230 research outputs found
Electron-Ion Interaction Effects in Attosecond Time-Resolved Photoelectron Spectra
Photoionization by attosecond (as) extreme ultraviolet (xuv) pulses into the
laser-dressed continuum of the ionized atom is commonly described in
strong-field approximation (SFA), neglecting the Coulomb interaction between
the emitted photoelectron (PE) and residual ion. By solving the time-dependent
Sch\"{o}dinger equation (TDSE), we identify a temporal shift in
streaked PE spectra, which becomes significant at small PE energies. Within an
eikonal approximation, we trace this shift to the combined action of Coulomb
and laser forces on the released PE, suggesting the experimental and
theoretical scrutiny of their coupling in streaked PE spectra. The initial
state polarization effect by the laser pulse on the xuv streaked spectrum is
also examined.Comment: 9 pages, Accepted by Phys. Rev.
Extended Classical Over-Barrier Model for Collisions of Highly Charged Ions with Conducting and Insulating Surfaces
We have extended the classical over-barrier model to simulate the
neutralization dynamics of highly charged ions interacting under grazing
incidence with conducting and insulating surfaces. Our calculations are based
on simple model rates for resonant and Auger transitions. We include effects
caused by the dielectric response of the target and, for insulators, localized
surface charges. Characteristic deviations regarding the charge transfer
processes from conducting and insulating targets to the ion are discussed. We
find good agreement with previously published experimental data for the image
energy gain of a variety of highly charged ions impinging on Au, Al, LiF and KI
crystals.Comment: 32 pages http://pikp28.uni-muenster.de/~ducree
Dielectric response effects in attosecond time-resolved streaked photoelectron spectra of metal surfaces
The release of conduction-band electrons from a metal surface by a
sub-femtosecond extreme ultraviolet (XUV) pulse, and their propagation through
the solid, provokes a dielectric response in the solid that acts back on the
photoelectron wave packet. We calculated the (wake) potential associated with
this photoelectron self-interaction in terms of bulk and surface plasmon
excitations and show that it induces a considerable, XUV-frequency-dependent
temporal shift in laser-streaked XUV photoemission spectra, suggesting the
observation of the ultrafast solid-state dielectric response in contemporary
streaked photoemission experiments.Comment: 4 pages and 4 figures, submitted to PR
Excitation and relaxation in atom-cluster collisions
Electronic and vibrational degrees of freedom in atom-cluster collisions are
treated simultaneously and self-consistently by combining time-dependent
density functional theory with classical molecular dynamics. The gradual change
of the excitation mechanisms (electronic and vibrational) as well as the
related relaxation phenomena (phase transitions and fragmentation) are studied
in a common framework as a function of the impact energy (eV...MeV). Cluster
"transparency" characterized by practically undisturbed atom-cluster
penetration is predicted to be an important reaction mechanism within a
particular window of impact energies.Comment: RevTeX (4 pages, 4 figures included with epsf
Enhanced high-harmonic generation from chromium-doped magnesium oxide
High-order harmonic generation (HHG) from crystals offers a new source of
coherent extreme ultraviolet (XUV) attosecond radiation.Comment: Significant change of conten
Validation of theory-based models for the control of plasma currents in W7-X divertor plasmas
A theory-based model for the control of plasma currents for steady-state operation in W7-X is proposed and intended for model-based plasma control. The conceptual outline implies the strength of physics-based models: it offer approaches applicable to future conditions of fusion devices or next-step machines. The application at extrapolated settings is related to the validity range of the theory model. Therefore, the predictive power of theory-based control models could be larger than for data-driven approaches and limitations can be predicted from the validity range for the prediction of bootstrap currents in W7-X. The model predicts the L/R response when density or heating power is changed. The model is based on neoclassical bootstrap current calculations and validated for different discharge conditions. While the model was found to be broadly applicable for conducted electron-cyclotron-heated discharges in W7-X, limits were found for cases when the polarization of the electron cyclotron heating was changed from X2 to O2-heating. The validity assessment attempts to quantify the potential of the derived model for model-based control in the operational space (density, heating power) of W7-X
- …