Title

Near-field imaging of optical antenna modes in the mid-infrared

Authors

Authors

R. L. Olmon; P. M. Krenz; A. C. Jones; G. D. Boreman;M. B. Raschke

Comments

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Abstract

Optical antennas can enhance the coupling between free-space propagating light and the localized excitation of nanoscopic light emitters or receivers, thus forming the basis of many nanophotonic applications. Their functionality relies on an understanding of the relationship between the geometric parameters and the resulting near-field antenna modes. Using scattering-type scanning near-field optical microscopy (s-SNOM) with interferometric homodyne detection, we investigate the resonances of linear Au wire antennas designed for the mid-IR by probing specific vector near-field components. A simple effective wavelength scaling is observed for single wires with lambda(eff) = lambda/(2.0 +/- 0.2), specific to the geometric and material parameters used. The disruption of the coherent current oscillation by introducing a gap gives rise to an effective multipolar mode for the two near-field coupled segments. Using antenna theory and numerical electrodynamics simulations two distinct coupling regimes are considered that scale with gap width or reactive near-field decay length, respectively. The results emphasize the distinct antenna behavior at optical frequencies compared to impedance matched radio frequency (RF) antennas and provide experimental confirmation of theoretically predicted scaling laws at optical frequencies. (C) 2008 Optical Society of America

Journal Title

Optics Express

Volume

16

Issue/Number

25

Publication Date

1-1-2008

Document Type

Article

First Page

20295

Last Page

20305

WOS Identifier

WOS:000261563100015

ISSN

1094-4087

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