Here the engineering of anisotropic plasmonic metasurfaces in the form of nanostripes or nanostripe dimers is demonstrated by a novel self-organization technique. Subwavelength quasi-1D glass templates are fabricated over large (cm2) area by ion beam induced wrinkling, enabling the maskless confinement of out-of-plane tilted gold nanostripe arrays supporting localized plasmon resonances easily tunable from the Visible to the Near-Infrared spectrum. A multi-step variant of the method allows to achieve plasmon hybridization in Au-silica-Au nanostrip dimer arrays with excitation of plasmonic electric dipole and magnetic dipole mode featuring strong subradiant near-field enhancement. The selforganized method enables to tune the hybridized plasmonic mode in the Visible and Near-Infrared spectrum opening the possibility to exploit these templates in highly sensitive biosensing and/or nonlinear optical spectroscopies.
Here we investigated the SH generation at the wavelength of 400 nm (pump laser at 800 nm, 120 fs pulses) of a “metasurface” composed by an alternation of GaAs nano-grooves and Au nanowires capping portions of flat GaAs. The nano-grooves depth and the Au nanowires thickness gradually vary across the sample. The samples are obtained by ion bombardment at glancing angle on a 150 nm Au mask evaporated on a GaAs plane wafer. The irradiation process erodes anisotropically the surface, creating Au nanowires and, at high ion dose, grooves in the underlying GaAs substrate (pattern transfer). The SHG measurements are performed for different pump linear polarization angle at different positions on the “metasurface” in order to explore the regions with optimal conditions for SHG efficiency. The pump polarization angle is scanned by rotating a half-wave retarder plate. While the output SH signal in reflection is analyzed by setting the polarizer in ‘s’ or ‘p’ configuration in front of the detector. The best polarization condition for SHG is obtained in the configuration where the pump and second harmonic fields are both ‘p’ polarized, and the experiments show a SH polarization dependence of the same symmetry of bulk GaAs. Thus, the presence of gold contributes only as field localization effect, but do not contributes directly as SH generator.
Here we show the way to easily tune and engineer the optical response of hybrid structures composed by self ordered dielectric nanospheres partially covered by anisotropic plasmonic structures. The overall structure is a hybrid plasmonic-photonics nanostructure acting as a meta-surface witch morphology allows efficient and versatile light manipulation both for linear polarized and circular polarized fields in the visible and near infrared frequencies.
Here we present the measurements of the second harmonic generation (SHG) signal raised by self ordered dielectric nanospheres partially covered by thin (10nm) Au layer. The measurement were performed by studying the SHG efficiency in different polarization states of the light. In particular measurement performed with circular polarized light show the presence of chiral response of the nanospheres that is induced by the particular geometry of the metasurface.
Gold nanowires in general demonstrate very interesting plasmonic properties. Here, by applying the generalized Snell’s law introduced by F. Capasso in 2011, we study how the resonant behavior of the nanowires and their geometrical feature such as the radius of curvature can produce a bent in the propagation direction of a transmitted light beam. The measurements that were performed at a wavelength larger than the nanopatterned features reveal information on the meatusurface morphology.
We present the application of a near infra red Mueller matrix imaging ellipsometer to the characterization of
plasmonic polarizers. The samples are prepared by evaporation of Au onto SiO<sub>2</sub> ripples. The nanostructured
ripple surface has been produced by ion beam sputtering at an off normal angle of incidence. Au was thereafter
evaporated onto the surface at an grazing angle. As a result, thin lines of nearly connected Au nanoparticles
form along the illuminated side of the ripples, resulting in a large in-plane anisotropy of the structure. Mueller
matrix imaging is used to determine the lateral uniformity of the optical signal in correlation to the real space
topography of the sample, and to determine to what degree the nanoparticles tend to form a connected wire, or
whether there are well separated Au particles. The success of this method in order to produce polarizers, lies
in controlling the process to allow well connected lines of Au particles along the ripples, with a high degree of
homogeneity. Mueller Matrix images of the sample recorded at normal incidence are shown, and the information
that can be extracted from such images is discussed.