Berlin 2015 – scientific programme

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O: Fachverband Oberflächenphysik

O 84: Focus Session: Structural Dynamics in Nanoscale Materials Probed by Ultrashort Electron Pulses

O 84.2: Talk

Thursday, March 19, 2015, 15:30–15:45, MA 005

Ultrafast transmission electron microscopy with nanoscopic electron sources — Armin Feist, Reiner Bormann, Katharina Echternkamp, Jakob Schauss, Nara Rubiano, •Sascha Schäfer, and Claus Ropers — 4th Physical Institute, University of Göttingen, Göttingen, Germany

Ultrafast transmission electron microscopy (UTEM) is a laser-pump/electron-probe technique, which promises to combine the ultrafast temporal resolution of pump-probe approaches with the spatial resolution of electron microscopy [1]. However, to harness the full capabilities of UTEM, novel laser-triggered electron sources are required, which deliver high-brightness sub-picosecond electron pulses.

Here, we present the development and application of an advanced UTEM instrument based on the custom modification of a commercial electron microscope. Specifically, we employ electron sources based on the localized photoemission [2] from a nanoscale needle photocathode. The enhanced optical field at the tip apex confines nonlinear photoemission to small emitter areas, enabling electron focal spot sizes on the sample of about 10 nm with electron pulse durations of less than 700 fs. First applications are presented, including time-resolved Lorentz microscopy and the nanoscale probing of quantum coherent interactions between free electrons and optical near-fields [3].

[1] A. H. Zewail, Science 328, 187-93 (2010). [2] M. Gulde, S. Schweda, G. Storeck, M. Maiti, H. K. Yu, A. M. Wodtke, S. Schäfer, C. Ropers, Science 345, 200-204 (2014). [3] A. Feist, K. Echternkamp, J. Schauss, S. V. Yalunin, S. Schäfer, C. Ropers, submitted.