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F Kelkensberg,
W Siu,
J F Pérez-Torres,
F Morales,
G Gademann,
A Rouzée,
P Johnsson,
M Lucchini,
F Calegari, J L Sanz-Vicario,
F Martín,
M J J Vrakking
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ABSTRACT: We report experiments where hydrogen molecules were dissociatively ionized by an attosecond pulse train in the presence of a near-infrared field. Fragment ion yields from distinguishable ionization channels oscillate with a period that is half the optical cycle of the IR field. For molecules aligned parallel to the laser polarization axis, the oscillations are reproduced in two-electron quantum simulations, and can be explained in terms of an interference between ionization pathways that involve different harmonic orders and a laser-induced coupling between the 1sσ(g) and 2pσ(u) states of the molecular ion. This leads to a situation where the ionization probability is sensitive to the instantaneous polarization of the molecule by the IR electric field and demonstrates that we have probed the IR-induced electron dynamics with attosecond pulses.
Physical Review Letters 07/2011; 107(4):043002. · 7.37 Impact Factor
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ABSTRACT: Circular dichroism is a consequence of chirality. However, nonchiral molecules can also exhibit it when the measurement itself introduces chirality, e.g., when measuring molecular-frame photoelectron angular distributions. The few such experiments performed on homonuclear diatomic molecules show that, as expected, circular dichroism vanishes when the molecular-frame photoelectron angular distributions are integrated over the polar electron emission angle. Here we show that this is not the case in resonant dissociative ionization of H2 for photons of 30-35 eV, which is the consequence of the delayed ionization from molecular doubly excited states into ionic states of different inversion symmetry.
Physical Review Letters 06/2010; 104(23):233003. · 7.37 Impact Factor
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G Sansone,
F Kelkensberg,
J F Pérez-Torres,
F Morales,
M F Kling,
W Siu,
O Ghafur,
P Johnsson,
M Swoboda,
E Benedetti,
F Ferrari,
F Lépine, J L Sanz-Vicario,
S Zherebtsov,
I Znakovskaya,
A L'huillier,
M Yu Ivanov,
M Nisoli,
F Martín,
M J J Vrakking
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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 has become possible only with the recent development of isolated attosecond (10(-18)-s) laser pulses. Such pulses have been used to investigate atomic photoexcitation and photoionization and electron dynamics in solids, 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 and controlled using few-cycle near-infrared laser pulses. 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.
Nature 06/2010; 465(7299):763-6. · 36.28 Impact Factor
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ABSTRACT: We show the relevance that molecular autoionizing states display in some recent experiments related to the symmetry-breaking in molecular-frame photoelectron angular distributions in H2 when exposed to intense xuv femtosecond laser pulses, and others related to the electron (proton) localization when subject to attosecond pump-probe laser schemes. Our theoretical method solves the time-dependent Schrödinger equation with an spectral method that expands the wave function in terms of H2 correlated stationary vibronic states including all electronic and vibrational degrees of motion. Time-resolved asymmetric electron angular distributions are obtained at specific proton kinetic energies due to the delayed autoionization from H2 doubly excited states, which induces interferences between gerade (1sσg) and ungerade (2pσu) ionization channels. We also study photoionization of H2 exposed to a xuv attosecond pump pulse plus a time-delayed IR femtosecond probe pulse. Fast alternating asymmetries in the proton ejection (electron localization) are obtained as a function of the time delay between the pump and the probe pulses. Finally, we deal with the process of (xuv) two-photon double ionization of H2 under the assumption of having both sequential and non-sequential absorption processes.
Journal of Physics Conference Series 12/2009; 194(1):012013.
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Y H Jiang,
A Rudenko,
K U Kühnel,
Th Ergler,
S Lüdemann,
K Zrost,
D Fischer,
J Pérez-Torres,
E Plésiat,
F Martín,
L Foucar,
J Titze,
M Schöffler,
R Dörner, J L Sanz-Vicario,
S Düsterer,
R Treusch,
C D Schröter,
R Moshammer,
J Ullrich
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ABSTRACT: Sequential and direct two-photon double ionization (DI) of D2 molecule is studied experimentally and theoretically at a photon energy of 38.8 eV. Experimental and theoretical kinetic energy releases of D++D+fragments, consisting of the contributions of sequential DI via the D2+(1sσg) state and direct DI via a virtual state, agree well with each other.
Journal of Physics Conference Series 12/2009; 194(3):032057.
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ABSTRACT: A theoretical study of two-photon ionization of H2 by low-intensity ultrashort xuv laser pulses is reported. The method is based on the solution of the time-dependent Schrödinger equation in a basis of stationary molecular vibronic states which include all electronic and vibrational degrees of freedom. In contrast with previous work, the doubly excited states, which also contribute to the ionization probabilities through autoionization, are explicitly included. We have found that, just below the one-photon ionization threshold, molecular autoionization leads to an enhancement of dissociative ionization, whose corresponding probability can be an order of magnitude larger than that of the nondissociative ionization process, and even larger than the corresponding dissociative probability in the one-photon absorption region. This result suggests that multicoincidence experiments, in which the orientation of the molecule with respect to the polarization axis is determined, might be easier to perform in the two-photon absorption regime than in the one-photon absorption regime. Electron angular distributions in the same range of photon energies are also reported.
Journal of Physics B Atomic Molecular and Optical Physics 12/2009; 43(1):015204. · 1.88 Impact Factor
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ABSTRACT: A theoretical approach to obtain accurate values for autoionizing states parameters in Be-like systems is presented. The method is based on the configuration-interaction expansion of the two-active (outer) electron wavefunction in terms of correlated coordinates containing r12 explicitly and by including a model potential to represent the effect of the 1s2 core. Within our approach, 1snl core states are removed from the basis of correlated configurations by using a Phillips–Kleinman projection operator, and resonance parameters (energies and widths) are determined through the stabilization method. Illustrative examples of our implementation are given for doubly-excited states of Be and Ne6+.
Journal of Physics B Atomic Molecular and Optical Physics 02/2008; 41(5):055003. · 1.88 Impact Factor
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ABSTRACT: We have measured the production of both Lyα and Hα fluorescence from atomic H and D for the photodissociation of H2 and D2 by linearly polarized photons with energies between 24 and 60 eV. In this energy range, excited photofragments result primarily from the production of doubly excited molecular species which promptly autoionize or dissociate into two neutrals. Our data are compared with ab initio calculations of the dissociation process, in which both doubly excited state production and prompt ionization (non-resonant) channels are considered. Agreement between our experimental data and that of earlier work, and with our theoretical calculations, is qualitative at best.
Journal of Physics B Atomic Molecular and Optical Physics 11/2006; 39(23):4871. · 1.88 Impact Factor
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ABSTRACT: Photoelectron angular distributions from fixed-in-space H2 molecules exposed to ultrashort xuv laser pulses have been evaluated. The theoretical method is based on the solution of the time-dependent Schrödinger equation in a basis of stationary states that include all electronic and vibrational degrees of freedom. Asymmetric angular distributions are observed as a consequence of the delayed ionization from the H2 doubly excited states, which induces interferences between gerade and ungerade ionization channels. The analysis of this asymmetry as a function of pulse duration can provide an estimate of the corresponding autoionization widths.
Phys. Rev. A. 80(1).
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Y H Jiang,
A Rudenko,
K U Kühnel,
Th. Ergler,
S Lüdemann,
K Zrost,
D Fischer,
J Pérez-Torres,
E Plésiat,
F Martín, [......],
L Foucar,
J Titze,
M Schöffler,
R Dörner, J L Sanz-Vicario,
S Düsterer,
R Treusch,
C D Schröter,
R Moshammer,
J Ullrich
J. Phys.: Conf. Ser. (ICPEAC2009). 194:032057.
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G Sansone,
F. Kelkensberg,
J. F. Pérez-Torres,
F. Morales,
Matthias F. Kling,
W Siu,
O. Ghafur,
P. Johnsson,
M. Swoboda,
E Benedetti,
F. Ferrari,
F. Lepine, J. L. Sanz-Vicario,
Sergey Zherebtsov,
Irina Znakovskaya,
Anne L'Huillier,
M. Y. Ivanov,
M Nisoli,
F. Martin,
M J J Vrakking
Nature, v.465, 763-767 (2010).
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Y. H. Jiang,
A. Rudenko,
E. Plésiat,
L. Foucar,
M. Kurka,
K. U. Kühnel,
T. Ergler,
J. F. Pérez-Torres,
F. Martin,
O. Herrwerth, [......],
M Schöffler,
J. van Tilborg,
A. Belkacem,
K Ueda,
T. J. M. Zouros,
S. Düsterer,
R. Treusch,
C. D. Schröter,
R. Moshammer,
J. Ullrich
Physical Review A, v.81 (2010).
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Y. H. Jiang,
A. Rudenko,
E. Plésiat,
L. Foucar,
M. Kurka,
K. U. Kühnel,
Th Ergler,
J. F. Pérez-Torres,
F Martín,
O. Herrwerth, [......],
M Schöffler,
J. van Tilborg,
A. Belkacem,
K Ueda,
T. J. M. Zouros,
S. Düsterer,
R. Treusch,
C. D. Schröter,
R. Moshammer,
J. Ullrich
Phys. Rev. A 81(2010),021401(R).
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Y. H. Jiang,
A. Rudenko,
J. F. Pérez-Torres,
Oliver Herrwerth,
L. Foucar,
M. Kurka,
K. U. Kühnel,
M. Toppin,
E. Plésiat,
F. Morales, [......],
J. van Tilborg,
A. Belkacem,
M Schulz,
K Ueda,
T. J. M. Zouros,
S. Düsterer,
R. Treusch,
C. D. Schröter,
R. Moshammer,
J. Ullrich
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ABSTRACT: We used a split-mirror setup attached to a reaction microscope at the free-electron laser in Hamburg (FLASH) to perform an XUV-pump–XUV-probe experiment by tracing the ultrafast nuclear wave-packet motion in the D2+(1sσg) with <10 fs time resolution. Comparison with time-dependent calculations shows excellent agreement with the measured vibrational period of 22±4 fs in D2+, points to the importance of accurately knowing the internuclear distance-dependent ionization probability, and paves the way to control sequential and nonsequential two-photon double-ionization contributions.
Physical Review A, v.81, 1-4 (2010).
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Y. H. Jiang,
A. Rudenko,
J. F. Pérez-Torres,
Oliver Herrwerth,
L. Foucar,
M. Kurka,
K. U. Kühnel,
M. Toppin,
E. Plésiat,
F. Morales, [......],
J. van Tilborg,
A. Belkacem,
M Schulz,
K Ueda,
T. J. M. Zouros,
S. Düsterer,
R. Treusch,
C. D. Schröter,
R. Moshammer,
J. Ullrich
Physical Review A, v.81 (2010).
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Y. H. Jiang,
A. Rudenko,
J. F. Pérez-Torres,
O. Herrwerth,
L. Foucar,
M. Kurka,
K. U. Kühnel,
M. Toppin,
E. Plésiat,
F. Morales, [......],
J. van Tilborg,
A. Belkacem,
M Schulz,
K Ueda,
T. J. M. Zouros,
S. Düsterer,
R. Treusch,
C. D. Schröter,
R. Moshammer,
J. Ullrich
Phys. Rev. A 81(2010),051402(R).
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Y. H. Jiang,
A. Rudenko,
E. Plésiat,
L. Foucar,
M. Kurka,
K. U. Kühnel,
Th. Ergler,
J. F. Pérez-Torres,
F. Martín,
O. Herrwerth, [......],
M. Schöffler,
J. van Tilborg,
A. Belkacem,
K. Ueda,
T. J. M. Zouros,
S. Düsterer,
R. Treusch,
C. D. Schröter,
R. Moshammer,
J. Ullrich
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ABSTRACT: Two-photon double ionization (TPDI) of D2 is studied for 38-eV photons at the Free Electron Laser in Hamburg (FLASH). Based on model calculations, instantaneous and sequential absorption pathways are identified as separated peaks in the measured D++D+ fragment kinetic energy release (KER) spectra. The instantaneous process appears at high KER, corresponding to ionization at the molecule’s equilibrium distance, in contrast to sequential ionization mainly leading to low-KER contributions. Measured fragment angular distributions are in good agreement with theory.
Phys. Rev. A. 81(2).
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ABSTRACT: An ab initio non-perturbative time dependent method to describe ionization of molecular systems by ultrashort (femtosecond) laser pulses has been developed. The method allows one to describe competing processes such as non dissociative ionization, dissociative ionization and dissociation into neutrals, including the possibility of autoionization. In this work we assess the validity of the method by applying it to different physical situations and by comparing with results previously obtained within stationary perturbation theory. In particular, it is shown that inclusion of the nuclear motion is essential to describe H2 resonance enhanced multiphoton ionization and interferences mediated by H2 autoionizing states.
Journal of Electron Spectroscopy and Related Phenomena.
