Propagation Of Surface Plasmon Polaritons Research Articles

Manipulation of Ultrafast Nonlinear Optical Response Based on Surface Plasmon Resonance

AbstractDue to the existence of surface plasmon resonances, enormous nonlinear optical effects are generated by plasmonic nanostructures, leading to the trend in which these nanostructures have gradually become ideal platforms for all‐optical manipulations. Here, it is discovered that an anomaly of the relationship between the sample reflectance and the pump‐light polarization angle occurs at the localized surface plasmons mode. Relatively, normal relationships exist at the interband transition and the propagating surface plasmon polaritons mode. Furthermore, electrical‐field enhancements are intentionally acquired by solely keeping either the pump beam or the probe beam on, so that the anomaly‐governing mechanism is identified as the aggregation of hot electrons within the probe‐detected sensitivity zone. The discovery of this anomaly and the associated mechanism can be applied to ultrafast all‐optical communications, computing, and the design of photonics‐related devices.

Controlling Surface Plasmon Polaritons Propagating at the Boundary of Low-Dimensional Acoustic Metamaterials

As a novel type of artificial media created recently, metamaterials demonstrate novel performance and consequently pave the way for potential applications in the area of functional engineering in comparison to the conventional substances. Acoustic metamaterials and plasmonic structures possess a wide variety of exceptional physical features. These include effective negative properties, band gaps, negative refraction, etc. In doing so, the acoustic behaviour of conventional substances is extended. Acoustic metamaterials are considered as the periodic composites with effective parameters that might be engineered with the aim to dramatically control the propagation of supported waves. Homogenization of the system under consideration should be performed to seek the calculation of metamaterial permittivity. The dispersion behaviour of surface waves propagating from the boundary of a nanocomposite composed of semiconductor enclosures that are systematically distributed in a transparent matrix and low-dimensional acoustic metamaterial and constructed by an array of nanowires implanted in a host material are studied. We observed the propagation of surface plasmon polaritons. It is demonstrated that one may dramatically modify the properties of the system by tuning the geometry of inclusions.

Unified treatments for localized surface plasmon resonance and propagating surface plasmon polariton based on resonance modes in metal nanowire

The understanding on surface plasmon polaritons (SPPs), which contain propagating surface plasmon polaritons (PSPP) and localized surface plasmon resonance (LSPR), are of significant. In this study, we approximately solve Maxwell’s Equations to obtain the properties of PSPP and LSPR supported in Ag nanowire and Au nanorod. The propagation length and the transmitted spectra are analyzed with the obtained formula and agree well with other researchers’ work. We find that both PSPP and LSPR result from the same mechanism, i.e., the propagating modes together with their constructive interference effects. Therefore, we unify the two phenomena. This work provides an alternative way to describe the phenomenon of SPP modes and is helpful to the applications which employ SPP.

Surface plasmon polaritons in a waveguide composed of Weyl and Dirac semimetals

We investigate features of the surface plasmon polaritons (SPPs) hosted by a slot waveguide comprised of a Weyl semimetal in Voigt/Faraday configuration and a Dirac semimetal connected via a dielectric layer. In the Voigt configuration, SPP dispersion is nonreciprocal possessing unidirectional SPP modes in a wide range of frequency. However, the reciprocal SPP dispersion of the Faraday configuration composes of two distinct dispersion bands existing below or above the bulk plasmon frequency depending on the selection of the materials realizing Weyl and Dirac semimetal phases. We explain that these SPP modes are tunable with the thickness of the dielectric layer, the chemical potentials of the semimetals and the separation of the Weyl nodes in the Weyl semimetal. These structures provide a high level of functionality and tunability and may be employed in optical devices based on the unidirectional SPPs. • The slot waveguide allows unidirectional propagation of surface plasmon polaritons. • Surface plasmon polariton modes show new features in the Faraday configuration. • Thickness of the dielectric layer can be used to control surface plasmon polariton modes. • Chiral anomaly effect of the Weyl semimetal can be utilized to control the surface plasmon polariton modes.

Mode splitting and multiple-wavelength managements of surface plasmon polaritons in coupled cavities

Resonance cavity is a basic element in optics, which has wide applications in optical devices. Coupled cavities (CCs) designed in metal-insulator-metal (MIM) bus waveguide are investigated through the finite difference time domain method and coupled-mode theory. In the CCs, the resonant modes of the surface plasmon polaritons (SPPs) split with the thickness decreasing of the middle baffle. Through the coupled-mode theory analysis, it is found that the phase differences introduced in opposite and positive couplings between two cavities lead to mode splitting. The resonant wavelength of positive coupling mode can be tuned in a large range (about 644 nm) through adjusting the coupling strength, which is quite different from the classical adjustment of the optical path in a single cavity. Based on the resonances of the CCs in the MIM waveguide, more compact devices can be designed to manipulate SPPs propagation. A device is designed to realize flexible multiple-wavelength SPPs routing. The coupling in CC structures can be applied to the design of easy-integrated laser cavities, filters, multiple-wavelength management devices in SPPs circuits, nanosensors, etc.

Experimental Verification of Shape‐Independent Surface Cloak Enabled by Nihility Transformation Optics

AbstractThe manipulation of electromagnetic surface waves on interfaces that have arbitrary shape geometrical disorders has gained a lot of interest owing to its wealth of advantages in modern photonics and plasmonics devices. In this paper, based on the well‐established method of transformation optics, a reconfigurable cloak that is competent in guiding the propagation of surface plasmon polaritons (SPPs) at a distorted metal‐dielectric interface is introduced. The presented cloak consists of a homogeneous anisotropic material, dubbed as optic null medium (ONM) that is independent of the cloak geometrical shape. Whilst the homogeneity property of ONMs leads to the feasibility in fabrication, the shape independency feature yields an on‐demand control over the flow of SPPs, simply by changing the shape of the cloak while leaving its constituent material unchanged. In order to authenticate the idea, a triangular‐shape SPP cloak is designed and fabricated experimentally at microwave frequency. It is observed that by utilizing the designed cloak almost total transmission can be obtained from the distorted interface. The unique designing approach introduced here may open a new horizon to nano‐optics and downscaling of photonic circuits.

Plasmon-Coupled Directional Emission from Soluplus-Mediated AgAu Nanoparticles for Attomolar Sensing Using a Smartphone

Although there are numerous techniques for the synthesis of plasmonic (metallic Ag and Au) nanomaterials, eco-friendly and biocompatible methodologies that present diverse applications in nanophotonics and biomedical domains are seldom reported. Soluplus is a graft copolymer of polyvinyl caprolactam–polyvinyl acetate–polyethylene glycol and is extensively used for improving the solubility and bioavailability of poorly water-soluble drugs. However, the utility of their amphiphilic chemical structure, strong UV-light absorbing, and bifunctional properties of the polymer matrix as well as its role as a solubilizer have not been explored for rapid synthesis of plasmonic bimetallic nanohybrids. Although a variety of nanoparticles (NPs) have been studied for surface plasmon-coupled emission (SPCE) spectroscopic applications, AgAu nanohybrids have not been examined in the subject platform hitherto. In this article, we demonstrate a synthesis route for obtaining AgNPs, AuNPs, and AgAu nanohybrids using soluplus as both the reducing and capping agent in a simple UV-light induced one-pot rapid technique. These hybrid nanomaterials were interfaced with propagating surface plasmon polaritons from a 50 nm Ag thin film to understand the plasmonic coupling phenomenon in spacer, cavity, and extended cavity nanoconfigurations. The obtained AgAu nanohybrids aided in addressing the three major long-standing challenges in SPCE technology development, namely, (i) unavoidable quenching in the presence of AuNPs, (ii) chemical instability in AgNPs, and (iii) intrinsic ohmic losses in plasmonic NPs. In addition to overcoming the above-mentioned caveats, unaccustomed >1200-fold sharply directional and polarized SPCE enhancements were achieved using AgAu nanohybrids. The multifold nanogaps generated in AgAu nanohybrid sustained multiple hotspots catering to attomolar sensitivity of the SPCE reporter molecule, rhodamine B (RhB). The proposed methodology to obtain dequenched as well as augmented SPCE enhancements is of utmost utility in biophysicochemical sensor development.

Near-infrared nanospectroscopy using a low-noise supercontinuum source

Unlocking the true potential of optical spectroscopy on the nanoscale requires development of stable and low-noise laser sources. Here, we have developed a low-noise supercontinuum (SC) source based on an all-normal dispersion fiber pumped by a femtosecond fiber laser and demonstrate high resolution, spectrally resolved near-field measurements in the near-infrared (NIR) region. Specifically, we explore the reduced-noise requirements for aperture-less scattering-type scanning near-field optical microscopy (s-SNOM), including inherent pulse-to-pulse fluctuation of the SC. We use our SC light source to demonstrate the first NIR, spectrally resolved s-SNOM measurement, a situation where state-of-the-art commercial SC sources are too noisy to be useful. We map the propagation of surface plasmon polariton (SPP) waves on monocrystalline gold platelets in the wavelength region of 1.34–1.75 μm in a single measurement, thereby characterizing experimentally the dispersion curve of the SPP in the NIR. Our results represent a technological breakthrough that has the potential to enable a wide range of new applications of low-noise SC sources in near-field studies.

Heavily doped silicon: A potential replacement of conventional plasmonic metals

The plasmonic property of heavily doped p-type silicon is studied here. Although most of the plasmonic devices use metal–insulator–metal (MIM) waveguide in order to support the propagation of surface plasmon polaritons (SPPs), metals that possess a number of challenges in loss management, polarization response, nanofabrication etc. On the other hand, heavily doped p-type silicon shows similar plasmonic properties like metals and also enables us to overcome the challenges possessed by metals. For numerical simulation, heavily doped p-silicon is mathematically modeled and the theoretically obtained relative permittivity is compared with the experimental value. A waveguide is formed with the p-silicon-air interface instead of the metal–air interface. Formation and propagation of SPPs similar to MIM waveguides are observed.

Propagating Surface Plasmon Polaritons Excited at the Graphene Oxide/AgAu Alloy Interface Enhance Nonlinearity

Graphene oxide (GO) contains intrinsic tunable plasmons, leading to highly attractive plasmonic phenomena, besides the GO coupling with metal nanostructures is promising for plasmonics. Herein, a system consisting of an AgAu alloy entangled in a protein network, AgAu@cages, coupled with a GO layer is designed and analyzed. To overcome the challenges posed by the synthesis of the hybrid GO/metal system, the AgAu alloy is grown inside a proteinaceous network. The approach allows control over the alloy size distribution and a close contact with the samples, with positive impact on the plasmonic analysis. The hybrid system reveals a strong dependence on the incident angle and a shorter linewidth as well as a redshift, motivating further investigations to elucidate the phenomenon. Combined experimental and numerical investigations lead to the displaying of the strong coupling that occurs between the plasmons and the molecular cavity of GO, and a coherent amplification of molecular motion. In conclusion, the versatility of GO‐based systems allows the manufacture of plasmonic and optical devices sensitive to a wide range of frequencies, from terahertz to the visible frequencies, with extremely low driving voltage.

Exploring Plasmonic Resonances Toward “Large‐Scale” Flexible Optical Sensors with Deformation Stability

AbstractThe next generation of sensors requires a simple yet compact lab on chip‐based precise optical detection mechanism where data interpretation can be achieved with minimum effort. Hereby, cost‐efficient strategies of manufacturing both propagating surface plasmon polariton (SPP) and localized surface plasmon resonance (LSPR) sensors on flexible platforms are explored via mechanical instabilities and oblique‐angled metal evaporation. Centimeter scaled dielectric grating structures produced by plasma oxidation of pre‐stressed polydimethylsiloxane film have comprised the substrates, thus imparting inherent flexibility. Subsequently, both continuous and discontinuous 1D‐metallic lattices are obtained via vapor deposition of gold at different angles. The optical isotropy (gold surface‐grating) and anisotropy (gold edge‐grating) are distinctly observed as a difference between forward and backward diffraction efficiencies, backed by analytical correlation to the observed orders. Supported with electromagnetic modeling, the SPP and LSPR excitations are experimentally characterized under reflectance and transmittance measurements, along with a demonstration of their sensing capabilities. The LSPR supported flexible sensor provides superiority in terms of sensitivity, which is investigated under mechanical deformations to exhibit consistency of the resonant wavelength. Such consistency is strategically unraveled via “finite element method” based approaches, thus providing a new paradigm of cost‐efficient, large‐scaled flexible sensors.

Space- and time-resolved second harmonic spectroscopy of coupled plasmonic nanocavities

Abstract Localized surface plasmon resonances of individual sub-wavelength cavities milled in metallic films can couple to each other to form a collective behavior. This coupling leads to a delocalization of the plasmon field at the film surface and drastically alters both the linear and nonlinear optical properties of the sample. In periodic arrays of nanocavities, the coupling results in the formation of propagating surface plasmon polaritons (SPP), eigenmodes extending across the array. When artificially introducing dislocations, defects and imperfections, multiple scattering of these SPP modes can lead to hot-spot formation, intense and spatially confined fluctuations of the local plasmonic field within the array. Here, we study the underlying coupling effects by probing plasmonic modes in well-defined individual triangular dimer cavities and in arrays of triangular cavities with and without artificial defects. Nonlinear confocal spectro-microscopy is employed to map the second harmonic (SH) radiation from these systems. Pronounced spatial localization of the SPP field and significant enhancements of the SH intensity in certain, randomly distributed hot spots by more than an order of magnitude are observed from the triangular arrays as compared to a bare silver film by introducing a finite degree of disorder into the array structure. Hot-spot formation and the resulting enhancement of the nonlinear efficiency are correlated with an increase in the lifetime of the localized SPP modes. By using interferometric SH autocorrelation measurements, we reveal lifetimes of hot-spot resonances in disordered arrays that are much longer than the few-femtosecond lifetimes of the localized surface plasmon resonances of individual nanocavity dimers. This suggests that hot spot lifetime engineering provides a path for manipulating the linear and nonlinear optical properties of nanosystems by jointly exploiting coherent couplings and tailored disorder.

On the performance of a tunable grating-based high sensitivity unidirectional plasmonic sensor.

Optical biosensing is currently an intensively active research area, with an increasing demand of highly selective, sensitivity-enhanced and low-cost devices where different plasmonic approaches have been developed. In this work we propose a tunable optimized grating-based gold metasurface that can act both as a high sensitivity sensor device (up to 1500 nm/RIU) and as an unidirectional plasmon source. The theory behind surface plasmon polariton generation is recalled to thoroughly understand the influence that every parameter of the grating source has on the performance of the proposed device. The results and conclusions discussed here offer a key step toward the design of biosensors based on excitation of surface plasmons polaritons by grating-based structures or in the process of creating new nanophotonic circuit devices.

Looking Into Surface Plasmon Polaritons Guided by the Acoustic Metamaterials

Acoustic metamaterials are introduced as the structures with the alternating elements possessing effective properties that can be tuned seeking for the dramatic control on wave propagation. Homogenization of the structure under consideration is needed aiming to calculate permittivity of metamaterial. We present theoretical outcomes studying an acoustic composite possessing negative effective parameters in the acoustic frequency range. An acoustic metamaterial with an the alternating nanowires arranged in a building block and embedded in a host material was investigated. Propagation of surface plasmon polaritons at the metamaterial interface was predicted.

Patterning of transition metal dichalcogenides catalyzed by surface plasmons with atomic precision

Summary Plasmon-induced charge transfer has drawn considerable interests and spurred rapid developments of photovoltaics and photocatalysis. Various plasmonic metal/transition metal dichalcogenide (TMD) heterostructures have been developed to promote charge separation. For plasmon-induced catalysis, the transformation of TMDs is rare, and the erosion of TMDs has not yet been reported. Here, we report the etching of two-dimensional TMDs by planar surface plasmon polaritons (SPPs). We found that SPPs can etch various TMDs into desired layers and lateral size through controlling the light power and incident direction. In aqueous media, the strong plasmonic coupling at Au/MoS2 interface generates holes in the valence band of MoS2 that can weaken its interlayer interaction. As a synergistic effect, the plasmonic hot electrons produce oxidizing H2O2 to dissolve MoS2 from the top layers. Our results provide a new perspective for understanding the plasmonic coupling at metal-TMD interfaces and a reliable route toward fabricating well-defined TMDs.

Plexciton in tip-enhanced resonance Stokes and anti-Stokes Raman spectroscopy and in propagating surface plasmon polaritons

New methods to improve the properties of surface-enhanced Raman scattering and propagating surface plasmon polaritons (PSPPs) are desirable. In this study, we theoretically employ the plasmon–exciton (plexciton) interaction to enhance the spectra in localized surface plasmon (LSP) and PSPP. The tip-enhanced resonance Raman spectroscopy (TERRS) configuration is used to enhance both Stokes and anti-Stokes Raman spectra of rhodamine 6G simultaneously. We achieve a huge enhancement factor of 1013∼ 1015. Furthermore, we obtain the plexciton by employing the Ag nanowire coated with rhodamine 6G, which improves the propagation properties.

Reflectionless plasmonic right-angled waveguide bend and divider using graphene and transformation optics.

In this work, a plasmonic right-angled waveguide bend and divider are proposed. Using the Transformation Optics (TO) approach the transformation media of a bend and a T-shaped divider are obtained. Such media with continuous refractive index are realized with the help of graphene in the terahertz frequency range, key to effectively guiding the surface plasmon polariton (SPP) propagation on the 90 degree curves. Components with such capability are promising for THz device applications.

Controlling plasmon propagation and enhancement via reducing agent in wet chemistry synthesized silver nanowires.

Silver nanowires with varying diameters and submillimeter lengths were obtained by changing a reducing agent used during hydrothermal synthesis. The control over the nanowire diameter turns out to play a critical role in determining their plasmonic properties, including fluorescence enhancement and surface plasmon polariton propagation. Advanced fluorescence imaging of hybrid nanostructures assembled of silver nanowires and photoactive proteins indicates longer propagation lengths for nanowires featuring larger diameters. At the same time, with increasing diameter of the nanowires, we measure a substantial reduction of fluorescence enhancement. The results point at possible ways to control the influence of plasmon excitations in silver nanowires by tuning their morphology.

Tunable THz Switch-Filter Based on Magneto-Plasmonic Graphene Nanodisk

We propose and analyze a new multifunctional THz device that can operate as a tunable switch and a tunable filter. The device consists of a circular graphene nanodisk coupled to two nanoribbons oriented at 90° to each other. The graphene elements are placed on a dielectric substrate. The nanodisk is magnetized by a dc magnetic field normal to its plane. The physical principle of the device is based on the propagation of surface plasmon-polariton (SPP) waves in the graphene nanoribbons and excitation of dipole mode in the nanodisk resonator. Numerical simulations show that 0.61 T dc magnetic field provides transmission (regime ON) at the frequency 5.33 THz with the bandwidth (BW) 12.7% and filtering with a Q-factor of 7.8. At the central frequency, the insertion loss (IL) is around -2 dB, and the reflection coefficient is -43 dB. The regime OFF can be achieved by means of switching the dc magnetic field to zero value or by switching the chemical potential of the nanodisk to zero. This results in the ON/OFF ratio better than 20 dB. A small central frequency tuning of the switch by chemical potential is possible with a fixed dc magnetic field.

Broadband mirrors for surface plasmon polaritons using integrated high-contrast diffraction gratings

We propose and numerically investigate integrated high-contrast gratings (HCGs) for surface plasmon polaritons (SPPs) propagating along metal-dielectric interfaces, which consist of periodically arranged silicon pillars located on the gold surface. We demonstrate that such on-chip HCGs can be used as broadband plasmonic mirrors, which have subwavelength footprint in the SPP propagation direction and mean reflectance exceeding 85% in a 200-nm-wide spectral range for both the cases of normal and oblique SPP incidence. In order to increase the HCG efficiency and design practically feasible structures, we utilize a parasitic scattering suppression technique based on the use of two-layer grating pillars. The presented results may find application in two-dimensional optical circuits for steering the SPP propagation.