We use a Photon Scanning Tunneling Microscope to probe the field of surface plasmon polaritons modes excited on finite width thin metal films (metal stripes). We first investigate the coupling between surface plasmons launched by a focused beam on a homogeneous thin film and the modes sustained by metal stripes of different widths. We show that, if the width of the metal stripe is about a few microns, a strong coupling with the stripe modes can be achieved at visible frequencies. A sharp transverse confinement of the field associated to the surface plasmon modes propagating on the metal stripe is unambiguously observed on the constant height Photon Scanning Tunneling Microscope (PSTM) images. The back-reflection of theses modes at the end of the stripe leads to a surface-wave interference pattern from which the wavelength of the stripe surface plasmon modes is directly measured. We finally demonstrate that metal stripes could be used for optical addressing purposes at the micron scale since a stripe with a triangularly shaped termination performs the focusing of the stripe surface plasmon field. PACS: 78.66.-w Optical properties of specific thin films, surfaces, and low-dimensional structures 71.36.+c Polaritons 07.79.Fc Near-field scanning optical microscopes Typeset using REVT E X

We report on the experimental observation of multipolar plasmon excitations in lithographically designed elongated silver particles. In contrast to spheres, where the extinction bands of the respective multipolar plasmons overlap considerably to form a broad spectrum, spectrally well-separated extinction bands corresponding to plasmons of multipolar order up to n=6 are found. The results agree well with numerical simulations based on the Green’s Dyadic method.

Efficient excitation of surface plasmon polaritons (SPPs) remains one of the most challenging issues in areas of plasmonics related to information communication technologies. In particular, combining high SPP excitation efficiency and acceptance of any polarization of incident light appeared to be impossible to attain due to the polarized nature of SPPs. Here we demonstrate plasmonic couplers that represent arrays of gap SPP resonators producing upon reflection two orthogonal phase gradients in respective linear polarizations of incident radiation. These couplers are thereby capable of efficiently converting incident radiation with arbitrary polarization into SPPs that propagate in orthogonal directions dictated by the phase gradients. Fabricated couplers operate at telecom wavelengths and feature the coupling efficiency of ,25% for either of two linear polarizations of incident radiation and directivity of SPP excitation exceeding 100. We further demonstrate that an individual wavelength-sized unit cell, representing a meta-scatterer, can also be used for efficient and polarization sensitive SPP excitation in compact plasmonics circuits. Keywords: gap surface plasmons; metamaterials; metasurfaces; surface plasmon polaritons INTRODUCTION Surface plasmon polaritons (SPPs) are electromagnetic excitations, in which electromagnetic field in dielectric are coupled to collective electron oscillations in metal, which propagate along and are tightly bound to metal/dielectric interfaces. 1 Modern plasmonics, which embraces various phenomena associated with excitation, propagation and scattering of SPPs, became ubiquitous in extremely diverse areas, ranging from biochemical sensing, 2 quantum optics 3 and information communication technologies 4 to sustained energy sources. 5 SPPs are essentially transverse magnetic waves with the magnetic field oriented perpendicular to the propagation plane, a very important feature that dictates the polarization sensitivity of the SPP excitation efficiency by free propagating radiation. It is therefore understandable that various SPP couplers developed in the quest for the efficient and unidirectional SPP excitation operate with only one (linear) polarization of the incident light, 6-10 resulting thereby in the loss of light power carried by the orthogonal polarization.The recent progress in optical metasurfaces, which influence transmitted and reflected optical fields by imposing additional (surface) gradients onto their phases, 11,12 opened new possibilities for efficient coupling of propagating and surface waves. 13,14 Very recently, polarization-controlled tunable directional SPP coupling has been demonstrated using arrays of narrow (elongated) apertures in an otherwise opaque metal film, so that the direction of SPP excitation was dictated by the helicity of a circularly polarized incident beam. 15,16 Note that, in these configurations, the SPP excitation involves both the transmission through narrow apertures and the coupling of the transmitted

The optical resonances of individual plasmonic dimer antennas are investigated using confocal darkfield spectroscopy. Experiments on an array of antennas with varying arm lengths and interparticle gap sizes show large spectral shifts of the plasmon modes due to a combination of geometrical resonances and plasmon hybridization. The resonances of the coupled-dimer antennas are considerably broadened compared to those of single nanorods, which is attributed to a superradiant damping of the coupled antenna modes. The scattering spectra are compared with electrodynamic model calculations that demonstrate both the near-field and far-field characteristics of a half-wave antenna.