Your search for "Uwe Thumm" returned 17 results

We calculate the time delay between photoemitted conduction-band and core-level electrons of a tungsten surface [1].

We study the pump-laser-induced nuclear dynamics in diatomic molecules in different electronic states by calculating the evolution of nuclear wave packets, starting with an initial Franck-Condon distribution.

We calculated the dynamic image potential of photoelectrons near an Al surface and show that this electronic self-interaction induces a considerable, XUV-frequency-dependent temporal shift in laser-streaked XUV photoemission spectra.

We present a new method to extract momentum distributions from time-dependent wavepacket calculations. In contrast to established Fourier transformation of the spatial wavepacket at a fixed time, the proposed 'virtual detector' method examines the time dependence of the wavepacket at a fixed position. In first applications to the ionization of model atoms and the dissociation of H₂⁺, we find a significant reduction of computing time and are able to extract reliable fragment momentum distributions by using a comparatively small spatial numerical grid for the time-dependent wavefunction.

Based on the numerical solutions of the time-dependent Schrödinger equation within the single-active-electron approximation, we propose a method for observing instantaneous atomic level shifts in an oscillating strong infrared (IR) field with sub-IR-cycle time resolution, by using a single tunable attosecond (SA) pulse to probe excited states of the perturbed atom. The ionization probability in the combined fields depends on both the frequency of the attosecond pulse and the time delay between both pulses, since the IR field periodically shifts SA-pulse-excited energy levels into and out of resonance.

By solving the time dependent Schrödinger equation for H₂⁺ in a pump-probe numerical experiment, we found that the electronic motion can follow or oppose the laser electric force. Our results show that the internal electron dynamics in H₂⁺ is determined by both, the external laser field and intra-molecular electron diffraction.

We apply a quantum-mechanical model to simulate infrared-streaked photoelectron emission by an ultrashort extreme ultraviolet pulse from adsorbate-covered metal surfaces. Incorporating effects of energy- dependent electron mean-free paths, the properties of initial states, photoelectron energy dispersion, and the screening of the streaking field, this model is able to reproduce recently measured photoelectron spectrograms and adsorbate-thickness-dependent photoemission time delays.

To study time-resolved photoemission from gold nanospheres, we introduce a semi-analytical quantum- mechanical model, including the plasmonic near-field-enhancement of the streaking field at the surface of the nanosphere. For an 800 nm incident near infrared (NIR) pulse and 10 nm diameter gold nanosphere, we find that the presence of the nanoplasmonic field enhances the oscillation amplitude by a factor of 3.

Upon ionization of ground state O₂ molecules in a short XUV pulse, we observe a time-dependent vibrational wave packet in the potential of the binding O⁺₂ (a⁴Π_u) state. Our pump–probe delay dependent kinetic-energy-release (KER) spectra are in qualitative agreement with the results of coupled-channel simulations that are based on calculated Born-Oppenheimer potential-energy curves (PECs). Using a Morse potential adjusted to the experimental data most features of the experimental spectra are reproduced quantitatively.

We study two-photon double ionization of helium by short XUV pulses by numerically solving the time-dependent Schrodinger equation in full dimensionality within a finite-element discrete-variable-representation scheme. Based on the emission asymmetries in joint photoelectron angular distributions, we identify sequential and non-sequential contributions to two-photon double ionization for ultrashort pulses whose spectrum overlaps the sequential (ħω > 54.4 eV) and non-sequential (39.5 eV < ħω < 54.4 eV) double-ionization regimes.