Utilizing solar energy requires perfect absorption by photovoltaic cells for efficient conversion of solar energy into useful electrical energy. Metasurfaces can, not only be used to absorb solar energy efficiently but, they do so with thickness of structure in nano-scale -effectively reducing the size of the device. To achieve aforementioned feature metasurface absorbers are developed which give better absorbance on narrow/wide frequency spectrum. These absorbers are fashioned with variable structures employing variable materials but still, perfect absorbance is not attained with a simple two-dimensional (not varying in z-direction) structure. This paper presents a simulated realization of a broadband metasurface absorber based on tungsten nano-structure. The design is two-dimensional, polarization insensitive, broadband and is predicted to give better response under high temperatures ascribed to high melting point of tungsten i.e. 3422°C. Cross alignment is found optimum for tungsten as it is impedance matched with the free space for visible spectrum. This cross arrangement is further tweaked by changing span, width and height of the cross resulting in 7 different optimized solutions giving an average absorbance greater than 98%. One, amongst these solutions, gave a maximum average absorbance of 99.3%.
Recently, nonlinear hybrid metasurface comes into an attractive new concept in the research of nanophotonics and nanotechnology. It is composed of semiconductors with an intrinsically large nonlinear susceptibility and traditional plasmonic metasurfaces, offering opportunities for efficiently generating and manipulating nonlinear optical responses. A high second-harmonic generation (SHG) conversion efficiency has been demonstrated in the mid-infrared region by using multi-quantum-well (MQW) based plasmonic metasurfaces. However, it has yet to be demonstrated in the visible region. Here we pres…
Based on an analytic approach, we present a theoretical review on the absorption, scattering, and extinction of both dipole scatterers and regular arrays composed of such scatterers i.e., metasurfaces. Besides offering a tutorial by outlining the maximum absorption limit for electrically/magnetically resonant dipole particles/metasurfaces, we give an educative analytical approach to their analysis. Moreover, we put forward the analysis of two known alternatives in providing perfect absorbers out of electrically and or magnetically resonant metasurfaces; one is based on the simultaneous presenc…
We demonstrate a broadband, polarization independent, omnidirectional absorber based on a metallic metasurface architecture, which accomplishes greater than 90% absorptance in the visible and near-infrared range of the solar spectrum, and exhibits low emissivity at mid- and far-infrared wavelengths. The complex unit cell of the metasurface solar absorber consists of eight pairs of gold nano-resonators that are separated from a gold ground plane by a thin silicon dioxide spacer. Our experimental measurements reveal high-performance absorption over a wide range of incidence angles for both s- an…
This article presents a novel approach for designing dual-band absorbers based on graphene and metallic metasurfaces for terahertz and mid-infrared regimes, respectively. The absorbers are composed of a two-dimensional (2D) array of square patches deposited on a dielectric film terminated by a metal plate. Using an analytical circuit model, we obtain closed-form relations for different parameters of the structure to achieve the dual-band absorber. Two absorption bands with obtained absorptivity of 98% at 0.55 and 1.54 THz for the graphene-based structure and 7 and 25 THz for the metallic-based…
We demonstrate that the metamaterial perfect absorber behaves as a meta-cavity bounded between a resonant metasurface and a metallic thin-film reflector. The perfect absorption is achieved by the Fabry-Perot cavity resonance via multiple reflections between the "quasi-open" boundary of resonator and the "closed" boundary of reflector. The characteristic features including angle independence, ultra-thin thickness and strong field localization can be well explained by this model. With this model, metamaterial perfect absorber can be redefined as a meta-cavity exhibiting high Q-factor, strong fie…
We explored a metal-insulator-metasurface structure exhibiting dual-band absorption in the visible and infrared regions with almost perfect absorbance. We demonstrated that the existence of the dual peak absorbance is due to the excitation of propagating surface plasmon and localized surface plasmon mode. We further utilized the excited degenerate propagating surface plasmon to enhance the fluorescence emission of an emitter located on top of the metasurface. This was accomplished by engineering a metasurface that excites a degenerate mode with resonance absorption bands close to the emission …
The heat-shielding properties of random metasurface, composed of spherical or spheroidal nanoparticles with random displacements and/or random deformation, were theoretically investigated using the finite difference time domain method. The effective coverage was defined using the total area of nanoparticles in the metasurface, and the robustness of the near-infrared light reflection against randomness was investigated. When the effective coverage was high, the near-infrared light reflection was reduced by at least 20% in both nanoparticle arrangement and shape randomness compared to the hexago…
Direct visualization of non-equilibrium heat extraction by a metasurface absorber
Tokyo University of Agriculture and Technology（东京农工大学）；University of Birmingham（伯明翰大学）；RIKEN Center for Advanced Photonics（理化学研究所先进光子研究中心）；RIKEN Cluster for Pioneering Research（理化学研究所先锋研究集群）；Gakushuin University（学习院大学）；Tokushima University（德岛大学）
This paper presents fabrication, measurement and modelling results for a metal-dielectric-metal metasurface absorber for solar thermal applications. The structure uses amorphous carbon as an inter-layer between thin gold films with the upper film patterned with a 2D periodic array using focused ion beam etching. The patterned has been optimised to give high absorptance from 400-1200nm and low absorptance above this wavelength range to minimise thermal radiation and hence obtain higher temperature performance. Wide angle absorptance results are shown and detailed modelling of a realistic nanost…
The trapped rainbow effect has been mostly found on tapered anisotropic metamaterials (MMs) made of low loss noble metals, such as gold, silver, etc. In this work, we demonstrate that an anisotropic MM waveguide made of high loss metal tungsten can also support the trapped rainbow effect similar to the noble metal based structure. We show theoretically that an array of tungsten/germanium anisotropic nano-cones placed on top of a reflective substrate can absorb light at the wavelength range from 0.3 micrometer to 9 micrometer with an average absorption efficiency approaching 98%. It is found th…
We analyze single and multilayered metamaterials by modeling each layer as a metasurface with effective surface electric and magnetic susceptibility derived through a thin film approximation. Employing a transfer matrix method, these metasurfaces can be assembled into multilayered metamaterials to realize certain functionalities. We demonstrate numerically that this approach provides an alternative interpretation of metamaterial-based perfect absorption, showing that the underlying mechanism is a modified Fabry-Perot resonance. This method provides a general approach applicable for decoupled o…
Most applications of metasurfaces require excitation and control of both electric and magnetic surface currents. For such purpose, the metasurface must have a finite thickness to handle magnetic surface currents. For metasurface sheets of negligible thickness that offer only electric response, coherent illumination can compensate the need to create discontinuities of the tangential electric field component using magnetic surface currents. Most of known coherent metasurfaces are space-uniform and can control only plane-wave absorption and specular reflection. However, it is also known that peri…
We discuss the possibility of realizing utlrabroadband omnidirectional absorbers and angularly selective coherent thermal emitters based on properly patterned plasmonic metastructures. Instead of relying on resonant concentration effects that inherently limit the bandwidth, we base our design on the combination of two inherently nonresonant effects: plasmonic Brewster funneling and adiabatic plasmonic focusing. With this approach, we demonstrate compact, broadband absorption and emission spanning terahertz, infrared and optical frequencies, ideal for various energy and defense applications.
Localized plasmons formed in ultrathin metallic nanogaps can lead to robust absorption of incident light. Plasmonic metasurfaces based on this effect can efficiently generate energetic charge carriers, also known as hot electrons, owing to their ability to squeeze and enhance electromagnetic fields in confined subwavelength spaces. However, it is very challenging to accurately identify and quantify the dynamics of hot carriers, mainly due to their ultrafast time decay. Their non-equilibrium temperature response is one of the key factors missing to understand the short time decay and overall tr…
We present an asymmetric bifacial graphene metasurface to realize tunable and broadband coherent perfect absorption (CPA) at terahertz (THz) frequencies. The proposed design is composed of two dissimilar graphene square patch metasurfaces stacked over an ultrathin dielectric substrate. Nonlinear CPA performance without resorting to optical nonlinearities and amplification are demonstrated based on wave interference phenomena taking place along and inside this subwavelength structure. Broadband asymmetric reflection from opposite directions is obtained in the case of single wave illumination. T…
In this study, we designed a metasurface based on Al/SiN/Al nano-sandwich optical absorbers. Parity-symmetric dark magnetic resonance modes, anti-symmetric bright magnetic resonance modes, and surface lattice modes are established simultaneously in such a meta-surface. By changing the structural parameters, the wavelength of the dark mode can be tuned to overlap with the lattice mode. Fano resonance is introduced by coupling between the dark and lattice modes. Angular-resolved thermal emission experiments showed that the thermal emission induced by Fano resonance exhibited a narrow wavelength …
Inverse Design of Realizable Metasurface based Absorbers using Improved Conditioning and Diversity Enhanced Progressively Growing GANs
Centre for Electromagnetics, CSIR-National Aerospace Laboratories（电磁研究中心，国家航空航天实验室）；Birla Institute of Technology and Science, Pilani, Rajasthan（比拉理工学院和科学学院，比里尼）；Indian Institute of Technology, Bombay, Maharashtra（孟买印度理工学院，马哈拉施特拉）
Metasurface saturable absorbers may result in versatile mode-locking that allows one to obtain stable ultrashort laser pulses with high repetition rates and peak powers, along with broadband operation, within fiber to solid-state laser cavities.
A metamaterial absorber converts solar radiation into heat for applications in thermoelectric generators and solar thermophotovoltaics. A metamaterial absorber typically consists of metallic parts separated by an insulator layer which does not allow the total heat extraction via direct heat conduction. Here, we propose wide-angle and broadband metamaterial absorber comprising an insulator layer, metal grating, and metal back plane (IMM) that allows the total heat extraction via direct heat conduction. We have formulated the quasi-analytical solution (QANS) of the IMM-absorber by applying the c…
Here we make use of vanadium dioxide (VO2) to design a bifunctional metasurface working at the same targeted frequency. With the increase of temperature, the functionality of the designed metasurface can switch from a multi-channel retroreflector to a perfect absorber, caused by the phase transition of VO2 from insulator to conductor. Different from traditional bifunctional metasurfaces designed by simple composition of two functionalities, our proposed bifunctional metasurface is based on the interaction between two functionalities. The device shows good potential for the combination of wavef…
Monitoring and controlling the state of polarization of electromagnetic waves is of significant interest for various basic and practical applications such as linear position sensing and medical imaging. Here, we propose the first conformal digital metamaterial absorber to detect the polarization state of THz incident waves. The proposed polarimeter is capable of characterizing four independent polarization states of (TE, TM, $\pm {45^\circ}$ linear, and RCP/LCP) by observing the reflectivity of the structure with respect to the x- and y-direction. Besides, the proposed structure displays a str…
Metamaterials and metasurfaces operating in the visible and near-infrared (NIR) offer a promising route towards next-generation photodetectors and devices for solar energy harvesting. While numerous metamaterials and metasurfaces using metals and semiconductors have been demonstrated, semimetals-based metasurfaces in the vis-NIR range are notably missing. Here, we experimentally demonstrate a broadband metasurface superabsorber based on large area, semimetallic, van der Waals PtSe2 thin films in agreement with electromagnetic simulations. Our results show that PtSe2 is an ultrathin and scalabl…
In this work, a metamaterial selective solar absorber made of nanostructured titanium gratings deposited on an ultrathin MgF2 spacer and a tungsten ground film is proposed and experimentally demonstrated. Normal absorptance of the fabricated solar absorber is characterized to be higher than 90% in the UV, visible and, near infrared (IR) regime, while the mid-IR emittance is around 20%. The high broadband absorption in the solar spectrum is realized by the excitation of surface plasmon and magnetic polariton resonances, while the low mid-IR emittance is due to the highly reflective nature of th…
