Surface Magnetic Polaritons Research Articles

A high-temperature solar selective absorber based on one-dimensional multilayer nanostructures

Selective absorbers play a crucial role in harvesting solar energy and realizing effective solar-thermal energy conversion in concentrated solar power systems and thermophotovoltaic systems. This study focuses on obtaining a high-temperature solar selective absorber which can well balance its thermal performance as well as structural complexity. Based on this, a selective absorber with simple one-dimensional multilayer nanostructures is designed to adapt to the high-temperature operation environments. The obtained absorber exhibits a total solar absorptance of 0.9504 to the AM1.5 solar radiation. Taking into account the infrared radiation loss, the solar-thermal efficiency of the absorber is found to be 91.2% under 1000 suns at 1273 K, and the total emittance is 0.1504 at the corresponding temperature. The absorber shows high insensitivity to both incident polarization angles and wide-angle incidence. Analysis of impedance and electromagnetic field distribution indicates that the selective absorption performance of the absorber is attributed to its impedance matching properties, resulting from the coupling effect of surface plasmon polaritons and magnetic polaritons.

UV–visible broadband polarization-independent metamaterial absorber based on two-dimensional Au grating

A broadband metamaterial absorber (BMA) based on a thin metamaterial nanostructure consisting of 2D Au square grating on graphene-SiO2 film and Au substrate is proposed and designed. The optimized structure can achieve nearly perfect absorption with absorption of exceeding 90 % spanning a broad range from deep UV light to visible light (100 nm−700 nm). The excitation of Rayleigh anomaly (RA), cavity resonance (CR), surface plasmon polaritons (SPPs) and magnetic polaritons (MPs) are responsible for nearly perfect broadband absorption, which have been analysed clearly by finite-difference time-domain (FDTD) method and the LC circuit model. Furthermore, the BMA is polarization and angle insensitive for incident light even at large angle. This proposed BMA not only has a simple geometry and ordinary metal-based material composition, but also shows a high performance in both bandwidth and absorptivity, suggesting that great potential in solar cell and photodetector applications.

Tailorable bandgap-dependent selective emitters for thermophotovoltaic systems

Selective emitters are crucial in thermophotovoltaic (TPV) systems as they can selectively tailor the incident light to match with the bandgap of photovoltaic (PV) cell, thus greatly increasing the system efficiency. However, further progress has been hampered by the limitation in designing high performance selective emitters with spectrally emissive selectivity and compatible ability to different PV cells. In this study, we propose a design strategy to realize tailorable bandgap-dependent selective emitters based on metasurfaces by combing the two-resonance response of surface plasmon polaritons (SPPs) and magnetic polaritons (MPs). The emission spectrum can be manipulated and matched to various PV cells with different bandgap by simply changing the size and period of the meta-atoms in metasurface. We design and experimentally demonstrate a selective emitter appealing to GaSb PV cells, which presents near-perfect emissivity (above 0.96) above the bandgap wavelength (from 0.9μm to 1.54μm) with polarization-insensitive and angle-insensitive features. Moreover, the emitter shows a high figure of merit (FOM, of 0.85), and the efficiency of TPV system can be expected to be 27% at 1473K. The proposed strategy and designed emitter may pave a reliable route for improving the performance of TPV systems.

Super-resolution imaging of Maxwell’s fish-eye lens based on surface polaritons

Super-resolution imaging plays a crucial role in the fields of nanolithography, high volume transmission and sensing. Relentless efforts have been made to realize super-resolution imaging in the past decades. In this work, inspired by the mechanism of surface plasmon polaritons (SPPs), we find that Maxwell’s fish-eye lens (MFEL) coated with cylindrical layer of negative permeability can achieve super-resolution imaging. The amplification of evanescent waves in the negative permeability layer facilitates the transmittance of high spatial frequency information from object point to imaging point in the form of magnetic surface polaritons (MSPs). Both analytical calculations and numerical simulations are employed to prove the super-resolution imaging performance of MSPs-assisted MFEL. Our results may pave a new way for super-resolution imaging in metallic systems.

Magnetic polaritons assisted effective excitation of multi-order anisotropic borophene surface plasmons in the infrared region

Anisotropic borophene surface plasmons with extraordinary features have triggered considerable research interest since its discovery. However, due to the atomically thin thickness of monolayer borophene, it is difficult to achieve borophene surface plasmons with high absorption, especially for high-order plasmonic resonant modes. In this paper, we theoretically proposed a hybrid plasmonic system consisting of a borophene monolayer and a periodic metallic grating separated by a dielectric spacer, where multi-order anisotropic borophene surface plasmons and magnetic polaritons can be simultaneously excited. Benefitting from the high electric field enhancement and localization of the magnetic polaritons, the intrinsic absorption of the multi-order borophene surface plasmons can be improved by at least 3 times when the resonant wavelengths of borophene plasmons and magnetic polaritons are tailored to match each other, either by passively tuning the height of grating slits or by actively adjusting the borophene electron density. By further designing compound grating with multiple slits in one period, the overall absorption of the system can be significantly improved within a wide infrared region. Such hybrid system with may find applications in the design of boron-based optoelectronics devices in the infrared region.

The Equivalent Thermal Conductivity of the Micro/Nano Scaled Periodic Cubic Frame Silver and Its Thermal Radiation Mechanism Analysis

Currently, there are few studies on the influence of microscale thermal radiation on the equivalent thermal conductivity of microscale porous metal. Therefore, this paper calculated the equivalent thermal conductivity of high-porosity periodic cubic silver frame structures with cell size from 100 nm to 100 µm by using the microscale radiation method. Then, the media radiation characteristics, absorptivity, reflectivity and transmissivity were discussed to explain the phenomenon of the radiative thermal conductivity changes. Furthermore, combined with spectral radiation properties at the different cross-sections and wavelength, the radiative transmission mechanism inside high-porosity periodic cubic frame silver structures was obtained. The results showed that the smaller the cell size, the greater radiative contribution in total equivalent thermal conductivity. Periodic cubic silver frames fluctuate more in the visible band and have better thermal radiation modulation properties in the near infrared band, which is formed by the Surface Plasmon Polariton and Magnetic Polaritons resonance jointly. This work provides design guidance for the application of this kind of periodic microporous metal in the field of thermal utilization and management.

Optimization configuration of selective solar absorber using multi-island genetic algorithm

Based on the demand for ideal selective solar absorbers to harvest a full solar spectrum, we present an auspicious method, the multi-island genetic algorithm (MIGA), to optimize the configuration of a universal selective solar absorber, which can avoid the premature phenomenon and superior to traditional genetic algorithm. The selective solar absorber equipped with the set of optimal geometric parameters exhibits the solar absorptance greater than 0.932 with 96% probability and mid-infrared emittance lower than 0.058 at the same time considering unavoidable 20% fabrication uncertainties in the design variables. In addition, the absorber is a combination of great characteristics, such as polarization independence and angle insensitivity. The hybrid resonance modes of Wood’s anomaly, surface plasmon polariton and magnetic polariton are responsible for the high absorption performance. The MIGA method presented is proved to be an effective and robust tool in the optimization of micro-nano structures with manufacturability for thermal and energy applications.

Characteristics of thermophotovoltaic emitter based on 2D cylindrical gear grating

A novel wavelength-selective thermophotovoltaic (TPV) emitter is proposed and analyzed with high emissivity. The suggested TPV emitter is based on cylindrical gear grating of tungsten with SiO2 spacer. The design geometry is studied to maximize its emissivity up to wavelength of 2.0 μm. The effect of oblique incidence at different polarizations on the design emissivity is also introduced. Additionally, the inductor-capacitor (LC) model is used to elucidate the behavior of magnetic resonance of the proposed grating. The reported TPV emitter exhibits high emissivity properties over large spectra range from ultraviolet to mid-infrared with spectral efficiency of 74% and 95% at 1000 and 2000 K, respectively. Further, high emissivity is achieved over a wide range of incident angles from 0 to 65° for the two polarized waves. The achieved perfect emissivity is due to the coupling between surface plasmon polariton, magnetic polariton and intrinsic loss of the tungsten material.

Effective Transmission Modulation at Telecommunication Wavelengths through Continuous Metal Films Using Coupling between Borophene Plasmons and Magnetic Polaritons

AbstractOptical modulation has been recognized as one of the most important operations in photonics. The use of 2D materials that support highly confined plasmonic modes allows one to manipulate light at the extreme subwavelength scale, thus significantly shrinking the size of the modulator, with potential for major advances in the state of art of existing devices. Here, a prototype plasmonic modulator is theoretically presented for the effective transmission modulation through a continuous metal film enabled by the strong coupling between anisotropic borophene surface plasmonic (BSP) modes and magnetic polaritons (MP) modes. Simulations reveal that plasmonic absorption in borophene within the grating slits can efficiently suppress the extraordinary optical transmission induced by the MP mode, resulting in the effective transmission modulation. By dynamically tuning the borophene electron density to decouple or couple BSP mode with MP mode, high modulation efficiency of 98.6% at 1550 nm can be achieved for borophene along both crystal axes, indicating excellent performance of the designed modulator via such mechanism. These results illustrate the potential of strong BSP–MP coupling as a promising strategy to realize the transmission modulation for optoelectronic applications.

Mechanism of polaritons coupling from perspective of equivalent MLC circuits model in slit arrays.

Magnetic polariton is a significant mode in tailoring thermal radiative properties with micro/nanostructures metamaterials and can be explained by equivalent inductor-capacitor circuit model. However, the equivalent inductor-capacitor circuit model is out of operation when the magnetic polariton resonance frequency is close to the surface plasmon polariton excitation frequency and cases of oblique incidence. In this work, we present a mutual inductor-inductor-capacitor circuit model to describe magnetic polariton resonance conditions. The mechanism of coupling between the surface plasmon polariton and magnetic polariton is explained from the perspective of equivalent circuits. The interaction between the surface plasmon polariton and magnetic polariton is studied and considered as a mutual inductance in the MLC circuit model. This model is still applicable in the case of oblique incidence. Slit arrays with different geometric parameters and incident angles are calculated to verify the rationality of the mutual inductor-inductor-capacitor circuit model. This study may allow us to predict features and parameters and achieve tailoring of the thermal radiative properties of the micro/nano-structures metamaterials.

Fluorescence emission mediated by metal-dielectric-metal fishnet metasurface: Spatially selective excitation and double enhancement

Enhancement of fluorescent radiation is of great importance for applications including biological imaging, high-sensitivity detectors, and integrated light sources. Strong electromagnetic fields can be created around metallic nanoparticles or in gap of nanostructures, where the local state density of radiating mode is then dramatically enhanced. While enhanced fluorescent emission has been demonstrated in many metallic nanoparticles and nanoparticle pairs, simultaneous mediation of absorption and emission processes of fluorescent emitters remains challenging in metallic nanostructures. Here, we investigate fluorescent emission mediated by metal-dielectric-metal fishnet metasurface, in which localized surface plasmon (LSP) and magnetic plasmon polaritons (MPPs) modes are coupled with absorption and emission processes, respectively. For absorption process, coupling of the LSP mode enables spatially-selective excitation of the fluorescent emitters by rotating the polarization of the pump laser beam. In addition, the polarization-dependent MPP mode enables manipulation of both polarization and wavelength of the fluorescent emission by introducing a rectangular fishnet structure. All the experimental observations are further corroborated by finite-difference time-domain simulations. The structure reported here has great potential for application to color light-emitting devices and nanoscale integrated light sources.

Engineering terahertz surface magnon-polaritons in hyperbolic antiferromagnets

Magnetic crystals were recently studied as a route to hyperbolic dispersion and the effects associated with it. These studies, however, concentrated on bulk waves and frequencies where transmission is possible and where negative refraction occurs. Here, in contrast, we concentrate on geometries which sample regions of the dispersion relations where bulk propagation is not possible. This is done by controlling the orientation of the uniaxial anisotropy axis with respect to the surface of the crystal. Furthermore, we find that new magnetic surface polaritons exist in these regions, and we investigate the nature of these waves. In addition, significant tunability can be introduced by applying an external field perpendicular to the easy axes of a uniaxial antiferromagnet, creating a canted structure and generally shifting the frequencies to higher values. This externally applied field dramatically changes the nature of both surface and bulk polaritons, making them highly nonreciprocal.

Study of W/HfO2 grating selective thermal emitters for thermophotovoltaic applications

This paper explores the performance potential of gratings based on tungsten/hafnia (W/HfO2) stacks for thermophotovoltaic thermal emitters via numerical simulations. Structures consisting of a W grating over a HfO2 spacer layer and a W substrate are analyzed over a range of geometries. For shallow gratings (W grating thickness much smaller than the grating pitch), an emittance of 99.9% can be achieved for transverse magnetic (TM) polarization, but the transverse electric (TE) performance is appreciably lower. For deep gratings (W grating thickness on the order of the grating pitch), peak emittances of 97.8% and 99.7% for TE and TM polarizations, respectively, are achieved. We find that both surface plasmon polaritons and magnetic polaritons play a crucial role in shaping the emittance for TM radiation. On the other hand, cavity resonances are responsible for the almost perfect emittance in the case of TE polarization. These results suggest that by introducing an HfO2 layer it is possible to reach high emittance for operating temperatures that match the absorption characteristics of GaSb and InGaAs photovoltaic cells.

Design of broadband metamaterial near-perfect absorbers in visible region based on stacked metal-dielectric gratings

A broadband near-perfect absorber in the visible region has been designed in this paper. This absorber consists of an alternating stack of metallic gratings and dielectric layers on the basis of a metallic substrate. Absorptivity and electromagnetic field distributions of the structure via the finite difference time domain (FDTD) method have been stimulated. The results show that the average absorptance of the absorber exceeds 95.2% in the wavelength range from 350 nm to 650 nm. The enhanced absorption can be ascribed to several mechanisms including surface plasmon polaritons, magnetic polaritons, and Fabry–Perot resonances. Besides, geometric effects on the resonance wavelengths have been investigated. Moreover, the effects of oblique incidence and polarization states on the spectral absorption have been analyzed. This designed absorber will be worth applying in solar energy harvesting via combining the study results mentioned above.

Selective dual-band metamaterial perfect absorber for infrared stealth technology

We propose a dual-band metamaterial perfect absorber with a metal–insulator–metal structure (MIM) for use in infrared (IR) stealth technology. We designed the MIM structure to have surface plasmon polariton (SPP) and magnetic polariton (MP) resonance peaks at 1.54 μm and 6.2 μm, respectively. One peak suppresses the scattering signals used by laser-guided missiles, and the other matches the atmospheric absorption band, thereby enabling the suppression of long-wavelength IR (LWIR) and mid-wavelength IR (MWIR) signals from objects as they propagate through the air. We analysed the spectral properties of the resonance peaks by comparing the wavelength of the MP peak calculated using the finite-difference time-domain method with that obtained by utilizing an inductor–capacitor circuit model. We evaluated the dependence of the performance of the dual-band metamaterial perfect absorber on the incident angle of light at the surface. The proposed absorber was able to reduce the scattering of 1.54 μm IR laser light by more than 90% and suppress the MWIR and LWIR signatures by more than 92%, as well as maintain MWIR and LWIR signal reduction rates greater than 90% across a wide temperature range from room temperature to 500 °C.

Grating-type mid-infrared light absorber based on silicon carbide material.

A kind of grating-type mid-infrared light absorber based on silicon carbide (SiC) material is designed and its absorption properties are studied using the finite-difference frequency-domain (FDFD) method. The results show that, its absorption mechanism is the excitation of surface plasmon and magnetic polariton as well as the loss of materials. Due to the optical characteristics of the SiC material in the mid-infrared band and the truncated pyramid structure in the grating, in the range of 10.5-12.5μm and 0-80°, absorptivity of higher than 80% can be obtained with optimized structural parameters. Among six structural parameters, the layer number of the composite layers has a relatively great influence on the absorption properties, while the thickness of the dielectric layer has less influence on the absorption properties.

Near-field thermal radiation between homogeneous dual uniaxial electromagnetic metamaterials

Recently, near-field thermal radiation has attracted much attention in several fields since it can exceed the Planck blackbody limit through the coupling of evanescent waves. In this work, near-field radiative heat transfer between two semi-infinite dual uniaxial electromagnetic metamaterials with two different material property sets is theoretically analyzed. The near-field radiative heat transfer is calculated using fluctuational electrodynamics incorporated with anisotropic wave optics. The underlying mechanisms, namely, magnetic hyperbolic mode, magnetic surface polariton, electrical hyperbolic mode, and electrical surface polariton, between two homogeneous dual uniaxial electromagnetic metamaterials are investigated by examining the transmission coefficient and the spectral heat flux. The effect of vacuum gap distance is also studied, which shows that the enhancement at smaller vacuum gap is mainly due to hyperbolic mode and surface plasmon polariton modes. In addition, the results show that the contribution of s-polarized waves is significant and should not be excluded due to the strong magnetic response regardless of vacuum gap distances. The fundamental understanding and insights obtained here will facilitate the finding and application of novel materials for near-field thermal radiation.

Extraordinary terahertz transmission through a double-layer metal array with closed ring resonators

In this paper, we numerically investigate the transmission properties of a terahertz metamaterial. This metamaterial is composed of metal-dielectric-metal, which consists of metallic layers with an air hole array and one coaxial closed ring resonator in the air hole. The metamaterial in the THz range of 0.2–1THz has three transmission peaks. We provide an explanation of the transmission peaks by means of the surface plasmon polaritons and magnetic polaritons resonance based on the distribution of the surface current. Then according to the magnetic polaritons resonance, the equivalent circuit model of the metamaterial is established. The effects of geometric parameters on the transmission peaks are discussed and studied by an equivalent circuit model and surface plasmon polaritons dispersion relation. Our metamaterial promises dual-band potential applications such as filters.

Two-dimensional trilayer grating with a metal/insulator/metal structure as a thermophotovoltaic emitter.

A thermophotovoltaic system that converts thermal energy into electricity has considerable potential for applications in energy utilization fields. However, intensive emission in a wide spectral and angular range remains a challenge in improving system efficiency. This study proposes the use of a 2D trilayer grating with a tungsten/silica/tungsten (W/SiO2/W) structure on a tungsten substrate as a thermophotovoltaic emitter. The finite-difference time-domain method is employed to simulate the radiative properties of the proposed structure. A broadband high emittance with an average spectral emittance of 0.953 between 600 and 1800 nm can be obtained for both transverse magnetic and transverse electric polarized waves. On the basis of the inductance-capacitance circuit model and dispersion relation analyses, this phenomenon is mainly considered as the combined contribution of surface plasmon polaritons and magnetic polaritons. A parametric study is also conducted on the emittance spectrum of the proposed structure, considering geometric parameters, polar angles, and azimuthal angles for both TM and TE waves. The study demonstrates that the emitter has good wavelength selectivity and polarization insensitivity in a wide geometric and angular range.

Electromagnetic resonance modes on a two-dimensional tandem grating and its application for broadband absorption in the visible spectrum.

In this work, we numerically investigate the electromagnetic resonances on two-dimensional tandem grating structures. The base of a tandem grating consists of an opaque Au substrate, a SiO(2) spacer, and a Au grating (concave type); that is, a well-known fishnet structure forming Au/SiO(2)/Au stack. A convex-type Au grating (i.e., topmost grating) is then attached on top of the base fishnet structure with or without additional SiO(2) spacer, resulting in two types of tandem grating structures. In order to calculate the spectral reflectance and local magnetic field distribution, the finite-difference time-domain method is employed. When the topmost Au grating is directly added onto the base fishnet structure, the surface plasmon and magnetic polariton in the base structure are branched out due to the geometric asymmetry with respect to the SiO(2) spacer. If additional SiO(2) spacer is added between the topmost Au grating and the base fishnet structure, new magnetic resonance modes appear due to coupling between two vertically aligned Au/SiO(2)/Au stacks. With the understanding of multiple electromagnetic resonance modes on the proposed tandem grating structures, we successfully design a broadband absorber made of Au and SiO(2) in the visible spectrum.