2,177 research outputs found
Relativistic mask method for electron momentum distributions after ionization of hydrogen-like ions in strong laser fields
Wavefunction-splitting or mask method, widely used in the non-relativistic
calculations of the photoelectron angular distributions, is extended to the
relativistic domain within the dipole approximation. Since the closed-form
expressions for the relativistic Volkov states are not available within the
dipole approximation, we build such states numerically solving a single
second-order differential equation. We calculate the photoelectron energy
spectra and angular distributions for highly charged ions under different
ionization regimes with both the direct and the relativistic mask methods. We
show that the relativistic mask method works very well and reproduces the
electron energy and angular distributions calculated by the direct method in
the energy range where both methods can be used. On the other hand, the
relativistic mask method can be applied for longer laser pulses and/or higher
photoelectron energies where the direct method may have difficulties
Theory of high-order harmonic generation from molecules by intense laser pulses
We show that high-order harmonics generated from molecules by intense laser
pulses can be expressed as the product of a returning electron wave packet and
the photo-recombination cross section (PRCS) where the electron wave packet can
be obtained from simple strong-field approximation (SFA) or from a companion
atomic target. Using these wave packets but replacing the PRCS obtained from
SFA or from the atomic target by the accurate PRCS from molecules, the
resulting HHG spectra are shown to agree well with the benchmark results from
direct numerical solution of the time-dependent Schr\"odinger equation, for the
case of H in laser fields. The result illustrates that these powerful
theoretical tools can be used for obtaining high-order harmonic spectra from
molecules. More importantly, the results imply that the PRCS extracted from
laser-induced HHG spectra can be used for time-resolved dynamic chemical
imaging of transient molecules with temporal resolutions down to a few
femtoseconds.Comment: 10 pages, 5 figure
Sfermion Pair Production in Polarized and Unpolarized Collisions
We calculate total and differential cross sections for the production of
sfermion pairs in photon-photon collisions, including contributions from
resolved photons and arbitrary photon polarization. Sfermion production in
photon collisions depends only on the sfermion mass and charge. It is thus
independent of the details of the SUSY breaking mechanism, but highly sensitive
to the sfermion charge. We compare the total cross sections for bremsstrahlung,
beamstrahlung, and laser backscattering photons to those in
annihilation. We find that the total cross section at a polarized photon
collider is larger than the annihilation cross section up to the
kinematic limit of the photon collider.Comment: 19 pages, Latex, 18 (e)ps-figure
Spontaneous vacuum decay in low-energy collisions of heavy nuclei beyond the monopole approximation
The problem of spontaneous vacuum decay in low-energy collisions of heavy
nuclei is considered beyond the scope of the monopole approximation. The
time-dependent Dirac equation is solved in a rotating coordinate system with
-axis directed along the internuclear line and the origin placed at the
center of mass. The probabilities of electron-positron pair creation and the
positron energy spectra are calculated in the approximation neglecting the
rotational coupling. The two-center potential is expanded over spherical
harmonics and the convergence with respect to the number of terms in this
expansion is studied. The results show that taking into account the two-center
potential instead of its spherically symmetric part preserves all the
signatures of the transition to the supercritical regime that have been found
in the framework of the monopole approximation and even enhances some of them.Comment: 7 pages, 4 figures, 1 tabl
Gold-plated processes at photon colliders
We review the most important topics and objectives of the physics program of
the gamma-gamma, gamma-electron collider (photon collider) option for an e+e-
linear collider.Comment: 36 pages, Latex, 11 figures(ps,eps), Talk at Intern. Workshop on High
Energy Photon Colliders; June 14-17, 2000, DESY, Hamburg, Germany; to be
published in Nucl. Instr. and Methods
Photo-electron momentum spectra from minimal volumes: the time-dependent surface flux method
The time-dependent surface flux (t-SURFF) method is introduced for computing
of strong-field infrared photo-ionization spectra of atoms by numerically
solving the time-dependent Schr\"odinger equation on minimal simulation
volumes. The volumes only need to accommodate the electron quiver motion and
the relevant range of the atomic binding potential. Spectra are computed from
the electron flux through a surface, beyond which the outgoing flux is absorbed
by infinite range exterior complex scaling (irECS). Highly accurate infrared
photo-electron spectra are calculated in single active electron approximation
and compared to literature results. Detailed numerical evidence for performance
and accuracy is given. Extensions to multi-electron systems and double
ionization are discussed.Comment: 18 pages, 5 figure
Backward scattering of low-energy antiprotons by highly charged and neutral uranium: Coulomb glory
Collisions of antiprotons with He-, Ne-, Ni-like, bare, and neutral uranium
are studied theoretically for scattering angles close to 180 and
antiproton energies with the interval 100 eV -- 10 keV. We investigate the
Coulomb glory effect which is caused by a screening of the Coulomb potential of
the nucleus and results in a prominent maximum of the differential cross
section in the backward direction at some energies of the incident particle. We
found that for larger numbers of electrons in the ion the effect becomes more
pronounced and shifts to higher energies of the antiproton. On the other hand,
a maximum of the differential cross section in the backward direction can also
be found in the scattering of antiprotons on a bare uranium nucleus. The latter
case can be regarded as a manifestation of the screening property of the
vacuum-polarization potential in non-relativistic collisions of heavy
particles.Comment: 14 pages, 5 figure
Hadronic Cross-sections in two photon Processes at a Future Linear Collider
In this note we address the issue of measurability of the hadronic
cross-sections at a future photon collider as well as for the two-photon
processes at a future high energy linear collider. We extend, to
higher energy, our previous estimates of the accuracy with which the \gamgam\
cross-section needs to be measured, in order to distinguish between different
theoretical models of energy dependence of the total cross-sections. We show
that the necessary precision to discriminate among these models is indeed
possible at future linear colliders in the Photon Collider option. Further we
note that even in the option a measurement of the hadron production
cross-section via \gamgam processes, with an accuracy necessary to allow
discrimination between different theoretical models, should be possible. We
also comment briefly on the implications of these predictions for hadronic
backgrounds at the future TeV energy collider CLIC.Comment: 20 pages, 5 figures, LaTeX. Added an acknowledgemen
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