4,977 research outputs found
Controlling high-harmonic generation and above-threshold ionization with an attosecond-pulse train
We perform a detailed analysis of how high-order harmonic generation (HHG)
and above-threshold ionization (ATI) can be controlled by a time-delayed
attosecond-pulse train superposed to a strong, near-infrared laser field. In
particular we show that the high-harmonic and photoelectron intensities, the
high-harmonic plateau structure and cutoff energies, and the ATI angular
distributions can be manipulated by changing this delay. This is a direct
consequence of the fact that the attosecond pulse train can be employed as a
tool for constraining the instant an electronic wave packet is ejected in the
continuum. A change in such initial conditions strongly affects its subsequent
motion in the laser field, and thus HHG and ATI. In our studies, we employ the
Strong-Field Approximation and explain the features observed in terms of
interference effects between various electron quantum orbits. Our results are
in agreement with recent experimental findings and theoretical studies
employing purely numerical methods.Comment: 10 pages revtex and 6 figures (eps files
Existence criteria for stabilization from the scaling behaviour of ionization probabilities
We provide a systematic derivation of the scaling behaviour of various
quantities and establish in particular the scale invariance of the ionization
probability. We discuss the gauge invariance of the scaling properties and the
manner in which they can be exploited as consistency check in explicit
analytical expressions, in perturbation theory, in the Kramers-Henneberger and
Floquet approximation, in upper and lower bound estimates and fully numerical
solutions of the time dependent Schroedinger equation. The scaling invariance
leads to a differential equation which has to be satisfied by the ionization
probability and which yields an alternative criterium for the existence of
atomic bound state stabilization.Comment: 12 pages of Latex, one figur
High-harmonic generation from a confined atom
The order of high harmonics emitted by an atom in an intense laser field is
limited by the so-called cutoff frequency. Solving the time-dependent
Schr\"odinger equation, we show that this frequency can be increased
considerably by a parabolic confining potential, if the confinement parameters
are suitably chosen.
Furthermore, due to confinement, the radiation intensity remains high
throughout the extended emission range. All features observed can be explained
with classical arguments.Comment: 4 pages(tex files), 4 figures(eps files); added references and
comment
Enhancement of bichromatic high-harmonic generation with a high-frequency field
Using a high-frequency field superposed to a linearly polarized bichromatic
laser field composed by a wave with frequency and a wave with
frequency , we show it is possible to enhance the intensity of a
group of high harmonics in orders of magnitude. These harmonics have
frequencies about 30% higher than the monochromatic-cutoff frequency, and,
within the three-step-model framework, correspond to a set of electron
trajectories for which tunneling ionization is strongly suppressed. Particular
features in the observed enhancement suggest that the high-frequency field
provides an additional mechanism for the electron to reach the continuum. This
interpretation is supported by a time-frequency analysis of the harmonic yield.
The additional high frequency field permits the control of this group of
harmonics leaving all other sets of harmonics practically unchanged, which is
an advantage over schemes involving only bichromatic fields.Comment: 6 pages RevTex, 5 figures (ps files), Changes in text, figures,
references and equations include
Fluxo gênico em feijoeiro comum: ocorrência e possíveis conseqüências.
Neste documento é apresentada uma revisão sobre a capacidade de hibridização natural em Phaseolus vulgaris e suas conseqüências com relação à segurança ambiental do feijoeiro geneticamente modificado.bitstream/CNPAF/23818/1/doc_185.pd
Local dynamics in high-order harmonic generation using Bohmian trajectories
We investigate high-order harmonic generation from a Bohmian-mechanical
perspective, and find that the innermost part of the core, represented by a
single Bohmian trajectory, leads to the main contributions to the high-harmonic
spectra. Using time-frequency analysis, we associate this central Bohmian
trajectory to an ensemble of unbound classical trajectories leaving and
returning to the core, in agreement with the three step model. In the Bohmian
scenario, this physical picture builds up non-locally near the core via the
quantum mechanical phase of the wavefunction. This implies that the flow of the
wavefunction far from the core alters the central Bohmian trajectory. We also
show how this phase degrades in time for the peripheral Bohmian trajectories as
they leave the core region.Comment: 7 pages, 3 figures; the manuscript has been considerably extended and
modified with regard to the previous version
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