The authors present their work in the preparation of nanoporous gold layers and their patterning with an original procedure preserving the porosity, to obtain the phenomenon of extraordinary transmission of light with a porous material. The design, fabrication, and characterization of nanoslit arrays made with bulk gold and nanoporous gold films are presented and their sensing performances are compared after coating with thiolated organic molecules. Thanks to a greatly enhanced surface-to-volume ratio, nanoporous gold reveals benefits for better reaction efficiency and detection sensitivity. Moreover, plasmonic properties in the near-IR range assure employment in plasmonic devices.

Metasurfaces offer unprecedented flexibility in the design and control of light propagation, replacing bulk optical components and exhibiting exotic optical effects. One of the basic properties of the metasurfaces, which renders them as frequency selective surfaces, is the ability to transmit or reflect radiation within a narrow frequency band that can be engineered on demand.Here we introduce and demonstrate experimentally in the THz domain the concept of wavevector selective surfaces -metasurfaces transparent only within a narrow range of light propagation directions operating effectively as tunnel vision filters. Practical implementations of the new concept include applications in wavefront manipulation, observational instruments, vision and free-space communication in light-scattering environments. Keywords: flat optics; metafilms; metasurfaces; planar metamaterials; wavefront manipulation INTRODUCTION Metasurfaces (also known as planar metamaterials or metafilms) are a special low-dimensional class of artificially structured media. This class is represented by thin metal films and surfaces periodically patterned on a sub-wavelength scale, which can be readily fabricated using the existing planar technologies. Apart from their spectral selectivity 1 metasurfaces have demonstrated intriguing electromagnetic effects such as asymmetric transmission 2,3 and optical activity without structural chirality 4 . They can exhibit resonant dispersion mimicking electromagnetically induced transparency and the slow-light phenomenon 5-7 , be invisible 8 , efficiently convert polarization 9-11 , or perfectly absorb radiation 12,13 . Metasurfaces with gradient structuring anomalously reflect and refract light [10][11][12][13][14][15] and can act as lenses, wave-plates, and diffraction gratings [16][17][18][19] . Planar metamaterials are also able to enhance the light-matter interaction facilitating sensing 20 , energy harvesting 21 , and generation of coherent radiation 22,23 . The functionality of the most common types of planar metamaterials is determined by the individual resonant response of their basic structural elements -metamolecules, which are only weakly coupled to each other. When electromagnetic coupling between the metamolecules is strong 24 the relative phase of their excitation becomes important and the resulting spectral response is no longer determined by the individual resonances of the metamolecules. The metamaterial spectrum is then shaped by the collective, spatially coherent modes of metamolecular excitations that engage a large ensemble of metamolecules 25 . The introduction of structural disorder in such an ensemble reduces the degree of coherency and leads to the weakening and broadening of its collective resonant response, which might be seen to vanish

This work presents an integrated plasmonic biosensing device consisting of a one-dimensional metallic lamellar grating designed to exploit extraordinary transmission of light toward an underlying silicon photodetector. By means of finite element simulations, the grating parameters have been optimized to maximize the light transmission variation induced by the functionalization of the gold nanostructures. An optimized grating was fabricated using an electron beam process and an optoelectronic test bench suitable for sample tests was developed. A clear difference in the grating transmitted light due to surface functionalization was observed in presence of TM polarized illumination.

In this work we propose a method to enhance and control the angular sensitivity of a grating coupled surface plasmon resonance (GCSPR) sensor. We lighted a silver grating, mounted in conical configuration, with a laser source and we measured the transmittance of the grating as a function of the azimuthal angle. To evaluate the sensitivity, grating surface was functionalized with four different alkanethiol self assembled monolayers (SAM) and the correspondent azimuthal transmittance peak shifts were measured. The sensitivity control was performed by simply change the light incident angle. This method offers the possibility to design dynamic GCSPR sensor benches that can be used to amplify the SPR angle shift at any step of a biological detection process