Regensburg 2007 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 6: Symposium: Ultrafast Nanooptics I
O 6.1: Hauptvortrag
Montag, 26. März 2007, 11:15–11:45, H38
A nanometer-sized femtosecond electron source — •Christoph Lienau1,2, Claus Ropers2, Daniel Solli2, Claus Peter Schulz2, and Thomas Elsaesser2 — 1Institut für Physik, Carl von Ossietzky Universität Oldenburg — 2Max-Born-Institut, Berlin
Femtosecond electron and X-ray diffraction are currently among the most intriguing topics in ultrafast science, allowing for probing structural dynamics of molecular and solid state systems with previously unachievable temporal resolution. In electron diffraction, overcoming temporal smearing due to spatial propagation effects and to Coulomb repulsion of electron bunches produced at kHz repetition rates presents a considerable experimental challenge. Ultimately, therefore, a point-like source of single electrons with temporal resolution in the regime of few femtoseconds would be highly desirable.
In this paper, we describe and demonstrate a novel approach towards realizing such a point-like ultrafast electron source. By illuminating ultrasharp gold tips with 7-fs pulses from an 80 MHz Ti:sapphire oscillator, we induce emission of an intense flux of up to 10^7 electrons per second. Due to the local field enhancement this emission is strongly localized at the apex of the metallic tip with a radius of curvature of only few tens of nanometers. We demonstrate the multiphoton character of the electron generation from a highly non-equilbrium electron distribution and report on quantitative measurements of the transient distribution function. The results of first imaging experiments using this novel electron source will be presented, demonstrating near-field imaging of local electric fields with sub-20 nm spatial resolution.