Plasmon Polaritons Research Articles

Optimal structure for resonant THz detection of plasmons–polaritons in the 2D quantum wells

We investigate terahertz plasmon-polariton (PP) resonances for hetero-structures (AlGaN/GaN, SiGe/Si/SiGe, AlGaAs/GaAs and InAlN/GaN) with grating coupler in order to find the optimal structure. We show a modeling work devoted to a parametric study (influence of geometry, temperature…) that the resonances are tunable in frequency allowing a control of the terahertz detection. The modeling shows that AlGaN/GaN and InAlN/GaN heterostructures present the highest PP resonances at 300K. Then we compare modeling with room temperature and cryogenic temperature FTIR measurements on group III-N heterostructures which are indeed the most promising.

Ultrastrong Coupling Regime and Plasmon Polaritons in Parabolic Semiconductor Quantum Wells

Ultrastrong coupling is studied in a modulation-doped parabolic potential well coupled to an inductance-capacitance resonant circuit. In this system, in accordance to Kohn's theorem, strong reduction of the energy level separation caused by the electron-electron interaction compensates the depolarization shift. As a result, a very large ratio of 27% of the Rabi frequency to the center resonance frequency as well as a polariton gap of width 2π × 670 GHz are observed, suggesting parabolic quantum wells as the system of choice in order to explore the ultrastrong coupling regime.

Unfolding of plasmon-polariton modes in one-dimensional layered systems containing anisotropic left-handed materials

The propagation of electromagnetic waves through a 1-dimensional layered system containing alternate layers of air and a uniaxial, anisotropic, left-handed material is investigated. The optical axis of this material is along the stacking direction and the components of the electric permittivity and magnetic permeability tensors that characterize the metamaterial are described by Drude-type responses. Different plasmon frequencies are considered for directions parallel and perpendicular to the optical axis. As in the isotropic case, plasmon polariton modes are found in the neighborhood of the plasmon frequency corresponding to the optical axis. Moreover, it is shown that, depending on the relation between the two plasmon frequencies of the metamaterial, anisotropy leads to the unfolding of an infinite number of nearly dispersionless plasmon-polariton bands either above or below the parallel plasmon frequency.

Opals with a thin-film metallic defect-hybrid colloidal plasmonic photonic crystals

Hybrid photonic crystals consisting of a thin-film opal and a thin profiled gold film situated on the surface or inside the opal have been prepared. The optical transmittance spectra of hybrid crystals have been studied. It has been found that the spectra exhibit minima due to diffraction resonances in the photonic crystal and bands of enhanced transmission due to transfer of radiation through the metal film surface by plasmon polaritons. It has been shown that the transmittance spectra of hybrid crystals with a metal film on the surface are subjected to a stronger modification than the hybrids having a metal film inside the crystal.

Cavity plasmon polaritons in monolayer graphene

Plasmon polaritons in a new system, a monolayer doped graphene embedded in optical microcavity, are studied here. The dispersion law for lower and upper cavity plasmon polaritons is obtained. Peculiarities of Rabi splitting for the system are analyzed; particularly, role of Dirac-like spinor (envelope) wave functions in graphene and corresponding angle factors are considered. Typical Rabi frequencies for maximal (acceptable for Dirac-like electron spectra) Fermi energy and frequencies of polaritons near polariton gap are estimated. The plasmon polaritons in considered system can be used for high-speed information transfer in the THz region.

An application of a plasmonic chip with enhanced fluorescence to a simple biosensor with extended dynamic range

Plasmonic chips coated with thin silver and SiO 2 layers were applied to a simple biosensor with wide dynamic range, which has some advantages in the points of sensitivity and surface selectivity in spite of a simple fluorescence detection system without complex optical stuffs. The enhanced fluorescence of fluorescent labeled-marker proteins, cy5-streptavidin (SA), excited by irradiation light from the rear panel of the chip was measured. To obtain the maximum fluorescence enhancement by excitation under an electric field enhanced by grating-coupled surface plasmon resonance from the rear irradiation, the optimal silver thickness was studied and found to be 30–35 nm. A directional fluorescence due to re-coupling between fluorescence and plasmon polaritons was also observed on the plasmonic chips and enhanced fluorescence 90 times compared with that on glass slides was superior to the others reported. The limit of detection (LOD) studied here was improved up to 50 pM after 10-min incubation and dynamic range was also extended by 2 order, compared with that on glass slides. The irradiation from the rear panel demonstrated advantage in the surface-selective detection of cy5-SA at 100 nM concentration. Our plasmonic chip has great potential in biosensing application due to its advantages of rapid detection, simple operation, high sensitivity (wide dynamic range), surface selectivity, and suppression of non-specific adsorption.

Electromagnetic field quantization in planar absorbing heterostructures

The quantization scheme for the electromagnetic field in planar absorbing heterostructures has been developed. The scheme is based on the field expansion over a complete set of orthonormal modes. We used two types of the field modes. The first one is defined as the field created by a plane wave incident at the surface of the structure from the non-absorbing half space. The second type of modes corresponds to the field generated by electric current fluctuations in the absorbing media. To normalize the field modes, the following conditions were used: 1) the time-averaged Poynting vector attributed to the incident wave equals the density of energy flow of elementary quanta of the field energy; 2) for the given frequency and polarization, the total time-averaged Poynting vector equals to zero. The theory is applied to calculate the rate of spontaneous transitions between electron subbands in a quantum well placed near the absorbing layer that can support the surface phonon or plasmon polaritons.

Plasmon polariton and〈n〉=0non-Bragg gaps in superlattices with metamaterials

We consider one-dimensional photonic superlattices made up of alternate layers of a right-handed nondispersive material and a metamaterial with Drude-type dielectric permittivity and magnetic permeability. By thoroughly investigating the dispersion relation for the propagation of obliquely incident optical fields obtained from Maxwell's equations and the transfer-matrix technique, we demonstrate that, in the long-wavelength limit, the dispersion is the same that one would obtain by considering a homogeneous effective medium with Drude-type responses at shifted electric and magnetic plasmon frequencies. Moreover, we show that the plasmon polariton and $\ensuremath{\langle}n\ensuremath{\rangle}=0$ non-Bragg gaps correspond to regions of the low-energy spectrum where the effective medium is absorptive, exhibiting an imaginary effective refraction index.

Principal component analysis based methodology to distinguish protein SERS spectra

Surface-enhanced Raman scattering (SERS) substrates were fabricated using electro-plating and e-beam lithography techniques. Nano-structures were obtained comprising regular arrays of gold nanoaggregates with a diameter of 80 nm and a mutual distance between the aggregates (gap) ranging from 10 to 30 nm. The nanopatterned SERS substrate enabled to have better control and reproducibility on the generation of plasmon polaritons (PPs). SERS measurements were performed for various proteins, namely bovine serum albumin (BSA), myoglobin, ferritin, lysozyme, RNase-B, α-casein, α-lactalbumin and trypsin. Principal component analysis (PCA) was used to organize and classify the proteins on the basis of their secondary structure. Cluster analysis proved that the error committed in the classification was of about 14%. In the paper, it was clearly shown that the combined use of SERS measurements and PCA analysis is effective in categorizing the proteins on the basis of secondary structure.

Huge light scattering from active anisotropic spherical particles

The light scattering by a spherical particle with radial anisotropic permittivity ε and permeability μ are discussed in detail by expanding Mie theory. With the modified vector potential formulation, the electric anisotropy effects on scattering efficiency are addressed by studying the extinction, scattering, absorption and radar cross sections following the change of the transverse permittivity ε(t), the longitudinal permittivity ε(r) and the particle size q. The huge scattering cross sections are shown by considering the possible coupling between active medium and plasmon polaritons and this will be possible to result in spaser from the active plasmons of small particle.

Plasmon-polariton waves in nanofilms on one-dimensional photonic crystal surfaces

The propagation of bound optical waves along the surface of a one-dimensional (1D) photonic crystal (PC) structure is considered. A unified description of the waves in 1D PCs for both s- and p-polarizations is done via an impedance approach. A general dispersion relation that is valid for optical surface waves with both polarizations is obtained, and conditions are presented for long-range propagation of plasmon-polariton waves in nanofilms (including lossy ones) deposited on the top of the 1D PC structure. A method is described for designing 1D PC structures to fulfill the conditions required for the existence of the surface mode with a particular wavevector at a particular wavelength. It is shown that the propagation length of the long-range surface plasmon polaritons in a thin metal film can be maximized by wavelength tuning, which introduces a slight asymmetry in the system.

Plasmon polaritons in photonic metamaterial Fibonacci superlattices

We study the properties of plasmon polaritons in one-dimensional photonic metamaterial superlattices resulting from the periodic repetition of a Fibonacci structure. We assume the system made up of positive refraction and metamaterial layers. A Drude-type dispersive response for both the dielectric permittivity and magnetic permeability of the left-handed material is considered. Maxwell's equations are solved for oblique incidence by using the transfer-matrix formalism. Our results show that the plasmon-polariton modes are considerably affected by the increasing of the Fibonacci-sequence order of the elementary cell. The loss of the long-range spatial coherence of the electromagnetic field along the growth direction, which is due to the quasiperiodicity of the elementary cell, leads to the splitting of the plasmon-polariton frequencies, resulting in a Cantor-type frequency spectra. Moreover, the calculated photonic dispersion indicates that if the plasma frequency is chosen within the photonic $⟨n(\ensuremath{\omega})⟩=0$ gap then the plasmon-polariton modes behave essentially as pure plasmon modes.

Plasmon-polariton band structures of asymmetric T-shaped plasmonic gratings

It is shown that asymmetric T-shaped plasmonic gratings can display plasmon-polariton band structures with wide range of band gaps and tunable group velocities. A structure gap is introduced in the post of Tshaped plasmonic gratings and it is found that the size of this gap plays an important role in controlling the plasmon-polariton band gap and group velocities. We obtained variation of energy band gap ranging from 0.4 eV to 0.0323 eV by changing the size of the structure gap from 0 to 250 nm. The plasmon-polariton band structures were obtained by using Rigorous Coupled Wave Analysis. We studied the difference between symmetric and asymmetric T-shaped gratings and found that the symmetric structure has a momentum gap in the photonic band structure, which can be avoided in the asymmetric structure. Furthermore, by varying the post and spacer (made of SiO2) thicknesses we can tune the energy band gap from 0.1 eV to 0.148 eV and from 0.183 eV to 0.19 eV, respectively. In this device, we obtain tunable group velocities ranging from one to several orders of magnitude smaller than the speed of light in the vacuum. This asymmetric T-shaped plasmonic grating is expected to have applications in surface plasmon polariton (SPP) based optical devices, such as filters, waveguides, splitters and lasers, especially for applications requiring large photonic band gap.

Hybrid long-range surface plasmon-polariton modes with tight field confinement guided by asymmetrical waveguides

A finite width dielectric-metal-dielectric (DMD) waveguide placed on a substrate is numerically investigated near the telecom wavelength lambda = 1550 nm by the finite element method. With proper waveguide sizes, the asymmetrical DMD waveguide can support hybrid long-range surface plasmon-polariton modes which have tight field confinement (approximately 700 nm) and long propagation lengths (L> 300 microm) simultaneously. Compact plasmonic waveguide-ring resonators (WRRs) based on such asymmetrical DMD waveguide show high quality factors compared with dielectric-loaded surface plasmon-polariton, channel plasmon polariton, plasmonic whispering-gallery microcavity, and pure dielectric waveguide cases.

Surface-enhanced Raman scattering in insulating materials by artificial plasmon production: Application to uranium compounds

The concept of surface-enhanced Raman scattering (SERS) is reviewed. The currently held position within the spectroscopic community is that the enormous SERS enhancement effect, sometimes as much as fourteen orders of magnitude, can be partially related to surface roughness but mostly to surface plasmons (polaritons). The plasmon states are absent in electrical insulators, thus precluding the applicability of the powerful SERS technique in analysing the surface conditions of these materials. This communication describes a technique for extending the SERS process to materials that have little or no intrinsic electrical conductivity.

Far-field optical coupling to semi-infinite metal-nanoparticle chains

External optical coupling into and out of semi-infinite chains of noncontacting noble-metal nanoparticles is found to be highly directional. While strong coupling of external radiation into and out of low-attenuation surface plasmon polaritons (PPs) in semi-infinite nanoparticle chains is predicted, the radiation patterns are quite complex indicating possible challenges in mode matching. We show that a treatment that neglects end effects provides an entirely inadequate description of both the PPs on the chain and of the scattered electromagnetic radiation.

Strip and gap plasmon polariton optical resonators

AbstractA rectangular silver strip and two strips separated by a narrow gap are considered as optical resonators. A surface integral equation method is used to study theoretically their scattering cross section and local enhancement of the electric field relative to the incident wave. Peaks in the scattering spectra are shown to be related to the excitation of standing waves caused by forward and backward travelling slow plasmon polaritons (PPs) in the silver strip or in the gap between two strips. This is shown via analysis of the electric near‐field inside and outside the strips, and by showing that an increase of the length of strips equal to half the slow PP wavelength re‐ sults in a scattering resonance at app. the same wavelength. We study the broadening of resonances with strip thickness or gap size, respectively, for the two types of resonators. For field enhancement purposes we consider taking advantage of the fact that the electric field component of slow PPs along the axis of PP propagation is dominating inside the metal strips. Due to this fact and the electromagnetics boundary conditions forcing the surface normal electric field component to jump across the silver‐air interface a small (5 nm) gap introduced in one of the strips leads to a factor ∼25 enhancement of the field magnitude. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Extraordinary scattering diagram for nanoparticles near plasmon resonance frequencies

Light scattering by a small spherical particle with low dissipation rate is discussed according to the Mie theory. It is shown that near plasmon (polariton) resonance frequencies one can see non-Rayleigh anomalous light scattering with quite unusual scattering diagrams.

Emission of light through thin silver films via near-field coupling to surface plasmon polaritons

We show that the emission of light from a dye layer through an adjacent thin silver film is maximal for a silver thickness of approximately 50 nm. This effect is explained as the result of competition between enhancement of the electric field at the metal surface due to the excitation of a surface plasmon-polariton mode, the amount of power coupled to the surface plasmon-polariton mode, and the attenuation of the field transmitted through the silver, all three of which vary with metal thickness. We indicate how these findings may be of relevance in the design of some surface plasmon-polariton-based fluorescence biosensing schemes.

Total Absorption of an Electromagnetic Wave by an Overdense Plasma

We show both theoretically and experimentally that an electromagnetic wave can be totally absorbed by an overdense plasma when a subwavelength diffraction grating is placed in front of the plasma surface. The absorption is due to dissipation of surface plasma waves (plasmons polaritons) that have been resonantly excited by the evanescent component of the diffracted electromagnetic wave. The developed theoretical model allows one to determine the conditions for the total absorption.