174 research outputs found
Energy Correlation in Above-Threshold Nonsequential Double Ionization at 800 nm
We have investigated the energy correlation of the two electrons from
nonsequential double ionization of helium atom in 800 nm laser fields at
intensities below the recollision threshold by quantum calculations. The
circular arcs structure of the correlated electron momentum spectra reveals a
resonant double ionization process in which the two electrons transit from
doubly excited states into continuum states by simultaneously absorbing and
sharing excess energy in integer units of the photon energy. Coulomb repulsion
between the two electrons in continuum states is responsible for the dominant
back-to-back electron emission and two intensity-independent cutoffs in the
two-electron energy spectra.Comment: 6 pages, 4 figure
Asymmetric electron energy sharing in strong-field double ionization of helium
With the classical three-dimensional ensemble model, we have investigated the
microscopic recollision dynamics in nonsequential double ionization of helium
by 800 nm laser pulses at 2.0 PW/cm^2. We demonstrate that the asymmetric
energy sharing between the two electrons at recollision plays a decisive role
in forming the experimentally observed V-shaped structure in the correlated
longitudinal electron momentum spectrum at the high laser intensity [Phys. Rev.
Lett. 99, 263003 (2007)]. This asymmetric energy sharing recollision leaves
footprints on the transverse electron momentum spectra, which provide a new
insight into the attosecond three-body interactions
Enhanced dissociation of H2+ into highly excited states via laser-induced sequential resonant excitation
We study the dissociation of H in uv laser pulses by solving the
non-Born-Oppenheimer time-dependent Schr\"{o}dinger equation as a function of
the photon energy of the pulse. Significant enhancements of the
dissociation into highly excited electronic states are observed at critical
. This is found to be attributed to a sequential resonant excitation
mechanism where the population is firstly transferred to the first excited
state by absorbing one photon and sequentially to higher states by absorbing
another one or more photons at the same internuclear distance. We have
substantiated the underlying dynamics by separately calculating the nuclear
kinetic energy spectra for individual dissociation pathways through different
electronic states
Anomalous isotopic effect on electron-directed reactivity by a 3-{\mu}m midinfrared pulse
We have theoretically studied the effect of nuclear mass on electron
localization in dissociating H_2^+ and its isotopes subjected to a few-cycle
3-{\mu}m laser pulse. Compared to the isotopic trend in the near-infrared
regime, our results reveal an inverse isotopic effect in which the degree of
electron-directed reactivity is even higher for heavier isotopes. With the
semi-classical analysis, we find, for the first time, the pronounced electron
localization is established by the interferences through different channels of
one- and, more importantly, higher-order photon coupling. Interestingly, due to
the enhanced high-order above-threshold dissociation of heavier isotopes, the
interference maxima gradually become in phase with growing mass and ultimately
lead to the anomalous isotopic behavior of the electron localization. This
indicates that the multi-photon coupling channels will play an important role
in controlling the dissociation of larger molecules with midinfrared pulses.Comment: 5 pages, 4 figure
Multiphoton Rabi Oscillations of Correlated Electrons in Strong Field Nonsequential Double Ionization
With quantum calculations, we have investigated the multiphoton nonsequential
double ionization of helium atoms in intense laser fields at ultraviolet
wavelengths. Very surprisingly, we find a so-far unobserved double-circle
structure in the correlated electron momentum spectra. The double-circle
structure essentially reveals multiphoton Rabi oscillations of two electrons,
which are strongly supported by the oscillating population of a certain doubly
excited state and by the oscillating double ionization signals. This
two-electron multiphoton Rabi effect provides profound understandings of
electronic correlations and complicated multiphoton phenomena and is expected
to be a new tool for broad applications, such as quantum coherent control.Comment: 5 pages, 5 figure
Revealing the role of electron correlation in sequential double ionization
The experimental observations of sequential double ionization (SDI) of Ar [A.
N. Pfeiffer {\it et al.}, Nature Phys. {\bf 7}, 428 (2011)], such as the
four-peak momentum distribution and the ionization time of the first and second
electrons, are investigated and reproduced with a quantum model by including
and excluding the - correlation effect. Based on the comparison of
experiment and simulation, the role of - correlation in SDI is discussed.
It is shown that the inclusion of - correlation is necessary to reproduce
the momentum distribution of electrons.Comment: 14 pages, 5 figures, submitte
Revealing Correlated Electron-Nuclear Dynamics in Molecules with Energy-Resolved Population Image
We explore a new fashion, named energy-resolved population image (EPI), to
represent on an equal footing the temporary electronic transition and nuclear
motion during laser-molecular interaction. By using the EPI we have intuitively
demonstrated the population transfer in vibrational H exposed to extreme
ultraviolet pulses, revealing the energy sharing rule for the correlated
electron and nuclei. We further show that the EPI can be extended to uncover
the origins of the distinct energy sharing mechanisms in multi-photon and
tunneling regimes. The present study has clarified a long-standing issue about
the dissociative ionization of H and paves the way to identify
instantaneous molecular dynamics in strong fields
Isolated sub-100-attosecond pulse generation via controlling electron dynamics
A new method to coherently control the electron dynamics is proposed using a
few-cycle laser pulse in combination with a controlling field. It is shown that
this method not only broadens the attosecond pulse bandwidth, but also reduces
the chirp, then an isolated 80-as pulse is straightforwardly obtained and even
shorter pulse is achievable by increasing the intensity of the controlling
field. Such ultrashort pulses allow one to investigate ultrafast electronic
processes which have never be achieved before. In addition, the few-cycle
synthesized pulse is expected to manipulate a wide range of laser-atom
interactions.Comment: 11 pages, 4 figure
Molecular orbital tomography beyond the plane wave approximation
The use of plane wave approximation in molecular orbital tomography via
high-order harmonic generation has been questioned since it was proposed, owing
to the fact that it ignores the essential property of the continuum wave
function. To address this problem, we develop a theory to retrieve the valence
molecular orbital directly utilizing molecular continuum wave function which
takes into account the influence of the parent ion field on the continuum
electrons. By transforming this wave function into momentum space, we show that
the mapping from the relevant molecular orbital to the high-order harmonic
spectra is still invertible. As an example, the highest orbital of
is successfully reconstructed and it shows good agreement with
the \emph{ab initio} orbital. Our work clarifies the long-standing controversy
and strengthens the theoretical basis of molecular orbital tomography
Interference of high-order harmonics generated from molecules at different alignment angles
We theoretically investigate the interference effect of high-order harmonics
generated from molecules at different alignment angles. It is shown that the
interference of the harmonic emissions from molecules aligned at different
angles can significantly modulate the spectra and result in the anomalous
harmonic cutoffs observed in a recent experiment [ Nature Phys. 7, 822 (2011)
]. The shift of the spectral minimum position with decreasing the degree of
alignment is also explained by the interference effect of the harmonic
emissions.Comment: 6 pages,5 figures,journa
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