Metasurfaces-Based Absorption and Reflection Control: Perfect Absorbers and Reflectors

In the past decade, the realisation of negative index materials has initiated extensive research into metamaterials. Perfect absorbers and reflectors are of particular interest as their usefulness is endless in a range of different fields and devices. Since it was originally shown that a device can achieve unity absorption of electromagnetic waves, it has become a hot area of research to develop perfect absorbers based on polarisation independence and incident angle independence, at a range of frequencies from microwave to optical ones. The amazing performance, flexibility, and tunability of these metamaterials will be discussed here, by presenting the different designs and working mechanisms that have been realised up to now. Their limitations and shortcomings will be addressed and future plans for perfect absorbers and reflectors will be suggested.112Ysciescopu

Fabrication of three-dimensional suspended, interlayered and hierarchical nanostructures by accuracy-improved electron beam lithography overlay

Nanofabrication techniques are essential for exploring nanoscience and many closely related research fields such as materials, electronics, optics and photonics. Recently, three-dimensional (3D) nanofabrication techniques have been actively investigated through many different ways, however, it is still challenging to make elaborate and complex 3D nanostructures that many researchers want to realize for further interesting physics studies and device applications. Electron beam lithography, one of the two-dimensional (2D) nanofabrication techniques, is also feasible to realize elaborate 3D nanostructures by stacking each 2D nanostructures. However, alignment errors among the individual 2D nanostructures have been difficult to control due to some practical issues. In this work, we introduce a straightforward approach to drastically increase the overlay accuracy of sub-20 nm based on carefully designed alignmarks and calibrators. Three different types of 3D nanostructures whose designs are motivated from metamaterials and plasmonic structures have been demonstrated to verify the feasibility of the method, and the desired result has been achieved. We believe our work can provide a useful approach for building more advanced and complex 3D nanostructures.114sciescopu

Metasurface zone plate for light manipulation in vectorial regime

Fresnel zone plates consisting of multiple concentric rings have been realized by tailoring amplitude, phase and polarization of light, but conventional Fresnel zone plates require totally different materials to control each property reducing light controllability. Here, a metasurface zone plate in which rings are composed of subwavelength antenna arrays is proposed to individually control amplitude, phase and polarization by the consistent material platform of metasurfaces. Hence, versatile degrees of freedom can be achieved to focus electromagnetic waves. We verify that dielectric metasurfaces can generate arbitrary poloarization states to cover the whole Poincare sphere in the visible regime, allowing light manipulation in the vectorial regime, which is not feasible by a conventional single liquid crystal film. Experimental demonstration of a polarization-modulated metasurface zone plate confirms the functional capability of dielectric metasurfaces exhibiting higher focusing efficiency than amplitude-modulated zone plates.11Ysciescopu

Symmetry adapted T-matrix retrieval

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Symmetry-enforced T-matrix retrieval

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Multipole methods for nanophotonics: Study on plasmon-enhanced circular dichroism

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Electrodynamic description of small chiral scattering objects: Application to chirality transfer and coupling

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Importance of higher-order multipole transitions on chiral nearfield interactions

Surface-enhanced circular dichroism (SECD) of chiral molecules adsorbed on plasmonic nanostructures can substantially enhance chiroptical molecular signals by several orders, which is otherwise very weak to be directly measured. Several mechanisms were proposed to explain this extreme enhancement, but the exact mechanism is still controversial. We investigate strong higher-order multipole contribution to SECD near plasmonic nanostructures using the superposition T-matrix method and discuss how 3-dimensional full-field simulations implementing a homogeneous chiral medium have succeeded in the reconstruction of the extreme enhancement. We also discuss how theoretical studies modeling chiral molecules based on dipole approximation have failed to reconstruct the extreme enhancement and show that SECD enhancement of such chiral dipoles is directly governed by optical chirality enhancement. In addition, strong multipolar transitions in subwavelength chiral plasmonic nanoparticles are discussed based on the T-matrix. This work reviews theoretical frameworks describing chiral molecules, demonstrates significant contribution of a multipolar transition on the extreme SECD enhancement near plasmonic nanostructures, and emphasizes the importance of a multipolar transition in chiral nearfield interaction