489 research outputs found
Long-range Energy Transfer and Ionization in Extended Quantum Systems Driven by Ultrashort Spatially Shaped Laser Pulses
The processes of ionization and energy transfer in a quantum system composed
of two distant H atoms with an initial internuclear separation of 100 atomic
units (5.29 nm) have been studied by the numerical solution of the
time-dependent Schr\"odinger equation beyond the Born-Oppenheimer
approximation. Thereby it has been assumed that only one of the two H atoms was
excited by temporally and spatially shaped laser pulses at various laser
carrier frequencies. The quantum dynamics of the extended H-H system, which was
taken to be initially either in an unentangled or an entangled ground state,
has been explored within a linear three-dimensional model, including two z
coordinates of the electrons and the internuclear distance R. An efficient
energy transfer from the laser-excited H atom (atom A) to the other H atom
(atom B) and the ionization of the latter have been found. It has been shown
that the physical mechanisms of the energy transfer as well as of the
ionization of atom B are the Coulomb attraction of the laser driven electron of
atom A by the proton of atom B and a short-range Coulomb repulsion of the two
electrons when their wave functions strongly overlap in the domain of atom B.Comment: 11 pages, 7 figure
Electronic dynamics and frequency-dependent effects in circularly polarized strong-field physics
We analyze, quantum mechanically, the dynamics of ionization with a strong,
circularly polarized, laser field. We show that the main source for
non-adiabatic effects is connected to an effective barrier lowering due to the
laser frequency. Such non-adiabatic effects manifest themselves through
ionization rates and yields that depart up to more than one order of magnitude
from a static-field configuration. Beyond circular polarization, these results
show the limits of standard instantaneous - static-field like - interpretation
of laser-matter interaction and the great need for including time dependent
electronic dynamics
Analysis of strong-field enhanced ionization of molecules using Bohmian trajectories
We theoretically investigate the mechanism of enhanced ionization in
two-electron molecules by analyzing Bohmian trajectories for a one-dimensional
H2 in an intense laser field. We identify both types of ionizing trajectories
corresponding to the ejection from the up-field and down-field cores. The
trajectories of the two electrons are correlated with each other in the former
while correlation is negligible in the latter. The contributions from the two
ionization types, though depending on laser intensity and internuclear
distance, are comparable to each other.Comment: 9 pages, 9 figure
Circularly Polarized Molecular High Harmonic Generation Using a Bicircular Laser
We investigate the process of circularly polarized high harmonic generation
in molecules using a bicircular laser field. In this context, we show that
molecules offer a very robust framework for the production of circularly
polarized harmonics, provided their symmetry is compatible with that of the
laser field. Using a discrete time-dependent symmetry analysis, we show how all
the features (harmonic order and polarization) of spectra can be explained and
predicted. The symmetry analysis is generic and can easily be applied to other
target and/or field configurations
Resonantly enhanced pair production in a simple diatomic model
A new mechanism for the production of electron-positron pairs from the
interaction of a laser field and a fully stripped diatomic molecule in the
tunneling regime is presented. When the laser field is turned off, the Dirac
operator has resonances in both the positive and the negative energy continua
while bound states are in the mass gap. When this system is immersed in a
strong laser field, the resonances move in the complex energy plane: the
negative energy resonances are pushed to higher energies while the bound states
are Stark shifted. It is argued here that there is a pair production
enhancement at the crossing of resonances by looking at a simple 1-D model: the
nuclei are modeled simply by Dirac delta potential wells while the laser field
is assumed to be static and of finite spatial extent. The average rate for the
number of electron-positron pairs produced is evaluated and the results are
compared to the single nucleus and to the free cases. It is shown that
positrons are produced by the Resonantly Enhanced Pair Production (REPP)
mechanism, which is analogous to the resonantly enhanced ionization of
molecular physics. This phenomenon could be used to increase the number of
pairs produced at low field strength, allowing the study of the Dirac vacuum.Comment: 11 pages, 4 figure
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