11,683 research outputs found
Quantum interference in laser-induced nonsequential double ionization in diatomic molecules: the role of alignment and orbital symmetry
We address the influence of the orbital symmetry and of the molecular
alignment with respect to the laser-field polarization on laser-induced
nonsequential double ionization of diatomic molecules, in the length and
velocity gauges. We work within the strong-field approximation and assume that
the second electron is dislodged by electron-impact ionization, and also
consider the classical limit of this model. We show that the electron-momentum
distributions exhibit interference maxima and minima due to the electron
emission at spatially separated centers. The interference patterns survive the
integration over the transverse momenta for a small range of alignment angles,
and are sharpest for parallel-aligned molecules. Due to the contributions of
transverse-momentum components, these patterns become less defined as the
alignment angle increases, until they disappear for perpendicular alignment.
This behavior influences the shapes and the peaks of the electron momentum
distributions.Comment: 12 pages, 7 figures; some discussions have been extended and some
figures slightly modifie
The quantum brachistochrone problem for non-Hermitian Hamiltonians
Recently Bender, Brody, Jones and Meister found that in the quantum brachistochrone problem the passage time needed for the evolution of certain initial states into specified final states can be made arbitrarily small, when the time-evolution operator is taken to be non-Hermitian but PT-symmetric. Here we demonstrate that such phenomena can also be obtained for non-Hermitian Hamiltonians for which PT-symmetry is completely broken, i.e. dissipative systems. We observe that the effect of a tunable passage time can be achieved by projecting between orthogonal eigenstates by means of a time-evolution operator associated with a non-Hermitian Hamiltonian. It is not essential that this Hamiltonian is PT-symmetric
Influence of the Coulomb potential on above-threshold ionization: a quantum-orbit analysis beyond the strong-field approximation
We perform a detailed analysis of how the interplay between the residual
binding potential and a strong laser field influences above-threshold
ionization (ATI), employing a semi-analytical, Coulomb-corrected strong-field
approximation (SFA) in which the Coulomb potential is incorporated in the
electron propagation in the continuum. We find that the Coulomb interaction
lifts the degeneracy of some SFA trajectories, and we identify a set of orbits
which, for high enough photoelectron energies, may be associated with
rescattering. Furthermore, by performing a direct comparison with the standard
SFA, we show that several features in the ATI spectra can be traced back to the
influence of the Coulomb potential on different electron trajectories. These
features include a decrease in the contrast, a shift towards lower energies in
the interference substructure, and an overall increase in the photoelectron
yield. All features encountered exhibit a very good agreement with the \emph{ab
initio} solution of the time-dependent Schr\"odinger equation.Comment: 12 pages, 10 figure
Laser-induced nonsequential double ionization: kinematic constraints for the recollision-excitation-tunneling mechanism
We investigate the physical processes in which an electron, upon return to
its parent ion, promotes a second electron to an excited state, from which it
subsequently tunnels. Employing the strong-field approximation and saddle-point
methods, we perform a detailed analysis of the dynamics of the two electrons,
in terms of quantum orbits, and delimit constraints for their momentum
components parallel to the laser-field polarization. The kinetic energy of the
first electron, upon return, exhibits a cutoff slightly lower than ,
where is the ponderomotive energy, as in rescattered above-threshold
ionization (ATI). The second electron leaves the excited state in a direct
ATI-like process, with the maximal energy of . We also compute
electron-momentum distributions, whose maxima agree with our estimates and with
other methods.Comment: 13 pages, 4 figure
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