Regensburg 2010 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 53: Plasmonics and Nanooptics IV

O 53.2: Vortrag

Mittwoch, 24. März 2010, 15:15–15:30, H32

Quantifying Excitation and Radiation Rate Enhancement Provided by Near-field Optical Antennas — •Miriam Böhmler, Nicolai Hartmann, Carsten Georgi, and Achim Hartschuh — Department Chemie und Biochemie & CENS, Ludwig-Maximilians-Universität, 81377 München

Tip-enhanced near-field optical microscopy provides nanoscale optical resolution beyond the diffraction limit [1]. This is due to the highly confined enhancement of the optical fields at the tip apex, which locally increases both excitation and radiation rates. In our experiments we use sharp gold tips to probe the photoluminescence (PL) of individual single-walled carbon nanotubes. We show that excitation and emission enhancement can be distinguished by imaging the radiation pattern in the back focal plane of the microscope objective. The analysis is based on the characteristic radiation patterns generated by single dipoles with a particular orientation in 3D [2]. We first find that the PL emission of a nanotube can be described by an in-plane oriented dipole. In the presence of our tip, the radiation pattern is strongly modified and dominated by the signatures of a vertical dipole corresponding to the tip axis. This observation illustrates the spatial redirection of the emission by the tip acting as an optical antenna [3]. By comparing radiation patterns with and without the influence of our tip, we estimate excitation and radiation rate enhancement quantitatively.

[1] A. Hartschuh, Angew. Chem. Int. Ed. 47, 8178 (2008)

[2] M. A. Lieb, J. Opt. Soc. Am. B 21, 1210 (2004)

[3] T. H. Taminiau, Nat. Photon. 2, 234 (2008)