Regensburg 2004 – scientific programme

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O: Oberflächenphysik

O 28: Postersitzung (Elektronische Struktur, Grenzfläche fest-flüssig, Halbleiteroberflächen und -grenzflächen, Magnetismus und Symposium SYXM, Methodisches, Nanostrukturen, Oberflächenreaktionen, Teilchen und Cluster, Zeitaufgelöste Spektroskopie)

O 28.74: Poster

Wednesday, March 10, 2004, 16:00–19:00, Bereich C

Space Charge Effects during Ultrashort Laser Pulse Photoemission Electron Microscopy — •D. Thien, M. Horn-von Hoegen, O. Heinz, P. Zhou, D. von der Linde, and F.-J. Meyer zu Heringdorf — Institut für Laser und Plasmaphysik, Universität Duisburg-Essen (Campus Essen), 45117 Essen

Visualization of the dynamics of electronic states in mesoscopic structures requires the simultaneous application of 3 different tools: Ultrashort fs-laser pulses offer time resolution, spectroscopy allows separation of different excited electronic states and Photoemission Electron Microscopy (PEEM) provides the crucial possibility to study surface areas on the nanoscale. We are currently combining an amplified Ti:Sapphire laser system (40fs pulses at 1kHz repetition rate), and a PEEM with imaging energy filter (ELMITEC) into a novel pump-probe experiment. While our laser oscillator (20fs, 80MHz) typically images excited electronic states via 2 Photon Photoemission, the amplifier system provides a greatly improved intensity of more than 10¹⁵W/cm² and opens the door for frequency conversion and photoemission experiments with photon energies of more than 30eV. The intense ultrashort pulses confine a great number of photoemitted electrons into a small area resulting in coulomb interaction. Here we analyze these space-charge effects using frequency doubled laser pulses on patterned in-situ grown low-workfunction Cs-layers on Si and SiO₂ substrates. At high photon flux we observe that the edges of our Cs-pads appear blurred. Subsequent reduction of the laser peak power leads to sharper edges as are also observed when the 80MHz oscillator is used for illumination.