182 research outputs found
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
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
Quantum-classical correspondence in circularly polarized high harmonic generation
Using numerical simulations, we show that atomic high order harmonic
generation, HHG, with a circularly polarized laser field offers an ideal
framework for quantum-classical correspondence in strong field physics. With an
appropriate initialization of the system, corresponding to a superposition of
ground and excited state(s), simulated HHG spectra display a narrow strip of
strong harmonic radiation preceded by a gap of missing harmonics in the lower
part of the spectrum. In specific regions of the spectra, HHG tends to lock to
circularly polarized harmonic emission. All these properties are shown to be
closely related to a set of key classical periodic orbits that organize the
recollision dynamics in an intense, circularly polarized field
Visualizing quantum entanglement and the EPR paradox during the photodissociation of a diatomic molecule using two ultrashort laser pulses
We investigate theoretically the dissociative ionization of a H2+ molecule
using two ultrashort laser (pump-probe) pulses. The pump pulse prepares a
dissociating nuclear wave packet on an ungerade surface of H2+. Next, an UV (or
XUV) probe pulse ionizes this dissociating state at large (R = 20 - 100 bohr)
internuclear distance. We calculate the momenta distributions of protons and
photoelectrons which show a (two-slit-like) interference structure. A general,
simple interference formula is obtained which depends on the electron and
protons momenta, as well as on the pump-probe delay on the pulses durations and
polarizations. This interference can be interpreted as visualization of an
electron state delocalized over the two-centres. This state is an entangled
state of a hydrogen atom with a momentum p and a proton with an opposite
momentum. -p dissociating on the ungerade surface of H2+. This pump-probe
scheme can be used to reveal the nonlocality of the electron which intuitively
should be localized on just one of the protons separated by the distance R much
larger than the atomic Bohr orbit
Coherent destruction of tunneling, dynamic localization and the Landau-Zener formula
We clarify the internal relationship between the coherent destruction of
tunneling (CDT) for a two-state model and the dynamic localization (DL) for a
one-dimensional tight-binding model, under the periodical driving field. The
time-evolution of the tight-binding model is reproduced from that of the
two-state model by a mapping of equation of motion onto a set of
operators. It is shown that DL is effectively an infinitely large dimensional
representation of the CDT in the operators. We also show that
both of the CDT and the DL can be interpreted as a result of destructive
interference in repeated Landau-Zener level-crossings.Comment: 5 pages, no figur
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