1,893 research outputs found
Spatial separation of large dynamical blue shift and harmonic generation
We study the temporal and spatial dynamics of the large amplitude and
frequency modulation that can be induced in an intense, few cycle laser pulse
as it propagates through a rapidly ionizing gas. Our calculations include both
single atom and macroscopic interactions between the non-linear medium and the
laser field. We analyze the harmonic generation by such pulses and show that it
is spatially separated from the ionization dynamics which produce a large
dynamical blue shift of the laser pulse. This means that small changes in the
initial laser focusing conditions can lead to large differences in the laser
frequency modulation, even though the generated harmonic spectrum remains
essentially unchanged.Comment: 4 pages, 5 figures. Under revisio
Coulomb focusing at above-threshold ionization in elliptically polarized mid-infrared strong laser fields
The role of Coulomb focusing in above-threshold ionization in an elliptically
polarized mid-infrared strong laser field is investigated within a
semiclassical model incorporating tunneling and Coulomb field effects. It is
shown that Coulomb focusing up to moderate ellipticity values is dominated by
multiple forward scattering of the ionized electron by the atomic core that
creates a characteristic low-energy structure in the photoelectron spectrum and
is responsible for the peculiar energy scaling of the ionization normalized
yield along the major polarization axis. At higher ellipticities, the electron
continuum dynamics is disturbed by the Coulomb field effect mostly at the exit
of the ionization tunnel. Due to the latter, the normalized yield is found to
be enhanced, with the enhancement factor being sharply pronounced at
intermediate ellipticities
Cross-Sections of Large-Angle Hadron Production in Proton- and Pion-Nucleus Interactions V: Lead Nuclei and Beam Momenta from +/-3 Gev/c to +/-15 Gev/c
We report on double-differential inclusive cross-sections of the production
of secondary protons, charged pions, and deuterons, in the interactions with a
5% nuclear interaction length thick stationary lead target, of proton and pion
beams with momentum from +/-3 GeV/c to +/-15 GeV/c. Results are given for
secondary particles with production angles 20 to 125 degrees. Cross-sections on
lead nuclei are compared with cross-sections on beryllium, copper, and tantalum
nuclei.Comment: 67 pages, 13 figures, 47 table
Comparison of Geant4 hadron generation with data from the interactions with beryllium nuclei of +8.9 GeV/c protons and pions, and of -8 GeV/c pions
Hadron generation in the Geant4 simulation tool kit is compared with
inclusive spectra of secondary protons and pions from the interactions with
beryllium nuclei of +8.9 GeV/c protons and pions, and of -8.0 GeV/c pions. The
data were taken in 2002 at the CERN Proton Synchrotron with the HARP
spectrometer. We report on significant disagreements between data and simulated
data especially in the polar-angle distributions of secondary protons and
pions.Comment: 15 pages, 13 figure
New determination of structure parameters in strong field tunneling ionization theory of molecules
In the strong field molecular tunneling ionization theory of Tong et al.
[Phys. Rev. A 66, 033402 (2002)], the ionization rate depends on the asymptotic
wavefunction of the molecular orbital from which the electron is removed. The
orbital wavefunctions obtained from standard quantum chemistry packages in
general are not good enough in the asymptotic region. Here we construct a
one-electron model potential for several linear molecules using density
functional theory (DFT). We show that the asymptotic wavefunction can be
improved with an iteration method and after one iteration accurate asymptotic
wavefunctions and structure parameters are determined. With the new parameters
we examine the alignment-dependent tunneling ionization probabilities for
several molecules and compare with other calculations and with recent
measurements, including ionization from inner molecular orbitals
Momentum Analysis in Strong-field Double Ionization
We provide a basis for the laser intensity dependence of the momentum
distributions of electrons and ions arising from strong-field non-sequential
double ionization (NSDI) at intensities in the range . To do this we use a completely classical method introduced previously
\cite{ho-etal05}. Our calculated results reproduce the features of experimental
observations at different laser intensities and depend on just two distinct
categories of electon trajectories.Comment: 5 pages, 7 figure
Influence of molecular symmetry on strong-field ionization: Studies on ethylene, benzene, fluorobenzene, and chlorofluorobenzene
Using the molecular strong-field approximation we consider the effects of
molecular symmetry on the ionization of molecules by a strong, linearly
polarized laser pulse. Electron angular distributions and total ionization
yields are calculated as a function of the relative orientation between the
molecule and the laser polarization. Our studies focus on ethylene
(CH), benzene (CH), fluorobenzene (CHF), and ortho
chlorofluorobenzene (1,2 CHClF), the molecules representing four
different point groups. The results are compared with experiments, when
available, and with the molecular tunneling theory appropriately extended to
non-linear polyatomic molecules. Our investigations show that the orientational
dependence of ionization yields is primarily determined by the nodal surface
structure of the molecular orbitals.Comment: 13 pages, 10 figures. Submitted to Physical Review
Cross-sections of large-angle hadron production in proton-- and pion--nucleus interactions VIII: aluminium nuclei and beam momenta from {\pm}3 GeV/c to {\pm}15 GeV/c
We report on double-differential inclusive cross-sections of the production
of secondary protons, charged pions, and deuterons, in the interactions with a
5% {\lambda}int thick stationary aluminium target, of proton and pion beams
with momentum from \pm3 GeV/c to \pm15 GeV/c. Results are given for secondary
particles with production angles between 20 and 125 degrees. Cross-sections on
aluminium nuclei are compared with cross-sections on beryllium, carbon, copper,
tin, tantalum and lead nuclei.Comment: 71 pages, 16 figures, 47 table
Enhancement of vibrational excitation and dissociation of H+2 in infrared laser pulses
We study vibrational excitations, dissociation, and ionization of Hþ2 in few-cycle laser pulses over a broad wavelength regime. Our results of numerical simulations supported by model calculations show a many orders-of-magnitude enhancement of vibrational excitation and dissociation (over ionization) of the molecular ion at infrared wavelengths. The enhancement occurs without any chirping of the pulse, which was previously applied to take account of the anharmonicity of the molecular vibrations. The effect is related to strong-field two- and higher-order photon transitions between different vibrational states
Cross-sections of large-angle hadron production in proton- and pion-nucleus interactions VI: carbon nuclei and beam momenta from \pm 3 GeV/c to \pm 15 GeV/c
We report on double-differential inclusive cross-sections of the production
of secondary protons, charged pions, and deuterons, in the interactions with a
5% nuclear interaction length thick stationary carbon target, of proton and
pion beams with momentum from \pm 3 GeV/c to \pm 15 GeV/c. Results are given
for secondary particles with production angles between 20 and 125 degrees.
Cross-sections on carbon nuclei are compared with cross-sections on beryllium,
copper, tantalum and lead nuclei.Comment: 67 pages, 13 figure
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