Regensburg 2016 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 11: Plasmonics and Nanooptics II: Microscopy

O 11.8: Vortrag

Montag, 7. März 2016, 17:00–17:15, S054

Nanoscale probing of optical near-fields by ultrafast transmission electron microscopy — •Armin Feist, Katharina E. Echternkamp, Murat Sivis, Sascha Schäfer, and Claus Ropers — 4th Physical Institute, University of Göttingen, Göttingen, Germany

Ultrafast transmission electron microscopy (UTEM) allows for the study of structural and electronic dynamics on nanometer length scales [1], as well as for the local probing of optical near-fields [2].

Here, we employ the inelastic scattering of swift electrons to characterize optical near-fields in metallic nanostructures. The experiments utilize a novel short-pulsed electron gun driven by localized photoemission from a nanotip emitter, yielding electron probes with a pulse duration of 300 fs and beam diameters down to 1.5 nm.

In the interaction with optical near-fields, the energy spectra of free electrons develop into a comb of spectral sidebands representing the absorption and emission of multiple photons [2]. The quantum coherence of this process is evidenced by the observation of multilevel Rabi oscillations in the sideband populations [3]. The interaction facilitates few nanometer spatial resolution in near-field imaging, as demonstrated by raster-scanning the focused electron probe across resonantly excited plasmonic nanostructures with feature sizes down to 5 nm.

[1] A.H. Zewail, Science, 328, 187 (2010).

[2] B. Barwick et al., Nature, 462, 902 (2009).

[3] A. Feist et al., Nature, 521, 200 (2015).