We investigate the geometric and electronic structure of various surfaces and their response to the excitation by femtosecond laser pulses. The research topics range from single electron dynamics at ferromagnetic metal and semiconductor surfaces to the collective response of the electronic system to intense laser excitation close to or above the ablation threshold. Thereby the coupling of electronic excitations to nuclear motion, including vibrations, phase transitions and eventually material removal is studied. The latter bridges the gap between fundamental science and technology.

Ongoing activities can be grouped into two main topics

1. Time-resolved photoelectron spectroscopy
   A first laser pulse excites the electronic system, while a second pulse (laser or synchrotron) probes the transient response at variable time delay. Due to the finite escape depth of the photoelectrons the technique is sensitive to the first few surface layers.
   

   Electron dynamics at semiconductor surfaces
   Jens Kopprasch, Kristof Zielke, and Christian Eickhoff

   Ultrafast vs. equilibrium phase transitions
   Beatrice Andres, Marko Wietstruk, and Kristian Döbrich
   supported by DFG
   in collaboration with Markus Donath and Anke Schmidt (Univ. Münster)

   Time-of-flight spectroscopy
   Jens Kopprasch, Thomas Kunze, and Martin Teichmann
   in collaboration with SPECS GmbH

   Time-resolved photoemission with Higher Harmonics
   Robert Carley, Kristian Döbrich, Cornelius Gahl, and Martin Teichmann
   supported by DFG
   in collaboration with the HHG group at BESSY.




2. Smart materials
   such as molecular switches, nanoparticles, and femtosecond-laser structured oxides
   

Carrier relaxation and switching efficiency of
photochrome molecular ensembles at surfaces
Roland Schmidt, Daniel Brete, Wolfgang Freyer, Robert Carley, Stefanie Wagner, and Cornelius Gahl
supported by DFG within Sfb 658
Elementary Processes in Molecular Switches at Surfaces
Photochromic materials are synthesized in our chemistry laboratory

Material Structuring with Femtosecond Technology
Sandra Höhm, Alexandre Mermillod, and Arkadi Rosenfeld
supported by DFG, International Office of the DFG (WTZ program with the Institute of Thermophysics, Novosibirsk, Russia)