Nanowire metamaterials with extreme optical anisotropy

We study perspectives of nanowire metamaterials for negative-refraction waveguides, high-performance polarizers, and polarization-sensitive biosensors. We demonstrate that the behavior of these composites is strongly influenced by the concentration, distribution, and geometry of the nanowires, derive an analytical description of electromagnetism in anisotropic nanowire-based metamaterials, and explore the limitations of our approach via three-dimensional numerical simulations. Finally, we illustrate the developed approach on the examples of nanowire-based high energy-density waveguides and non-magnetic negative index imaging systems with far-field resolution of one-sixth of vacuum wavelength.Comment: Updated version; accepted to Appl.Phys.Let

Sub-diffraction light propagation and imaging in planar negative refraction waveguides

In this dissertation we study the electromagnetic properties of planar waveguides with non-magnetic strongly anisotropic dielectric cores. We develop an analytical description of the mode propagation in these systems and show that the index of refraction can be either positive or negative depending on the specific material parameters. Propagating modes are supported even when the waveguide size is much smaller than the wavelength allowing light propagation and beam steering in micro- and nano-scale areas. We further demonstrate that it is possible to combine same-sized planar waveguide structures to build a planar lens. We determine the far-field resolution limit of such a lens and show that it is feasible to achieve resolution better than the free-space diffraction limit. For example, with incident light at the optical wavelength, λ = 1.5µm, we obtain an image with resolution ∆ ≈ 0.3µm. We further study the coupling to and from sub-wavelength planar waveguides of different sizes and compare the transmission through a negative-index structure to the behavior of positive index waveguides. We use numerical simulations to model electromagnetic wave propagation in arbitrary waveguide configurations. Included is a derivation of analyical expressions for the transmission and reflection coefficients along with a comparison of these expresssions to our numerical results. The extension of the planar lens is explored with three-dimensional imaging in chosen waveguide configurations with a focus on designing and optimizing planar-waveguide based beam-steering photonic devices. These results bring forth applications including sub-diffraction planar lens imaging, photonic funnels, highperformance optical sensing, and all-optical computing

Non-magnetic nano-composites for optical and infrared negative refraction index media

We develop an approach to use nanostructured plasmonic materials as a non-magnetic negative-refractive index system at optical and near-infrared frequencies. In contrast to conventional negative refraction materials, our design does not require periodicity and thus is highly tolerant to fabrication defects. Moreover, since the proposed materials are intrinsically non-magnetic, their performance is not limited to proximity of a resonance so that the resulting structure has relatively low loss. We develop the analytical description of the relevant electromagnetic phenomena and justify our analytic results via numerical solutions of Maxwell equations

Nanowire metamaterials with extreme optical anisotropy

The authors study perspectives of nanowire metamaterials for negative-refraction waveguides, high-performance polarizers, and polarization-sensitive biosensors. They demonstrate that the behavior of these composites is strongly influenced by the concentration, distribution, and geometry of the nanowires, derive an analytical description of electromagnetism in anisotropic nanowire-based metamaterials, and explore the limitations of their approach via three-dimensional numerical simulations. Finally, they illustrate the developed approach on the examples of nanowire-based high-energy-density waveguides and nonmagnetic negative-index imaging systems with far-field resolution of one-sixth of vacuum wavelength

United Nations Environment Programme (UNEP), Plastics in the environment in the context of UV radiation, climate change and the Montreal Protocol. 2023 Assessment Update of the UNEP Environmental Effects Assessment Panel

This Assessment Update by the Environmental Effects Assessment Panel (EEAP) of the United Nations Environment Programme (UNEP) considers the interactive effects of solar UV radiation, global warming, and other weathering factors on plastics. The Assessment illustrates the significance of solar UV radiation in decreasing the durability of plastic materials, degradation of plastic debris, formation of micro- and nanoplastic particles and accompanying leaching of potential toxic compounds. Micro- and nanoplastics have been found in all ecosystems, the atmosphere, and in humans. While the potential biological risks are not yet well-established, the widespread and increasing occurrence of plastic pollution is reason for continuing research and monitoring. Plastic debris persists after its intended life in soils, water bodies and the atmosphere as well as in living organisms. To counteract accumulation of plastics in the environment, the lifetime of novel plastics or plastic alternatives should better match the functional life of products, with eventual breakdown releasing harmless substances to the environment.</p