Experimental observation of plasmon polariton waves supported by a thin metal film of finite width

What are believed to be the first experimental observations of the existence of long-range plasmon-polariton waves, guided by a thin metal film of finite width, are presented. A waveguide composed of an 8-mum-wide, 20-nm-thick, 3.5-mm-long Au metal film embedded in SiO (2) was successfully excited at a free-space wavelength of 1.55 mum in an end-fire experiment. The theoretical nature of the phenomenon is described, and experimental observations of field confinement provided by this metal waveguide are presented in detail.     

Coupled surface polariton with guided wave polariton modes in asymmetric metal clad dielectric waveguides

It is emphasized that in metal-dielectric layered systems with a thin metallic layer, surface plasmon-polaritons (SP) can couple with guided wave polaritons (GWP) and form new hybrid modes with properties of both SP and GWP. This is illustrated by analyzing the properties of electromagnetic modes in an asymmetric metal-clad-dielectric-slab waveguide and their dependence on the thickness of metal cladding.     

Plasmon surface polariton luminescence from periodic metal gratings

When a gold grating is illuminated at an appropriate energy, polarization, and angle to excite a plasmon surface polariton (SP) all lower energy radiative SP states emit light. This enables the dispersion of SP states to be mapped by luminescence providing an alternative to reflectivity measurements. A similar effect has been observed for bare silver gratings, and silver gratings coated with several layers of cadmium arachidate by Langmuir-Blodgett technique. Two additional effects have been observed for Au gratings. First, one can obtain emission from radiative SP states by exciting the interband transition directly with photons of energy greater than approximately 2.4 eV. At these energies, SP states do not exist because the metal dielectric function has a large imaginary part. This is significant because it suggests that the degradation pathway involves electron-hole pair states as intermediates. Second, some gold gratings show $\text{surface enhanced Raman}$ of molecular species superimposed on the SP luminescence emission.     

Plasmon modes of double-layer graphene at finite temperature

We calculate the dynamical dielectric function of doped double-layer graphene (DLG), made of two parallel graphene monolayers with carrier densities n₁ and n₂, and an interlayer separation of d at finite temperature. The results are used to find the dispersion of plasmon modes and loss functions of DLG for several interlayer separations and layer densities. We show that in the case of n₂=0, the finite-temperature plasmon modes are dramatically different from the zero-temperature ones.     

Plasmon mechanism of light transmission through a metal film or a plasma layer

It is shown that a smooth metal film (or a plasma layer) can be made transparent for an electromagnetic wave when two identical subwavelength diffraction gratings are placed on both sides of the film. The electromagnetic wave transmission through the metal film is caused by excitation of evanescent surface waves (plasmons) and their transformation into propagating waves at the gratings. A model which is developed analytically shows that the problem of the wave transmission is physically equivalent to the problem of excitation of two coupled resonators of evanescent waves which are formed at the two film surfaces.     

Calculation of nonlinear modes guided by step-index fibers with finite cladding thickness

A circular optical fiber consisting of a nonlinear core bounded by a nonlinear cladding with a finite thickness is considered here. In this paper, the influence of the cladding radius in comparison with the core radius in the Power – effective index relations P(/k ₀) is examined. Numerical results indicate that the radius ratio between the cladding and the core is an important factor in changing the Power – effective index relations P(/k ₀) when the cladding has a stronger nonlinearity than that of the core.     

Laser generation of surface acoustic modes guided by copper lines of sub-micron width on silicon

Surface acoustic waves guided by a copper line embedded in a silica film on a silicon wafer were generated and detected optically using the laser-induced transient grating technique. Lines as narrow as ∼0.2 μm yield a good signal despite the much larger size of the laser spot. The phase velocity of the guided mode is slightly lower than the surface acoustic wave velocity in the thin film structure. Good correlation between the acoustic frequency and the electrical resistivity of the copper lines results from the dependence of both measurements on the line width.     

Surface guided modes in an aluminum oxide thin film

Energy losses due to the excitation of surface guided waves have been observed in inelastic electron scattering from thin films of aluminum oxide.     

Modification of the total reflection modes in a dielectric film by one metal boundary

The optical modes in a dielectric slab are considerably changed by replacing the dielectric medium on one side of the slab by a metal. In particular, the TH mode m = 0 shows the behavior of a surface plasma wave. The modes were excited in a reflection experiment by the use of prism film coupling in an Al-LiF-air system, the results are in satisfactory agreement with theory.     

Surface-plasmon-polariton waves guided by the uniformly moving planar interface of a metal film and dielectric slab

We explored the effects of relative motion on the excitation of surface-plasmon-polariton (SPP) waves guided by the planar interface of a metal film and a dielectric slab, both materials being isotropic and homogeneous. Electromagnetic phasors in moving and non-moving reference frames were related directly using the corresponding Lorentz transformations. Our numerical studies revealed that, in the case of a uniformly moving dielectric slab, the angle of incidence for SPP-wave excitation is highly sensitive to (i) the ratio β of the speed of motion to speed of light in free space and (ii) the direction of motion. When the direction of motion is parallel to the plane of incidence, the SPP wave is excited by p-polarized (but not s-polarized) incident plane waves for low and moderate values of β, while at higher values of β the total reflection regime breaks down. When the direction of motion is perpendicular to the plane of incidence, the SPP wave is excited by p-polarized incident plane waves for low values of β, but s-polarized incident plane waves at moderate values of β, while at higher values of β the SPP wave is not excited. In the case of a uniformly moving metal film, the sensitivity to β and the direction of motion is less obvious.     

Surface plasmon polariton coupling between a metal nanowire and a metal helix

The transmittance and steady-state electrical field distribution of a silver nanowire–helix system are investigated using the finite-difference time-domain method. In the nanowire–helix system, surface plasmon polaritons are coupled into the helix or squeezed into the space between the nanowire and helix. The transmittance strongly depends on the topologic shapes of the helix, especially the pitch height. Thus, the nanowire–helix system enables the detection of the displacement associated with helical deformation.     

Hybrid waveguide-surface plasmon polariton modes in a guided-mode resonance grating

We analyze the coupling between surface plasmon polaritons in a metal grating and the guided modes of a dielectric waveguide. Our model structure is a gold wire grating on a slab waveguide made of silicon nitride on silica wafer. The excitation of guided-mode resonances, surface plasmon polariton modes and hybrid waveguide-plasmon modes are observed in numerical simulations. Our experiments verify the existence of the predicted modes. These hybrid modes add significant degrees of freedom in designing structures for plasmonic applications.     

Coupling of isotopic polariton modes in sodium chlorate

The coupling of two isotopic polariton modes in sodium chlorate was studied experimentally by laser Raman spectroscopy and the observed line shapes were fitted on the basis of the theoretical treatment given by Benson and Mills.     

Resonant scattering of surface-plasmon polariton pulses by nanoscale metal defects

We have theoretically investigated the dynamics of the scattering of surface-plasmon polariton (SPP) pulses by single nanoscale metal defects through a rigorous calculation of the time dependence of the reflected and transmitted SPP and of the angular distribution of the scattered light. SPP resonances that occur at deep Gaussian grooves are probed with SPP pulses, the resonant scattering being unequivocally manifested by (a) the exponential tails of the scattered SPP and light pulses and (b) the delay time of the transmitted SPP pulse.     

Plasmon modes at a wedge using a non-local dielectric function

Plasmon modes at a wedge have been obtained by using a non-local dielectric function. It is shown that the effect of this dielectric function is roughly equivalent to rounding the edge of the wedge but using a local dielectric function.     

Room-temperature polariton parametric scattering driven by a one-dimensional polariton condensate

We demonstrate a novel way to realize room-temperature polariton parametric scattering in a one-dimensional ZnO microcavity. The polariton parametric scattering is driven by a polariton condensate, with a balanced polariton pair generated at the adjacent polariton mode. This parametric scattering is experimentally investigated by the angle-resolved photoluminescence spectroscopy technique under different pump powers and it is well described by the rate equation of interacting bosons. The direct relation between the intensity of the scattered polariton signal and that of the polariton reservoir is acquired under nonresonant excitation, exhibiting the explicit nonlinear characteristic of this room-temperature polariton parametric process.     

On multiple surface-plasmon-polariton waves guided by the interface of a metal film and a rugate filter in the Kretschmann configuration

The excitation of multiple surface-plasmon-polariton (SPP) waves—of different linear polarization states, phase speeds and spatial profiles—guided by the interface of a metal film and a rugate filter in the Kretschmann configuration was investigated. A plane wave of either of the two linear polarization states was made incident on the metal-capped rugate filter of finite thickness and the absorptances were calculated using a stable algorithm. The excitation of SPP waves was inferred by the presence of those peaks in the absorptance curves that were independent of the thickness of the rugate filter. The absorptance peaks representing the excitation of s-polarized SPP waves are narrower than those representing p-polarized SPP waves. For efficient excitation of multiple SPP waves, the metal film's thickness should be close to the penetration depth of the metal. The solution of a canonical boundary-value problem of SPP-wave propagation guided by a metal film, with a semi-infinite homogeneous dielectric material on one side and a semi-infinite rugate filter on the other side, reinforced the results obtained for the Kretschmann configuration. The thin metal film in the Kretschmann configuration may lead to coupling of its two interfaces.     

Plasmon modes of a superlattice — Classical vs quantum limits

The collective plasmon excitations of a superlattice are investigated in both the classical and quantum limits. Using a model that is applicable to superlattices whose constituent layers are either semiconductor- semiconductor, semiconductor-metal, or metal-metal, we show that the surface plasmon interface modes of each layer (slab) couple via the long range Coulomb interaction into two bands of plasmons with dispersion along the superlattice axis. Results for plasmon dispersion are presented for the classical limit (de Broglie wavelength less than the layer width) where the response is treated via a solution of Maxwell's equations using the bulk 3-D dielectric constant to describe each intervening layer. These results are compared to the plasmon dispersion in the quantum regime where the wave-vector frequency dependent dielectric constant of the superlattice is calculated taking into account quantization effects (subband structure). The relationship between the modes in both limits is derived.     

Characterization of polarization states of surface plasmon polariton modes by Fourier-plane leakage microscopy

We demonstrate that the polarization states of guided wave surface plasmon polariton (SPP) modes can be unambiguously identified by introducing a linear polarizer in the optical path of the light within a leakage-based microscope. We show the use of Fourier-plane leakage-based microscopy as a polarization characterization method to study the polarization states of SPP modes excited in plasmonic waveguides. Our results indicate that the inclusion of a linear polarizer provides additional image processing capabilities to leakage-based microscopes.