Berlin 2005 – wissenschaftliches Programm
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O: Oberflächenphysik
O 5: Zeitaufgelöste Spektroskopie I
O 5.3: Vortrag
Freitag, 4. März 2005, 11:15–11:30, TU EB107
Second-harmonic generation from nanoscopic metal tips: Generalized symmetry selection rules for single nanostructures — •Catalin C. Neacsu1, Georg A. Reider2, and Markus B. Raschke1 — 1Max-Born-Insitut für Nichtlineare Optik und Kurzzeitspektroskopie, D-12489 Berlin — 2Institut für Photonik, Technische Universität Wien, A-1040 Wien
Second-harmonic generation from individual nanoscopic metal tips has been investigated. As a partially asymmetric (∞ m m) nanostructure with the mirror symmetry broken in the axial direction the tip geometry allows for the first time to directly distinguish otherwise inseparable local surface and nonlocal bulk second-harmonic polarizations. Distinct second-harmonic-emission directions and polarization selection rules are observed that are different compared not only to linear light scattering but also compared to SHG from both, planar interfaces as well as spherical or ellipsoidal nanoparticles. In addition, the local field enhancement at the tip apex has been quantified ranging from 8 to 25 for Au tips with radii of 50 nm down to 10 nm and drops significantly for W or PtIr as tip material. The large sensitivity of SHG with respect to this local field enhancement together with the new selection rules being generally applicable to partially asymmetric nanoscopic systems provide new degrees of freedom for surface-specific second-harmonic investigations of nanostructures and the optical coupling in scattering-type near-field microscopy.