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Collinear helium under periodic driving: Stabilization of the asymmetric stretch orbit Schlagheck, Peter ; ; in Physical Review. A (2003), 68(5), 053410 The collinear eZe configuration of helium, with the electrons on opposite sides of the nucleus, is studied in the presence of an external electromagnetic (laser or microwave) field. We show that the ... [more ▼] The collinear eZe configuration of helium, with the electrons on opposite sides of the nucleus, is studied in the presence of an external electromagnetic (laser or microwave) field. We show that the classically unstable "asymmetric stretch" orbit, on which doubly excited intrashell states of helium with maximum interelectronic angle are anchored, can be stabilized by means of a resonant driving where the frequency of the electromagnetic field equals the frequency of Kepler-like oscillations along the orbit. A static magnetic field, oriented parallel to the oscillating electric field of the driving, can be used to enforce the stability of the configuration with respect to deviations from collinearity. Quantum Floquet calculations within a collinear model of the driven two-electron atom reveal the existence of nondispersive wave packets localized on the stabilized asymmetric stretch orbit, for double excitations corresponding to principal quantum numbers of the order of Ngreater than or similar to10. [less ▲] Detailed reference viewed: 8 (0 ULg)Resonance-assisted tunneling ; Schlagheck, Peter ; in Annals of Physics (2002), 300(1), 88-136 We present evidence that tunneling processes in near-integrable systems are enhanced due to the manifestation of nonlinear resonances and their respective island chains in phase space. A semiclassical ... [more ▼] We present evidence that tunneling processes in near-integrable systems are enhanced due to the manifestation of nonlinear resonances and their respective island chains in phase space. A semiclassical description of this "resonance-assisted" mechanism is given, which is based on a local perturbative description of the dynamics in the vicinity of the resonances. As an underlying picture, we obtain that the quantum state is coupled, via a succession of classically forbidden transitions across nonlinear resonances, to high excitations within the well, from where tunneling occurs with a rather large rate. The connection between this description and the complex classical structure of the underlying integrable dynamics is furthermore studied, giving ground to the general coherence of the description as well as guidelines for the identification of the dominant tunneling paths. The validity of this mechanism is demonstrated within the kicked Harper model, where good agreement between quantum and semiclassical (resonance-assisted) tunneling rates is found. (C) 2002 Elsevier Science (USA). [less ▲] Detailed reference viewed: 26 (2 ULg)Algebraic decay of the survival probability in chaotic helium Schlagheck, Peter ; in Physical Review. A (2001), 63(2), 024701 We demonstrate that the classical helium atom exhibits algebraic decay of the survival probability in the autoionizing eZe configuration. Excitation towards asymptotic orbits of marginal stability is ... [more ▼] We demonstrate that the classical helium atom exhibits algebraic decay of the survival probability in the autoionizing eZe configuration. Excitation towards asymptotic orbits of marginal stability is identified as the cause of the nonexponential decay. Since one electron travels along a bound Kepler trajectory of infinite excitation in these orbits, we argue that the classical decay law will prevail in the quantum dynamics of a wave packet launched along the eZe configuration. [less ▲] Detailed reference viewed: 9 (1 ULg)Resonance-assisted tunneling in near-integrable systems ; Schlagheck, Peter ; in Physical Review Letters (2001), 87(6), 064101 Dynamical tunneling between symmetry related invariant tori is studied in the near-integrable regime. Using the kicked Harper model as an illustration, we show that the exponential decay of the wave ... [more ▼] Dynamical tunneling between symmetry related invariant tori is studied in the near-integrable regime. Using the kicked Harper model as an illustration, we show that the exponential decay of the wave functions in the classically forbidden region is modified due to coupling processes that are mediated by classical resonances. This mechanism leads to a substantial deviation of the splitting between quasidegenerate eigenvalues from the purely exponential decrease with 1/(h) over bar obtained for the integrable system. A simple semiclassical framework, which takes into account the effect of the resonance substructure on the invariant tori, allows one to quantitatively reproduce the behavior of the eigenvalue splittings. [less ▲] Detailed reference viewed: 13 (0 ULg)Laser-induced transitions between triply excited hollow states ; Schlagheck, Peter ; in Physical Review. A (2000), 62(6), 062719 Using complex scaling and a correlated basis constructed in terms of B splines, we calculate the Li+ photoion yield in the presence of a laser-induced coupling between the triply excited 2s(2)2p(P-2(0 ... [more ▼] Using complex scaling and a correlated basis constructed in terms of B splines, we calculate the Li+ photoion yield in the presence of a laser-induced coupling between the triply excited 2s(2)2p(P-2(0)) and 2s2p(2)(D-2(e)) resonances in lithium, the first of which is assumed to be excited by synchrotron radiation from the ground state. The laser coupling between the triply excited states is shown to lead to a significant and readily measurable modification of the line profile which provides a unique probe of the dipole strength between highly correlated triply excited states. We also present results for some higher-lying triply excited states of P-2(0) symmetry. [less ▲] Detailed reference viewed: 7 (1 ULg)Laser-induced transitions between triply excited hollow states ; Schlagheck, Peter ; in Physical Review Letters (2000), 85(1), 42-45 We present an ab initio calculation of the Li+ photoion yield in the presence of laser coupling between the triply; excited 2s(2)2p(2)P(o) and 2s2p(2) D-2(e) resonances in lithium, the first of which is ... [more ▼] We present an ab initio calculation of the Li+ photoion yield in the presence of laser coupling between the triply; excited 2s(2)2p(2)P(o) and 2s2p(2) D-2(e) resonances in lithium, the first of which is assumed excited by synchrotron radiation from the ground state. The laser coupling between the triply excited states is shown to lead to a significant and readily measurable modification of the line profile which provides a unique probe of the dipole strength between highly correlated triply excited states. [less ▲] Detailed reference viewed: 4 (1 ULg)Das Drei-Körper-Coulombproblem unter periodischem Antrieb Schlagheck, Peter Doctoral thesis (1999) Detailed reference viewed: 44 (15 ULg)Stable classical configurations in strongly driven helium Schlagheck, Peter ; in Physica D: Nonlinear Phenomena (1999), 131(1-4), 110-124 We present a detailed analysis of the classical dynamics of the frozen-planet configuration of helium in an external, linearly polarized electromagnetic field. It is shown that the phase space of the ... [more ▼] We present a detailed analysis of the classical dynamics of the frozen-planet configuration of helium in an external, linearly polarized electromagnetic field. It is shown that the phase space of the collinear frozen planet in the held is mixed regular-chaotic and exhibits regular islands corresponding to nonlinear resonances between the periodic external force and the frozen-planet dynamics. An analysis of the transverse stability properties of the configuration shows that - except for regular regions corresponding to high-order atom-field resonances - the configuration is generally unstable with respect to deviations from collinearity. We find that stability of the driven frozen planet in all phase space dimensions can be enforced by the application of an additional, static electric field. The minimum atomic excitation necessary fur the localization of a quantum state on the thereby stabilized atom-field resonances is estimated. (C) 1999 Elsevier Science B.V. All rights reserved. [less ▲] Detailed reference viewed: 16 (5 ULg)Nondispersive two-electron wave packets in the collinear driven helium atom Schlagheck, Peter ; in Europhysics Letters [=EPL] (1999), 46(1), 24-30 Nondispersive two-electron wave packets are found in the Floquet spectrum of the driven, one-dimensional helium atom. In classical phase space, they are anchored to the principal nonlinear resonance ... [more ▼] Nondispersive two-electron wave packets are found in the Floquet spectrum of the driven, one-dimensional helium atom. In classical phase space, they are anchored to the principal nonlinear resonance between the collinear frozen planet orbit and the driving field linearly polarized along the orbit. These novel, highly correlated eigenstates of the driven three-body Coulomb problem, exhibit lifetimes of the order of 10(3)...10(7) periods of the driving field, with strong fluctuations reminiscent of chaos-assisted tunneling. [less ▲] Detailed reference viewed: 6 (0 ULg)Comment on "physical reality of light-induced atomic states" Schlagheck, Peter ; ; in Physical Review Letters (1999), 82(3), 664-664 Detailed reference viewed: 12 (0 ULg)Laser-assisted dielectronic recombination in C4+ ions ; ; et al in Journal of Physics : B Atomic Molecular & Optical Physics (1998), 31(14), 3263-3280 We study the effect of laser-driven transitions between autoionizing resonances on the dielectronic recombination rates observed after the formation of such resonances in electron-ion collisions. The ... [more ▼] We study the effect of laser-driven transitions between autoionizing resonances on the dielectronic recombination rates observed after the formation of such resonances in electron-ion collisions. The autoionizing states of S-1(e) and P-1(0) symmetry belonging to the 2l2l' and 2l3l' configurations of C4+ are considered. The resonance parameters are calculated in the Feshbach formalism and compared with other accurate calculations, and transition dipole moments between the autoionizing states are obtained. The rates of dielectronic recombination and autoionization under the influence of the laser field are calculated using the density matrix approach for realistic parameters. A simple formulation of the problem is also proposed in the resolvent operator technique. The feasibility of an experiment is discussed. [less ▲] Detailed reference viewed: 9 (1 ULg)Classical support for non-dispersive two electron wave packets in the driven helium atom Schlagheck, Peter ; in Journal of Physics : B Atomic Molecular & Optical Physics (1998), 31(11), 489-495 We present numerical evidence for the existence of a classically non-ionizing, highly correlated two-electron configuration which emerges from the frozen planet configuration of helium exposed to an ... [more ▼] We present numerical evidence for the existence of a classically non-ionizing, highly correlated two-electron configuration which emerges from the frozen planet configuration of helium exposed to an electromagnetic field of linear polarization. A static electric field parallel to the polarization axis prevents this configuration from transverse ionization. We argue that the corresponding nonlinear resonance island in 12D phase space supports nondispersive wave packets of the helium atom in combined oscillating and static electric fields. [less ▲] Detailed reference viewed: 13 (0 ULg)A theoretical description of laser induced dielectronic recombination Schlagheck, Peter ; in Hyperfine Interactions (1997), 108(1-3), 267-271 We present the theoretical description of a dielectronic recombination process in which the autoionizing state is coupled to a bound state by a laser field, The system is described by density matrix ... [more ▼] We present the theoretical description of a dielectronic recombination process in which the autoionizing state is coupled to a bound state by a laser field, The system is described by density matrix equations in which the continuum components of the density matrix have been eliminated. Model calculations with these density matrix equations have been performed in order to compare the spectra of laser induced dielectronic recombination with the corresponding autoionization spectra. [less ▲] Detailed reference viewed: 8 (3 ULg)Theory of laser-induced dielectronic recombination: A case study in Helium Schlagheck, Peter ; in Zeitschrift für Physik. D, Atoms, Molecules, and Clusters (1997), 39(3), 173-180 We present the theoretical description of laser-induced dielectronic recombination in the density matrix formalism and show how the continuum components can be eliminated. The resulting equations are ... [more ▼] We present the theoretical description of laser-induced dielectronic recombination in the density matrix formalism and show how the continuum components can be eliminated. The resulting equations are applied to the calculation of specific recombination processes in Helium from the point of view of resolving the involved autoionizing states in the recombination spectrum. We examine how the shape of the spectrum depends on the laser pulse duration in processes in which the autoionizing state to which the system recombines is coupled to a bound state. In addition, we consider processes in which the autoionizing state is coupled to another autoionizing state and discuss the possibility of resolving the resonance in the recombination spectrum. [less ▲] Detailed reference viewed: 4 (0 ULg)Theorie laserinduzierter Rekombinationsprozesse Schlagheck, Peter Master's dissertation (1996) Detailed reference viewed: 35 (15 ULg)Theory of laser-induced two-step electron-ion recombination Schlagheck, Peter ; ; in Zeitschrift für Physik. D, Atoms, Molecules, and Clusters (1996), 37(1), 19-27 A theoretical framework for the quantitative interpretation of laser-induced electron-ion recombination is presented in terms of the density matrix taking into account stochastic bandwidth and pulse ... [more ▼] A theoretical framework for the quantitative interpretation of laser-induced electron-ion recombination is presented in terms of the density matrix taking into account stochastic bandwidth and pulse duration of the laser. The theory deals with recombination induced from the continuum into one group of states by one laser and further stabilized into a lower group of states by a second laser. Rate equations are then derived from the complete density matrix, and the conditions for their validity are discussed. Both density matrix and rate equations are applied to the interpretation of a recent experiment with equally good agreement. [less ▲] Detailed reference viewed: 14 (0 ULg) |
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