Propagation Length Of Surface Plasmon Polaritons Research Articles

Amplification and excitation of surface plasmon polaritons via four-wave mixing process

We suggest a scheme for the excitation and amplification of surface plasmon polaritons (SPPs) along the interface between metal and semiconductor quantum well (SQW), employing a four-wave mixing (FWM) process. The SQW consists of four-level asymmetric double quantum wells that exhibit quantum interference effects, which leads to the coupler-free excitation of SPPs. In our proposed system, the inherent losses of SPPs are compensated by introducing gain through the FWM process, resulting in a significant enhancement in the propagation length and penetration depth of SPPs. We further analyze the effect of gain on the long-range and short-range SPPs and observe that the propagation distance and lifetime of both types of SPPs are increased.

A Floquet engineering approach to optimize Schottky junction-based surface plasmonic waveguides

The ability to finely control the surface plasmon polariton (SPP) modes of plasmonic waveguides unveils many potential applications in nanophotonics. This work presents a comprehensive theoretical framework for predicting the propagation characteristics of SPP modes at a Schottky junction exposed to a dressing electromagnetic field. Applying the general linear response theory towards a periodically driven many-body quantum system, we obtain an explicit expression for the dielectric function of the dressed metal. Our study demonstrates that the dressing field can be used to alter and fine-tune the electron damping factor. By doing so, the SPP propagation length could be controlled and enhanced by appropriately selecting the intensity, frequency and polarization type of the external dressing field. Consequently, the developed theory reveals an unexplored mechanism for enhancing the SPP propagation length without altering other SPP characteristics. The proposed improvements are compatible with existing SPP-based waveguiding technologies and could lead to breakthroughs in the design and fabrication of state-of-the-art nanoscale integrated circuits and devices in the near future.

Narrow-area average method for measurement of the propagation length of surface plasmon polaritons using nanoslit-grating structures

The propagation attenuation of surface plasmon polaritons (SPPs) has an important impact on the performance of plasmonic devices, so measuring their propagation length is important for designing plasmonic devices. Here we propose a method using a single nanoslit surrounded on both sides by surface gratings to measure the propagation length of SPPs. In this method, the propagation length of SPPs is obtained by using a narrow-area statistical averaging method to process the data of the intensity ratio of two diffracted light waves, which are converted from two SPPs that have the same initial intensity but travel different distances in opposite directions in a narrow area of a surface of a metal film. We demonstrate experimentally that at the illumination wavelength of 632.8 nm, the mean value of the propagation length of SPPs propagating at the interface between the air and a gold film with a thickness of about 360 nm measured using the proposed method is 9.88 μm, with a standard deviation of 0.23 μm (i.e., 2.33 % of the mean value). In addition, we demonstrate experimentally that the measurement error of the proposed method in measuring the intensity ratio of the two diffracted light waves, which is the dominant error of the proposed method in measuring the propagation length of SPPs, can be smaller than 2 % of its theoretical value.

Surface plasmon polariton at the interface of dielectric and graphene medium using the Doppler broadening effect

We theoretically investigate the control of surface plasmon polariton (SPP) generated at the interface of dielectric and graphene due to effective variation of dielectric functions. The input light pulse is controlled and modified in a Doppler broadening dielectric medium. The controlled and modified output, from Doppler broadening dielectric medium is used to excite SPPs at the interface of graphene and dielectric medium. It is noted that at high Doppler width the absorption/dispersion and propagation length of SPPs become saturated and significantly affected by strength of the control fields. The inverse Doppler effect enhances the group speed of SPPs but suddenly decreases at the region of SPPs hole burning. These results have potential applications in optical tweezers, nano-photonics, radiations guiding, plasmonster technology, photovoltaic devices, data storage devices, biosensor technology and solar cells.

Coherence Between Different Propagating Surface Plasmon Polariton Modes Excited by Quantum Mechanical Tunnel Junctions

AbstractCoherence between different surface plasmon polariton (SPP) modes excited by inelastically tunneling electrons in biased metal–insulator–metal tunnel junctions (MIM‐TJs) is demonstrated. By employing a dedicated SPP stripe waveguide with MIM‐TJ, an effective double‐slit configuration similar to the Young's experiment is realized for an electrically biased SPP source. The spatial correlation between different SPP modes originates from a single inelastic tunneling event and leads to strong interference in the far‐field, observed as alternate bright and dark fringes in the Fourier plane. The measured fringe‐spacing inversely follows the stripe waveguide length, with upper limit dictated by the SPP propagation length, confirming the SPP mediated spatial correlation. Finite difference time domain simulations support the experimental findings. Also, the experimental and simulation results unambiguously demonstrate the two‐step plasmonic decay process in plasmonic MIM‐TJs. The results presented here provide a simple and robust demonstration of the inherent coherence existing between different decay channels (plasmons and photons) of the inelastically tunneling electrons and can be exploited for plasmonic applications with tailored spatial coherence with implications in plasmon amplification and quantum information processing.

Long-ranged surface plasmon polaritons and their coupling with upconversion emissions in indium-tin-oxide-coated erbium and iron codoped LiNbO3

Long-ranged surface plasmon polaritons (SPPs) and their coupling with upconversion emissions (UCEs) were studied in indium tin oxide (ITO)-coated erbium and iron codoped L i N b O 3 (Er,Fe:LN). In this work, ITO is coated on Er,Fe:LN grains to form a noble-metal-like modified ITO layer, namely, a two-dimensional electron gas layer. By meeting phase-matching conditions, SPPs with a definite wave vector can be excited most efficiently. By calculating the attenuated total reflection spectra of the sandwich structure of unmodified ITO/modified ITO layer/LN, the propagation length of SPP can reach as long as 2.0 cm due to the subnanometer ITO modified layer. Experimentally, the location of missing spectral lines in the diffraction pattern and a valley in the transmission spectra are consistent well with the calculations of the phase-matching condition, both serving as valid proofs for SPP excitation. In the ITO-coated Er,Fe:LN grains, a sharp dropping-down process was observed in the UCE’s dynamics, indicating high coupling efficiency from UCEs to SPPs. This work advances the fundamental understanding in electrostatic modification of transparent oxides into visible nonmetal plasmonic materials by simply neighboring to ferroelectric oxides and leads a way toward designing and implementing shortwave plasmonic devices, apart from conventionally used lossy metal constituents.

Surface plasmon polaritons of higher-order mode and standing waves in metallic nanowires.

The surface plasmon polaritons (SPPs) of higher-order mode propagating along a plasmonic nanowire (NW) or an elongated nanorod (NR) are studied theoretically. The dispersion relations of SPPs in NWs of different radii, obtained from a transcendental equation, show that the propagation lengths of SPPs of mode 1 and 2 at a specific frequency are longer than that of mode 0. For the higher-order mode, the spatial phase of the longitudinal component of electric field at a cross section of a NW exhibits the topological singularity, which indicates the optical vortex. Of importance, the streamlines of Poynting vector of these SPPs exhibit a helical winding along NW, and the azimuthal component of orbital momentum density exists in the nearfield of NW to produce a longitudinal orbital angular momentum (OAM). Two types of standing wave of counter-propagating SPPs of mode 1 and 2 are also studied; they perform as a string of beads or twisted donut depending on whether the handedness of two opposite-direction propagating SPPs is same or opposite. In addition, a SPP of mode 1 propagating along an elongated NR can be generated by means of an end-fire excitation of crossed electric bi-dipole with 90° phase difference. If the criterion of a resonator for a mode-1 standing wave (string of beads) is met, the configuration of a plasmonic NR associated with a pair of bi-dipoles with a phase delay (0° or 180°) at the two ends can be applied as a high-efficiency nanoantenna of transmission. Our results may pave a way to the further study of SPPs of higher-order mode carrying OAM along plasmonic waveguides.

Absorption Enhancement in Hyperbolic Metamaterials by Means of Magnetic Plasma

The main features of surface plasmon polaritons (SPPs) that can propagate in a metamaterial–magnetic plasma structure are studied from theoretical perspectives. Both the conventional and imaginary parts of the dispersion relation of SPPs are demonstrated considering transverse magnetic (TM) polarization. We examine and discuss the influence of the external magnetic field. The results demonstrate that this factor dramatically alters the nature of SPPs. It is concluded that the positions and propagation lengths of SPPs can be engineered. Moreover, we present an approach allowing for an absorption enhancement that is a pivotal factor in antenna design. A unified insight into the practical methods aiming to attain hyperbolic dispersion by means of nanostructured and nanowire metamaterials is demonstrated.

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.

Particle-in-cell simulation of surface plasmon polaritons excited by external introduction of electron density

Plasmonic devices work at visible and near-infrared frequencies, where a large number of bound electrons (polarization) in metals are excited. However, the existing particle-in-cell (PIC) software cannot take into account these bound electrons. In this paper, a new PIC simulation method is developed to study plasmonic devices, which has the ability to model both free electrons and bound electrons in metals. In this study, surface plasmon polaritons (SPPs) are excited by depositing excess electrons at one end of the metal film of thickness 140 nm (surrounded by air), thus initiating nonequilibrium in the electron density to start the oscillations. The spectrum, mode size, and propagation length of SPPs are calculated to confirm the electrical excitation of SPPs and characterize their properties. The excited SPPs are of a broad range of frequencies. Unlike SPPs excited by inelastic electron tunneling, the spectrum of SPPs excited in this way is not determined by eVbias but only by the properties of metals and dielectrics, and therefore the excited SPPs are intrinsic. The mode sizes of the intrinsic SPPs in the Ag–air geometry are 30 nm in Ag and 120 nm in air. The propagation length is ∼730 nm. The excited SPPs are converted into radiation modes by a sub-wavelength slit etched on the back side of the film to enable the detection of the radiation modes.

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.

Hybrid Electro-Optical Pumping of Active Plasmonic Nanostructures.

Surface plasmon polaritons (SPPs) offer a unique opportunity to overcome the diffraction limit of light. However, this opportunity comes at the cost of the strong absorption of the SPP field in a metal, which unavoidably limits the SPP propagation length to a few tens of micrometers in nanostructures with deep-subwavelength mode confinement. The only possibility to avoid the propagation losses is to compensate for them by optical gain in the adjacent active medium. Different approaches for surface plasmon amplification by stimulated emission of radiation have been proposed based on either optical or electrical pumping. However, each has its own disadvantages caused by the selected type of pumping scheme. Here, we study, for the first time, hybrid electro-optical pumping of active plasmonic waveguide structures, and by using comprehensive self-consistent numerical simulations, demonstrate that this hybrid approach can outperform both pure electrical pumping and pure optical pumping. The SPP modal gain is higher than under pure optical pumping, while one can precisely and locally adjust it by tuning the electric current, which allows the reduction of amplification noise and provides additional functionalities. We believe that our findings lay a solid foundation for the development of a new generation of active plasmonic devices and stimulate further research in this area.

Over-the-Horizon Terahertz Surface Plasmon Locator

The article demonstrates the possibility of creating an over-the-horizon locator with an information carrier of surface plasmon polaritons (SPPs), a kind of surface electromagnetic waves, of the terahertz (THz) spectral range. This possibility is based on the macroscopic propagation length (decimeters) of THz SPPs, as well as on their ability to propagate along convex surfaces of metals. Two schemes of location measurements on gold convex samples using THz SPPs were developed and tested for SPPs generated by free-electron laser radiation with a wavelength of 130 μm. It was found that the intensity of SPPs reflected by an object placed on a conducting surface about 4 cm beyond the horizon line depended on the height of the object above the surface, in accordance with the distribution of the SPP field in the air (a few millimeters or fractions of a millimeter). The distance, orientation, coordinates, and height of an object placed beyond the horizon line can be determined using the SPP locator, which can be applied for localization of hard-to-reach objects on a convex surface.

Modeling of dielectric function in plasmonic quantum dot nanolaser

In this work we present a model of the dielectric function in plasmonic quantum dot (QD) nanolaser. A metal/semiconductor/metal structure was considered to attain plasmonic nanocavity with active region containing: QD, wetting layer and barrier. The dielectric function was calculated for both metal (Ag) and QD structure. The propagation constant of surface plasmon polariton (SPP) at the interface of Ag/InAs-QD structure was calculated and the dispersion relation of the plasmonic QD structure was evaluated. For frequencies far from plasma one, the gap between real and imaginary parts was large and a deviation from linear relation was obvious. The SPP field was strongly localized at the interface due to the effect of zero-dimensional QD structure which has application in the super-resolution and best sensitivity in optical imaging. Results of propagation length of SPP ($$L_{spp}$$) also support this. According to the $$L_{spp}$$ results, the damping in the SPP energy was low in the Ag/InAs-QD compared to that in the Ag/air interface. The obtained results are in the range of experimental ones.

Brightening and Guiding Single‐Photon Emission by Plasmonic Waveguide–Slit Structures on a Metallic Substrate

AbstractBy designing a plasmonic waveguide–slit structure (a nanoslit etched in a silver nanowire) on a silver substrate, an ultrahigh Purcell factor and ultralarge figure of merit (FOM) are numerically predicted. Because of the large field enhancement (>150 times the incident field) and the ultrasmall optical volume (V ≈ 2 × 10−5λ3) of the resonant mode in the metallic nanoslit, the simulations show that the Purcell factor in the system can reach up to FP = 1.68 × 105, which is more than ten times the maximum Purcell factor in previous work (by placing metallic nanoparticles on a metal surface with a nanogap). Because of the utilization of a silver substrate rather than the common dielectric substrate, the mode cutoff of the surface plasmon polariton (SPP) waveguide mode is completely eliminated, which provides a large selection range of the nanowire radii to support the resonant mode in the nanoslit. Moreover, the SPP propagation length is significantly increased by more than 30 times. As a result, an ultralarge FOM of 1.40 × 107 is obtained, which is more than 80 times the maximum FOM in previous work where the metallic nanowire is placed on or surrounded by dielectric materials.

Surface plasmons in metamaterial heterostructures

ABSTRACT The extensive research of layered materials has revealed that it is possible to obtain a new degree of freedom for tuning the dispersion properties. Based on this concept, researchers have investigated the hyperbolic metamaterials. Recently, several kinds of photonic crystals have been proposed as classical counterparts of the layered materials. However, observation of nanostructured metamaterials from the perspective of the metamaterial structural design properties has remained difficult until now. Thus, we consider the propagation of surface plasmon polaritons (SPPs) at the boundary of geometrically different metamaterials. Herein, we consider two-layered and multilayered composites. All the heterostructures under consideration are made of the alternating graphene and dielectric sheets. We analytically estimate dispersion properties, absorption and propagation lengths of SPPs. The variation of graphene dielectric functions is described by the Drude model. On top of all, we analytically identify the key factors influencing propagation length along with the absorption enhancement highly desirable in terahertz photoconductive antennas and consider analytical variations aiming to tune the dispersion relations.

Surface plasmons at the interface of metamaterial and topological insulator

We investigate the propagation of surface plasmon polaritons (SPPs) at the boundary of metamaterial and topological insulators. Instances of Bi2Se3, Bi2Te3 and metamaterial boundaries are investigated. The topological insulators under consideration are three dimensional topological insulators of the second generation. Dispersion relations, absorption characteristics and propagation lengths of SPPs are calculated. The variation of bulk dielectric functions of topological insulators and metamaterial is considered by means of the Drude model and effective medium approximation theory. The key parameters making a dramatic impact on propagation lengths are acknowledged and mechanisms for engineering dispersion properties are suggested.

Incoherent and coherent manipulation of surface plasmon hole burning

We theoretically investigate the spectral hole burning of surface plasmon polaritons (SPPs) at an interface between rubidium (87Rb) atomic medium and silver. A typical Lamb dip can be observed at a certain frequency where the absorption of SPPs is suddenly reduced. By applying Kerr-type nonlinearity to the 87Rb atomic gas, the slope of dispersion becomes more normal and steeper. Under the effect of Doppler broadening, a group index of at the SPPs hole burning region is obtained and is further enhanced to with the application of Kerr-nonlinearity. Similarly, the propagation length of SPPs is increased at the hole burning region and is further enhanced with Kerr-nonlinearity. Further, we show that this nonlinear effect results in the enhancement of the phase shift from 0.02 to 1.5 radian at the hole burning region. These results may find important applications in nano-photonics, optical tweezers, photovoltaic devices and sensing technology.

Improving propagation lengths of ultraviolet surface plasmon polaritons on thin aluminium films by ion milling

Ultraviolet plasmonics provides several benefits over the visible or infrared spectral range. The intrinsic optical properties of aluminium make it the best material for ultraviolet-based plasmonic systems, but in practice thin aluminium films exhibit higher roughnesses than those of other metals grown by physical vapour deposition. This roughness increases scattering losses, decreasing surface plasmon polariton propagation length. Here we experimentally demonstrate a method for improving the optical quality of aluminium films using an ion milling post-deposition processing step to reduce surface roughness. The propagation length of surface plasmon polaritons has been measured in the ultraviolet spectral range using grating pairs fabricated by focused ion beam milling. The propagation length for as-deposited films has been compared with films produced by normal incidence and oblique angle milling. An increase in propagation length of about 20% was observed for both normal and oblique angle milling.

Surface plasmon polariton at the interface of dielectric and graphene medium using Kerr effect

We theoretically investigate the control of surface plasmon polariton (SPP) generated at the interface of dielectric and graphene medium under Kerr nonlinearity. The controlled Kerr nonlinear signal of probe light beam in a dielectric medium is used to generate SPPs at the interface of dielectric and graphene medium. The positive, negative absorption, and dispersion properties of SPPs are modified and controlled by the control and Kerr fields. A large amplification (negative absorption) is noted for SPPs under the Kerr nonlinearity. The normal/anomalous slope of dispersion and propagation length of SPPs is modified and controlled with Kerr nonlinearity. This leads to significant variation in slow and fast SPP propagation. The controlled slow and fast SPP propagation may predict significant applications in nano-photonics, optical tweezers, photovoltaic devices, plasmonster, and sensing technology.