Dresden 2006 – scientific programme

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O: Oberflächenphysik

O 12: Methods

O 12.3: Talk

Monday, March 27, 2006, 15:30–15:45, WIL B321

Improvement of temporal resolution on Ultrafast Electron Diffraction (UED) experiments — •Matthias Wielens, Anja Hanisch, Boris Krenzer, and Michael Horn-von Hoegen — Universität Duisburg-Essen, Institut für Experimentelle Physik, Lotharstrasse 1, 47057 Duisburg

For Ultrafast Electron Diffraction experiments studying transient phenomena at surfaces and in bulks upon laser excitation a high temporal resolution is essential. In our surface sensitive Reflection High Energy Electron Diffraction setup the resolution is limited by the so called “velocity mismatch” between the velocity of light and the much lower velocity of high energy electrons. Due to their grazing incidence the electron pulse needs a few 10 ps to travel across the sample. The excitation by the fs laser pulses at normal incidence with the pulse front parallel to the surface, however, occurs instantaneously. Thus, temporal overlap is not given. In consequence, this leads to an averaging of the observation of transient phenomena during the time the electron pulse probes the sample.
A solution to this problem is to tilt the pulse front of the laser pulses with respect to the propagation direction at such an angle that ensures temporal overlap between the pulse fronts of the two beams. For 10 keV electrons with a grazing angle of incidence of 5^∘ this requires a tilt angle of almost 80^∘!
We present an experimental setup that facilitates such a large tilt angles and will demonstrate the improvement in temporal resolution of our ultrafast electron diffraction setup.