Abstract

The improvement of nanoscale fabrication technologies has allowed in recent years the investigation of optical phenomena on metallic nanostructures, leading to the concept of nanoantennas [1]. The latter are now being widely explored to convert optical free-space propagating waves into highly localized fields for applications dealing with the enhancement and control of single emitter’s fluorescence [2]. In here, we report on the fabrication of a novel hybrid antenna probe designed to work as a background-free broadband nano-light source [3]. The device is composed of three different optical elements: a tapered optical fiber, a bowtie nanoaperture antenna [4] and a monopole antenna [5]. By coupling these three elements (Fig. 1a) we demonstrate that our design allows broadband adiabatic field enhancement and nanofocusing of light down to about 20 nm (Fig. 1b). We show dual color antenna excitation of highly dense samples of fluorescent molecules allowing direct discrimination of individual emitters separated by distances smaller than 2 nm (Fig. 2) and with Angstrom precision even using a low fluorescent photon budget. Moreover, we describe through polarization studies, that the interaction between the hybrid antenna and fluorescent molecules can be directly decoupled from the influence of each antenna on these molecules, highlighting their coupled behavior.

© 2015 IEEE