Plasmon Waves Research Articles

Refractive index sensing characteristics of PCF-SPR based on dual-plasmon materials

Abstract In this paper, a photonic crystal fiber (PCF) refractive index sensor based on surface plasmon resonance with dual plasmonic materials (indium tin oxide and gold) is proposed. We innovatively designed a dual-core PCF structure and pore arrangement effectively enhancing the coupling effect. Using two different plasma materials, phase matching is achieved at two different wavelengths for the evanescent and surface plasmon waves, resulting in dual resonance peaks. The refractive index sensing is accomplished by measuring the dual-peak resonance shift, which expands the detection wavelength and RI detection ranges. The sensor can detect analytes with refractive indices ranging from 1.32 to 1.43 at wavelengths between 0.4 µm and 1.4 µm. We optimized the PCF structure and studied the sensing performance of the sensor, improving its sensitivity. Simulation results indicate that the designed PCF sensor exhibits outstanding maximum dual-peak shift sensitivity, reaching up to 28 000 RIU−1, along with maximum amplitude sensitivity and wavelength sensitivity of 18 500 RIU−1 and 34 500 RIU−1, respectively, in the direction of y-polarization. Furthermore, the sensor achieves high resolution, and the figure of merit (FOM) values can reach up to 5.134 × 10−7 and 2758. Consequently, the proposed sensor can provide high-precision and extensive-range measurements of solution refractive indices within the visible and infrared light spectrum, and it holds potential application prospects in numerous fields, such as food safety testing and chemical substance detection.

Negative damping of terahertz plasmons in counter-streaming double-layer two-dimensional electron gases

Abstract The plasmon excitation in two-dimensional electron gases (2DEGs) is a significant way of achieving micro-nanoscale terahertz (THz) devices. Here, we establish a kinetic simulation model to study the THz plasmons amplification in a semiconductor double-quantum-well system with counter-streaming electron drift velocities. By comparing the simulation results with theoretical dispersion relations, we confirm two competing mechanisms of negative damping suitable for THz amplification: Cherenkov-type two-stream instability and a new non-Cherenkov mechanism called kinetic relaxation instability. The former is caused by the interlayer coupling of two slow plasmon modes and only exists when the drift velocities are much greater than the fermi velocities. The latter is a statistical effect caused by the momentum relaxation of electron-impurity scattering and predominates at lower drift velocities. We show that an approximate kinetic dispersion relation can accurately predict the wave growth rates of the two mechanisms. The results also indicate that the saturated plasmonic waves undergo strong nonlinearities such as wave distortion, frequency downshift, wave-packet formation, and spectrum broadening. The nonlinear evolution can be interpreted as the merging of bubble structures in the electron phase-space distribution. The present results not only reveal the potential mechanisms of the plasmonic instabilities in double-layer 2DEGs, but also provide a new guideline for the design of on-chip THz amplifiers.

Chitosan-coated iron(III) oxide nanoparticles and tungsten disulfide quantum dots-immobilized Fiber-based WaveFlex Biosensor for Staphylococcus Aureus bacterial detection in real food samples

The research proposes and investigates an extraordinarily sensitive, label-free WaveFlex biosensor utilizing optical fiber technology for the detection of Staphylococcus aureus (S. aureus), a common foodborne bacterium. The WaveFlex biosensor (plasmon Wave based Flexible optical fiber Biosensor) is based on a novel flexible tapered single-mode fiber structure, utilizing gold nanoparticles (AuNPs) to trigger the phenomenon of localized surface plasmon resonance (LSPR). Additionally, the sensitivity is further enhanced using chitosan-coated iron(III) oxide nanoparticles (Fe3O4–CS NPs) and tungsten disulfide quantum dots (WS2-QDs). The optical fiber surface is functionalized with antibodies to achieve specific detection of S. aureus. For S. aureus concentrations at 1 × 108 CFU/mL (colony-forming units per milliliter), the sensor's maximum sensitivity of 2.74 nm/lg (CFU/mL), and a detection limit (LOD) of 6.67 CFU/mL. This ultra-sensitive biosensor holds great potential for widespread applications in various fields, including disease detection, medical diagnostics, and food safety inspection.

A Retrospective Study: Are the Multi-Dips in the THz Spectrum during Laser Filamentation Caused by THz–Plasma Interactions?

During the process of terahertz (THz) wave generation via femtosecond laser filamentation in air, as well as through the mixing of THz waves with externally injected plasma filaments, THz waves engage in interactions with the plasma. A characteristic feature of this interaction is the modulation of the THz radiation spectrum by the plasma, which includes the generation of THz spectral dips. This information is essential for understanding the underlying mechanisms of THz–plasma interactions or for inferring plasma parameters. However, a current debate exists on the number of THz spectral dips observed after the interaction, with different opinions of single versus multiple dips, thus leaving the interaction mechanisms still ambiguous. In this work, we retrospectively analyzed the experimental appearance of multiple dips in the THz spectrum and found that the current observations of such dips are predominantly a result of the water vapor absorption with a low spectral resolution. Additionally, we observed that altering the acquisition width of the temporal THz signal also influenced the dips’ number. Hence, in future research, simultaneous attention should be paid to the following two aspects of THz–plasma interactions: (1) It is necessary to ensure a sufficiently wide time-domain window to accurately represent the spectral dip characteristics. (2) The spectral dips should be carefully distinguished from the water absorption lines before being further studied. On the other hand, for the case of a single dip in the THz spectrum, we also put forward a new viewpoint of the resonance between surface plasmon waves and THz waves, which should also be taken into consideration in future studies.

On-chip transfer of ultrashort graphene plasmon wave packets using terahertz electronics

On-chip transfer of ultrashort graphene plasmon wave packets using terahertz electronics

VO2-Based metasurface for dynamically tunable terahertz surface plasmonic waves

Surface plasmonic waves (SPWs), which propagate along metal-dielectric interfaces, play a pivotal role in various photonic applications such as highly integrated photonic devices, super-resolution imaging, high-sensitivity sensing, on-chip integrated systems, etc. The ability to control the excitation direction of the SPWs is of great importance in these applications. In this work, we propose a terahertz on-chip metasurface device whose SPWs propagation direction can be dynamically tuned at the excitation source by exploiting the vanadium dioxide (VO2). Under circularly polarized light incidence, destructive or constructive interference formed in the subwavelength square ring slit resonators (SRSRs) arrays, resulting in the unidirectional propagation of terahertz SPWs. By adjusting the conductivity of VO2, the flexible control over the propagation direction of SPWs is realized. This approach significantly enhances the level of control compared to previous traditional polarization control method which can only be modulated by the polarization state, marking a notable advancement in the development of functional devices that harness the power of SPWs.

Insights into Photopolymerization at the Nanoscale Using Surface Plasmon Resonance Imaging.

Near-field photopolymerization (NFPP) driven by surface plasmon resonance has attracted increasing attention in nanofabrication. This interest comes from the nanometer-scale control of polymer thickness, due to the confinement of the evanescent wave within a highly restricted volume at the surface. In this study, a novel approach using a multi-spectral surface plasmon resonance instrument is presented that gives access to real-time images of polymer growth during NFPP with nanometer sensitivity. Using the plasmonic evanescent wave for both polymerization and real-time sensing, the influence of irradiance, concentration of dye, and initiator are investigated on the threshold energy and kinetics of NFPP. How oxygen inhibition in the near field strongly affects photopolymerization is highlighted, more than in the far field.

Plasmons in the Kagome metal CsV3Sb5

Plasmon polaritons, or plasmons, are coupled oscillations of electrons and electromagnetic fields that can confine the latter into deeply subwavelength scales, enabling novel polaritonic devices. While plasmons have been extensively studied in normal metals or semimetals, they remain largely unexplored in correlated materials. In this paper, we report infrared (IR) nano-imaging of thin flakes of CsV3Sb5, a prototypical layered Kagome metal. We observe propagating plasmon waves in real-space with wavelengths tunable by the flake thickness. From their frequency-momentum dispersion, we infer the out-of-plane dielectric function ϵc\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{{{{{\\boldsymbol{\\epsilon }}}}}}}_{{{{{{\\boldsymbol{c}}}}}}}$$\\end{document} that is generally difficult to obtain in conventional far-field optics, and elucidate signatures of electronic correlations when compared to density functional theory (DFT). We propose correlation effects might have switched the real part of ϵc\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{{{{{\\boldsymbol{\\epsilon }}}}}}}_{{{{{{\\boldsymbol{c}}}}}}}$$\\end{document} from negative to positive values over a wide range of middle-IR frequencies, transforming the surface plasmons into hyperbolic bulk plasmons, and have dramatically suppressed their dissipation.

Plasmon Dynamics in Electron‐Doped Graphene and AA‐ versus AB‐Stacked Bilayer Graphene

This study investigates low‐frequency plasmons and single‐particle excitations (SPEs) in monolayer and bilayer graphene with various stacking configurations. The dynamics of wave propagation under different time‐dependent perturbation scenarios are elucidated using the random‐phase approximation dielectric function and tight‐binding Hamiltonian. The modulation of coherent excitations, particularly affecting plasmon waves, provides insights into the spatial and temporal dynamics on graphene sheets. A 2D acoustic plasmon mode is observed in monolayer graphene under extrinsic doping effects, while in bilayer graphene, it is accompanied by higher frequency optical plasmons. The predicted dynamic behavior, indicative of plasmon resonance, SPEs, and Landau damping with respect to stacking and doping effects, can be detected through ultrafast coherent dynamics observed via nanoimaging and nanospectroscopy techniques.

Computational study of optical force on a dielectric and a plasmonic nanowire

In this paper, the optical force exerted on a dielectric and a plasmonic nanowire with a circular cross-section of sub-micrometer radius anw is numerically calculated using the Muller boundary integral equations and the Minkowski electromagnetic stress tensor. A Complex Point Source (CPS) of micrometer lateral size b is used as the incident light in the visible spectral range. Computations show that the optical force acting on the dielectric nanowire is always smaller than that on the plasmonic one under the same conditions which originates from the excitation of surface plasmon waves. Calculations also reveal that the optical force in both nanowires has an oscillatory dependence on λ but there are sharp peaks for the dielectric nanowire due to the excitation of whispering gallery modes. In the plasmonic wire, however, the force angle is positive for all of the studied wavelengths but for the dielectric wire it is negative. This means that, the optical force in the plasmonic nanowire is mainly scattering-dominated but for dielectric one it is gradient-dominated.

Azimuthal Scanning Excitation Surface Plasmon Resonance Holographic Microscopy

AbstractSurface plasmon resonance (SPR) holographic microscopy exploits surface plasmon wave as illumination and acquires both SPR intensity and phase images. It detects extremely tiny variations of weakly interacting objects owing to high sensitivity and has been applied in cell biology, material science, surface chemistry, etc. However, it is very challenging to solve the problem of poor spatial resolution due to the transverse propagation of surface plasmon wave. In this paper, an azimuthal scanning excitation method is proposed in SPR holographic microscopy to improve the spatial resolution by engineering the Fourier spectra of SPR images from dual‐arc to circular shape. The study modulates the light field with spatial position, wavevector, and polarization to realize azimuthal scanning excitation of SPR. Systematic experiments of dielectric spheres, nanowires, two‐dimension materials, and complex nanostructure are conducted to show the resolution improvement with one order of magnitude, the higher detection sensitivity of SPR phase than that of SPR intensity, and the necessities of both of high‐resolution SPR intensity and phase images to retrieve sample information in certain scenarios. Benefiting from the high detection sensitivity and spatial resolution, the proposed microscopy will find wide applications in nanoparticle analysis, low‐dimensional material characterization, and imaging extremely thin or transparent samples.

Plasmonic wave assessment via optomechatronics system for biosensor application

Transduction biosensor (mass-based, optical and electrochemical) involves analysis, recognition and amplification in the acquired sample. In this work, the plasmonic-based biosensor was employed without using tags. It is crucial to determine angles of Brewster (Ɵb) and critical (Ɵc) for generating plasmonic resonance (Ɵr). The objective is to verify a cost-effective plasmonic biosensor through Fresnel simulation and experimentation of a developed optomechatronics system. The borosilicate glass, Au and Air layers were simulated with the Winspall 3.02 simulator. The optomechatronics system consists of: 1-optics (650 nm laser, slit, polarizer, photodiode), 2-mechanical (bipolar stepper motors, gears, stages) and 3-electronics (PIC18F4550, liquid crystal display (LCD) and drivers). Later, the software performs angular interrogation by reading the reflected beam from a rotating prism at 0.1125. Experimentation to simulation accuracy indicates that percentage differences for Ɵr and Ɵc are 1% and 0.2%, respectively. In conclusion, excellence verification was successfully achieved between experimentation and simulation. It proved that the low-cost optomechatronics system is capable and reliable to be deployed for the biosensor application.

Tuning optical properties of Au thin film using electric field for surface plasmon resonance biosensor application

The effect of electric field application on the optical properties of gold (Au) thin film for spectroscopic ellipsometry-based surface plasmon resonance (SPR) biosensor applications has been successfully studied. The optical properties, such as the complex refractive index, complex dielectric constant, real optical conductivity, and absorption coefficient, were determined by fitting data from the ψ and Δ functions obtained through measurements using a homemade rotating analyzer ellipsometer. The applied electric fields of 0.8 V/cm, 1.6 V/cm, 2.4 V/cm, and 3.2 V/cm were induced by applying voltages of 1 V, 2 V, 3 V, and 4 V for ellipsometer tests, and 1.6 V/cm to 3.2 V/cm for the SPR test. The Au thin film was deposited onto a glass slide using an evaporator for ellipsometer testing and a BK7 half-cylinder prism was employed for SPR testing. The experimental results show that the real part of the refractive index (n) increases in the spectral range from 1.5 eV to 2.2 eV and from 3 eV to 5 eV and tends to be constant in the range from 2.3 eV to 2.8 eV. Conversely, the imaginary part of the refractive index (k) decreases from 2.8 eV to 3.6 eV and tends to remain consistent from 3.9 eV to 5.0 eV. The dielectric constant (ε1) consistently shows a significant increase within the spectral range of 3 eV–5.0 eV, with a tendency to decrease between 2.1 eV and 2.4 eV. Meanwhile, the imaginary part (ε2) demonstrates an increase in the spectral range of 1.5 eV–2.4 eV and 3.3 eV–5.0 eV while maintaining relatively stable values in the energy spectral range of 2.6 eV–3.0 eV. Moving to the real part of optical conductivity (σ1), it increases within the spectral range from 1.5 eV to 2.4 eV and from 3.5 eV to 5 eV, with relatively constant values between 2.6 eV and 3.1 eV. The absorption coefficient (α) exhibits a decrease in the spectrum between 2.8 eV and 3.6 eV, but the values remain stable within the range of 3.9 eV–5.0 eV. The α slightly decreases in the energy range of 1.8 eV–2.6 eV. The outcomes obtained from these experiments are directly linked to the SPR results, revealing a noticeable shift in the SPR angle (θSPR) of 45.51°, 45.61°, and 45.73° and an increase in the minimum reflectance (Rmin) of 0.05, 0.09, and 0.13 for electric field strengths of 0 V/cm, 1.6 V/cm, and 3.2 V/cm, respectively. These results imply that the application of an external electric field to the surface of the Au thin film disrupts the matching condition between the evanescent wave vector and the surface plasmon wave vector, thereby altering the reflected light under resonance conditions indicated by an increase in the minimum reflectance and SPR angle. This development holds significant promise to further enhance the sensitivity of electro-optic modulation-based biosensors.

Current-Driven Terahertz Oscillations in Diamond TeraFET

We report on sub-terahertz plasmonic wave generation in the 2DEG channel of diamond TeraFET when biased by a DC current at the drain. Our numerical results demonstrated that p-diamond can support resonant oscillation of 300 GHz at room temperature, allowing it to function as a sub-THz emitter. We investigated the impact of different channel lengths, gate biases, drift velocities, and temperatures on the fundamental mode oscillation. The model incorporated the decay factors owing to electron scattering and electron fluid viscosity.

Propagating surface plasmon polaritons in graphene under applied uniform strain

In this work, we theoretically investigate the propagation length of plasmon waves in graphene layer under uniform strain surrounded by two dielectric media of dielectric constants ε1 and ε2, respectively. The plasmon losses (plasmon damping), plasmon propagation length and the penetration depth of the electric field associates with the charge fluctuations can be controlled by varying the direction and the strength of the applied strain and the direction of the plasmon wave propagation with respect to the direction of the applied strain. Because strain induces anisotropy in graphene optical conductivity, the strain-dependent orientation plays an important role to manipulate the direction and variations of the graphene plasmon energy, which may be useful to tune graphene properties in plasmonic devices to enhance light-matter interaction.

Surface Plasmon Resonance Biosensors: A Review of Molecular Imaging with High Spatial Resolution.

Surface plasmon resonance (SPR) is a powerful tool for determining molecular interactions quantitatively. SPR imaging (SPRi) further improves the throughput of SPR technology and provides the spatially resolved capability for observing the molecular interaction dynamics in detail. SPRi is becoming more and more popular in biological and chemical sensing and imaging. However, SPRi suffers from low spatial resolution due to the imperfect optical components and delocalized features of propagating surface plasmonic waves along the surface. Diverse kinds of approaches have been developed to improve the spatial resolution of SPRi, which have enormously impelled the development of the methodology and further extended its possible applications. In this minireview, we introduce the mechanisms for building a high-spatial-resolution SPRi system and present its experimental schemes from prism-coupled SPRi and SPR microscopy (SPRM) to surface plasmonic scattering microscopy (SPSM); summarize its exciting applications, including molecular interaction analysis, molecular imaging and profiling, tracking of single entities, and analysis of single cells; and discuss its challenges in recent decade as well as the promising future.

Active control of polarization-dependent terahertz surface plasmonic wave excitation using coupled graphene-metal hybrid metasurfaces

Active control of terahertz surface plasmonic wave (SPW) intensity in the propagation direction holds substantial significance for advanced terahertz functional devices. In this study, we propose a graphene-metal hybrid split-ring slit resonator (SRSR) array metasurfaces and employ the concept of electromagnetically induced transparency (EIT) to achieve excitation of asymmetric SPWs under various polarization states. By individually integrating two graphene ribbons into the two split-ring slit gaps and applying different bias voltages, we observed a gradual transition in the excitation behavior of asymmetric terahertz SPWs, ultimately resembling that of a single SRSR. Near-field simulations reveal that this phenomenon is attributed to the short-connection effect of graphene. Our proposed graphene-metal active hybrid metasurface introduces a novel approach to realize active SPWs devices, holding potential applications in terahertz on-chip communication.

Edge magnetoplasmon dispersion and time-resolved plasmon transport in a quantum anomalous Hall insulator

A quantum anomalous Hall (QAH) insulator breaks reciprocity by combining magnetic polarization and spin-orbit coupling to generate a unidirectional transmission of signals in the absence of an external magnetic field. Such behavior makes QAH materials a good platform for the innovation of circulator technologies. However, it remains elusive as to how the wavelength of the chiral edge plasmon relates to its frequency and how the plasmon wave packet is excited in the time domain in a QAH insulator. Here, we investigate the edge magnetoplasmon (EMP) resonances in Cr-(Bi,Sb)2Te3 by frequency and time domain measurements. From disk shaped samples with various dimensions, we obtain the dispersion relation of EMPs and extract the drift velocity of the chiral edge state. From the time-resolved transport measurements, we identify the velocity of the plasmon wave packet and observe a transition from the edge to bulk transport at an elevated temperature. We show that the frequency and time domain measurements are well modeled by loss from the microwave induced dissipative channels in the bulk area. Our results demonstrate that the EMP decay rate can be significantly reduced by applying a low microwave power and fabricating devices of larger diameter ≥100µm. In a R=125µm sample, a nonreciprocity of 20 dB has been realized at 1.3 GHz, shining light on using QAH insulators to develop on-chip nonreciprocal devices. Published by the American Physical Society 2024

Observation of Plasmonics Talbot effect in graphene nanostructures

We report on the theoretical models of the plasmoincs Talbot effect in graphene nanostructure. The Talbot effect for the plasmonics applications in the IR range is theoretically studied and the respective Talbot effect for the novel advanced plasmonics structures are numerically investigated for the first time. It is shown that the metamaterial structures with periodic grating configuration represents a complex three-dimensional lattice of beamlet-like graphene plasmonics devices. The calculated results agree well with the experimental ones. The results obtained can be used to create and optimize the structures considering diffraction limit for a wide range of application areas. Effective focusing of plasmonic waves with exact focal spots and a subwavelength full width at half maximum can be obtained by using periodic graphene grating.

Electrochemically modulated surface plasmon waves for characterization and interrogation of DNA-based sensors.

This work reports on a comparative analysis of electrical and optical measurements for structural characterization and for assessing signal transduction performance of a redox-labeled DNA-based sensing platform. We conducted complementary investigations employing conventional electrochemical techniques with electric current measurements in cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) and confronted those results with optical measurements using surface plasmon waves while the redox assembly was undergoing similar electrochemical modulation as in the electrical CV and EIS measurements. The specific sensor configuration deployed here was composed of a methylene blue (MB)-modified single-stranded DNA (ssDNA) signaling probe and an unlabeled capture ssDNA probe that complements the signaling probe. Two types of signaling probes were employed: one with MB attached to the 3' end, which positions the redox marker closer to the electrode surface upon hybridization with the capture probe, and the other with MB attached to the 5' end, which places the redox marker farther from the electrode surface. For each molecular assembly and for each electrochemical modulation protocol, both the electrical and optical experimental data were quantitatively analyzed to determine the surface density of electro-active species and the rate of electron transfer between the redox marker and the electrode surface. Our experimental results highlight the consistency of the confronted methodologies and indicate that optical impedance spectroscopy utilizing electrochemically modulated surface plasmon waves, which is a transduction protocol immune from non-faradaic interferents that invariably are present in the electrical methodology, can provide a powerful route for developing a redox-labeled DNA-hybridization biosensing strategy.