Properties Of Surface Plasmon Polaritons Research Articles

Microscopy of terahertz spoof surface plasmons propagating on planar metamaterial waveguides

Surface plasmon polaritons (SPPs) are electromagnetic waves that have attracted significant interest owing to their subwavelength confinement and the strong field enhancement that they provide. Yet in the terahertz (THz) frequency region of the spectrum, which is well below the plasma frequency of metals, these surface waves are characterized by extremely weak confinement that has severely limited their exploitation for information processing and sensing. One means to circumvent this limitation is through subwavelength structuring of a metallic surface, which can thereby be engineered to support the propagation of spoof surface plasmon polaritons (SSPPs) that closely mimic the properties of SPPs. In this work, we report the design and experimental characterization of an ultra-thin metamaterial planar waveguide that supports SSPPs at THz frequencies. Finite-element method simulations are shown to predict the excitation of SSPPs on the surface of our devices under free-space illumination at 3.45 THz. We investigate these structures experimentally using THz scattering-type scanning near-field microscopy (THz-s-SNOM) to map directly the out-of-plane electric field associated with the propagation of SSPPs on the surface of the waveguides. Our work paves the way for the future development of plasmonic integrated circuit technologies and components operating in the THz frequency band.

Dispersive Propagation of Terahertz Pulses in a Plasmonic Fiber

The dispersion properties of surface plasmon polaritons (SPPs) during propagation on metal wires with a dielectric coating in the terahertz frequency range were investigated theoretically. An analytical expression was obtained for a pulsed electric field using the solution of Maxwell equations taking into account high-order dispersion terms. The influence of the dielectric coating on the distortion of the pulse shape was investigated. Unlike uncoated wire, the propagation of surface plasmon pulses along a coated wire is highly dispersive. It was shown that the coating leads to the appearance of a long-chirped signal with a propagation of only a few millimeters, i.e., when a terahertz pulse propagates along a coated wire, it acquires a long oscillatory tail, the frequency of which depends on time.

Nonlinearity in surface plasmon polaritons at interface between triple quantum dot and nanocomposite medium

This paper focuses on investigating the generation and manipulation of surface plasmon polaritons (SPPs) at the interfaces between quantum dot (QD) molecules and nanocomposite media. We utilize three different gate voltage values and incident laser field strengths to control the propagation of SPPs. We find a significant improvement in the SPPs' propagation length at the interfaces between the QD molecules and nanocomposite media. Additionally, under the Kerr effect, the gate voltage variation provides opportunities to control the SPPs' propagation. Through modifying the intensity and frequency of the incident probe field, we can manipulate various properties of SPPs at the suggested model's interfaces. Our results indicate a large enhancement in the SPPs' propagation length at the interfaces. Notably, we estimate the skin depth and wavelength of SPPs for three distinct values of the incident probe field and gate voltage applied in the QD molecules.

Ultra-confined Propagating Exciton–Plasmon Polaritons Enabled by Cavity-Free Strong Coupling: Beating Plasmonic Trade-Offs

Hybrid coupling systems consisting of transition metal dichalcogenides (TMD) and plasmonic nanostructures have emerged as a promising platform to explore exciton–plasmon polaritons. However, the requisite cavity/resonator for strong coupling introduces extra complexities and challenges for waveguiding applications. Alternatively, plasmonic nano-waveguides can also be utilized to provide a non-resonant approach for strong coupling, while their utility is limited by the plasmonic confinement-loss and confinement-momentum trade-offs. Here, based on a cavity-free approach, we overcome these constraints by theoretically strong coupling of a monolayer TMD to a single metal nanowire, generating ultra-confined propagating exciton–plasmon polaritons (PEPPs) that beat the plasmonic trade-offs. By leveraging strong-coupling-induced reformations in energy distribution and combining favorable properties of surface plasmon polaritons (SPPs) and excitons, the generated PEPPs feature ultra-deep subwavelength confinement (down to 1-nm level with mode areas ~ 10–4 of λ2), long propagation length (up to ~ 60 µm), tunable dispersion with versatile mode characters (SPP- and exciton-like mode characters), and small momentum mismatch to free-space photons. With the capability to overcome the trade-offs of SPPs and the compatibility for waveguiding applications, our theoretical results suggest an attractive guided-wave platform to manipulate exciton–plasmon interactions at the ultra-deep subwavelength scale, opening new horizons for waveguiding nano-polaritonic components and devices.

Surface plasmon polaritons at an interface between silver and quantum dots hybrid nanocomposite

Surface plasmon polaritons (SPPs) are investigated theoretically at the interface between silver metal and a hybrid system containing silver metal nanoparticles (MNPs) and semiconductor triple quantum dot (STQD). Various properties of SPPs are studied by varying the distance between silver MNP and SQD, radii of the MNP in the hybrid medium, and gate voltage applied to the TQD. A remarkable modification up to 315 μm is obtained in the SPPs’ propagation length by considering different sizes of silver MNPs in the hybrid medium. The wavelength of the SPPs is controlled via changing the distance between the MNPs and TQD, and gate voltages applied to TQD in the hybrid medium. Furthermore, we have studied the effect of various parameters such as gate voltages and radii of the MNPs on the penetration depth of SPPs into both sides of the interface of silver metal and hybrid medium. Plasmonic regions consisting of hybrid medium and silver metal provide multiple dimensions for the generation and control of SPPs. Therefore, it is assumed that these findings may have important applications in bio-sensors, atomic spectroscopy, photovoltaic devices, surface-enhanced Raman spectroscopy, solar cells, and plasmon technology.

THE NUMERICAL STUDY OF SURFACE PLASMON POLARITON AT THE SINGLE INTERFACE BETWEEN METAL AND VEGETABLE OILS DIELECTRICS

We report the numerical studies of the properties of surface plasmon polaritons which are generated at the single interface between metal and dielectric. In this numerical work, we used parameters representing natural dielectrics. Using Maxwell equations and also the continuity of the fields at the interface between metal and dielectrics, the dispersion relation of the surface plasmon polaritons were derived. The dispersion relations were solved by taking parameters for metal appropriate for gold. For natural dielectric, we used parameters which are correspond to castor oil, coconut oil and sun flower oil with the range of dielectric constants were from tens to sixties. The results showed that the lower part of dispersion curves of surface plasmon polaritons approach SPP frequencies. We found that the highest surface plasmon frequency was resulted by using crude palm oil (CPO) as liquid dielectric. The usage of sunflower oil as dielectric lead to the lowest surface plasmon polaritons frequency.

Quantum coherence-assisted optical properties and drag of SPPs on quantum dots and resonantly-coupled dots-metal plasmonic interfaces via interbands tunneling and Fano resonance

Owing to their peculiar properties of great fundamental and practical implications, surface plasmons and exciton-plasmons interaction have attracted immense interest in the recent decades. In this regard, quantum dots and dots-metal waveguides and interfaces are promising candidates. In this article, we report first theoretical demonstration on the detailed optical and optotransport properties and surface plasmon polaritons (SPPs) dragging via quantum dots interbands tunneling-induced quantum coherence. For the required properties of SPPs, we proposed a resonantly coupled dots-metal plasmonic interface, which comprises of ensemble of three-level double quantum dot molecules (DQDMs) placed on the flat surface of gold thin film. For the theoretical results, we first solved analytically the density-matrix equation for the eigenvalues of the DQDMs in the Λ− type configuration. In view of the dressed-states picture, we interpreted the results further with regard to EIT (electromagnetically induced transparency), PIT (plasmonic induced transparency) and Fano interference. In particular, we elaborate on the role of interplay of the quantum dots and the coupled plasmonic resonances on the optical, optical-cum transport properties and drag of SPPs. We predict ultrafast superluminal group velocity for SPPs of the order 1.5×1010 m/s, quality factor of 38.48, confinment factor 1.52 and the optimum drag for SPPs of order 0.2 micro meter/radian.

Controlling optical properties and drag of photon and surface plasmon polaritons in triple quantum dot molecules and dots-metal plasmonic interface via tunneling-assisted quantum coherence

Optical properties of surface plasmon polaritons (SPPs) and drag of photon and SPPs attracted great attention owing to multi-fold potential fundamental and technological implications. In this paper, we investigate the nature of light propagation, optical properties of probe field and SPPs and drag of photon and SPPs in a four-level triple quantum dot molecule (TQDM) well and a dots-metallic plasmonic interface (DMPI). The quantum coherence in TQDM and coupled DMPI interface is achieved via interbands tunneling-assisted quantum coherence namely- classical electromagnetically induced transparency (EIT) and plasmonic induced transparency (PIT). In contrast to earlier studies, herein we employed Drude-model type dielectric constant of metal with inclusion of size-dependent correction term to account for the reduced electron relaxation rate near the thin metal interface. In particular, after solving the master density-matrix equation of the quantum dot system for the eigenvalues, we interpreted the calculated theoretical results on light dragging and optical properties of probe field and SPPs via tunneling-assisted dressed-state picture of EIT/PIT in the proposed TQDM system and DMPI interface. The tunneling parameter considerably tuned the nature of light propagation from subluminal to superluminal and vice versa, optical properties and drag of photon and SPPs. The maximum positive (negative) value of the group index for photon is of order 3.68×106 (2.685×106) while for SPPs it is of order 3×105. The maximum value of lateral drag for photon and SPPs is ±5×10-2m and ±1.173×10-3m, respectively. The calculated propagation length and wavelength for SPPs are 6.25×10-7m and 3.78×10-7 m which correspond to the quality factor of 10.38.

Independently tunable dual resonant dip refractive index sensor based on metal–insulator–metal waveguide with Q-shaped resonant cavity

A plasmonic resonator system consisting of a metal–insulator–metal waveguide and a Q-shaped resonant cavity is proposed in this paper. The transmission properties of surface plasmon polaritons in this structure are investigated by using the finite difference in time domain (FDTD) method, and the simulation results contain two resonant dips. The physical mechanism is studied by the multimode interference coupled mode theory (MICMT), and the theoretical results are in highly consistent with the simulation results. Furthermore, the parameters of the Q-shaped cavity can be controlled to adjust the two dips, respectively. The refractive index sensor proposed in this paper, with a sensitivity of 1578 nm/RIU and figure of merit (FOM) of 175, performs better than most of the similar structures. Therefore, the results of the study are instructive for the design and application of high sensitivity nanoscale refractive index sensors.

Role of quantum-coherence dressed states on the Fresnel–Fizeau drag and optical properties of surface plasmon polaritons through asymmetric double quantum dot-metallic plasmonic interfaces

Owing to the exceptional structural-design flexibility and tunability of physical properties of quantum dots, the manipulation of light in view of surface plasmons via dots–based hybrid nanostructures and dots-metallic interfaces finds promising device applications. Hereby, we first demonstrate theoretically the role of intense laser-excited dressed states on the light propagation, optical properties, and lateral and rotary drag of surface plasmon polaritons (SPPs), via plasmon-assisted induced transparency (PIT). For this, we employed a scheme of plasmonic interface comprising an asymmetric double quantum dot molecule GaAs/AlGaAs in the Λ − type configuration embedded in gold metallic surface. In particular, using density-matrix formulation, we present a detailed analytical solution of the quantum dot system for the required eigenvalues in view of the dressed eigenstates. The dressed states played a vital role in the formation of PIT transparency and hence the manipulation of SPPs propagation, optical properties and SPPs drag, via quantum interference. The calculated theoretical results on the optical properties such as absorption and dispersion spectrum, group index, group velocity, group delay, phase delay, wave vector, propagation length and SPPs drag are further elaborated with aid of numerical simulation. The maximum calculated lateral and rotary SPPs drag was of order ± 6.0 × 10−8 m or rad, respectively. The value of SPPs propagation lengths calculated along and perpendicular to the dot-metallic interface are 3.3 × 10−7 m and 2.0 × 10−9 m, respectively.

Hybrid surface plasmon polariton (SPPs) modes between metal and anisotropic plasma interface

This manuscript investigates the properties of surface plasmon polaritons (SPPs) at anisotropic plasma metal interface. It has been shown that magnetized plasma surface plasmon waves have unique features such as hybridization nature, the existence of cutoff frequency and the dependence of normalized prorogation constant and prorogation length on plasma parameters such as cyclotron frequencies (𝜔𝑐) and plasma frequency (𝜔𝑝). The influence of plasma features on normalized propagation constant and propagation as the function of frequency under different values of plasma frequency and cyclotron frequencies are studied. This suggest SPPs at magnetized plasma metal interface may be exploited for Plasma-on-Chip for cancer treatment.

Surface plasmon polariton pulse shaping via two-dimensional Bragg grating pairs

Abstract We demonstrate control over the spatial and temporal properties of surface plasmon polaritons (SPPs) launched from nanohole arrays in silver. The arrays provide wave vector matching to allow the conversion of free-space photons into counter-propagating SPPs. SPPs launched from multiple arrays interfere at well-defined spatial positions, and the interference fringes form an all-SPP periodic nano-optical grating which evolves in space and time as the SPPs propagate. The spatio-temporal characteristics of the optical grating can be tuned through various nanohole array parameters such as tilt angle, separation, and array width. In addition, we examine multiperiodic arrays (MPAs) consisting of arrays with different pitches placed adjacent to one another. This platform allows the temporal interference of SPPs with different central wavelengths to be tailored through the MPA geometric and structural parameters. The temporal interference serves as an encoded signal, whereby the frequency components can be controlled by the array properties.

Theoretical study of SPP properties based on black phosphorus–graphene van der Waals heterostructure

We theoretically investigate the surface plasmon polariton (SPP) properties based on black phosphorus–graphene van der Waals heterostructures that can be tuned by both the incident light angle of black phosphorus and Fermi level of graphene. We elucidate the angle-dependent SPP properties for the hybrid structure from the visible regime to mid-infrared regime. The results show that the largest SPP propagation distance is obtained in the zigzag direction of black phosphorus except when the wavelength is tuned from 380 nm to 480 nm in the visible regime and 1 µm–1.2 µm in the near infrared regime. We also reveal the quasi-linear and quasi-square linear relationship between the SPP propagation distance and Fermi level of graphene for different regimes. Our work would be of great value to construct and optimize the angle-dependent and tunable SPP devices based on the hybridization of different 2D materials.

Surface plasmon polaritons in plasma-dielectric-magnetic plasma structure

The properties of surface plasmon polaritons (SPPs) excited in the plasma-dielectric-magnetic plasma structure are investigated theoretically. Both the normal and the absorbing dispersion relations of SPPs are derived and presented for transverse-magnetic polarization. The influences of the external magnetic field, collision frequency of plasma, background material dielectric constant, and thickness on the characteristics of SPPs are explored and discussed. Results show that these factors greatly alter the properties of SPPs. The results imply that the locations and propagation length of SPPs can be tuned. In addition, the results also show that a one-way dispersion relation of SPPs can be realized in the low-frequency regions when the external magnetic field is introduced.

Understanding the Electromagnetic Response of Graphene/Metallic Nanostructures Hybrids of Different Dimensionality

Plasmonic excitations such as surface-plasmon-polaritons (SPPs) and graphene-plasmons (GPs), carry large momenta and are thus able to confine electromagnetic fields to small dimensions. This property makes them ideal platforms for subwavelength optical control and manipulation at the nanoscale. The momenta of these plasmons are even further increased if a scheme of metal-insulator-metal and graphene-insulator-metal are used for SPPs and GPs, respectively. However, with such large momenta, their far-field excitation becomes challenging. In this work, we consider hybrids of graphene and metallic nanostructures and study the physical mechanisms behind the interaction of far-field light with the supported high momenta plasmon modes. While there are some similarities in the properties of GPs and SPPs, since both are of the plasmon-polariton type, their physical properties are also distinctly different. For GPs we find two different physical mechanism related to either GPs confined to isolated cavities, or large area collective grating couplers. Strikingly, we find that although the two systems are conceptually different, under specific conditions they can behave similarly. By applying the same study to SPPs, we find a different physical behavior, which fundamentally stems from the different dispersion relations of SPPs as compared to GPs. Furthermore, these hybrids produce large field enhancements that can also be electrically tuned and modulated making them the ideal candidates for a variety of plasmonic devices.

Impact of the Interband Transitions in Gold and Silver on the Dynamics of Propagating and Localized Surface Plasmons.

Understanding and modeling of a surface-plasmon phenomenon on lossy metals interfaces based on simplified models of dielectric function lead to problems when confronted with reality. For a realistic description of lossy metals, such as gold and silver, in the optical range of the electromagnetic spectrum and in the adjacent spectral ranges it is necessary to account not only for ohmic losses but also for the radiative losses resulting from the frequency-dependent interband transitions. We give a detailed analysis of Surface Plasmon Polaritons (SPPs) and Localized Surface Plasmons (LPSs) supported by such realistic metal/dielectric interfaces based on the dispersion relations both for flat and spherical gold and silver interfaces in the extended frequency and nanoparticle size ranges. The study reveals the region of anomalous dispersion for a silver flat interface in the near UV spectral range and high-quality factors for larger nanoparticles. We show that the frequency-dependent interband transition accounted in the dielectric function in a way allowing reproducing well the experimentally measured indexes of refraction does exert the pronounced impact not only on the properties of SPP and LSP for gold interfaces but also, with the weaker but not negligible impact, on the corresponding silver interfaces in the optical ranges and the adjacent spectral ranges.

Quantum teleportation mediated by surface plasmon polariton

Surface plasmon polaritons (SPPs) are collective excitations of free electrons propagating along a metal-dielectric interface. Although some basic quantum properties of SPPs, such as the preservation of entanglement, the wave-particle duality of a single plasmon, the quantum interference of two plasmons, and the verification of entanglement generation, have been shown, more advanced quantum information protocols have yet to be demonstrated with SPPs. Here, we experimentally realize quantum state teleportation between single photons and SPPs. To achieve this, we use polarization-entangled photon pairs, coherent photon–plasmon–photon conversion on a metallic subwavelength hole array, complete Bell-state measurements and an active feed-forward technique. The results of both quantum state and quantum process tomography confirm the quantum nature of the SPP mediated teleportation. An average state fidelity of 0.889pm 0.004 and a process fidelity of 0.820pm 0.005, which are well above the classical limit, are achieved. Our work shows that SPPs may be useful for realizing complex quantum protocols in a photonic-plasmonic hybrid quantum network.

Plasmonic analogue of geometric diodes realizing asymmetric optical transmission.

Geometric diodes represent a relatively new class of diodes used in rectennas that rely on the asymmetry of a conducting thin film. Here, we numerically investigate a plasmonic analogue of geometric diodes to realize nanoscale optical asymmetric transmission. The device operates based on spatial symmetry breaking that relies on a unique property of surface plasmon polaritons (SPPs), namely, adiabatic nanofocusing. We show that the structure can realize on-chip asymmetric electromagnetic transmission with a total dimension of ∼2µm×6µm. We demonstrate a signal contrast of 0.7 and an asymmetric optical transmission ratio of 4.77 dB. We investigate the origin of the asymmetric transmission and show that it is due mainly to asymmetric out-coupling of SPPs to far-field photons. We highlight the role of evanescent field coupling of SPPs in undermining the asymmetric transmission efficiency and show that by adjusting the plasmonic waveguide dimensions, a signal contrast of 0.94 and an asymmetric optical transmission ratio of 5.18 dB can be obtained. Our work presents a new paradigm for on-chip nanoscale asymmetric optical transmission utilizing the unique properties of SPPs.

Visualization of Surface Plasmons Propagating at the Buried Organic/Metal Interface with Silver Nanocluster Sensitizers.

Visualization of surface plasmon polariton (SPP) propagation at dielectric/metal interfaces is indispensable in providing opportunities for the precise designing and controlling of the functionalities of future plasmonic nanodevices. Here, we report the visualization of SPPs propagating along the buried organic/metal interface of fullerene (C60)/Au(111), through dual-colored two-photon photoemission electron microscopy (2P-PEEM) which precisely visualizes the SPP propagation of plasmonic metal nanostructures. Although SPPs excited by near-infrared photons at the few monolayer C60/Au(111) interface are clearly visualized as interference beat patterns between the SPPs and incident light, faithfully reflecting SPP properties modulated by the overlayer, photoemission signals are suppressed for thicker C60 films, due to less valence electrons participating in 2P-photoemission processes. With the use of silver (Agn (n = 21 and 55)) nanoclusters, which exhibit enhancement of overall photoemission intensities due to localized surface plasmons functioning as SPP sensitizers, it is revealed that the 2P-PEEM is applicable to the imaging of SPPs for thick C60/Au(111) interfaces, where SPP properties are hardly modulated by the added small amount (∼0.1 monolayer) of Agn sensitizers.

Nonreciprocal and collimated surface plasmons in drift-biased graphene metasurfaces

We explore the unusual non-reciprocal and diffraction-less properties of surface plasmon polaritons propagating in drift-biased graphene-based metasurfaces. We show that applying a drift-current on a graphene sheet leads to extremely asymmetric in-plane modal dispersions from terahertz to infrared frequencies, associated with plasmons with low-loss (high-loss and ultra-high confinement) traveling along (against) the bias. Strikingly, truly unidirectional wave propagation is prevented by the intrinsic nonlocal response of a graphene, a mechanism that shapes the energy flow over the surface. We also show that highly-directive hyperbolic plasmons completely immune to backscattering propagate obliquely along the drift in nanostructured graphene. Finally, we discuss how spin-orbit interactions can be exploited in this platform to efficiently launch collimated plasmons along a single direction while maintaining giant non-reciprocal responses. Our findings open a new paradigm to excite, collimate, steer, and process surface plasmons over a broad frequency band.