THz streaking at metal nanotips
von Lara Simone Wimmer
Datum der mündl. Prüfung:2018-01-30
Erschienen:2018-03-20
Betreuer:Prof. Dr. Claus Ropers
Gutachter:Prof. Dr. Claus Ropers
Gutachter:Prof. Dr. Stefan Mathias
Dateien
Name:Wimmer.pdf
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Zusammenfassung
Englisch
This thesis addresses various aspects of terahertz (THz) streaking at metallic nanotips. In THz near-field streaking, electron pulses emitted by femtosecond near-infrared (NIR) pulses are accelerated in a THz-induced near-field at the tip apex. The energy of the electrons is measured in streaking spectrograms as a function of the relative time delay between the THz and the NIR pulses. The spatial confinement of the enhanced THz near-field facilitates characteristic electron dynamics, in which the electrons escape the near-field within a small fraction of an optical half-cycle. In the first part of this thesis, the influence of a static voltage onto the electron dynamics is investigated. The measurements show that a bias voltage applied to the tip acts as an additional control parameter of the spectrograms. For a spatiotemporal characterization of the near-field, the streaking spectrograms are simulated numerically using parameters such as the field strength at the tip surface and the spatial field decay length. In addition, the simulations enable the analysis of the electron trajectories and the study of the temporal evolution of the electron pulse in phase space demonstrating a control of the phase space volume. In a second study, THz streaking at plasmonic nanotapers is employed to determine the propagation velocity of plasmons. The experimental results are in agreement with simulations of the plasmon velocity as a function of the taper diameter. The possibilities of THz streaking at metal nanotips for the control and manipulation of electron pulses can be used for example in time-resolved electron microscopy and diffraction.
Keywords: nano-optics; terahertz radiation; streaking; metal nanotip; phase space; plasmonics; electron pulse control; photoemission