Characteristic Surface Plasmon Research Articles

Spinning spoof surface plasmons and their topological responses

Spoof surface plasmons (SSPs) mimic characteristics of optical surface plasmons in microwave and terahertz frequencies. Manipulating SSPs has attracted widespread attention for extending plasmon applications into the low-frequency range. In this Letter, we show that spinning SSPs can be excited on a twisted groove (TG) metallic cylinder by oblique incident waves. The incident angle of waves and the twist angle of the grooves play essential roles in manipulating the propagation orientation and the rotation direction of spinning SSPs (SSSPs). Finally, we discuss an application of the SSSPs in topological photonic systems. By periodically arranging the TG cylinders, we show that this spinning feature will lead to topologically non-trivial bands in such a photonic crystal, where the topologically protected edge modes arise near the boundary.

A comparative study of coherent and incoherent drives in a four-level quantum dot–based spaser

Abstract In this article, we theoretically investigate a spaser (surface plasmon amplification by stimulated emission of radiation) comprising a spherical silver nanoparticle surrounded by a four-level gain medium of quantum dots. The spaser system is pumped coherently and incoherently with the same excitation rate, and the characteristics of the resultant coherent localized surface plasmon (LSP) mode are compared for the two pumping scenarios. We provide a detailed analytical expression for the steady state and demonstrate that the incoherent pump is more suitable for the continuous spaser mode. The reason is better understood by studying the temporal evolution of the number of LSPs N n , where the LSP oscillation starts earlier for an incoherent drive and relaxes to a steady state with a large value of N n . At a large pump rate, the spaser curve shows saturation. In addition, we have found that the resonance peak of the spaser field is independent of coherent and incoherent pumping, whereas the peak amplitude of the field depends on the pump rate.

Logic operation and all-optical switch characteristics of graphene surface plasmons.

Terahertz logic gates play a crucial role in optical signal processing and THz digitization. In this paper, we propose a design strategy for graphene-based metamaterial THz all-optical logic gate devices based on the induced transparency effect of surface isolated. Theoretically, we realize Boolean operations by coupling of a hexagonal graphene resonant cavity with dual embedded rotatable ellipses. Based on the coupled mode theory, the elliptical rotation angle of the resonator is an important factor affecting the PIT phenomenon. We control the logic input by adjusting the rotation angles of the two embedded ellipses. The analysis results show that: under the incidence of y-polarized light, the ellipse deflection angle of 0° represents the input signal '0', and the ellipse deflection angle of 30° represents the input signal '1'. Through numerical simulation, the structure realizes two logical operations of NAND and AND. Under the incidence of x-polarized light, the ellipse deflection angle of 0° represents the input signal '0', and the ellipse deflection angle of 90° represents the input signal '1'. Through numerical simulation, the structure realizes three logical operations of NAND, XNOR and OR. Finally, we analyze the performance of the logic gates by extinction ratio. The extinction ratio of the logic gate is up to 10.38 dB when performing OR Boolean operations. Numerically simulated all-optical logic gates can be key components of optical processing and telecommunication equipment.

МОДЕЛЮВАННЯ ПЛАЗМОННИХ ВЛАСТИВОСТЕЙ ЧАСТИНОК МОНОСУЛЬФІДУ МІДІ В БЛИЖНЬОМУ ІЧ ДІАПАЗОНІ

This paper is devoted to the theoretical study of the extinction spectra of copper monosulfide particles under conditions of localized surface plasmon resonance. The study was conducted for plasmonic copper monosulfide particles of spherical and ellipsoidal shapes of variable size in media with different values of the refractive index. The simulation results reveal that increasing the radius of CuS nanoparticles leads to a significant enhancement in the amplitude of the plasmon peak and a shift of the peak towards longer wavelengths. It was investigated how the positions of the extinction peaks on the spectral scale and their amplitudes change when the particles deviate from the spherical shape. Simulations were performed for spherical and elongated ellipsoidal particles with fixed cross-sectional radius and variable length. Specifically, we varied the length of the major axis while keeping the lengths of the minor axes constant. It is shown that the deviation from the sphericity of the particles will affect both the position of the extinction maximum on the spectral scale and the shape of the spectral curve. An increase in the ratio of the ellipsoid semi-axes lengths leads to a significant increase in the amplitude of the extinction peak and its shift to the long-wavelength region. Besides, the position of the plasmonic peak on the spectral scale is influenced not only by the geometric parameters of the particles such as size and shape but also by the dielectric properties of the surrounding medium, including its refractive index. We assess the impact of changing the refractive index of the surrounding medium on the shape, amplitude, and position of the extinction maxima of CuS nanoparticles. It is showed that increasing the refractive index of the surrounding medium leads to a significant shift of the plasmon resonance peak into the long-wavelength region of the spectrum an increase in the peak width, and a decrease in its amplitude. Thus, ellipsoid copper monosulfide particles show improved surface plasmon characteristics compared to spherical ones and can be effectively used in the near-infrared spectral region.

Femtosecond Autocorrelation of Localized Surface Plasmons.

Plasmon electronic dephasing lifetime is one of the most important characteristics of localized surface plasmons, which is crucial both for understanding the related photophysics and for their applications in photonic and optoelectronic devices. This lifetime is generally shorter than 100 fs and measured using the femtosecond pump-probe technique, which requires femtosecond laser amplifiers delivering pulses with a duration even as short as 10 fs. This implies a large-scale laser system with complicated pulse compression schemes, introducing high-cost and technological challenges. Meanwhile, the strong optical pulse from an amplifier induces more thermal-related effects, disturbing the precise resolution of the pure electronic dephasing lifetime. In this work, we use a simple autocorrelator design and integrate it with the sample of plasmonic nanostructures, where a femtosecond laser oscillator supplies the incident pulses for autocorrelation measurements. Thus, the measured autocorrelation trace carries the optical modulation on the incident pulses. The dephasing lifetime can be thus determined by a comparison between the theoretical fittings to the autocorrelation traces with and without the plasmonic modulation. The measured timescale for the autocorrelation modulation is an indirect determination of the plasmonic dephasing lifetime. This supplies a simple, rapid, and low-cost method for quantitative characterization of the ultrafast optical response of localized surface plasmons.

Near-field manipulation of Tamm plasmon polaritons.

Tamm plasmon polaritons (TPPs) arise from electromagnetic resonant phenomena which appear at the interface between a metallic film and a distributed Bragg reflector. They differ from surface plasmon polaritons (SPPs), since TPPs possess both cavity mode properties and surface plasmon characteristics. In this paper, the propagation properties of TPPs are carefully investigated. With the aid of nanoantenna couplers, polarization-controlled TPP waves can propagate directionally. By combining nanoantenna couplers with Fresnel zone plates, asymmetric double focusing of TPP wave is observed. Moreover, radial unidirectional coupling of the TPP wave can be achieved when the nanoantenna couplers are arranged along a circular or a spiral shape, which shows superior focusing ability compared to a single circular or spiral groove since the electric field intensity at the focal point is 4 times larger. In comparison with SPPs, TPPs possess higher excitation efficiency and lower propagation loss. The numerical investigation shows that TPP waves have great potential in integrated photonics and on-chip devices.

Recent progress of gold nanostructures and their applications.

For noble metals, such as gold (Au) and silver (Ag), it is well-known that surface plasmons of their nanocrystals have significant spatial confinement and propagation loss due to the strong damping effect and the scattering between the plasmons and phonons. Noble metal nanostructures are usually referred to as "plasmonic nanostructures" in many studies. Based on the resonance effect of surface plasmons, the electromagnetic field can be localized on the subwavelength scale, which induces a booming new field of nanophotonics. Among the various nanostructures, Au nanostructures have received extensive attention both in fundamental research and technological fields due to their unique localized surface plasmon characteristics. These characteristics include strong optical extinction, near-field enhancement, and far-field scattering. By changing either the morphological parameters or the surrounding medium of nanostructures, the localized surface plasmon resonance (SPR) of Au nanostructures can be tuned in a large spectral region from visible to near infrared (Vis-NIR) wavelength. Corresponding to the experimental research, there are several numerical techniques that enable modeling the optical characteristics of Au nanostructures in different shapes and assemblies. The most popular technique is the finite-difference time-domain (FDTD) method for modeling various nanostructures and nanoscale optical devices. The accuracy of the computational models has been proven by reliable experimental data. In this review, we focused on Au nanostructures of different morphologies, such as nanorods, nanocubes, nanobipyramids and nanostars. Then combined with FDTD simulations, we described the effect of morphological parameters and the surrounding medium on the SPR properties of Au nanostructures. More and more achievements indicate that the surface plasmon effect is promising in many technical fields. In the last part, we summarize some typical applications of plasmonic Au nanostructures, such as high sensitivity sensors, photothermal conversion with hot electron effects and photoelectric devices, as well as plasmonic nanolasers.

Surface plasmon resonance of the W nanowires

The Surface plasmon resonance (SPR) of metal materials has been widely used in photocatalysis, light sensing, biomarkers, solar cells and other fields. In this study, the surface plasmon characteristics of tungsten (W) nanowires with different diameters and lengths are analyzed using the finite element method. The thermal effect in the gap of crossed nanowires induced by the plasma resonance is studied. Results show that the resonance peak shifts red, and the resonance intensity increases with the increase in diameter. The increasing diameter results in decreasing electric field intensity and heat in the gap of the crossed tungsten (W) nanowires. The frequency of resonance peaks almost remains unchanged with increasing length. The two to six wave belly plasma modes are visible with increasing nanowire length. With exposure to incident light, the SPR in the shortened spacing results in increasing electric field intensity and the generated heat of gap between the two crossed tungsten (W) nanowires. Once the two crossed nanowires are welded, the heat production in the crossed part decreases, which indicates the self-limitation of plasma welding.

Enhanced electron transfer due to rGO makes Ag–CaTiO3@rGO a promising plasmonic photocatalyst

Herein, the synthesis of a new ternary nanocomposite, Ag–CaTiO 3 @rGO, exhibiting high photocatalytic dye degradation efficiency is reported. The photocatalytic activity of Ag–CaTiO 3 @rGO was studied under natural sunlight with a model dye pollutant sulforhodamine B. This photocatalyst's high degradation efficiency is attributed to the synergistic effect of plasmon-induced visible light-harvesting due to Ag and enhanced adsorption and electron–transport properties due to rGO. It is found that the Ag-induced surface plasmon characteristics of the nanocomposites are sensitive to rGO concentration. Absorption spectra of the nanocomposites indicated that Ag and rGO enhance and extend the absorbance in the visible region, which is beneficial for creating photo-carriers during the photocatalytic reaction under sunlight. In the X-ray photoelectron spectra, ∼0.7–0.8 eV positive binding energy shift is observed in Ca 2p, Ti 2p, and O 1s peaks of typical Ag–CaTiO 3 @rGO compared to Ag–CaTiO 3 and CaTiO 3 , indicating that electrons are transferred to the electron acceptor, rGO. The reusability of this photocatalyst Ag–CaTiO 3 @rGO was analyzed by conducting repeated dye degradation tests. The adsorption characteristics of the designed catalyst followed the Langmuir isotherm model. A model for the plausible mechanism of enhanced sunlight-driven photocatalysis by Ag–CaTiO 3 @rGO with 7.5 wt% GO is also proposed.

Remotely controlled near-infrared-triggered photothermal treatment of brain tumours in freely behaving mice using gold nanostars.

Current clinical brain tumour therapy practices are based on tumour resection and post-operative chemotherapy or X-ray radiation. Resection requires technically challenging open-skull surgeries that can lead to major neurological deficits and, in some cases, death. Treatments with X-ray and chemotherapy, on the other hand, cause major side-effects such as damage to surrounding normal brain tissues and other organs. Here we report the development of an integrated nanomedicine-bioelectronics brain-machine interface that enables continuous and on-demand treatment of brain tumours, without open-skull surgery and toxicological side-effects on other organs. Near-infrared surface plasmon characteristics of our gold nanostars enabled the precise treatment of deep brain tumours in freely behaving mice. Moreover, the nanostars' surface coating enabled their selective diffusion in tumour tissues after intratumoral administration, leading to the exclusive heating of tumours for treatment. This versatile remotely controlled and wireless method allows the adjustment of nanoparticles' photothermal strength, as well as power and wavelength of the therapeutic light, to target tumours in different anatomical locations within the brain.

Tunable narrow-linewidth surface plasmon resonances of graphene-wrapped dielectric nanoparticles in the visible and near-infrared

We investigate the plasmon resonance in the light interaction with a graphene nanoshell which consists of graphene wrapped around a low − loss dielectric core. In this work, Polystyrene (PS) and Titanium dioxide (TiO 2 ) cores are proposed. This study is restricted to small nanoparticles with diameters significantly smaller than the wavelength of incident light. Therefore, we adopt the quasi − static approach that provides in − depth insights into the plasmon resonance of core − shell nanoparticles. The proposed graphene nanoshell can support two localized surface plasmon resonances (LSPRs). These plasmon resonance modes correspond to the symmetric and antisymmetric dipole-like modes described in the hybridization theory. The observed resonance modes are characterized by a narrow bandwidth and a broadband resonance tunability in the visible to near-infrared (NIF) range. The impacts of the optical properties of graphene, core material, and nanoshell geometry on surface plasmon features are explored. We show that the features of each plasmonic resonance meet the demands for specific nanoscale applications such as biosensing, photothermal therapy, and in vivo imaging. • We study the plasmon resonance of graphene nanoshells with low − loss dielectric core. • In our model, Polystyrene (PS) and Titanium dioxide (TiO 2 ) cores are proposed. • Graphene nanoshells exhibits two plasmon resonances, sphere and cavity plasmons. • Plasmon resonances have a very narrow bandwidth with a broadband tunability. • Features of plasmon resonances are attractive for nanosensing/medical applications.

Recent advances in ultrafast plasmonics: from strong field physics to ultraprecision spectroscopy

Abstract Surface plasmons, the collective oscillation of electrons, enable the manipulation of optical fields with unprecedented spatial and time resolutions. They are the workhorse of a large set of applications, such as chemical/biological sensors or Raman scattering spectroscopy, to name only a few. In particular, the ultrafast optical response configures one of the most fundamental characteristics of surface plasmons. Thus, the rich physics about photon–electron interactions could be retrieved and studied in detail. The associated plasmon-enhanced electric fields, generated by focusing the surface plasmons far beyond the diffraction limit, allow reaching the strong field regime with relatively low input laser intensities. This is in clear contrast to conventional optical methods, where their intrinsic limitations demand the use of large and costly laser amplifiers, to attain high electric fields, able to manipulate the electron dynamics in the non-linear regime. Moreover, the coherent plasmonic field excited by the optical field inherits an ultrahigh precision that could be properly exploited in, for instance, ultraprecision spectroscopy. In this review, we summarize the research achievements and developments in ultrafast plasmonics over the last decade. We particularly emphasize the strong-field physics aspects and the ultraprecision spectroscopy using optical frequency combs.

Resonantly enhanced absorption in bifurcation plasmonic nanostructure for refractive index sensing

By changing or fine-tuning the surface structure of the metal, the characteristics of surface plasmon – especially the interaction with light – can be customized. In this work, we numerically design a plasmonic nanostructure composed of a pair of symmetrical bifurcation nanostructures. An underlying optical property of the observed scattering and absorption cross section spectra and physical mechanism is illustrated by analyzing spatial distributions of the magnetic field, electric field, and surface current component at resonant wavelengths. Moreover, the extremely intense and highly confined electromagnetic fields induced in the bifurcation plasmonic nanostructure provide a sensitive environment to probe minor changes in the dielectric environment. Such high-performance composite nanostructure provides great potential for the application of sensing.

Effect of surface plasmon coupling with radiating dipole on the polarization characteristics of AlGaN-based light-emitting diodes

The optical polarization characteristics of surface plasmon (SP) coupled AlGaN-based light emitting diodes (LEDs) are investigated theoretically by analyzing the radiation recombination process and scattering process respectively. For the Al0.5Ga0.5N/Al/Al2O3 slab structure, the relative intensity of TE-polarized and TM-polarized spontaneous emission (SE) rate into the SP mode obviously depends on the thickness of the Al layer. The calculation results show that TM dominated emission will be transformed into TE dominated emission with the decrease of the Al thickness, while the emission intensities of both TE/TM polarizations will decrease significantly. In addition, compared with TM polarized emission, TE polarized emission is easier to be extracted by SP coupling. For the Al0.5Ga0.5N/Al nano-particle structure, the ratio of transmittance for TE/TM polarized emission can reach ∼ 3.06, while for the Al free structure, it is only 1.2. Thus, the degree of polarization of SP coupled LED can be improved by the reasonable structural design.

Numerical simulation of strong coupling between silver nanorod and dielectric layer detected by electron energy loss spectrum

The strong coupling phenomenon between surface plasmons and quantum emitters has received extensive attention in recent years. It is usually studied by the far-field spectral detection method such as scattering, absorption, and fluorescence. In the electron energy loss spectroscopy (EELS), highly focused electron beams are used for implementing the local detection on a sub-nanometer scale, which can be more effective to study strong coupling. In this work, the electron energy loss spectrum of silver nanorods, dielectric materials and their composite core-shell nanostructures are theoretically simulated respectively, and the energy and mode characteristics of surface plasmons on the silver nanorods and the excitation characteristics of dielectric materials are obtained. The electron energy loss spectrum of surface plasmon is basically consistent with the related experimental result. Rabi splitting of spectral peaks is observed in the electron energy loss spectra of the above composite structures, and the effect of Ag nanorod size on Rabi splitting is explored. The strong coupling between the radiative dipolar and non-radiative higher-order plasmon with the excitation of the dielectric materials in the infrared and visible band is discussed, and the corresponding dispersion relation is analyzed with the coupled oscillator mode. Furthermore, the plexciton caused by strong coupling are discussed from the perspective of spatial distribution of loss spectrum imaging. Our study builds the basis for further theoretical study, and can guide the further experimental research.

Design of dual-core photonic crystal fiber for temperature sensor based on surface plasmon resonance effect

A toluene-ethanol filled dual-core photonic crystal fiber (PCF) based on surface plasmon resonance effect is designed for temperature sensing. The toluene with higher refractive index is injected into the central air hole in order to support the core mode. In contrast, the ethanol, whose refractive index is lower, is injected into the sideward air hole coated by gold film to support the mode induced by surface plasmon polariton. The resonance characteristics of surface plasmon in the designed PCF are numerically investigated by using finite element method. It is shown that the influences of structure parameters on temperature sensing performance are different. On the other hand, the resulting resonance wavelength of the spectrum of confinement loss moves to longer wavelength to satisfy the phase matching when the detective temperature is increased. After optimizing structure parameters, the sensitivity of temperature sensor can reach 6.32 nm/°C in the range from 10 °C to 70 °C, indicating its potential applications in temperature measurement with wide temperature range.

Dispersion properties of plasmonic sub-wavelength elliptical wires wrapped with graphene

One fundamental motivation to know the dispersive or frequency dependent characteristics of localized surface plasmons (LSPs) supported by elliptical shaped particles wrapped with a graphene sheet, as well as their scattering characteristics when these elliptical LSPs are excited, is related to the design of plasmonic structures capable of manipulating light at sub-wavelength scale. The anisotropy imposed by ellipse eccentricity can be used as a geometrical tool for controlling plasmonic resonances. Unlike the metallic case, where multipolar eigenmodes are independent of each other, we find that the induced current on a graphene boundary couples multipolar eigenmodes with the same parity. In the long wavelength limit, a recursive relation equation for LSPs in terms of the ellipse eccentricity parameter is derived, and explicit solutions at lowest order are presented. In this approximation, we obtain analytical expressions for both the anisotropic polarizability tensor elements and the scattered power when LSPs are excited by plane wave incidence.

Plasmon resonance at the interface dielectric - nanocomposite material with superconducting inclusions

This article theoretically considers surface plasmon resonance in composite structures. The features of the surface plasmon resonance arising at the interface with media containing nanoparticles from a high-temperature superconductor are investigated. The dielectric constant of spherical superconducting inclusions is considered taking into account Gorter-Casimir two-fluid model. The temperature dependence of the electrodynamic parameters of the superconductor is taken into account. The two-fluid model, the dependence of the concentration of non-superconducting electrons in a superconductor is often used as the fourth power of temperature nn~T4. In this work, a phenomenological model is used, according to which the electron concentration of non-superconducting electrons in a superconductor is determined by the formula nn~Tγ with γ=1.3÷2. This model is in good agreement with experimental data for high-temperature ceramic superconductors. The dispersion characteristics of surface plasmons arising in a planar structure with a thin nanocomposite superconductor layer are investigated. It is shown that the dispersion characteristics depend significantly on temperature.

High-performance tunable resonant electro-optical modulator based on suspended graphene waveguides.

The exceptional tunable waveguiding characteristics of graphene surface plasmons have remained unrivaled since it has inspired many electro-optical (EO) devices in terahertz (THz) and mid-infrared (MIR) photonic circuits. We propose and numerically investigate a low-loss, highly extinctive resonant EO modulator based on a suspended graphene plasmonic waveguide. Unlike other resonance-based modulators, the input power has negligible interaction with lossy resonance cavity in on-state, remarkably reducing the losses. Achieving the insertion loss (IL) of 1.3 dB and the extinction ratio (ER) of 22 dB within a footprint less than 3 µm2 substantiates the superiority of the proposed structure. The charge transport simulations are first conducted to calculate the steady-state charge distribution. The three-dimensional finite-difference time-domain (3D-FDTD) method is utilized to monitor the guided wave propagation and modulation properties. We show that the transmission spectrum is highly dependent upon geometric parameters of the structure, and the modulator can be effectively tuned to operate at the desired wavelength by applying a suitable gate voltage. Simulation results show the modulation bandwidth of 71 GHz corresponding to the total capacitance of 4.8 fF within the active area. The novel EO modulator structure has shown great potentiality and flexibility to find other applications in MIR and THz integrated circuits like controllable notch filters and switches.

Propagation and diffraction of surface plasmons on a resistive half-plane

The propagation, radiation and diffraction characteristics of surface plasmons, on a discontinuous dielectric layer, are investigated. The layer is modeled by a resistive surface. The physical optics based formulation of the surface waves is taken into account. The physical optics integral includes the propagating and diffracting fields. These wave components are evaluated asymptotically and their behaviors are studied numerically.