Excitation Of Surface Plasmon Polaritons Research Articles

Дослідження ефективності збудження поверхневих плазмон-поляритонів на алюмінієвих гратках з урахуванням дифрагованого випромінювання

Detailed studies of the efficiency of excitation of surface plasmon-polaritons (SPP) on aluminum gratings with a period a = 694 nm, which exceeds the incident wavelength of λ = 632,8 nm, have been carried out. The gratings relief depth (h) range was 6–135 nm. Research samples were formed on As40S30Se30 chalcogenide photoresist films using interference lithography and vacuum thermal deposition of an opaque aluminum layer about 80 nm thick. An atomic force microscope was used to determine the groove profile shape and the grating relief depth. The study of the SPP excitation features was carried out on a stand mounted on the basis of a G5M goniometer and an FS-5 Fedorov stage by measuring the angular dependences of the intensity of specularly reflected and diffracted p-polarized radiation of He-Ne laser. When determining the SPP excitation efficiency, the resonance values of both specular reflection and reflection in the -1st DO were taken into account. It was found that the dependence of the integral plasmon absorption on the grating modulation depth (h/a) is described by a somewhat asymmetric curve with a wide maximum, the position of which corresponds to an h/a value of about 0.07 and a half-width of about 0.123. This allows to excite SPP with an efficiency ≥ 80% of the maximum value on the gratings with the 0,05-0,105 h/a range. The half-width of the plasmon minimum of the reflection in the -1st DO is less than in the specular reflection, which can increase sensitivity of sensor devices when registering the shift of the minimum from angular measurements. The dependence of the half-width of the SPP reflection minima on the grating modulation depth is close to quadratic. In the investigated h/a range (from 0.009 to 0.194), the maximum dynamic range of the reflection coefficient is two orders of magnitude and is achieved in specular reflection for gratings with h/a ≈ 0.075.

Impact of Pre-Patterned Structures on Features of Laser-Induced Periodic Surface Structures.

The efficiency of light coupling to surface plasmon polariton (SPP) represents a very important issue in plasmonics and laser fabrication of topographies in various solids. To illustrate the role of pre-patterned surfaces and impact of laser polarisation in the excitation of electromagnetic modes and periodic pattern formation, Nickel surfaces are irradiated with femtosecond laser pulses of polarisation perpendicular or parallel to the orientation of the pre-pattern ridges. Experimental results indicate that for polarisation parallel to the ridges, laser induced periodic surface structures (LIPSS) are formed perpendicularly to the pre-pattern with a frequency that is independent of the distance between the ridges and periodicities close to the wavelength of the excited SPP. By contrast, for polarisation perpendicular to the pre-pattern, the periodicities of the LIPSS are closely correlated to the distance between the ridges for pre-pattern distance larger than the laser wavelength. The experimental observations are interpreted through a multi-scale physical model in which the impact of the interference of the electromagnetic modes is revealed.

The effect of surface plasmon-polaritons on the photostimulated diffusion in light-sensitive Ag–As4Ge30S66 structures

The effect of surface plasmon-polaritons (SPPs) excited at the interface between the profiled surface of the silver layer (in the form of a diffraction grating) and the As4Ge30S66 layer on the photostimulated diffusion of silver into chalcogenide has been studied. The gratings with the period a = 519 nm and modulation depth h/a ≈ 0.037 (where h is the grating depth) were formed on chalcogenide photoresist films by using interferential lithography and covered with the 80-nm-thick aluminum layer, 85-nm-thick silver layer, and thin As4Ge30S66 layer. Photostimulated changes in this structure were studied measuring the angular dependences of specular reflection (Rp) of p-polarized light with the wavelength 632.8 nm. It was found that as a result of exposure, “degradation” (broadening, increase in reflection at the minimum) of the minimum in the angular dependence of Rp (which is associated with the SPP resonance) occurs faster, when the samples are irradiated at the angle corresponding to SPP excitation. This observation indicates acceleration of the photostimulated diffusion process in this structure under the plasmon field action.

Kramers-Kronig Relation for Attenuated Total Reflection from a Metal-Dielectric Interface Where Surface Plasmon Polaritons Are Excited.

The applicability of the Kramers–Kronig relation for attenuated total reflection (ATR) from a metal–dielectric interface that can excite surface plasmon polaritons (SPP) is theoretically investigated. The plasmon-induced attenuation of reflected light can be taken as the resonant absorption of light through a virtual absorptive medium. The optical phase shift of light reflected from the SPP-generating interface is calculated using the KK relation, for which the spectral dependence of ATR is used at around the plasmonic resonance. The KK relation-calculated phase shift shows good agreement with that directly obtained from the reflection coefficient, calculated by a field transfer matrix formula at around the resonance. This indicates that physical causality also produces the spectral dependence of the phase of the leakage field radiated by surface plasmons that would interfere with the reflected part of light incident to the interface. This is analogous with optical dispersion in an absorptive medium where the phase of the secondary field induced by a medium polarization, which interferes with a polarization-stimulating incident field, has a spectral dependence that stems from physical causality.

Geometric Control Over the Edge Diffraction of Electrically Excited Surface Plasmon Polaritons by Tunnel Junctions

Plasmonic metal–insulator–metal tunnel junctions (MIM-TJs) readily excite surface plasmon polaritons (SPPs) by inelastic electron tunneling, well below the diffraction limit, eliminating the need for bulky optical elements. The highly confined MIM cavity mode (MIM-SPP) excited by the tunneling electrons dominantly outcouples to photons and single-interface SPPs which further outcouple as photons and give characteristic features in the Fourier plane of observation. Here, we employ SPP waveguides, directly integrated with MIM-TJs, to explore the diffraction of single-interface SPPs at the edges of the metal stripe waveguides. In addition to the leakage of the SPP modes through the metal electrodes, SPP edge diffraction presents as an additional channel for SPP outcoupling, not limited by the thickness of the waveguide. Edge diffraction manifests as a straight-line feature in the Fourier plane of the far-field and by systematically varying the width of the waveguides, we show that the in-plane momentum of the SPPs can be controlled, which in turn leads to control over the edge diffraction. We fabricated MIM-TJs with integrated plasmonic stripe waveguides of different widths, and the propagation and confinement of the SPP modes along the edges of the SPP waveguides are directly identified by the experimental back focal plane imaging, which are further corroborated by numerical simulations. Our findings can be exploited for applications ranging from sensing to nonlinear plasmonics, where focusing and localization of SPP fields are necessary.

Absorption Spectrum‐Compensating Configuration Reduces the Energy Loss of Nonfullerene Organic Solar Cells

AbstractUsing narrow bandgap nonfullerene acceptors (NFAs) can broaden the absorption spectrum of organic solar cells (OSCs) to the near‐infrared region. However, the simultaneously decreased extinction coefficient of the active layer at the blue region results in inevitable light escaping and energy loss. Herein, a blazed grating‐based device configuration consisting of a patterned rear electrode is employed to compensate for the low absorption of nonfullerene OSCs. Experimental results reveal that the normal incidence light, especially blue light, that bounces off the patterned rear electrode is concentrated in a large tilted angle and subsequently trapped in waveguide mode. Along with the excitation of surface plasmon polariton, the structured nonfullerene OSCs using a new‐designed PM6:M36 active layer obtain the broadband absorption enhancement with 1.5 times increase at the blue region. The optimized device achieves an 8.95% increase in photocurrent and a champion power conversion efficiency of approaching 18%, which is the highest reported value among all the devices based on A‐D‐A type NFAs.

Sub-100-nm periodic nanostructure formation induced by short-range surface plasmon polaritons excited with few-cycle laser pulses

We have demonstrated that intense 7-fs, ∼810-nm laser pulses can produce a much finer periodic nanostructure on a diamond-like carbon film through ablation in air than that formed with intense 100-fs, ∼800-nm laser pulses. The minimum period size is ∼60 nm, corresponding to ∼1/13 of the center wavelength. To understand the physical mechanism responsible for the finer nanostructuring, we have observed a bonding structural change in the nanostructure with micro-Raman spectroscopy and a scanning transmission electron microscope. It has been found that the modified layer thickness with the 7-fs pulses is much thinner than that with the 100-fs pulses. The results show that the 7-fs pulses create a few-nm-thick layer with high-density electrons and excite short-range surface plasmon polaritons, which have a large wave number around the layer and induce the plasmonic near-field nanoablation. The period size estimated by using a model target reproduces well the observed size of nanostructures.

Sensing enhancement ammonia gas sensor based on a hybrid film fiber

A sensing enhancement sensor based on hybrid film fiber has been proposed to detect ammonia. The hybrid film coated on the MMF-SMF-MMF (Multimode Fiber–Single-mode Fiber–Multimode Fiber) structure is composed of single-walled carbon nanotubes with carboxylic acid groups (SWCNTs-COOH) self-assembled film and the silver film that was used to excite surface plasmon polariton (SPP) which contribute to enhancing the sensitive for refractive index (RI). The presence of free carboxylic acid functional groups and large surface area on the SWCNTs-COOH leads to high adsorption and selectivity toward amine compounds. The sensor works under a wavelength modulation scheme. And the resonance wavelength showed a red shift with an increase of the effective RI of the SWCNTs-COOH self-assembled film affected by ammonia concentration. The experimental results show that the sensor coated with hybrid film has high sensitivity and selectivity to ammonia gas. The proposed sensor is linearly responsive to ammonia concentration in the range 0 - 30 ppm, with a maximum sensitivity of 0.8 nm/ppm, the resolution 0.375 ppm, and the measured response 30 s, respectively. Finally, the sensor also has the advantages of simple structure and compact size, excellent stability, and low cost.

Nonlinear TMOKE enhancement in 1D Au/Py magnetoplasmonic crystals

Resonant optical properties of the magnetoplasmonic crystals, which support propagation of surface plasmon polaritons (SPPs) accompanied by magnetooptical effects, have found success in magnetic field driven control of optical radiation. In this work we investigate the resonant magnetooptical effects in the second harmonic generation in the magnetoplasmonic crystal formed by gold/pemalloy bifilm covering dielectric grating. Strong transverse magnetooptical Kerr with the contrast up to 30% is revealed in the spectral vicinity of the SPP excitation.

Maximizing spectral sensitivity of plasmonic photonic crystal fiber sensor

We propose a novel design for a plasmonic photonic crystal fiber (PCF) sensor. Our design includes a metal film incorporated within the PCF structure. Compared to previously discussed sensing configurations, the metal surface does not come in direct contact with the sample being tested in our design. The metal film serves to provide absorption due to the excitation of surface plasmon-polaritons (SPP). This absorption is enhanced when a PCF-guided mode resonantly couples to the SPP, or in other words when phase matching between the mode and the SPP is satisfied. We consider a configuration where a hollow PCF core is filled with a liquid sample, while the metal surfaces are kept tens of microns away within the PCF cladding. Our sensor detects small changes in the sample's refractive index, over a broad wavelength range, by taking advantage of the refractive index sensitivity of the resonance/phase-matching condition. We model the sensor and characterize its performance by using the COMSOL environment based on the finite element method. We evaluate and compare three elements: gold, silver, and copper, in order to increase the absorption at particular wavelengths. We also vary the thickness of the metal layer and optimize it to enhance the sensitivity. The results show a performance that exceeds a minimal sensor resolution over an ultra-broad spectral range while maintaining a reasonable amplitude sensitivity.

Modification of Tin (Sn) metal surfaces by surface plasmon polariton excitation

We report on the modification of tin (Sn) film surfaces under a laser beam irradiation that triggers surface plasmon polariton (SPP) excitations. The observed surface features in the form of small raised grains, with well-defined rooting, look similar to tin whisker nodules. We attribute the appearance of those features to the field-induced nucleation caused by the SPP related strong electric field. Possible implications of our findings include accelerated-life testing for tin whisker growth related reliability as well as applications to nanoparticle nucleation.

Ultra-Narrow SPP Generation from Ag Grating.

In this study, we investigate the potential of one-dimensional plasmonic grating structures to serve as a platform for, e.g., sensitive refractive index sensing. This is achieved by comparing numerical simulations to experimental results with respect to the excitation of surface plasmon polaritons (SPPs) in the mid-infrared region. The samples, silver-coated poly-silicon gratings, cover different grating depths in the range of 50 nm–375 nm. This variation of the depth, at a fixed grating geometry, allows the active tuning of the bandwidth of the SPP resonance according to the requirements of particular applications. The experimental setup employs a tunable quantum cascade laser (QCL) and allows the retrieval of angle-resolved experimental wavelength spectra to characterize the wavelength and angle dependence of the SPP resonance of the specular reflectance. The experimental results are in good agreement with the simulations. As a tendency, shallower gratings reveal narrower SPP resonances in reflection. In particular, we report on 2.9 nm full width at half maximum (FWHM) at a wavelength of 4.12 µm and a signal attenuation of . According to a numerical investigation with respect to a change of the refractive index of the dielectric above the grating structure, a spectral shift of can be expected, which translates to a figure of merit (FOM) of about 1421 . The fabrication of the suggested structures is performed on eight-inch silicon substrates, entirely accomplished within an industrial fabrication environment using standard microfabrication processes. This in turn represents a decisive step towards plasmonic sensor technologies suitable for semiconductor mass-production.

Condensation of plasmon-polaritons in dispersive carbon nanotubes assisted by a fast charge

Capturing the energy of fast charged particles by nanostructures opens up access to new affordable and environmentally friendly solutions in the field of energy. However, the condition for this (Cherenkov emission) in dispersionless media is attainable only for very fast particles. We propose to use for this purpose the excitation of surface plasmon polaritons in a three-dimensional (3D) array of dispersive carbon nanotubes (CNTs) assisted by a fast charge. In such a dispersive system, the radiation occurs even if the particle speed is less than the speed of light in the material (E.Fermi). The inclusion of an array of CNTs leads to that such a composite system becomes spatially inhomogeneous, which significantly modifies the field dynamics. Our numerical 3D modeling shows that the properties of the field created in such a composite drastically depend on the value of the plasma frequency ω p of carbon nanotubes. Local short-wave fields of plasmon-polaritons arise here already in the subcritical region. At large ω p , the reconnection of local fields leads to transition in a delocalized state (plasmon-polaritons condensate), when collective field oscillations occupy macroscopicaly large region of the CNT and the inverse partisipation ratio attains a minimum. This effect can find interesting applications in modern ‘laboratory-on-a-chip’ technologies for capturing and accumulation of the pure energy of fast particles by plasmon-polaritons of carbon nanostructures.

Controllable Excitation of Surface Plasmon Polaritons in Graphene‐Based Semiconductor Quantum Dot Waveguides

AbstractThe research aim of this study is the development of a theoretical semiclassical model of the controllable excitation and propagation of surface plasmon polaritons (SPPs) in planar graphene waveguides by the application of external voltage. The model is based on the numerical solution of the SPP's dispersion equation formulated for a system including two coupled graphene sheets with embedded quantum dots. Using the developed model, the different near‐field patterns realized in the waveguides depending on the quantum dots' ordering and an external voltage applied independently to each graphene sheet with additional gold electrodes are numerically investigated. The obtained results show that the application of external voltage can locally change the chemical potential of graphene and, thereby, lead to controllable excitation of SPPs in the corresponding graphene waveguide. Furthermore, we revealed that the propagation direction of the excited SPPs is determined by the geometrical configurations of the gold electrodes that provide the required SPP routing. The investigated system offers new opportunities for near‐field energy transport and concentration, which can be applied to develop ultra‐compact photonic devices.

U-grooved dual-channel plasmonic sensor for simultaneous multi-analyte detection

A photonic crystal fiber (PCF)-based surface plasmon resonance (SPR) sensor is proposed for real-time multi-analyte detection. Semicircular U-shaped slots are excavated inside the PCF to facilitate the excitation of surface plasmon polaritons by reducing the distance between the core and external analyte channels. The evanescent field is controlled via engineered scaled-down air holes. A plasmonic metal layer (gold) is deposited over the U-curved microchannel to enhance the surface plasmons. This asymmetric PCF SPR structure enables superior birefringence controllability, which results in a dominant y -polarized response in comparison to the x -polarized mode. The light-guiding and sensor performance parameters are numerically analyzed using the full vector finite element method. The proposed sensor can detect a wide refractive index (RI) range from 1.33 to 1.43. It demonstrates the maximum wavelength sensitivities of 2000 nm/RIU and 12,800 nm/RIU with sensor resolutions of 5 × 1 0 − 5 R I U and 7.813 × 1 0 − 6 R I U for channels 1 and 2, respectively. The sensor also exhibits a maximum amplitude sensitivity of 1119 R I U − 1 with a high figure of merit of 474 R I U − 1 . The simultaneous dual-analyte detection capability and highly sensitive response with a broad detection range make the proposed sensor distinct and will pave the way for miniaturized medical diagnostics and sensing applications.

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.

Zirconium Nitride: Optical Properties of an Emerging Intermetallic for Plasmonic Applications

Finding new plasmonic materials with prominent optical properties and unique physical and chemical characteristics, which are merits of traditional gold and silver, is of great interest to many applications. This work uses a series of powerful numerical methods, such as density functional theory (DFT) and electromagnetic modeling approaches, to predict the plasmonic response of a mechanically well‐known material, zirconium nitride (ZrN). DFT first delivers an electronic analysis and optical dispersion data between 1 and 8 eV, experimentally verified in the lower energy regime (), and extremely valuable for any subsequent optical modeling. Subsequent electromagnetic modeling steps, including the transfer matrix method (TMM) and Mie theory, demonstrate the excitation of surface plasmon polaritons and localized surface plasmon resonances in ZrN thin films and nanoparticles. Furthermore, the finite‐difference time‐domain (FDTD) method exhibits the excitation of distinct electric (plasmon) and magnetic (LC) resonances in a periodic array of u‐shaped ZrN split‐ring resonators (SRRs). The findings showcase an optical behavior comparable with structures made from noble metals such as gold and silver and support the introduction of ZrN as a new and appropriate candidate for plasmonic applications, specifically in technological applications where optical and mechanical properties are of simultaneous concern.

High-Performance Asymmetric Optical Transmission Based on a Dielectric-Metal Metasurface.

Asymmetric optical transmission plays a key role in many optical systems. In this work, we propose and numerically demonstrate a dielectric–metal metasurface that can achieve high-performance asymmetric transmission for linearly polarized light in the near-infrared region. Most notably, it supports a forward transmittance peak (with a transmittance of 0.70) and a backward transmittance dip (with a transmittance of 0.07) at the same wavelength of 922 nm, which significantly enhances operation bandwidth and the contrast ratio between forward and backward transmittances. Mechanism analyses reveal that the forward transmittance peak is caused by the unidirectional excitation of surface plasmon polaritons and the first Kerker condition, whereas the backward transmittance dip is due to reflection from the metal film and a strong toroidal dipole response. Our work provides an alternative and simple way to obtain high-performance asymmetric transmission devices.

Efficient and wavelength-dependent directional launching of a nondiffracting surface plasmon polariton beam device

The high-efficiency excitation and dynamic manipulation of the nondiffracting surface plasmon polariton (SPP) beam are important prerequisites for practical applications including the next-generation on-chip devices, near field optical trapping, and micromanipulation. Here we proposed two kinds of high-efficiency coupling and wavelength-dependent nondiffracting SPP beam unidirectional devices, which can generate and manipulate Bessel-like SPP beam or SPP Bottle beam, respectively. Different from the conventional groove or ridge structure that equally split SPP power to propagate from the boundary to both sides, the compact coupling element directs all of the SPP power of the matched wavelength to one side, resulting in higher collecting efficiency. Besides, as the wavelength of the incident light is changed, the generated Bessel-like SPP beam or SPP Bottle beam can be directionally excited on one side of the device. The design of the proposed devices provides a new means for constructing plasmonic devices with wavelength-dependent dynamic manipulation of nondiffracting SPP beams and has potential applications in on-chip interconnect circuits and near-field optical trapping.

Enhanced Absorption with Graphene-Coated Silicon Carbide Nanowires for Mid-Infrared Nanophotonics

The mid-infrared (MIR) is an exciting spectral range that also hosts useful molecular vibrational fingerprints. There is a growing interest in nanophotonics operating in this spectral range, and recent advances in plasmonic research are aimed at enhancing MIR infrared nanophotonics. In particular, the design of hybrid plasmonic metasurfaces has emerged as a promising route to realize novel MIR applications. Here we demonstrate a hybrid nanostructure combining graphene and silicon carbide to extend the spectral phonon response of silicon carbide and enable absorption and field enhancement of the MIR photon via the excitation and hybridization of surface plasmon polaritons and surface phonon polaritons. We combine experimental methods and finite element simulations to demonstrate enhanced absorption of MIR photons and the broadening of the spectral resonance of graphene-coated silicon carbide nanowires. We also indicate subwavelength confinement of the MIR photons within a thin oxide layer a few nanometers thick, sandwiched between the graphene and silicon carbide. This intermediate shell layer is characteristically obtained using our graphitization approach and acts as a coupling medium between the core and outer shell of the nanowires.