129 research outputs found
Collisions of Slow Highly Charged Ions with Surfaces
Progress in the study of collisions of multiply charged ions with surfaces is
reviewed with the help of a few recent examples. They range from fundamental
quasi-one electron processes to highly complex ablation and material
modification processes. Open questions and possible future directions will be
discussed.Comment: 13 pages, 16 figures, review pape
Electron guiding through insulating nanocapillaries
We simulate the electron transmission through insulating Mylar (PET)
capillaries. We show that the mechanisms underlying the recently discovered
electron guiding are fundamentally different from those for ion guiding.
Quantum reflection and multiple near-forward scattering rather than the
self-organized charge-up are key to the transmission along the capillary axis
irrespective of the angle of incidence. We find surprisingly good agreement
with recent data. Our simulation suggests that electron guiding should also be
observable for metallic capillaries
Probing scattering phase shifts by attosecond streaking
Attosecond streaking is one of the most fundamental processes in attosecond
science allowing for a mapping of temporal (i.e. phase) information on the
energy domain. We show that on the single-particle level attosecond streaking
time shifts contain spectral phase information associated with the
Eisenbud-Wigner-Smith (EWS) time delay, provided the influence of the streaking
infrared field is properly accounted for. While the streaking phase shifts for
short-ranged potentials agree with the associated EWS delays, Coulomb
potentials require special care. We show that the interaction between the
outgoing electron and the combined Coulomb and IR laser fields lead to a
streaking phase shift that can be described classically
Simulation of attosecond streaking of electrons emitted from a tungsten surface
First time-resolved photoemission experiments employing attosecond streaking
of electrons emitted by an XUV pump pulse and probed by a few-cycle NIR pulse
found a time delay of about 100 attoseconds between photoelectrons from the
conduction band and those from the 4f core level of tungsten. We present a
microscopic simulation of the emission time and energy spectra employing a
classical transport theory. Emission spectra and streaking images are well
reproduced. Different contributions to the delayed emission of core electrons
are identified: larger emission depth, slowing down by inelastic scattering
processes, and possibly, energy dependent deviations from the free-electron
dispersion. We find delay times near the lower bound of the experimental data
Semiclassical two-step model for strong-field ionization
We present a semiclassical two-step model for strong-field ionization that
accounts for path interferences of tunnel-ionized electrons in the ionic
potential beyond perturbation theory. Within the framework of a classical
trajectory Monte-Carlo representation of the phase-space dynamics, the model
employs the semiclassical approximation to the phase of the full quantum
propagator in the exit channel. By comparison with the exact numerical solution
of the time-dependent Schr\"odinger equation for strong-field ionization of
hydrogen, we show that for suitable choices of the momentum distribution after
the first tunneling step, the model yields good quantitative agreement with the
full quantum simulation. The two-dimensional photoelectron momentum
distributions, the energy spectra, and the angular distributions are found to
be in good agreement with the corresponding quantum results. Specifically, the
model quantitatively reproduces the fan-like interference patterns in the
low-energy part of the two-dimensional momentum distributions as well as the
modulations in the photoelectron angular distributions.Comment: 31 pages, 7 figure
Simulation of guiding of multiply charged projectiles through insulating capillaries
Recent experiments have demonstrated that highly charged ions can be guided
through insulating nanocapillaries along the direction of the capillary axis
for a surprisingly wide range of injection angles. Even more surprisingly, the
transmitted particles remain predominantly in their initial charge state, thus
opening the pathway to the construction of novel ion-optical elements without
electric feedthroughs. We present a theoretical treatment of this
self-organized guiding process. We develop a classical trajectory transport
theory that relates the microscopic charge-up with macroscopic material
properties. Transmission coefficients, angular spread of transmitted particles,
and discharge characteristics of the target are investigated. Partial agreement
with experiment is found
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