Interaction Of Surface Plasmon Polaritons Research Articles

Spatiotemporal observation of surface plasmon polariton mediated ultrafast demagnetization

Surface plasmons offer a promising avenue in the pursuit of swift and localized manipulation of magnetism for advanced magnetic storage and information processing technology. However, observing and understanding spatiotemporal interactions between surface plasmons and spins remains challenging, hindering optimal optical control of magnetism. Here, we demonstrate the spatiotemporal observation of patterned ultrafast demagnetization dynamics in permalloy mediated by propagating surface plasmon polaritons with sub-picosecond time- and sub-μm spatial- scales by employing Lorentz ultrafast electron microscopy combined with excitation through transient optical gratings. We discover correlated spatial distributions of demagnetization amplitude and surface plasmon polariton intensity, the latter characterized by photo-induced near-field electron microscopy. Furthermore, by comparing the results with patterned ultrafast demagnetization dynamics without surface plasmon polariton interaction, we show that the demagnetization is not only enhanced but also exhibits a spatiotemporal modulation near a spatial discontinuity (plasmonic hot spot). Our findings shed light on the intricate interplay between surface plasmons and spins, offer insights into the optimized control of optical excitation of magnetic materials and push the boundaries of ultrafast manipulation of magnetism.

Nanometer-Scale Lateral p–n Junctions in Graphene/α-RuCl3 Heterostructures

The ability to create nanometer-scale lateral p–n junctions is essential for the next generation of two-dimensional (2D) devices. Using the charge-transfer heterostructure graphene/α-RuCl3, we realize nanoscale lateral p–n junctions in the vicinity of graphene nanobubbles. Our multipronged experimental approach incorporates scanning tunneling microscopy (STM) and spectroscopy (STS) and scattering-type scanning near-field optical microscopy (s-SNOM) to simultaneously probe the electronic and optical responses of nanobubble p–n junctions. Our STM/STS results reveal that p–n junctions with a band offset of ∼0.6 eV can be achieved with widths of ∼3 nm, giving rise to electric fields of order 108 V/m. Concurrent s-SNOM measurements validate a point-scatterer formalism for modeling the interaction of surface plasmon polaritons (SPPs) with nanobubbles. Ab initio density functional theory (DFT) calculations corroborate our experimental data and reveal the dependence of charge transfer on layer separation. Our study provides experimental and conceptual foundations for generating p–n nanojunctions in 2D materials.

Mapping optical Bloch modes of a plasmonic square lattice in real and reciprocal spaces using cathodoluminescence spectroscopy.

Strong electron-light interactions supported by the surface plasmon polaritons excited in metallic thin films can lead to faster optoelectronic devices. Merging surface polaritons with photonic crystals leads to the formation of Bloch plasmons, allowing for the molding of the flow of polaritons and the controlling of the optical density of states for even stronger electron-light interactions. Here, we use a two-dimensional square lattice of holes incorporated inside a plasmonic gold layer to investigate the interaction of surface plasmon polaritons with the square lattice and the formation of plasmonic Bloch modes. Cathodoluminescence spectroscopy and hyperspectral imaging are used for imaging the spatio-spectral near-field distribution of the optical Bloch modes in the visible to near infrared spectral ranges. In addition, the higher-order Brillouin zones of the plasmonic lattice are demonstrated by using angle-resolved cathodoluminescence mapping. We further complement our experimental results with numerical simulations of the optical modes supported by the plasmonic lattice that helps to better resolve the superposition of the various modes excited by the electron beam. Next to previous works in this context, our results thus place cathodoluminescence scanning spectroscopy and angle-resolved mapping as complementary techniques to uncover the spatio-spectral distribution of optical Bloch modes in real and reciprocal spaces.

Effect of dynamic ions on band structure of plasmon excitations

In this paper, we develop a new method to study the plasmon energy band structure in multispecies plasmas. Using this method, we investigate a plasmon dispersion band structure of various quasineutral plasma systems with arbitrary degree of electron degeneracy. The linearized Schrödinger–Poisson model is used to derive an appropriate coupled pseudoforce system from which the energy dispersion structure is calculated. It is shown that the introduction of ion dynamics, as opposed to static ion assumption in the jellium model with a wide plasmon bandgap, can significantly modify the plasmon dispersion character leading to a new low-level energy band caused by the electron–ion interactions. The investigation on the effect of ion charge-state and chemical potential of electrons on the plasmonic band structure indicates some interesting features and reveals the fundamental role played by ions in the phonon assisted plasmon excitations in different kinds of plasma systems. Moreover, our study confirms that ion charge screening has a significant impact on plasmon excitations in multispecies plasmas. The plasmon band structure in pair-ion or electron–positron plasmas indicates the unique role of positive charges on collective excitations. Current research helps us to better understand the underlying mechanisms of collective interactions in charged environment and the important role played by heavy charged particles on elementary plasmon excitations, which have important applications in plasmonic devices. The method developed in this research may also be extended to study magnetized quantum plasmas as well as to investigate surface plasmon–polariton interactions in nanometallic structures.

Optical binding via surface plasmon polariton interference

Optical binding allows creation of mechanically stable nanoparticle configurations owing to formation of self-consistent optical trapping potentials. While the classical diffraction limit prevents achieving deeply subwavelength arrangements, auxiliary nanostructures enable tailoring optical forces via additional interaction channels. Here, a dimer configuration next to metal surface was analyzed in details and the contribution of surface plasmon polariton waves was found to govern the interaction dynamics. It was shown that the interaction channel, mediated by resonant surface waves, enables achieving subwavelength stable dimers. Furthermore, the vectorial structure of surface modes allows binding between two dipole nanoparticles along the direction of their dipole moments, contrary to vacuum binding, where a stable configuration is formed in the direction oriented perpendicularly to the polarization of dipole moments. In addition, the enhancement of optical binding stiffness for one order of magnitude was predicted owing to the surface plasmon polariton interaction channel. These phenomena pave a way for developing new flexible optical manipulators, allowing for the control over a nanoparticle trajectory on subwavelength scales and opens a room of opportunities for optical-induced anisotropic, i.e. with different periods along the field polarization as well as perpendicular to it, organization of particles on a plasmonic substrate.

Theoretical analysis of graphene plasmon cavities

Unprecedented physical properties make graphene a very promising plasmonic candidate material from the terahertz to mid-infrared frequencies. However, a theoretical model for graphene plasmon cavities has not been fully established. In this work, we analyse the graphene surface plasmon polaritons supported on silicon carbide or metallic cavities. We derive an analytical expression for the dispersion relation of graphene plasmon waves in a multilayer system, providing a useful tool to illustrate the dependence on the cavity's geometric properties. The results show that the analytical description can precisely predict the excitation of cavity graphene plasmon waves. Complete absorption can be achieved under certain parameters, which can be predicted precisely using two Fabry–Pérot models. We further show that the interaction of surface plasmon polaritons with surface phonon polaritons can be used to tune the cavity resonances. The tunability of the Fermi energy and the geometric parameters of the cavities make for flexible system design. High enhancement (∼4000) and extraordinary compression (∼λ0/400) of graphene plasmon waves are also realized under certain conditions. These findings make this an ideal setup for molecular sensing, pushing the potential for enhanced, broadly tunable spectroscopy into the mid-infrared, while also offering distinct advantages for integrated optics.

Interaction of surface plasmon polaritons and acoustic waves inside an acoustic cavity.

In this Letter, we introduce an approach for manipulation of active plasmon polaritons via acoustic waves at sub-terahertz frequency range. The acoustic structures considered are designed as phononic Fabry-Perot microresonators where mirrors are presented with an acoustic superlattice and the structure's surface, and a plasmonic grating is placed on top of the acoustic cavity so formed. It provides phonon localization in the vicinity of the plasmonic grating at frequencies within the phononic stop band enhancing phonon-light interaction. We consider phonon excitation by shining a femtosecond laser pulse on the plasmonic grating. Appropriate theoretical model was used to describe the acoustic process caused by the pump laser pulse in the GaAs/AlAs-based acoustic cavity with a gold grating on top. Strongest modulation is achieved upon excitation of propagating surface plasmon polaritons and hybridization of propagating and localized plasmons. The relative changes in the optical reflectivity of the structure are more than an order of magnitude higher than for the structure without the plasmonic film.

Enhanced and tunable electric dipole–dipole interactions near a planar metal film

We investigate the enhanced electric dipole–dipole interaction of surface plasmon polaritons (SPPs) supported by a planar metal film waveguide. By taking two nitrogen-vacancy (NV) center electric dipoles in diamond as an example, both the coupling strength and collective relaxation of two dipoles are studied with the numerical Green Function method. Compared to two-dipole coupling on a planar surface, metal film provides stronger and tunable coupling coefficients. Enhancement of the interaction between coupled NV center dipoles could have applications in both quantum information and energy transfer investigation. Our investigation provides systematic results for experimental applications based on a dipole–dipole interaction mediated with SPPs on a planar metal film.

Probing semiconductor confined excitons decay into surface plasmon polaritons

The study of the interaction of surface plasmon polaritons (SPPs) with quantum emitters has become very important in the last few years. The ability to design optical devices as well as investigate the physics of strongly interacting systems is some of its useful applications. In this paper, we will show some results on the decay of excitons confined in a InAs/GaAs quantum dot into SPP modes confined in a metallic thin film made of Au, an important step toward the investigation of the basic features of the SPP–exciton interaction. The lifetime of the ground state level was investigated and shown to decrease with the presence of the metallic film.

Interaction of surface plasmon polaritons in heavily doped GaN microstructures with terahertz radiation

We present the results of experimental and theoretical studies of the surface plasmon polariton excitations in heavily doped GaN epitaxial layers. Reflection and emission of radiation in the frequency range of 2–20 THz including the Reststrahlen band were investigated for samples with grating etched on the sample surface, as well as for samples with flat surface. The reflectivity spectrum for p-polarized radiation measured for the sample with the surface-relief grating demonstrates a set of resonances associated with excitations of different surface plasmon polariton modes. Spectral peculiarities due to the diffraction effect have been also revealed. The characteristic features of the reflectivity spectrum, namely, frequencies, amplitudes, and widths of the resonance dips, are well described theoretically by a modified technique of rigorous coupled-wave analysis of Maxwell equations. The emissivity spectra of the samples were measured under epilayer temperature modulation by pulsed electric field. The emissivity spectrum of the sample with surface-relief grating shows emission peaks in the frequency ranges corresponding to the decay of the surface plasmon polariton modes. Theoretical analysis based on the blackbody-like radiation theory well describes the main peculiarities of the observed THz emission.

Extraordinary Transmission through Fractal-Featured Metallic and Superconducting Films at Terahertz Frequency

We report on fractal-featured square and ring-shaped apertures with a Sierpinski carpet pattern (SCP) on metallic and superconducting NbN films. Multiple extraordinary terahertz (THz) transmission peaks are studied in the transmission spectra using both THz time-domain spectroscopy and numerical simulation. The characteristic transmission peaks are found to be associated with the interaction of surface plasmon polaritons (SPPs) and localized surface plasmons (LSPs) for ring-shaped apertures. The effect of LSPs is less remarkable in the square apertures. For the superconducting NbN film, when the temperature is slightly lower than the critical transition temperature Tc, the peak magnitude of SPP resonances is most prominent due to the non-monotonic temperature dependence of kinetic inductance. These results provide a new way to design compact and efficient THz devices.

Plasmon beams interaction at interface between metal and dielectric with saturable Kerr nonlinearity

We present a novel theory of surface plasmon polariton interaction on the surface of dielectric with saturable Kerr nonlinearity. The effect of the total internal reflection of a weak signal plasmon beam from a high-power reference beam is discussed. Both ray and wave theories are used to describe signal propagation. The effect of the signal tunneling through the narrow inhomogeneity induced by the reference beam is considered.

Beaming light into the nanoworld

An antenna for optical frequencies that operates by tuning into the interaction of surface-plasmon polaritons, supported by an array of nanometre-sized holes in a thin metal film, represents another step towards the manipulation of light at the nanoscale.

Adiabatic bends in surface plasmon polariton band gap structures

Propagation and interaction of surface plasmon polaritons (SPPs) excited in the wavelength range 700-860 nm with periodic triangular arrays of gold bumps placed on gold film surfaces are investigated using a collection near-field microscope. We observe the inhibition of SPP propagation into the arrays within a certain wavelength range, i.e., the band gap (BG) effect. We demonstrate also the SPP propagation along a 30 degrees bent channel obtained by an adiabatic rotation of the periodic array of scatterers. Numerical simulations using the Lippmann-Schwinger integral equation method are presented and found in reasonable agreement with the experimental results.

Near-field imaging of surface plasmon-polariton guiding in band gap structures at telecom wavelengths

Using a collection near-field microscope, we image interaction of surface plasmon-polaritons (SPPs) excited locally at telecom wavelengths with periodic triangular arrays of gold bumps placed on gold film surfaces. We observe the inhibition of SPP propagation into the arrays within a certain wavelength range depending on their period and orientation, i.e., the band gap (BG) effect, as well as the SPP propagation along bent channels cut through these arrays. Prospects and challenges in realization of compact and efficient SPPBG waveguiding structures are discussed.