Superfocussing in a metal-coated tetrahedral tip by dimensional reduction of surface-to edge-plasmon modes |
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Authors: | K Tanaka G W Burr T Grosjean T Maletzky U C Fischer |
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Institution: | 1.Department of Electronics and Computer Engineering,Gifu University,Yanagido 1-1,Japan;2.IBM Almaden Research Center,San Jose,USA;3.Laboratoire d’Optique P. M. Duffieux UMR 6603,CNRS/Université de Franche-Comté, IMFC FR67 UFR Sciences et Technique,Bésa?on cedex,France;4.Physikalisches Institut,Westf?lische Wilhelms-Universit?t Münster,Münster,Germany |
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Abstract: | Metal-coated dielectric tetrahedral tips (T-tip) have long been considered to be interesting structures for the confinement
of light to nanoscopic dimensions, and in particular as probes for scanning near-field optical microscopy. Numerical investigations
using the Finite-Difference Time-Domain (FDTD) method are used to explore the operation of a T-tip in extraction mode. A dipole
source in close proximity to the apex excites the tip, revealing the field evolution in the tip, the resulting edge and face
modes on the metal-coated surfaces, and the coupling from these modes into highly directional radiation into the dielectric
interior of the tip. These results are the starting point for illumination-mode numerical investigations by a Volume Integral
equation method, which compute the field distribution that develops in a T-tip when a Gaussian beam is incident into the tip,
and which show that a highly confined electric field is produced at the apex of the tip. The process of light confinement
can be considered as a superfocussing effect, because the intensity of the tightly confined light spot is significantly higher
than that of the focussed yet much wider incident beam. The mechanism of superfocussing can be considered as a dimensional
reduction of surface plasmon modes, where an edge plasmon is the most important link between the waveguide-modes inside the
tip and the confined near field at the apex. |
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Keywords: | PACS" target="_blank">PACS 07 79 Fc 78 67 -n 42 82 Gw |
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