment performed at an x-ray free-electron laser. The observed alignment dependence of the bromine 2p photoelectron angular distributions is compared to density functional theory calculations and interpreted in terms of photoelectron diffraction. While no clear time-dependent effects are observed in the angular distribution of the Br(2p) photoelectrons, other, low-energy electrons show a pronounced dependence on the time delay between the near-infrared laser and the x-ray pulse.
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9. |
- Sansone, G., et al.
(författare)
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Attosecond excitation of electron wavepackets
- 2008
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Ingår i: Quantum Electronics and Laser Science Conference, QELS 2008. - 9781557528599
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Konferensbidrag (refereegranskat)abstract
- We present experiments, supported by time-dependent Schrödinger simulations, on the dynamics of Helium bound states after an attosecond excitation in the presence of a strong infrared laser field.
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10. |
- Sansone, G., et al.
(författare)
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Electron localization following attosecond molecular photoionization
- 2010
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 465:7299, s. 3-763
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Tidskriftsartikel (refereegranskat)abstract
- For the past several decades, we have been able to directly probe the motion of atoms that is associated with chemical transformations and which occurs on the femtosecond (10(-15)-s) timescale. However, studying the inner workings of atoms and molecules on the electronic timescale(1-4) has become possible only with the recent development of isolated attosecond (10(-18)-s) laser pulses(5). Such pulses have been used to investigate atomic photoexcitation and photoionization(6,7) and electron dynamics in solids(8), and in molecules could help explore the prompt charge redistribution and localization that accompany photoexcitation processes. In recent work, the dissociative ionization of H-2 and D-2 was monitored on femtosecond timescales(9) and controlled using few-cycle near-infrared laser pulses(10). Here we report a molecular attosecond pump-probe experiment based on that work: H-2 and D-2 are dissociatively ionized by a sequence comprising an isolated attosecond ultraviolet pulse and an intense few-cycle infrared pulse, and a localization of the electronic charge distribution within the molecule is measured that depends-with attosecond time resolution-on the delay between the pump and probe pulses. The localization occurs by means of two mechanisms, where the infrared laser influences the photoionization or the dissociation of the molecular ion. In the first case, charge localization arises from quantum mechanical interference involving autoionizing states and the laser-altered wavefunction of the departing electron. In the second case, charge localization arises owing to laser-driven population transfer between different electronic states of the molecular ion. These results establish attosecond pump-probe strategies as a powerful tool for investigating the complex molecular dynamics that result from the coupling between electronic and nuclear motions beyond the usual Born-Oppenheimer approximation.
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