Regensburg 2013 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 89: Surface Dynamics II

O 89.8: Vortrag

Freitag, 15. März 2013, 12:15–12:30, H33

Improving the Temporal Resolution of a Time Resolved Electron Diffraction Experiment with Tilted Laser Pulse Fronts — •Annika Kalus, Carla Streubühr, Tim Frigge, Anja Hanisch-Blicharski, Boris Krenzer, Manuel Ligges, Ping Zhou, Uwe Bovensiepen, Dietrich von der Linde, and Michael Horn-von Hoegen — Universität Duisburg-Essen, Fakultät für Physik und Center for Nanointegration Duisburg-Essen (CENIDE)

Time resolved reflection high energy electron diffraction (RHEED) is an ideal tool to study the response of the surface lattice upon femtosecond laser pulse excitation. To achieve ps time resolution a laser pulse is used in a pump probe setup to excite the sample and to generate an electron pulse via photoemission that probes the sample. The temporal resolution of the experiment is limited by the velocity mismatch between laser pump pulse and the probing electron pulse at grazing incidence. To compensate this mismatch we realized an optical setup to tilt the laser pulse front by 70° in order to achieve temporal and spatial overlap with the 30 keV electron pulse over the entire width of the sample. The tilted laser pulse was characterized by a cross-correlator based on second harmonic generation.

Using the thermal response of thin Pb films on Si(111) upon laser excitation we optimized the optical setup and determined an improved temporal resolution of less than 1.8 ps at 29 keV electron energy. Electron phonon coupling in Bi is much weaker and results in a slow down of the heating of thin Bi films: a time constant for the excitation of about 10 ps was observed.