Giant Goos–Hnchen shifts of waveguide coupled long-range surface plasmon resonance mode

A hybrid structure based on a planar waveguide(PWG) mode coupling a long-range surface plasmon resonance(LRSPR) mode is proposed to enhance the GH shift. Both the PWG mode and LRSPR mode can be in strong resonance, and these two modes can be coupled together due to the normal-mode splitting. The largest GH shift of PWG-coupled LRSPR structure is 4156 times that of the incident beam, which is 23 times and 3.6 times that of the surface plasmon resonance(SPR) structure and the LRSPR structure, respectively. As a GH shift sensor, the highest sensitivity of 4.68 × 10~7λ is realized in the coupled structure. Compared with the sensitivity of the traditional SPR structure, the sensitivity of our structure is increased by more than 2 orders, which theoretically indicates that the proposed configuration can be applied to the field of high-sensitivity sensors in the future.     

Periodic surface structures on Ni–Fe film induced by a single femtosecond laser pulse with diffraction rings

This Letter reports the formation of periodic surface structures on Ni–Fe film irradiated by a single femtosecond laser pulse. A concave lens with a focus length of-150 mm is placed in front of an objective(100×, NA=0.9),which transforms the Gaussian laser field into a ring distribution by the Fresnel diffraction. Periodic ripples form on the ablation area after the irradiation of a single femtosecond laser pulse, which depends on the laser polarization and laser fluence. We propose that the ring structure of the laser field leads to a similar transient distribution of the permittivity on the sample surface, which further launches the surface plasmon polaritons. The interaction of the incident laser with surface plasmon polaritons dominates the formation of periodic surface structures.     

Acoustic plasmonics of Au grating/Bi_2Se_3 thin film/sapphire hybrid structures

The surface plasmon polaritons of the topological insulator Bi_2Se_3 can be excited by using etched grating or grave structures to compensate the wave vector mismatch of the incident photon and plasmon. Here, we demonstrate novel gold grating/Bi_2Se_3 thin film/sapphire hybrid structures, which allow the excitation of surface plasmon polaritons propagating through nondestructive Bi_2Se_3 thin film with the help of gold diffractive gratings. Utilizing periodic Au surface structures,the momentum can be matched and the normal-incidence infrared reflectance spectra exhibit pronounced dips. When the width of the gold grating W(with a periodicity 2 W) increases from 400 nm to 1500 nm, the resonant frequencies are tuned from about 7000 cm~(-1) to 2500 cm~(-1). In contrast to the expected ■ dispersion for both massive and massless fermions,where q ～π/W is the wave vector, we observe a sound-like linear dispersion even at room temperature. This surface plasmon polaritons with linear dispersion are attributed to the unique noninvasive fabrication method and high mobility of topological surface electrons. This novel structure provides a promising application of Dirac plasmonics.     

Narrowband perfect terahertz absorber based on polar-dielectrics metasurface

We theoretically propose a narrowband perfect absorber metasurface(PAMS) based on surface phonon polaritons in the terahertz range. The PAMS has unit cell consisting of a silver biarc on the top, a thin polar-dielectric in the middle and a silver layer at the bottom. The phonon polaritons are excited at the interface between the silver biarc and the polar dielectric, and enhance the absorption of the PAMS. The absorption peak is at 36.813 μm and the full width half maximum(FWHM) is nearly 36 nm, independent of the polarization and incidence angle. The electric fields are located at the split of the biarc silver layer and the quality factor Q is 1150. The FWHM decreases with the decreasing split width. When the thickness of the bottom layer is larger than 50 nm, the narrow band and high absorption are insensitive to the thickness of those layers. The designed absorber may have useful applications in terahertz spectra such as energy harvesting, thermal emitter, and sensing.     

Complex Modulation in Plasmon-Assisted Transmission Spectra of a Two-Slit Structure

We study the plasmon-assisted transmission of two kinds of slit structures in a 290-nm-thick silver film on a glass substrate. For the two-slit structure, the total transmission intensity spectra displays a complex modulation, which is attributed to different propagation constants of the surface plasmon polaritons （SPPs） on the silver-air and silver-glass interfaces. Replacing one of the two slits by a shallow corrugation results in a simple sinusoidal intensity modulation because of the only effective SPP excitation and propagation on the silver-air interface. These confirm the role of different SPP propagations and interference in the transmission properties of metal nanoslits.     

Long-range surface plasmon polaritons at THz frequencies in thin semiconductor layers

We present a theoretical investigation of THz long-range surface plasmon polaritons propagating on thin layers of InSb.The metallic behavior of doped semiconductors at THz frequencies allows the excitation of surface plasmon polaritons with propagation and confinement lengths that can be actively controlled.This control is achieved by acting on the free carrier density,which can be realized by changing the temperature of InSb.     

Coupling effect of surface plasmon polaritons in single-negative lamellar heterostructure

Propagation characteristics of surface plasmon polaritons(SPPs)in the lamellar heterostructure,which is actually a SPP waveguide array,constructed by two kinds of single negative(SNG)material layers stacked alternatively are investigated.Based on the finite element method(FEM),the negative-refraction(NR) property is demonstrated when the electromagnetic wave penetrates through free space into such SNG lamellar structure.A clear view of the underlying physics of NR is presented qualitatively that is mainly related to the coupled SPPs.The strong coupling effect leads to the novel SPP dispersion curves and then the anomalous propagation characteristics.     

Effects of a one-dimensional surface defect on designer surface plasmon polaritons

By using a finite difference time domain(FDTD) method,the effects of a one-dimensional(1D) surface defect on designer surface plasmon polaritons(designer SPPs) supported by a 1D metallic grating in THz domain are investigated.When the size of the defect is in a special range which is not too large,the designer SPPs reflected and scattered by the defect are weak enough to be neglected.The defect only induces a disturbance in the energy distribution of the designer SPP supported by the whole defect grating.If the defect size exceeds the said range,the reflecting and scattering are dominant in the influences of the defect on designer SPPs.Our analysis opens opportunities to control and direct designer SPPs by introducing a 1D defect,especially in low frequency domain.     

The theoretic analysis of maskless surface plasmon resonant interference lithography by prism coupling

The use of an attenuated total reflection-coupling mode of prism coated with metal film to excite the interference of the surface plasmon polaritons （SPPs） was proposed for periodic patterning with a resolution of subwavelength scale. High intensity of electric field can be obtained because of the coupling between SPPs and evanescence under a resonance condition, which can reduce exposure time and improve contrast. In this paper, several critical parameters for maskless surface plasmon resonant lithography are described, and the preliminary simulation based on a finite difference timedomain technique agrees well with the theoretical analysis, which demonstrates this scheme and provides the theoretical basis for further experiments.     

Active modulation of plasmonic signal with a subwavelength metal/nonlinear dielectric material/metal structure

<正>Light propagation through a metal/nonlinear dielectric material/metal(M-NL-M) structure is numerically studied.The design parameters of the M-NL-M structure are found with the waveguide theory so that the structure only supports the symmetric surface plasmon polaritons(SPP(0)) mode and the antisymmetric surface plasmon polaritons(SPP(1)) mode.The coupling between the two modes within the M-NL-M structure is exploited.Through controlling the propagation constants of the two modes with the intensity-dependent dielectric constant of the nonlinear Kerr material,an effective all-optical control of plasmonic signal modulator can be realized with this M-NL-M structure.     

The surface plasmon polariton dispersion relations in a nonlinear-metal-nonlinear dielectric structure of arbitrary nonlinearity

The analytic surface plasmon polaritons(SPPs) dispersion relation is studied in a system consisting of a thin metallic film bounded by two sides media of nonlinear dielectric of arbitrary nonlinearity is studied by applying a generalised first integral approach.We consider both asymmetric and symmetric structures.Especially,in the symmetric system,two possible modes can exist:the odd mode and the even mode.The dispersion relations of the two modes are obtained.Due to the nonlinear dielectric,the magnitude of the electric field at the interface appears and alters the dispersion relations.The changes in SPPs dispersion relations depending on film thicknesses and nonlinearity are studied.     

SURFACE PLASMON OF Ag CLUSTERS ON ALUMINA FILMS

The deposition of silver on an ordered alumina film prepared on Re(0001) surface has been studied by Auger electron spectroscopy (AES), low energy electron diffraction (LEED) and high resolution electron energy loss spectroscopy (HREELS). The results show that Ag grows initially as clusters at 90K and 300K. A red shift of the Ag surface plasmon as a function of decreasing coverage is observed, which is related to the cluster size effect. A surface plasmon characteristic of metallic Ag appears at coverages higher than 2.8 monolayer equivalent.     

Giant transmission Goos–Hnchen shift in surface plasmon polaritons excitation and its physical origin

Excitation of surface plasmon polaritons(SPPs) propagating at the interface between a dielectric medium and a silver thin film by a focused Gaussian beam in a classical Kretschmann prism setup is studied theoretically. We find that the center of the transmitted Gaussian evanescent wave has a giant lateral shift relative to the incident Gaussian beam center for a wide range of incident angle and Gaussian beam wavelength to excite SPPs, which can be more than two orders of magnitude larger than the silver film thickness. The phenomenon is closely related with the conventional Goos–Hnchen effect for total internal reflection of light beam, and it is called the transmission Goos–Hnchen shift. We find that this lateral shift depends heavily on the excitation wavelength, incident angle, and the silver layer thickness. Finite-difference time-domain simulations show that this transmission Goos–Hnchen shift is induced by a unique dynamical process of excitation, transport, and leakage of SPPs.     

Tapered dielectric structure in metal as a wavelength-selective surface plasmon polariton focuser

Symmetric tapered dielectric structures in metal have demonstrated applications such as the nanofocusing of surface plasmon polaritons, as well as the waveguiding of V-channel polaritons. Yet the fabrication of smooth-surfaced tapered structure remains an obstacle to most researchers. We have successfully developed a handy method to fabricate metal-sandwiched tapered nanostructures simply with electron beam lithography. Though these structures are slightly different from conventional symmetric V-shaped structures, systematic simulations show that similar functionality of surface plasmon polariton nanofocusing can still be achieved. When parameters are properly selected, wavelength-selective nanofocusing of surface plasmon polaritons can be obtained.     

High sensitivity refractive index gas sensing enhanced by surface plasmon resonance with nano-cavity antenna array

The surface plasmon resonance gas sensor is presented for refractive index detection using nano-cavity antenna array.The gas sensor monitors the changes of the refractive index by measuring the spectral shift of the resonance dip,for modulating the wavelength of incident light.It is demonstrated that minute changes in the refractive index of a medium close to the surface of a metal film,owing to a shift in the resonance dip of the wavelength,can be detected.The average detection sensitivity is about 3200 nm/RIU(refractive index units),which is more than twice that of a metal grating-based gas sensor.The reflectivity of the surface plasmon resonance dip is only ～ 0.03%,and the full widths at half maximum(FWHMs) of bandwidth of the angle and wavelength are ～ 0.20° and 4.71nm,respectively.     

Polar Oscillation of Interface and Surface Optical Phonons in Free-Standing Cylindrical Quantum-Well Wires

Under dielectric continuum approximation, interface optical (IO) and surface optical (SO) phonon modes as well as the corresponding Fro^ehlich electron-phonon interaction Hamiltonian in a free-standing cylindrical quantum-well wire (QWW) are derived and studied. Numerical calculations on GaAs/AlzGa1-x As cylindrical QWW are performed. Results reveal that there are two branches of IO phonon modes and one branch of SO phonon mode, and the dispersion frequencies of IO or SO phonon modes sensitively depend on the Al mole fraction x in AlzGa1-x As material and the wavevector in z direction, kz. With the increasing of kz and quantum number m, the frequency of each IO mode approaches one of the two frequency values of the single GaAs/AlxGa1-x As heterostructure, and the electrostatic potential distribution of the phonon mode tends to be more and more localized at a certain interface or surface, meanwhile, the coupling between the electron-IO and -SO phonons becomes weaker.     

Tuning of plasmonic behaviours in coupled metallic nanotube arrays

We theoretically investigate the influence of the shape of nanoholes on plasmonic behaviours in coupled elliptical metallic nanotube arrays by the finite-difference time-domain (FDTD) method.We study the structure in two cases:one for the array aligned along the minor axis and the other for the array aligned along the major axis.It is found that the optical properties and plasmonic effects can be tuned by the effective surface charges as a result of the variation in the minor axis length.Based on the localized nature of electric field distributions,we also clearly show that the presence of localized plasmon resonant modes originates from multipolar plasmon polaritons and a large magnitude of opposing surface charges build up in the gap between adjacent nanotubes.     

Analysis of waveguide structure for surface plasmon polariton interference

This paper describes a multi-reflected mode based on a narrow waveguide to enlarge the interferential area of surface plasmon polaritons (SPPs). A reasonable thickness of metal film is coated under the waveguide, the incident angle and the waveguide thickness are optimized in order to effectively increase interferential area. This is a key point for research into the Goos--H\"anchen shift to optimize the waveguide thickness. Finally, the SPP interferential field is simulated with the finite-difference time-domain (FDTD) technique to prove the optimized results, and indicates that not only is the interferential area enlarged, but the high contrast is also maintained. Furthermore, the mode can fabricate some specific interferential patterns by adding some modulating techniques to the waveguide. So the mode has potential application in the fabrication of sub-wavelength patterns.     

Polar Oscillation of Interface and Surface Optical Phonons in Free-Standing Cylindrical Quantum-Well Wires

Under dielectric continuum approximation, interface optical (IO) and surface optical (SO) phonon modes aswell as the corresponding Frohlich electron-phonon interaction Hamiltonian in a free-standing cylindrical quantum-wellwire (Q WW) are derived and studied. Numerical calculations on GaAs/AlxGa1-xAs cylindrical QWW are performed.Results reveal that there are two branches of IO phonon modes and one branch of SO phonon mode, and the dispersionfrequencies ofIO or SO phonon modes sensitively depend on the Al mole fraction x in Alx Ga1-x As material and the wave-vector in z direction, kz. With the increasing of κz and quantum number m, the frequency of each IO mode approaches oneof the two frequency values of the single GaAs/Alx Ga1-xAs heterostructure, and the electrostatic potential distributionof the phonon mode tends to be more and more localized at a certain interface or surface, meanwhile, the couplingbetween the electron-IO and -SO phonons becomes weaker.     

A high figure of merit localized surface plasmon sensor based on a gold nanograting on the top of a gold planar film

We investigate the sensitivity and figure of merit （FOM） of a localized surface plasmon （LSP） sensor with gold nanograting on the top of planar metallic film. The sensitivity of the localized surface plasmon sensor is 317 nm/RIU, and the FOM is predicted to be above 8, which is very high for a localized surface plasmon sensor. By employing the rigorous coupled-wave analysis （RCWA） method, we analyze the distribution of the magnetic field and find that the sensing property of our proposed system is attributed to the interactions between the localized surface plasmon around the gold nanostrips and the surface plasmon polarition on the surface of the gold planar metallic film. These findings are important for developing high FOM localized surface plasmon sensors.