Dresden 2017 – scientific programme
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O: Fachverband Oberflächenphysik
O 28: Plasmonics and Nanooptics IV: Light-Matter Interaction
O 28.5: Talk
Tuesday, March 21, 2017, 11:30–11:45, TRE Ma
Resonant excitation of isolated helical nanostructures in the visible range — Katja Höflich2, Enno Hansjürgen1, Heiko Kollmann1, Silke Christiansen2, Christoph Lienau1, and •Martin Silies1 — 1AG Ultrafast Nano-Optics, Carl von Ossietzky Universität Oldenburg, Germany — 2Nanoscale Structures and Microscopic Analysis, Helmholtz-Zentrum Berlin, Germany
Circular dichroism is a phenomenon that describes the extinction difference in chiral objects when excited by left and right-handed circular polarized light. While the circular dichroism of single biomolecules is rather low, the signal can be enhanced by several orders of magnitude using artificial, i.e. plasmonic chiral nanostructures. Thus, the study of these plasmonic structures is a vivid field of research. Here, confocal white-light spectro-microscopy is employed to measure extinction spectra of single silver helices with sub-micrometer dimensions fabricated using electron beam induced deposition for left- and right-handed circular excitation. Circular dichroism spectra of isolated right-handed helices show - besides a near-IR resonance for light at the same handedness - a distinct resonance for left-handed circular polarized light in the visible range around 600 nm. While the resonant behavior for the right-handed circular polarized light is expected [1], the emergence of a pronounced left-handed resonance is surprising. Finite element modeling reliably reproduces the observed spectral features and suggests that a pseudo current at the outer surface of the helices locally switches the polarization state of the incident polarization. [1] Gansel et al. Science 325, 1513 (2009)