Berlin 2015 – scientific programme

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O: Fachverband Oberflächenphysik

O 11: Ultrafast and Nonlinear Plasmonics

O 11.2: Talk

Monday, March 16, 2015, 15:15–15:30, MA 004

Probing electron relaxation in single metal nanotips with terahertz-induced field emission — •Lara Wimmer, Georg Herink, Sergey V. Yalunin, and Claus Ropers — 4. Physical Institute - University of Göttingen, Göttingen, Germany

We implemented a streaking-type photoemission experiment at individual metal nanotips [1], employing single-cycle terahertz (THz) transients and femtosecond near-infrared (NIR) pulses. In a first scenario, the photoelectrons are generated by the NIR pulses and subsequently accelerated in the local THz electric field. Due to the high confinement of the THz-induced near-field at the tip apex, the photoelectrons leave the electric field in much less than one optical half-cycle [2]. This allows for a phase-resolved characterization of the THz near-field and for a control of the photoelectron kinetic energy spectra.

In a second set of measurements, we increase the local THz field strength to above 3 V/nm, inducing THz field emission [3]. Slightly below the threshold for cold field emission, the THz transient triggers the emission of NIR-excited hot electrons in the metal. The electron relaxation is quantitatively characterized by varying the relative time delay between the two pulses, and we find direct evidence for a confinement-induced prolongation of cooling times as compared with planar surfaces.

[1] Wimmer et al., Nature Physics 10, 432-436 (2014).

[2] Herink et al., Nature 483, 190-193 (2012).

[3] Herink et al., New Journal of Physics, in press (2014).