Berlin 2012 – scientific programme

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O: Fachverband Oberflächenphysik

O 3: Plasmonics and nanooptics I

O 3.5: Talk

Monday, March 26, 2012, 11:30–11:45, MA 005

Revealing nonlinear plasmon-photon interactions using k-space spectroscopy — •Jan Heckmann, Nicolai B. Grosse, and Ulrike Woggon — Institut für Optik und Atomare Physik, Technische Universität Berlin

Surface plasmon (SP) excitation in metal-dielectric structures is exemplified by an enhanced local electromagnetic field, which boosts nonlinear effects. Since the first demonstration of SP-related second-harmonic generation (SHG) by Simon et al., understanding the microscopic origin of the nonlinearity has remained an active research topic.

We propose that all permutations of plasmon (p) and photon (f) are allowed in the second-order nonlinear process of SHG (which can generate either p or f), and that each process can be identified by its own requirement for nonlinear k-vector-matching. Hence, the type of nonlinear interaction can be identified by resolving the SHG intensity as a function of exit angle, while the fundamental excitation angle is varied. To test this hypothesis, we built a k-space spectrograph that analysed SHG from a thin metal film in the Kretschmann geometry which was driven by femtosecond-pulsed laser light.

Our experimental results show that for excitation angles in the vicinity of the SHG peak, there is an off-diagonal component which is consistent with the signature of the pp-f interaction. This is in contrast to the purely photonic ff-f interaction which lies on the diagonal. Hence, in plasmon SHG, two plasmons at the fundamental frequency are annhiliated to create a second-harmonic photon.