A novel three-dimensional (3D) metallic metamaterial structure with asymmetric transmission for linear polarization is demonstrated in the infrared spectral region. The structure was fabricated by direct laser writing and selective electroless silver coating, a straightforward, novel technique producing mechanically and chemically stable 3D photonic structures. The structure unit cell is composed of a pair of conductively coupled magnetic resonators, and the asymmetric transmission response results from interplay of electric and magnetic responses; this equips the structure with almost total opaqueness along one propagation direction versus satisfying transparency along the opposite one. It also offers easily adjustable impedance, 90° one-way pure optical activity and backward propagation possibility, resulting thus in unique capabilities in polarization control and isolation applications. We show also that scaling down the structure can make it capable of exhibiting its asymmetric transmission and its polarization capabilities in the optical region.

We present an experimental demonstration and interpretation of an ultrafast optically tunable, graphene-based thin film absorption modulator for operation in the THz regime. The graphene-based component consists of a uniform CVD-grown graphene sheet stacked on an SU-8 dielectric substrate that is grounded by a metallic ground plate. The structure shows enhanced absorption originating from constructive interference of the impinging and reflected waves at the absorbing graphene sheet. The modulation of this absorption, which is demonstrated via a THz time-domain spectroscopy setup, is achieved by applying an optical pump signal, which modifies the conductivity of the graphene sheet. We report an ultrafast (on the order of few ps) absorption modulation on the order of 40% upon photoexcitation. Our results provide evidence that the optical pump excitation results in the degradation of the graphene THz conductivity, which is connected with the generation of hot carriers, the increase of the electronic temperature, and the dominant increase of the scattering rate over the carrier concentration as found in highly doped samples.

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aiming to design and fabricate biomimetic structures. [7] Research in this field indicated several methodologies to develop bioinspired surfaces, exhibiting hierarchical structuring at the nano-and micro-lengthscales. [8][9][10][11] Laser fabrication is a maskless process allowing material modifications with a high precision over size and the shape of the fabricated features. [12] However, due to optical diffraction, the feature size resolution is limited to the order of wavelength (i.e., microscale); therefore, the challenge in biomimetic laser processing is to beat the diffraction limit and realize the structural complexity of natural surfaces, also, at the nanoscale. Materials' structuring using ultrashort (less than 1 ps) laser pulses, in particular, proved to be a precise and highly versatile tool to realize artificial surfaces that quantitatively mimic the morphological features and functionalities of their natural archetypes. [13][14][15][16][17][18][19] This capability comes as the outcome of the optimal combination of the ultrafast laser field and material properties that enable the production of features with sizes beyond the diffraction limit (i.e., nanoscale). A prominent example is the formation of self-organized subwavelength, laser-induced periodic surface structures (LIPSS), which have been proven an important asset for the fabrication of nanostructures with a plethora of geometrical features. [13,[20][21][22][23][24][25] This work is the first report on direct laser nanofabrication of biomimetic omnidirectional antireflective glass surfaces. It was inspired from the unique antireflection properties of the wings of the glasswing butterfly, Greta oto, and the Cicada Cretensis species. [2,3] This property is due to the presence of arrays (with periodicity in the range of 150-250 nm) of nonreflective nanosized (sub-100 nm size) pillars on both the top and the bottom surface of the wing. The current state-of-the-art technologies employed for the production of antireflection surfaces require either complex multiple steps and time-consuming procedures or chemical processes, [8,[26][27][28][29][30][31][32] which, in some cases, produce hazardous wastes. At the same time, the chemical coatings' quality tends to degrade with time. [27,33,34] Here, we demonstrate a single-step laser texturing approach for the structuring of biomimetic antireflective nanopillars, on fused silica glass (SiO 2 ) surfaces. The overall properties of the produced surfaces were found remarkably similar to the natural butterfly and Cicada archetypes, both in terms of the surface morphology Here, a single-step, biomimetic approach for the realization of omnidirectional transparent antireflective glass is reported. In particular, it is shown that circularly polarized ultrashort laser pulses produce self-organized nanopillar structures on fused silica (SiO 2 ). The laser-induced nanostructures are selectively textured on the glass surface in order to mimic the spatial randomness, pillar-like morphology, as well as the remarkable antir...

Five different chiral metamaterials in the terahertz (THz) regime, fabricated on fully flexible polyimide substrates, are comparatively studied via numerical calculations and experimental measurements. The chiral properties of these metamaterials, which are discussed based on their optical activity, circular dichroism, and the retrieved effective parameters, show pronounced pure optical activity (larger than 300°/wavelength), as well as important circular polarization generation and filtering capabilities. Negative refractive index is also obtained for all the considered designs.

Switchable and tunable chiral metamaterial response is numerically demonstrated here in different uniaxial chiral metamaterial structures operating in the THz regime. The structures are based on the bi-layer conductor design and the tunable/switchable response is achieved by replacing parts of the metallic components of the structures by photoconducting Si, which can be transformed from an insulating to an almost conducting state through photoexcitation, achievable under external optical pumping. All the structures proposed and discussed here exhibit frequency regions with giant tunable circular dichroism, as well as regions with giant tunable optical activity, showing unique potential in the achievement of active THz polarization components, like tunable polarizers and polarization filters.

We report on preliminary results regarding the electromagnetic shielding effectiveness of various 3D printed polymeric composite structures. All studied samples were fabricated using 3D printing technology, following the fused deposition modeling approach, using commercially available filaments as starting materials. The electromagnetic shielding performance of the fabricated 3D samples was investigated in the so called C-band of the electromagnetic spectrum (3.5-7.0 GHz), which is typically used for long-distance radio telecommunications. We provide evidence that 3D printing technology can be effectively utilized to prepare operational shields, making them promising candidates for electromagnetic shielding applications for electronic devices.

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