Refractive Index Sensor Using Long-Range Surface Plasmon Resonance with Prism Coupler

Plasmonics - Long-range surface plasmon resonance (LRSPR)-based sensors exhibit high sensitivity as compared to the conventional SPR sensors due to low losses. A high refractive index prism and low...     

High Q Long-Range Surface Plasmon Polariton Modes in Sub-wavelength Metallic Microdisk Cavity

Metal-capped microdisk cavity supporting surface plasmon polaritons (SPP)-guided whispering gallery mode (WGM) can achieve higher cavity factor Q than traditional microdisk cavity in sub-wavelength dimensions. We have numerically analyzed the limiting factors on Q using finite difference time domain method. The Q of SPP-guided WGM is primarily limited by the loss of metal. A thin metal-sandwiched microdisk cavity supporting long-range surface plasmon polariton mode was proposed to reduce the metal loss. The proposed cavities have been shown to increase cavity Q by more than 15-fold and reduce threshold gain by more than threefold as opposed to traditional microdisk cavities.     

Simultaneous Excitation of Surface Plasmon Polaritons on Both Interfaces in an Asymmetric Dielectric-Metal Corrugated Structure

The simultaneous excitation of plasmon polaritons on both surfaces of metal film was studied for asymmetric dielectric-metal-dielectric corrugated structures. Due to the small resonant absorption of the incident light on the transmission side of the structure, we investigated the enhancement of the surface plasmon polaritons on the mentioned side by controlling the structure parameters. When the illuminate light changes from normal incidence to non-normal incidence, the resonant absorption peak splits into a doublet. The simultaneous excitation of surface plasmon polaritons on both surfaces of the metal film can be achieved by controlling the incident angle. Since the wave vector matching condition is not satisfied, there is no coupling between the plasmon polaritons modes on the two surfaces of the corrugated metallic film. The excitation and control of the non-coupled surface plasmon polartions simultaneously propagating on the different interfaces of one metallic film have potential applications for designing novel compact and tunable nano-photonic devices at visible frequency.     

Enhanced Photonic Spin Hall Effect with a Bimetallic Film Surface Plasmon Resonance

Plasmonics - The surface plasmon resonance (SPR) with the bimetallic film can achieve minimum reflectivity and higher evanescent field enhancement than the SPR configuration with the single gold...     

Sensitivity Enhancement for Surface Plasmon Resonance Imaging Biosensor by Utilizing Gold�CSilver Bimetallic Film Configuration

Gold–silver bimetallic film configuration is brought forward to realize surface plasmon resonance imaging (SPRI) biosensor with the virtues of both high sensitivity and chemical stability. The theoretical calculation is adopted to optimize the thicknesses of the metal films, and bimetallic film configuration with high refractive index sensitivity and a good linearity between reflectivity and refractive index is presented. Then, the property of the detection system is discussed. The results show that in comparison to most commercial SPRI biosensors which use single gold films, the sensitivity and molecule detection ability of the gold–silver bimetallic film configuration can be improved to a great extent. For the substrate of BAK3 glass used in this paper, the sensitivity enhancement reaches as high as 80%, which makes it a much better choice for SPRI biosensing applications.     

Propagation Loss of Long-Range Surface Plasmon Polariton Gold Stripe Waveguides in the Thin-Film Limit

Propagation loss experienced by long-range plasmon polaritons in ultrathin gold stripe waveguides embedded in different polymer cladding materials was studied and correlated with atomic-scale characterization of the gold film structure. We identify the main sources of experimentally observed propagation loss which deviates from ideal values in the thin-film limit. Increased loss can be translated to an increased effective thickness of the ultrathin films due to incomplete surface coverage and the presence of diffuse interfaces, both of which depend significantly on the choice of cladding material. The results illustrate the importance of atomic-scale dynamics of metal film formation for the selection of optimum substrate materials for surface plasmon polariton waveguides, resonant transmission structures, and semitransparent electrical contacts.     

Imaging and Characterizing Long-Range Surface Plasmon Polaritons Propagating in a Submillimeter Scale by Two-Color Two-Photon Photoelectron Emission Microscopy

Long-range surface plasmon polaritons (SPPs), which propagate along metal/dielectric interfaces to submillimeter distances in the range of near-infrared (NIR) excitation wavelength, were examined by two-color two-photon photoelectron emission microscopy (2P-PEEM). Interferences between incident NIR photons and SPPs excited by the NIR photons at surface defects were imaged by detecting photoelectrons emitted from a gold surface, assisted by simultaneously irradiated ultraviolet photons which are to overcome the workfunction of the surface. The wavelength of the interference beat depends sensitively on the NIR wavelength. By analyzing the interference beat, the dispersion curve as well as phase and group velocities of SPP’s were experimentally obtained. The results closely match the theoretical one based on the Drude free electron model, indicating that two-color 2P-PEEM is applicable not only to the visualization of NIR-excited SPPs but also to the quantitative analysis of its physical properties. This method will be widely used to observe SPPs for various artificial plasmonic devices.     

A Performance-Enhanced Bimetallic Chip for the Detection of Cadmium Ions with Surface Plasmon Resonance

We demonstrate that a designed bimetallic chip is capable of improving the performance of a surface plasmon resonance (SPR) sensor based on angular interrogation. Through a numerical simulation and a refractometry experiment, we prove that this bimetallic chip can effectively reduce the noise level by about a factor of 2 compared to the traditional SPR sensors that only use a single gold film. The bimetallic chip presents a lower refractive index resolution of 5.3 × 10⁻⁷ refractive index units. In addition, the enhancement of the electric field intensity at the surface of the configuration by a factor of 2 makes it possible to have a high sensitivity in a larger region, which promotes the biosensing applications of the chip. Through a simple and novel method for the detection of cadmium ions (Cd²⁺) based on the bimetallic configuration, a detection level for Cd²⁺ (0.01 μM or 1.12 ppb) can be realized, which compares favorably with similar studies.

     

Imaging of Surfaces by Concurrent Surface Plasmon Resonance and Surface Plasmon Resonance-Enhanced Fluorescence

Surface plasmon resonance imaging and surface plasmon induced fluorescent are sensitive tools for surface analysis. However, existing instruments in this area have provided limited capability for concurrent detection, and may be large and expensive. We demonstrate a highly cost-effective system capable of concurrent surface plasmon resonance microscopy (SPRM) and surface plasmon resonance-enhanced fluorescence (SPRF) imaging, allowing for simultaneous monitoring of reflectivity and fluorescence from discrete spatial regions. The instrument allows for high performance imaging and quantitative measurements with surface plasmon resonance, and surface plasmon induced fluorescence, with inexpensive off-the-shelf components.     

Surface Plasmon Resonance Intensification by Cavity-Ring Plasma Structure in the Giga-Hertz Regime

In this paper, we propose a novel sub-wavelength plasma structure that can effectively enhance surface plasmon resonance (SPR) to achieve a significant local field. On the basis of a plasma ring structure, we add a slit and two thin plasma layers, working as a metal-insulator-metal (MIM) waveguide at a specific incident wave frequency and generate the Fabry-Perot resonance (FPR). The structure thus couples the incident wave energy to the vicinity of the slit and intensifies the SPR inside the plasma ring. In addition, we also find the coupling and competing between SPR and FPR. For the coupling mode, the average field enhancement in the ring is up to a factor of 9.7. Moreover, the optimized thickness of the plasma layer is much thinner than the skin depth of the plasma to ensure the incident wave easily entering the MIM waveguide. We further calculate the dispersion relationship of surface plasmon polaritons in the waveguide cavity. The simulation results and theoretical dispersion function are in good agreements.

     

Long-Range Surface Plasmon Polaritons for Efficient Optical Coupling in AlGaN/GaN Quantum Well Infrared Photodetector

In this paper, the supermodes, long-range surface plasmon polaritons (LRSPPs), have been theoretically studied to enhance the optical coupling of AlGaN/GaN quantum well infrared photodetector (QWIP) based on gold–Si₃N₄ hybrid architecture. The electromagnetic field, energy flow, and current density are analyzed by finite element method (FEM). In time domain, the electric field component E _z and current density J _z perpendicular to the multi-quantum wells (MQWs) are symmetric and asymmetric distributions over the gold grating, respectively, which precisely prove the existence of LRSPPs. The averaged |E _z |² across the whole quantum well region reaches 1.51?(V/m)² when the electric field intensity (|E ₀|²) of normal incidence is 1?(V/m)² at 4.65 μm. Extraordinarily low loss of the LRSPPs results in a coupling efficiency enhancement ratio of 2.23 in AlGaN/GaN QWIP compared with that obtained via bare gold grating with different polarized sources, exhibiting great potential for application in the focal plane arrays.     

Influence of Plasma Polymerized Dielectric Buffer Layer and Gold Film on the Excitation of Long-Range Surface Plasmon Resonance

Recently, long-range surface plasmon resonance (LRSPR) sensor has attracted a great deal of attention as a potentially non-destructive and label-free technique for cellular studies in real time. Thus, much effort has been placed on the fabrication and optimization of multilayered structure required for the excitation of LRSPR. In this work, a detailed study about the influence of both plasma polymerized dielectric buffer layer (DBL) and thin gold film on the excitation of LRSPR was performed. The DBLs of different thicknesses were deposited directly onto SF11 glass slides by radio frequency plasma polymerization (pp) of perfluorooctyl ethylene (PFOE). Thereafter, Au films of different thicknesses were thermally evaporated onto the ppPFOE layers. Atomic force microscopy (AFM) results suggest that the resulting SF11/ppPFOE/Au structure has a smooth surface regardless of Au film’s thickness. LRSPR measurements indicate that the excitation of LRSPR relies not only on the thickness of the ppPFOE buffer layer, but also on the thickness and optical property of thin Au film. Theoretical simulation based on Fresnel’s equation allows for the determination of both the thickness and optical constant of each layer supporting the LRSPR, and also enables us to predict the optimum combination of ppPFOE and Au film in a LRSPR sensor. The performance of various LRSPR sensors to monitor the bulk refractive index variation has also been investigated.     

Surface Plasmon Polariton Enhancement in Silver Nanowire–Nanoantenna Structure

The surface plasmon polariton (SPP) coupling and enhancement in silver nanowire–nanoantenna structure is proposed and simulated by using finite difference time domain method. The results demonstrate that three-arm antenna can effectively enhance the coupling efficiency at the incident end and the SPP field intensity at the emission end. The enhancement factor, which is defined as the ratio of the SPP field intensity at the emission end with and without the three-arm antenna, for the various antenna arm lengths and incident wavelengths under different incident angles are calculated. The suggested structure can be served as an enhanced plasmonic waveguide for the nanophotonic and plasmonic circuits in the future.     

Graphene-MoS2 Hybrid Structure Enhanced Fiber Optic Surface Plasmon Resonance Sensor

Plasmonics - In this paper, a fiber optic surface plasmon resonance sensor based on graphene-MoS2 hybrid structure is presented. The wavelength interrogation method is employed to analyze the...     

The Study of Surface Plasmon Resonance in Au-Ag-Au Three-Layered Bimetallic Nanoshell: The Effect of Separate Ag Layer

Localized surface plasmon resonance (LSPR) properties of Au-Ag-Au three-layered nanoshell are investigated theoretically using the quasi-static electricity. Triple-bands LSPRs have been observed in the absorption spectrum. Both the peak wavelength and intensity could be fine tuned by altering the thickness and radius of the separate Ag layer. The properties and physical origin of the LSPR in the Au-Ag-Au three-layered nanoshell is much different from that of Au-dielectric-Au three-layered nanoshell. The corresponding physical mechanism has been illustrated by plotting the local electric field patterns and analyzing the interaction of the surface charges from different metal interfaces. Although the LSPR of Au-Ag-Au three-layered nanoshell is affected by the plasmon hybridization from all metal surfaces, it has been found that the plasmon coupling in different metallic layer takes main effect on the LSPR properties of different absorption peaks. These results indicate that the different type of metallic layers appearing alternately in the multilayered nanoshells could create abundant tunable LSPR modes, which provides potential for multiplex biosensing based on LSPR.     

A Waveguide-Coupled Surface Plasmon Resonance Sensor Using an Au-MgF2-Au Structure

Plasmonics - We describe an Au-MgF2-Au trilayered waveguide-coupled surface plasmon resonance (WCSPR) sensor in this article. The characteristics of this sensing structure are compared with those...     

A Phase Sensitivity-Enhanced Surface Plasmon Resonance Biosensor Based on ITO-Graphene Hybrid Structure

Plasmonics - In this paper, a surface plasmon resonance (SPR) sensor based on the hybrid structure of silver (Ag)-indium tin oxide (ITO)-graphene is proposed and investigated. SPR biosensors are...     

Nano-gap-Enhanced Surface Plasmon Resonance Sensors

This paper analyzes how dual-mode surface plasmon resonance sensors can be further improved if one were to introduce small (∼20 nm) gaps in the film surface. First, a figure of merit, the sensor’s limit of detection (LOD), is defined in order to optimize the design of the nano-gap sensor. Secondly, the LOD of this design is compared with that of an optimized planar dual-mode design. Through this analysis, it is shown that the LOD of the planar sensor can be improved upon by around a factor of 7 when compared with the nano-gap-enhanced design. Furthermore, with the nano-gap design, the lower wavelength plasmon mode demonstrates remarkably improved selectivity when compared with the conventional sensor. In order to explain these results, the dispersion of each plasmon mode along with the electromagnetic field profiles are modeled and analyzed.     

Tunability of Multipolar Plasmon Resonances and Fano Resonances in Bimetallic Nanoshells

Plasmonics - We study the multipolar surface plasmon modes and its link to Fano resonances in bimetallic nanoparticles. General expressions for the multipolar surface plasmon frequencies and...