Optical antennas are nanostructures designed to efficiently convert free-propagating optical radiation to localized energy and vice versa. They are based on localized surface plasmon resonances (LSPRs) that generally exist in metal nanoparticles (NPs). The excitation of LSPRs can lead to large near field enhancements and to an increase of the near field effective area up to several times the physical cross section of the nanoparticle. These properties can be used to increase the interaction of any object located in their vicinity with free space radiation. In this thesis, we investigate experimentally and numerically the interactions of nanoantennas with different systems like organic emitters,
graphene and dielectric waveguides.
we have numerically reviewed important experimental factors that generally control the optical antennas properties. Substrates, metal sticking layers, geometries or dimensions can significantly influence the maximum near field enhancement and the resonance
wavelength that optical antennas can provide for spectroscopies like Surface enhanced Raman Scattering, (SERS) and Photoluminiscence, (PL). In particular, we experimentally analyse the influence of the incorporation of a metallic reflecting layer. This provide
a straightforward way to increase the photoluminescence enhancement of nanoemitters induced by optical nanotantennas.
Regarding SERS applications, we probe with surface-enhanced Raman scattering the plasmonic properties of an isolated Au double disk nanostructure interfaced with suspended graphene. By rotating the polarization of the excitation, we switch between the dots acting as single plasmonic particles and a coupling regime, realizing a plasmonic
cavity. we observe a Raman intensity enhancement of the order of 1000 resulting from the near- field enhancement at the antenna cavity.