Leaky Surface Plasmon Research Articles

Photonic-plasmonic hot-electron-based photodetection with diffracted-order-resolved leaky plasmonic mechanisms.

Although hot-carrier-based photodetection using plasmonic effects has been widely investigated, photodetectors of this type with an external quantum efficiency (EQE) and an active area of mm2 remain out of reach even in the visible frequencies. In this work, a novel hot-electron-based, non-trench-type photodetector exploiting pure photoexcitation in a thin aluminum (Al) film and leaky plasmonic modes at and between its heterojunctions is proposed, analyzed, and experimentally demonstrated. Combining diffracted-order-resolved analytical analysis and numerical computations unravels the optical absorption mechanism of the innovative design. Leaky surface plasmon resonance (with leakage radiation into the air) produced by a propagating diffracted order and quasibound supermodes (with power leakage via coupled gap plasmon polariton and bound surface plasmon polariton modes) excited by evanescent diffracted orders are shown to significantly contribute to the absorptance in the preferred thin Al film where hot electrons are generated. At 638.9nm and electric bias -0.9951 V, the measured per-unit-area responsivity, detectivity, and the external quantum efficiency reach 298.1444μA/mW/mm2, 4.3809 × 109 cm Hz1/2/W, and 2.6878%, respectively, from an active area of 4.6457 × 10-2 mm2. The performance is among the best of those previously reported operating at similar wavelengths and biases. The RC time constant is estimated to be about 1.673 μs from the current-voltage measurements. The physical insight into the innovative, experimentally demonstrated device could lay the groundwork for the practical use of low-voltage, metal-based photodetection.

A numerical study on the closed packed array of gold discs as an efficient dual mode plasmonic tweezers

In this report, we propose the closed pack array of gold discs on glass, as a dual mode plasmonic tweezers that benefits from two trapping modes. The first trapping mode is based on leaky surface plasmon mode (LSPM) on the gold discs with a longer penetration depth in the water and a longer spatial trapping range, so that target nanoparticles with a radius of 100 nm can be attracted toward the gold surface from a vertical distance of about 2 µm. This trapping mode can help to overcome the inherent short range trapping challenge in the plasmonic tweezers. The second trapping mode is based on the dimer surface plasmonic mode (DSPM) in the nano-slits between the neighboring gold discs, leading to isolated and strong trapping sites for nanoparticles smaller than 34 nm. The proposed plasmonic tweezers can be excited in both LSPM and DSPM modes by switching the incident wavelength, resulting in promising and complementary functionalities. In the proposed plasmonic tweezers, we can attract the target particles towards the gold surface by LSPM gradient force, and trap them within a wide half widthhalfmaximum (HWHM) that allows studying the interactions between the trapped particles, due to their spatial proximity. Then, by switching to the DSPM trapping mode, we can rearrange the particles in a periodic pattern of isolated and stiff traps. The proposed plasmonic structure and the presented study opens a new insight for realizing efficient, dual-mode tweezers with complementary characteristics, suitable for manipulation of nanoparticles. Our thermal simulations demonstrate that the thermal-induced forces does not interefe with the proposed plasmonic tweezing.

Ultrathin InP annular nanohole arrays for efficient light absorption solar cells

This Letter proposes ultrathin InP films consisting of annular nanohole arrays (ANAs) for highly efficient solar cells. By tailoring the inner and outer radii of ANAs properly and combining antireflection coating (ZnO) and back-reflector (Ag), the photocurrent generated in the InP based dielectric-semiconductor-metal (DSM) configuration can be increased dramatically by 124.6% with respect to the planar solar cell of equal geometric thickness (100 nm). The fact that the DSM-ANA structure is able to harvest broadband and wide-angle incident light can be attributed to the excitation of leaky waveguide modes, Bloch modes, and surface plasmon polariton modes. This work provides a promising and feasible way to design and fabricate efficient ultrathin InP photovoltaic and other optoelectronic devices.

Simultaneous excitation of leaky mode resonance and surface plasmon resonance in tilted fiber Bragg grating

This paper presents the first work that theoretically demonstrates simultaneous excitation of both enhanced leaky mode resonance (eLMR) and surface plasmon resonance in ultra-thin Au film coated tilted fiber Bragg grating. The mechanism is discussed by investigating the influence of Au film on mode characteristics of leaky modes and guided modes. A stable transmission spectrum that is only composed of strong dense comb-like eLMR in a wide window is realized. The eLMR excited by metal film exhibits insensitive response to external perturbation, which makes it ideal for tunable devices like optical filters and fiber lasers.

Au Plasmonic Shofar Structures

We demonstrate a simple two-step etching method to fabricate Au plasmonic shofars (“shofar” is the Hebrew name for certain types of curved and tapered horns, such as from a ram). The structural, optical, and morphological properties were studied by using X-ray diffraction, UV-Vis spectrophotometry, and scanning electron microscopy (SEM). The etching mechanism and the light-guiding properties for this unique morphology are described. The leaky surface plasmon propagation (SPP) and guiding properties of shofars are investigated by using leakage radiation microscopy (LRM).

Efficient Plasmonic 2D Arrangement and Manipulation System, Suitable for Controlling Particle–Particle Interactions

Investigating interactions between biological or artificial micro and nanoparticles (NPs) are vital for understanding processes such as intercellular communications, and quantum and optical effects in an array of NPs. In this line of research, methods to precisely trap and manipulate NPs are essential to investigate such inter-particle interactions. Exciting higher order counter-propagating leaky surface plasmon modes (LSPMs) of a thin gold stripe, we present a simple and efficient method to arrange NPs into a two-dimensional (2D) periodic pattern, allowing precise control over inter-particle interactions. We demonstrate that the 2D lattice of traps is generated by interference of totally reflected surface plasmons from the gold stripe edges and also interference of two counter-propagating LSPMs. Analytical calculations and numerical simulations are in good agreement with the observed modal behavior of LSPMs. Due to the modal dependency of LSPMs on the incident wavelength, we show that in this system different inter-particle distance with nanometer resolution can be achieved by adjusting the wavelength of the incident laser beams. Moreover, we show that the trapped NP array shows waveguiding behavior, enhances the mode intensities and the resulted potential wells consequently. We expect that this self-induced enhancement of trapping efficiency is beneficial for the periodic arrangement of NPs and array formation. The proposed approach implemented in a simple plasmonic optophoresis system, opens the possibility to develop integrated optical manipulation chips, which allows simple and low-cost approach for controlling and studying the inter-particle interactions. Furthermore, the proposed approach is also promising for controllable assembling of NPs without the need for complicated and time consuming nano-lithography techniques.

Radiation characteristics of Leaky Surface Plasmon polaritons of graphene

High efficient coupling of graphene surface plasmons to far field radiation is possible by some techniques and can be used in the radiating applications. Besides of the coupling efficiency, the angular distribution of the radiated power is an important parameter in the radiating devices performance. In this paper we investigate the gain of the far field radiation related to the coupling of graphene surface plasmons via a high permittivity medium located close to the graphene. Our results show that high directive radiation and high coupling efficiency can be obtained by this technique and gain and directivity of radiation can be modified by graphene characteristics such as chemical potential and also quality of the graphene. Raising the chemical potential of graphene leads to increase the gain of the radiation as the result of amplifying the directivity of the radiation. Furthermore, high values of relaxation time lead to high directive and strong coupling which raises the maximum value of gain in efficient coupling angle. Tunable characteristics of gain and directivity in this structure can be important designing reconfigurable THz radiating devices.

Strong Exciton-Plasmon Coupling in Silver Nanowire Nanocavities.

The interaction between plasmonic and excitonic systems and the formation of hybridized states is an area of intense interest due to the potential to create exotic light-matter states. We report herein coupling between the leaky surface plasmon polariton (SPP) modes of single Ag nanowires and excitons of a cyanine dye (TDBC) in an open nanocavity. Silver nanowires were spin-cast onto glass coverslips, and the wavevector of the leaky SPP mode was measured by back focal plane (BFP) microscopy. Performing these measurements at different wavelengths allows the generation of dispersion curves, which show avoided crossings after deposition of a concentrated TDBC-PVA film. The Rabi splitting frequencies (Ω) determined from the dispersion curves vary between nanowires, with a maximum value of Ω = 390 ± 80 meV. The experiments also show an increase in attenuation of the SPP mode in the avoided crossing region. The ability to measure attenuation for the hybrid exciton-SPP states is a powerful aspect of these single nanowire experiments because this quantity is not readily available from ensemble experiments.

Surface waves guided by metamaterials with rotational disorder

The analytical analysis of the metamaterial boundary with the rotational disorder reveals both bound and leaky surface plasmon (SP) modes. The dispersion relations of SPs propagating on a surface of these metamaterials are presented along with the propagation lengths. The rigorous modeling and analysis of surface waves at the boundary of two metamaterials possessing rotational disorder are presented. Dispersion properties of two different metamaterial boundaries have been investigated. The results show that the boundary of the metamaterials having different dielectrics employed allows for the presence of the particular modes crossing the light line with the significant portion at lower frequencies lying above the free space light line.

Selective excitation of surface plasmon modes propagating in Ag nanowires.

Surface plasmon modes propagating in metal nanowires are conveniently excited by focusing a laser beam on one extremity of the nanowire. We find that the precise positioning of the nanowire inside the focal region drastically influences the excitation efficiency of the different SPP modes sustained by the plasmonic waveguide. We demonstrate a spatially selective excitation of bound and leaky surface plasmon modes with excitation maps that strongly depend on the orientation of the incident linear polarization. We discuss this modal selection by considering the inhomogeneous distribution of the field components inside the focus. Our finding provides a way to discriminate the effective indices of the modes offering thus an increased coupling agility for future nanowire-based plasmonic architectures.

Analytical model for the excitation of leaky surface plasmon polaritons in the attenuated total reflection configuration

We propose a fully-analytical model for the excitation of leaky surface plasmon polariton (SPP) in the attenuated total reflection (ATR) configuration under illumination by a finite-width beam of electromagnetic wave. The model is built up on the basis of the general unconjugated-form reciprocity theorem and is able to predict the excitation amplitude and phase of the leaky SPP at a quantitative level. The validity of the model is carefully supported through a comparison with the numerical results obtained with the mode orthogonality. With the model a physical understanding of the resonant excitation of the leaky SPP is achieved and the optimal parameters such as the incidence angle and the beam width to ensure an efficient SPP excitation are demonstrated for design tasks.

Non-universal behavior of leaky surface waves in a one dimensional asymmetric plasmonic grating

We report on a non-universal behavior of leaky surface plasmon waves on asymmetric (Si/Au/analyte of different height) 1D grating through numerical modelling. The occurrence of the leaky surface wave was maximized (suppressing the Fabry–Perot cavity mode), which can be identified in a reflection spectrum through characteristic minimum. Beyond a specific analyte height (h), new sets of surface waves emerge, each bearing a unique reflection minimum. Furthermore, all of these minima depicted a red-shift before saturating at higher h values. This saturation is found to be non-universal despite the close association with their origin (being leaky surface waves). This behavior is attributed to the fundamental nature and the origin of the each set. Additionally, all of the surface wave modes co-exit at relatively higher h values.

Experimental demonstration of a novel bio‑sensing platform via plasmonic band gap formation in gold nano‑patch arrays

In this paper we discuss the possibility of implementing a novel bio-sensing platform based on the observation of the shift of the leaky surface plasmon mode that occurs at the edge of the plasmonic band gap of metal gratings, when an analyte is deposited on top of the metallic structure. We report numerical calculations, fabrication and experimental measurements to prove the sensing capability of a two-dimensional array of gold nano-patches in the detection of a small quantity of Isopropyl Alcohol (IPA) deposited on top of sensor surface. The calculated sensitivity of our device approaches a value of 1000 nm/RIU with a corresponding Figure of Merit (FOM) of 222 RIU(-1). The presence of IPA can also be visually estimated by observing a color variation in the diffracted field. We show that color brightness and intensity variations can be ascribed to a change in the aperture size, keeping the periodicity constant, and to different types of analyte deposited on the sample, respectively. Moreover, we demonstrate that unavoidable fabrication imperfections revealed by the presence of rounded corners and surface roughness do not significantly affect device performance.

Omnidirectional Reflector Based on Dual Effect of Leaky Mode Resonance and Surface Plasmon Resonance

not Available.

Vector frequency-comb Fourier-transform spectroscopy for characterizing metamaterials

We determine infrared transmission amplitude and phase spectra of metamaterial samples at well-defined incidence and polarization with a vector (‘asymmetric’) frequency-comb Fourier-transform spectrometer (c-FTS) that uses no moving elements. The metamaterials are free-standing metallic hole arrays; we study their resonances in the 7–13 μm and 100–1000 μm wavelength regions due both to interaction with bulk waves (Wood anomaly) and with leaky surface plasmon polaritons (near-unity transmittance, coupling features and dispersion). Such complex-valued transmission and reflection spectra could be used to compute a metamaterial's complex dielectric function directly, as well as its magnetic and magneto-optical permeability functions.

Surface plasmon modes of finite, planar, metal-insulator-metal plasmonic waveguides

The numerical analysis of finite planar metal-insulator-metal waveguide structures using the transfer-matrix formalism reveals both bound and leaky surface plasmon (SP) modes. The dispersion relations, propagation lengths and confinement factors of these SP modes are presented. The highest energy SP mode consists of non-radiative (bound) and radiative (leaky) portions separated by a spectral gap. The leaky regime is further divided into antenna and reactive mode regions. The antenna mode may be used for both free-space coupling and beam steering devices.

Comment on “Large negative lateral shifts from the Kretschmann-Raether configuration with left-handed materials” [Appl. Phys. Lett. 87, 221102 (2005)

The negative shifts seen by Wang and Zhu [Appl. Phys. Lett. 87, 221102 (2005)] are not due to the excitation of surface plasmons but to leaky modes of the slab propagating backward. Provided the characteristics of the left-handed material slab are chosen correctly, it is shown that a leaky surface plasmon can actually be excited using the Kretschmann-Raether configuration.

Near-field characterization of guided polariton propagation and cutoff in surface plasmon waveguides

We present a series of near-field experiments characterizing cutoff for the three lowest order leaky surface plasmon modes supported by Au stripes on glass substrates. These studies demonstrate that the propagation of light along surface plasmon waveguides is mediated by a discrete number of guided polariton modes as well as a continuum of radiation modes. To distinguish the contribution of the guided modes from that of the radiation continuum, a parametric study of propagation length as a function of varying stripe width is performed. Discontinuities consistent with the loss of a guided mode are observed near cutoff widths predicted by numerical simulations, and a severe decrease in propagation length is observed below cutoff for the fundamental surface plasmon mode. Contrary to previous interpretations, experimental and numerical investigations confirm that the finite propagation lengths observed along the narrowest stripes are in good agreement with an intuitive model for the radiation continuum. Furthermore, multimode interference studies provide direct evidence for multiple guided modes and support previous findings with regard to modal cutoff.

Beaming of light at broadside through a subwavelength hole: Leaky wave model and open stopband effect

The optical transmission through a subwavelength hole in a metal film is usually very small, and the beam radiated from its exit aperture is very broad. However, the transmission may be increased by orders of magnitude, and the output beam sharply narrowed, when the tiny hole is surrounded by a properly designed periodic structure, which may take the form of an array of grooves or indentations on the metal surface. We have shown that these dramatic effects are due to the excitation of a leaky surface plasmon mode by the periodic structure on the metal film. Following this understanding, we introduce a simple but effective leaky wave antenna model, which we use to further explain and to quantify these dramatic effects. Particular attention is given to optimizing the structure to achieve maximum radiation at broadside, which offers a significant challenge in view of the open stopband in precisely the broadside direction.

Leaky and bound modes of surface plasmon waveguides

While theoretical studies of finite width plasmonic waveguides have focused on the bound modal solutions of metallic structures in homogeneous or near-homogeneous dielectric matrices, experimental studies have mainly probed the leaky surface plasmon modes along the air-exposed surfaces of metallic stripes on glass substrates. Combining a full-vectorial, magnetic field finite-difference method with complex coordinate stretching perfectly matched layer boundary conditions, we have solved for both the leaky and bound modes of metallic slab and stripe waveguides. Solutions for the leaky modes excited via attenuated total reflection in the Kretschmann configuration provide added insight into the results of recent near and far-field experimental studies. For these cases, an analytical approximation for the number of allowed modes as a function of waveguide width is derived based upon the guidance condition of dielectric waveguide theory. Then, consistent with a ray optics interpretation for surface plasmon-polariton propagation, a direct comparison is made between our simulations and published results with regard to field profiles and propagation lengths.