Berlin 2015 – scientific programme

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O: Fachverband Oberflächenphysik

O 29: Near-Field Microscopy

O 29.6: Talk

Tuesday, March 17, 2015, 15:15–15:30, MA 042

Analysis of light depolarization in near-field apertureless optical techniques — •Evgeniya Sheremet, Vladimir Kolchuzhin, Raul D. Rodriguez, Jan Mehner, Dietrich R.T. Zahn, and Michael Hietschold — Technische Universität Chemnitz, Chemnitz, Germany

Apertureless near-field methods mostly rely on localized surface plasmons generated at the apex of gold or silver tips under illumination. This allows the spatial resolution of near-field optical microscopy and spectroscopies to be decreased from hundreds of nanometers to the sub-10 nm scale. The near-field has a different polarization from that of the incident field due to the presence of the tip. This can lead to loss of information about inherent selection rules of the sample, or used to our benefit for separating the near-field signal from the far-field contribution. Here, we analyze the polarization of the enhanced field on the tip apex using finite element method. The simulations are performed for tips with apex radii from 10 to 50 nm in free space placed above dielectric or metallic surfaces, or without substrate. We find that a gold tip placed above a gold substrate efficiently rotates the incident field of any polarization along the tip axis. The same tip in air shows a homogeneous distribution of the field components polarized along different directions thus depolarizing the incident field regardless of its polarization. The simulations also show a drastic improvement in spatial resolution for a tip above a gold substrate as compared to the tip in air. These results demonstrate the importance of the substrate nature in near-field optical techniques.