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

Optimization of colour generation from dielectric nanostructures using reinforcement learning

Recently, a novel machine learning model has emerged in the field of reinforcement learning known as deep Q-learning. This model is capable of finding the best possible solution in systems consisting of millions of choices, without ever experiencing it before, and has been used to beat the best human minds at complex games such as, Go and chess, which both have a huge number of possible decisions and outcomes for each move. With a human-level intelligence, it has solved the problems that no other machine learning model has done before. Here, we show the steps needed for implementing this model to an optical problem. We investigate the colour generation by dielectric nanostructures and show that this model can find geometrical properties that can generate much purer red, green and blue colours compared to previously reported results. The model found these results in 9000 steps from a possible 34.5 million solutions. This technique can easily be extended to predict and optimise the design parameters for other optical structures. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement11Ysciescopu

Metamaterial-Based Radiative Cooling: Towards Energy-Free All-Day Cooling

In the light of the ever increasing dangers of global warming, the efforts to reduce energy consumption by radiative cooling techniques have been designed, but are inefficient under strong sunlight during the daytime. With the advent of metamaterials and their selective control over optical properties, radiative cooling under direct sunlight is now possible. The key principles of metamaterial-based radiative cooling are: almost perfect reflection in the visible and near-infrared spectrum (0.3-3 mu m) and high thermal emission in the infrared atmospheric window region (8-13 mu m). Based on these two basic principles, studies have been conducted using various materials and structures to find the most efficient radiative cooling system. In this review, we analyze the materials and structures being used for radiative cooling, and suggest the future perspectives as a substitute in the current cooling industry.11Ysciescopu

All-dielectric metasurface imaging platform applicable to laser scanning microscopy with enhanced axial resolution and wavelength selection

Metasurfaces composed of artificially fabricated nano-sized structures have shown extraordinary potential for the precise control of light. Here, we demonstrate for the first time, a metasurface application to reduce the axial size of the point spread function in laser scanning microscopy. The all-dielectric metasurface has wavelength selectivity over the whole visible range, and confinement of the excitation point spread function of the electromagnetic field. These two unique features allow the metasurface to be applied to laser scanning microscope systems. Numerical and experimental demonstrations of the proposed all-dielectric metasurface are reported, showing sharp implicit spectral filtering in the visible range and enhanced axial confinement by observing actin filaments in NIH3T3 cells. We believe that our approach can provide a useful insight on the practicality of using metasurfaces as an imaging platform. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement11Ysciescopu

Gallium nitride-based metasurface for full spectral colour gradients

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Dual-mode anti-counterfeiting system via Hydrogel-based Reconfigurable metasurface

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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

Gallium nitride based reflective structural colour printing

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