Polariton Resonance Research Articles

Design and analysis of Matts-shaped perfect metamaterial absorber using equivalent circuit model

A mid-infrared perfect metamaterial absorber (PMA) consisting of well-engineered unit cells, composed of metallic backed layer (Cu), dielectric layer (Al2O3), matts-shaped meta cell (Cu), and an anti-oxidation layer from bottom to top, is proposed in this paper. The electromagnetic response of the designed PMA is analyzed using 3D full-wave computational model. Our analysis demonstrates that the maximum absorption is enhanced to 99.9% at the resonance wavelength of 7.35 µm, which is caused by magnetic polaritons (MPs) resonance between the incident beam and magnetic polaritons formed by three fluxing currents. Specially, a three-circulation equivalent circuit model is proposed to predict the resonant wavelength of the designed PMA, which comprehensively considers the influence of coupling capacitance not only between neighboring unit cells, but also between the metal lines inside the top metal pattern for the first time. The influence of geometrical parameters on resonant wavelength is predicted by the equivalent circuit model proposed in this paper, and the prediction error is less than 5% as compared with that of computational analysis. With well-engineered plasmonic meta-atoms, the designed PMA presents the characteristics of angle and polarization- independent with a smaller relative size (0.245λ) and a thinner relative thickness (0.053λ). Besides, an obvious red-shift of the resonance frequency of PMA is observed as the permittivity of dielectric layers is increased. The approach of establishing equivalent circuit model will provide methods for the analysis of PMA based on MPs with complex electromagnetic behavior.

Tunable Nonlinearity and Efficient Harmonic Generation from a Strongly Coupled Light–Matter System

Strong light–matter coupling within electromagnetic environments provides a promising path to modify and control chemical and physical processes. The origin of the enhancement of nonlinear optical processes such as second-harmonic and third-harmonic generation (SHG and THG) due to strong light–matter coupling is attributed to distinct physical effects, which questions the relevance of strong coupling in these processes. In this work, we leverage a first-principles approach to investigate the origins of the experimentally observed enhancement of resonant SHG and THG under strong light–matter coupling. For the proposed system under consideration, we find that the enhancement of the nonlinear conversion efficiency has its origins in a modification of the associated nonlinear optical susceptibilities as polaritonic resonances emerge in the nonlinear spectrum. Further, we find that the nonlinear conversion efficiency can be tuned by increasing the light–matter coupling strength. Finally, we provide an alternative framework to compute the harmonic generation spectra from the displacement field as opposed to the standard approach, which computes the harmonic spectrum from the matter-only induced polarization. Our results provide useful insights that shed light on this key debate in the field and pave the way for predicting and understanding quantum nonlinear optical phenomena in strongly coupled light–matter systems.

Ultrafast dynamics in plasmon-exciton core-shell systems: the role of heat.

Strong coupling between plasmons and excitons gives rise to new hybrid polariton states with potential applications in various fields. Despite a plethora of research on plasmon-exciton systems, their transient behaviour is not yet fully understood. Besides Rabi oscillations in the first few femtoseconds after optical excitation, coupled systems show interesting non-linear features on the picosecond time scale. Here, we conclusively show that the source of these features is heat that is generated inside the particles. Until now, this hypothesis was only based on phenomenological arguments. We investigate the role of heat by recording the transient spectra of plasmon-exciton core-shell nanoparticles with excitation off the polariton resonance. We present analytical simulations that precisely recreate the measurements solely by assuming an initial temperature rise of the electron gas inside the particles. The simulations combine established strategies for describing uncoupled plasmonic particles with a recently published model for static spectra. The simulations are consistent for various excitation powers, confirming that heating of the particles is indeed the root of the changes in the transient signals.

An electrical/thermal dual-controlled quad-functional terahertz metasurface absorber.

Although the design of graphene-based tunable broadband terahertz (THz) absorbers has attracted much attention, improving the functionality of the absorbers to adapt to different scenarios is still worth studying. This paper presents an innovative design of a quad-functional metasurface absorber (QMA) in the THz region, which can switch the absorption frequency/band by means of dual voltage/thermal manipulation. By electrically manipulating the chemical potential of graphene, the QMA can switch freely between the narrowband absorption mode ("NAM") and the broadband absorption mode ("BAM"), while thermally manipulating the phase transition of VO2 allows switching between the low-frequency absorption mode ("LAM") and the high-frequency absorption mode ("HAM"). Detailed mechanistic analysis shows that the "NAM" and "BAM" are due to the switching of the fundamental and second order graphene surface plasmon polariton (SPP) resonances, respectively, and the switching between "LAM" and "HAM" is due to the phase transformation of VO2. Furthermore, the QMA is polarization insensitive in all absorption modes and maintains excellent absorption performance at large angular incidence of TE- and TM-polarized waves. All the results indicate that the proposed QMA has great potential for stealth, sensing, switching, and filtering applications.

Broadband optical transmission through two-dimensional hole arrays

We suggest that a metal film perforated with two-dimensional (2D) hole arrays can support broadband optical transmission. This phenomenon is based on the impedance matching between the perforated metal film and incoming light waves at oblique incidence. Theoretical formulas for the effective impedance of the hole arrays and Brewster angle of broadband transmission have been derived in the infrared regime, taking account of the field penetration effect on the hole walls. With the numerical simulations, the predicted optical effect has also been demonstrated. Compared with the narrow transmission band due to surface-plasmon polariton resonance, our results present a non-resonant, broadband, and robust transmission channel for the 2D hole arrays.

Simulated Performance of a Broadband Solar Absorber Composed of Sectioned Au Disk Structures and ZnS/Au Thin Layers

Solar energy is considered an essential source of energy because of cleanliness and ubiquity. However, how to effectively absorb solar energy within the range of solar radiation is an urgent problem to be solved. The design of high-performance broadband perfect absorbers is an important way to collect solar energy efficiently. In this paper, we propose a novel broadband solar energy absorber based on zinc sulfide (ZnS). It is a three-layer (Au-ZnS-Au) structure with new types of sectioned disks employed in the top layer. The sectioned disks can enhance the absorption efficiency. Surface plasmon polariton (SPP) and electric dipole resonance increase the absorption of light, so the proposed absorber can achieve broadband perfect absorption. Simulation by a finite element analysis (COMSOL) method shows that absorption with a bandwidth of 354 THz from 430 THz–784 THz has been achieved, and the average absorption is 95%. This indicates that the perfect absorption range of the proposed absorber is 78.7% of the visible range. The perfect absorber has four perfect absorption peaks, which can reach a maximum absorption rate of 99.9%. In addition, our absorber is polarization insensitive due to the design of the rotational symmetry structure of the sectioned disks. The absorber is composed of refractory metals so that it can work under actual solar radiation and high-temperature conditions. The proposed solar energy absorber is important for many applications such as solar cells, thermal photovoltaic technology, and sensing.

Resonant Polariton Thermal Transport Along a Vacuum Gap

Going with the flow: The authors show that, in contrast to the well-known cross-plane heat transport in a cavity, the in-plane transport increases with gap distance up to 1 cm, where it takes on a maximum value that increases with temperature. This resonance occurs due to the thermal activation of hundreds of electromagnetic cavity modes, which are standing waves in the cross-plane direction, yet propagate within the plane. The energy of these modes leads to thermal emission comparable to the radiation predicted by Planck's law, and this effect could be useful for generating and evacuating super-Planckian heat currents along macroscale cavities.

Radiative cooling performance and life-cycle assessment of a scalable MgO paint for building applications

Passive daytime radiative cooling reduces building cooling load by simultaneously radiating infrared to the outer space (∼3 K) and reflecting solar irradiation without energy input. Developing a paint-format radiative cooling material and improving evaluation methods are critical for commercialization. Taking the advantage of high bandgap (7.6 eV) for low solar absorption, a facile, scalable, and high-performance MgO paint was developed in this work. Model Building cooling experiment and the corresponding thermodynamic modeling were carried out to investigate the cooling potential of the proposed paint in building applications. In addition, for the first time, a life-cycle assessment has been conducted for the developed MgO radiative cooling paint. Results show that the MgO paint exhibits a broadband infrared emissivity of ∼0.93 over the mid-IR region (2.5–25 μm) via phonon polariton resonances, simultaneously delivering a high solar reflectivity of ∼0.95 by particle scattering. A sub-ambient temperature reduction of ∼3.5 °C and a net cooling power of ∼61.2 W/m2 were experimentally demonstrated even on a humid and cloudy day with a peak solar irradiation of 868 W/m2. Furthermore, the MgO paint-coated building can achieve an indoor temperature reduction of ∼9.2 °C and a maximum cooling energy saving of ∼10 kWh/(m2⋅yr). The total environmental impact can be reduced by 7.92–24.75% with the developed MgO paint compared to the commercial one in the non-severe cold areas of China. This work provided a potentially scalable radiative cooling material and opened a new pathway for comprehensively evaluating radiative cooling materials.

Ultrafast All-Optical Polarization Switch Controlled by Optically Excited Picosecond Acoustic Perturbation of Exciton Resonance in Planar Microcavities

All-optical switching of the polarization of exciton polaritons is studied using a picosecond acoustic perturbation of the exciton resonance in high-$Q$ planar $\mathrm{Ga}\mathrm{As}$/$\mathrm{Al}\mathrm{As}$ microcavities. An irreversible switching of the degree of circular polarization from $22\mathrm{%}$ up to $82\mathrm{%}$ is realized in a microcavity pumped by a laser with a photon energy slightly exceeding the lower polariton resonance. The polarization switch is performed by a short-term, about 30-ps-long, blueshift of the exciton energy of ($\mathrm{In},\mathrm{Ga}$)$\mathrm{As}$ quantum wells in the cavity active layer by a 10-ps strain pulse generated in the $\mathrm{Ga}\mathrm{As}$ substrate by a violet femtosecond laser pulse and injected into the microcavity. The proposed all-optical control of light polarization using acoustic modulation of a polariton resonance opens the way for fast and easily tunable optical polarization switches.

Electrically controlled molecular fingerprint retrieval with van der Waals metasurface

Polaritons in two-dimensional van der Waals (vdW) materials possess extreme light confinement, which have emerged as a potential platform for next-generation biosensing and infrared spectroscopy. Here, we propose an ultra-thin and electric tunable graphene/hexagonal boron nitride/graphene metasurface for detecting molecular fingerprints over a broad spectrum. The vdW metasurface supports hybrid plasmon–phonon polariton resonance with high-quality factor (Q > 120) and electrically controlled broadband spectra tunability from 6.5 to 7 μm. After coating a thin layer of bio-molecular (e.g., CBP) on top of the metasurface, the molecular absorption signatures can be readout at multiple spectral points and, thus, achieve broadband fingerprint retrieval of bio-molecules. Additionally, our electric tunable metasurface works as an integrated graphene-based field-effect transistor device, without the need of multiple resonance generators such as angle-resolved or pixelated dielectric metasurfaces for broadband spectra scanning, thereby paving the way for highly sensitive, miniaturized, and electrically addressed biosensing and infrared spectroscopy.

Surface exciton polariton resonances (SEPR)–based sensors

A new type of resonance in the development of sensors using long-range surface exciton polariton (LRSEP) phenomena has been coined: surface exciton polariton resonance (SEPR). The resonance was obtained in the reflected spectrum of a Kretschmann-Raether setup with a two-coupled-interface structure composed of 412 nm magnesium fluoride and 50 nm chromium thin films. The roles of different parameters such as thicknesses of the films and the incidence angles have been simulated. Some preliminary experimental results show a promising performance with a shift of the resonance central wavelength with changes in the incidence angle of -136.52 nm/° and a sensitivity of 23,221 nm/refractive index unit.

Versatile terahertz graphene metasurface based on plasmon-induced transparency

A monolayer terahertz graphene metasurface is designed to achieve tunable plasmon-induced transparency (PIT) effect in two perpendicular polarization directions based on surface plasmon polariton resonance. The penta-frequency and dual-frequency switch can be easily implemented by adjusting the Fermi levels of graphene, and the switch has excellent performances including modulation degree of amplitude (81.4 % < MDA < 97.1 %) and insertion loss (0.01 dB < IL < 0.04 dB). Moreover, the metasurface has high sensitivity, which can be up to 30500 nm/RIU. Also, the designed PIT metasurface has a good slow light effect, and group indexes are respectively 1100 and 2396 corresponding to x-polarized and y-polarized light. This work demonstrates that graphene metasurface has potential applications in switch, sensor and slow-light devices.

Enhanced graphene surface plasmonics through incorporation into metallic nanostructures.

A methodology for enhancing the surface plasmon polariton (SPP) resonance associated with graphene, through nanoscale metal-dielectric-metal (MDM) gaps, is proposed. The modulation of the resonances, in the range of 0.7 µm to 1 µm was done through tuning the carrier density in graphene and has been shown to be of potential utility for surface analyte sensing. It was shown, from finite element simulations in the frequency domain, that the related hybrid SPP modes could be clearly delineated in far field spectroscopy.

Modal approximation for time-domain elastic scattering from metamaterial quasiparticles

This paper aims at quantitatively understanding the elastic wave scattering due to negative metamaterial structures under wide-band signals in the time domain. Specifically, we establish the modal expansion for the time-dependent field scattered by metamaterial quasiparticles in elastodynamics. By Fourier transform, we first analyze the modal expansion in the time-harmonic regime. With the presence of quasiparticles, we validate such an expansion in the static regime via quantitatively analyzing the spectral properties of the Neumann-Poincaré operator associated with the elastostatic system. We then approximate the incident field with a finite number of modes and apply perturbation theory to obtain such an expansion in the perturbative regime. In addition, we give polariton resonances as simple poles for the elastostatic system. Finally, we show that the low-frequency part of the scattered field in the time domain can be well approximated by using the resonant modal expansion with sharp error estimates.

Organic Anisotropic Excitonic Optical Nanoantennas (Adv. Sci. 23/2022)

Optical Nanoantennas Optical nanoantennas based on organic anisotropic J-aggregate materials with strong exciton absorption provide dual functionality in the same nanostructure. The shadows of the nanoantenna represent the hyperbolic localized surface exciton polariton resonance and the elliptic Mie resonance on either spectral side of the exciton resonance. More details can be found in article number 2201907 by Evan S. H. Kang, Magnus P. Jonsson, and co-workers.

Atomic-Void van der Waals Channel Waveguides

Layered van der Waals materials allow creating unique atomic-void channels with subnanometer dimensions. Coupling light into these channels may further advance sensing, quantum information, and single molecule chemistries. Here, we examine theoretically limits of light guiding in atomic-void channels and show that van der Waals materials exhibiting strong resonances, excitonic and polaritonic, are ideally suited for deeply subwavelength light guiding. We predict that excitonic transition metal dichalcogenides can squeeze >70% of optical power in just <λ/100 thick channel in the visible and near-infrared. We also show that polariton resonances of hexagonal boron nitride allow deeply subwavelength (<λ/500) guiding in the mid-infrared. We further reveal effects of natural material anisotropy and discuss the influence of losses. Such van der Waals channel waveguides while offering extreme optical confinement exhibit significantly lower loss compared to plasmonic counterparts, thus paving the way to low-loss and deeply subwavelength optics.

Polariton Resonance in the Self-Modulation of the Asymmetric State of a Superradiant Laser

Polariton Resonance in the Self-Modulation of the Asymmetric State of a Superradiant Laser

Independently tunable triple-band infrared perfect absorber based on the square loops-shaped nano-silver structure

Recently, the keen demand for multi-band perfect absorbers in spectroscopy, infrared detection, and other fields has intensified. To meet the energy demand, here we propose an Ag-Dielectric-Ag multilayer triple-band perfect absorber exhibiting perfectly resonance absorption in the near-infrared region. And the numerical calculations indicate that we obtain three resonance absorption peaks (908 nm, 1085 nm, and 1216 nm) with the maximal absorption of 99.09%, 99.84%, and 99.21%, respectively. Based on this, we propose that the physical formation mechanism of three resonance peaks are the Fabry-Pérot resonance effect and Localized surface plasmon polaritons resonance. Theoretically combined with the electromagnetic coupling theory to explain how the resonance-enhanced absorption. At the same time, by the comparison with the complementary structure, it is theoretically proposed that the MIM structure has a Fabry-Pérot resonance effect in the near-infrared region and then computationally verified the Fabry-Pérot formula. Furthermore, we can adjust the amplitude and wavelength of resonance peaks by modifying the geometry unit cell. And our proposed triple-band perfect absorber has some excellent properties, such as high absorptivity, multi-band, tunable, suitability for wide incidence angles, excellent angle tolerance, polarization tolerance, etc. In addition, our TBPA has a simple structure, which simplifies the processing technology and economically saves processing costs. Furthermore, the following simulations investigate the absorption spectrum of our TBPA exhibit property changes significantly as the environment changes. So we can calculate the sensitivity of three modes (sorted by resonance wavelength from short to long) is S1 = 70.09 nm/RIU, S2 = 208.26 nm/RIU, and S3 = 50.06 nm/RIU, respectively. Therefore, we believe that this triple-band perfect absorber can capture maximize optical energy and apply it in devices and materials for light conversions, like plasmon-enhanced photovoltaics, optical absorption switching, and modulator-optical communications.

Polarization-Multiplexed Incoherent Broadband Surface Plasmon Resonance: A New Analytical Strategy for Plasmonic Sensing.

Surface plasmon resonance (SPR) is an interfacial phenomenon, and the plasmonic sensors are based on the optical excitation of the collective oscillations of free electrons at a metal-dielectric interface. Here, we present the new development of an incoherent broadband (IBB)-SPR probe combining the wavelength interrogation technique with polarization-multiplexing (PM). The performance characteristics of the so-called PMIBB-SPR strategy was validated for the detection of nonenzymatic aqueous urea samples as a representative example for plasmonic sensing with an excellent wavelength and phase sensitivities of 0.1363 nm/mM and 10.34597 mM/deg, respectively. We further explored the missing link between plasmonic polariton resonance (PPR) and polarization modulation via the measurements of the Stokes parameters of the reflected light. This deepens our understanding of the fundamentals of polarization-multiplexed SPR phenomenon at the interface. This study thus paves the way to develop a new-generation analytical technique with the aim of tracking various real-time chemical and biological molecular interactions occurring at the interfaces.

Giant Photoelasticity of Polaritons for Detection of Coherent Phonons in a Superlattice with Quantum Sensitivity.

The functionality of phonon-based quantum devices largely depends on the efficiency of the interaction of phonons with other excitations. For phonon frequencies above 20GHz, generation and detection of the phonon quanta can be monitored through photons. The photon-phonon interaction can be enormously strengthened by involving an intermediate resonant quasiparticle, e.g., an exciton, with which a photon forms a polariton. In this work, we discover a giant photoelasticity of exciton-polaritons in a short-period superlattice and exploit it to detect propagating acoustic phonons. We demonstrate that 42GHz coherent phonons can be detected with extremely high sensitivity in the time domain Brillouin oscillations by probing with photons in the spectral vicinity of the polariton resonance.