Stuttgart 2012 – scientific programme

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Q: Fachverband Quantenoptik und Photonik

Q 54: Poster 3

Q 54.42: Poster

Thursday, March 15, 2012, 16:30–19:00, Poster.I+II

Tip-based electron source for femtosecond electron diffraction — •Jan-Paul Stein, Johannes Hoffrogge, Markus Schenk, Michael Krüger, Peter Baum, and Peter Hommelhoff — Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Strasse 1, 85748 Garching bei München

Illumination of a sharp tungsten tip with femtosecond laser pulses leads to the emission of ultrashort, high brightness electron pulses that are ideally suited for ultrafast electron diffraction (UED) experiments [1]. The tip’s small virtual source size (∼5 nm) results in a large transverse coherence length of the electron pulse and therefore better spatial resolution as compared to a conventional flat cathode design. The enhanced electric field at the tip apex (2 GV/m) is about two orders of magnitude larger than the maximum electric field applicable in a plate capacitor based setup (20 MV/m). This reduces the influence of the initial energy distribution on the pulse duration at the target and improves the timing jitter. Simulations show that a setup with a sharp tip as the cathode in combination with two anodes yields an electron pulse duration of about 50 fs at the sample. The electron energy is 30 keV and the gun to sample distance is 3 cm. We implemented the two anode setup with the tip experimentally. We will present the experimental characteristics of the emitted electron beam both in static field emission and in laser triggered emission.
P. Hommelhoff, C. Kealhofer et al., Ultramicroscopy 109, 423-429 (2009)