Dispersion curves for phonon-polaritons associated with an overdamped vibration mode

For an overdamped vibration mode, it is shown that polariton dispersion curves derived from various measurable quantities are different according to the kind of experiments considered and the way they are performed. Experimental results are given for BaTiO₃ and show that a resonant spectrum is observed when polaritons are studied by coherent excitation leading to an easier determination of the overdamped polariton mode parameters.     

One and two mode behaviors of surface phonon-polaritons of ternary mixed crystal films

One and two mode behaviors of surface phonon-polaritons of ternary mixed crystal (TMC) films are studied in the framework of the modified random-element-isodisplacement model and the Born-Huang approximation, based on the Maxwell's equations with the usual boundary conditions. The numerical results for the frequencies and splitting energies of the surface phonon-polaritons as functions of the composition in several II-VI and III-V compound semiconductor ternary mixed crystal films are obtained. The “two-mode” and “one-mode” behaviors for different types of systems are clearly shown in the curves of the splitting energies of surface phonon-polaritons. The theoretical conclusion obtained is agreement with the reported experiment results for bulk TMC systems.     

The Brewster effect for a one-dimensional random surface

By the use of a unitarity and reciprocity conserving theory for the scattering of p-polarized light from a one-dimensional random dielectric surface the we determine the shift in the Brewster angle toward smaller angles of incidence caused by the surface roughness, and the (non-zero) value of the reflectivity at its minimum. Both quantities may be useful in the characterization of the roughness of such surfaces.     

The Brewster effect for a one-dimensional random surface

Abstract

By the use of a unitarity and reciprocity conserving theory for the scattering of p-polarized light from a one-dimensional random dielectric surface the we determine the shift in the Brewster angle toward smaller angles of incidence caused by the surface roughness, and the (non-zero) value of the reflectivity at its minimum. Both quantities may be useful in the characterization of the roughness of such surfaces.     

Thermal image encryption obtained with a SiO2 space-variant subwavelength grating supporting surface phonon-polaritons

Space-variant partially polarized thermal emission is investigated. We show that by coupling surface phonon-polaritons to a propagating field, large anisotropy of the emissivity is obtained within a narrow spectral range. We experimentally demonstrate this effect by fabricating a space-variant subwavelength grating on a SiO2 substrate to encrypt an image in the polarization state of a thermal radiation field.     

Dispersion of doppleron-phonon modes in strong coupling regime

The dispersion equation for doppleron-phonon modes was constructed and solved analytically in the strong coupling regime. The Fermi surface model proposed previously for calculating the doppleron spectrum in an indium crystal was used. It was shown that in the vicinity of doppleron-phonon resonance, the dispersion curves of coupled modes form a gap qualitatively different from the one observed under helicon-phonon resonance: there is a frequency interval forbidden for existence of waves of definite circular polarization depending upon direction of the external DC magnetic field. The physical reason for it is interaction of the waves which have oppositely directed group velocities.     

Dispersion of collective modes at inhomogeneous metal surfaces

A simple model in which electrons are assumed to be specularly reflecting on a plane located a distance u above the boundary of a homogeneous metallic region is proposed for studying dynamical properties of metal surfaces. This model is believed to incorporate essential effects of the inhomogeneity of a pure jellium surface in a new way. It leads to a strong reduction of hydrodynamic dispersion effects for long wavelengths surface plasmons, in agreement with experiment and with various previous calculations. The model is also applied to surface phonons and exact numerical dispersion curves for both surface phonons and plasmons at arbitrary wavelengths are presented.     

Dispersion relations of wave modes in helium II layers

Dispersion relations of (sound-like) wave modes, which can exist in a helium II layer of arbitrary width, are calculated numerically. The basis of our considerations is the complete system of the linearized Landau-Khalamikov equations, in which only the dissipative processes involved with η and ζ₂ are taken into account. Apart from the linearization, no approximation or averaging is performed. The thermal expansion of helium II is taken into account. Symmetry properties of the velocities of flow, usually required, are dropped here. A hint is given as to how all the Khalatnikov coefficients may be measured by sound absorption experiments.     

Dispersion of tubular modes propagating in multimode optical fibres

We have already used interferometric techniques for measuring, first, the impulse response of optical fibres and further the different times of flight of modes of a multimode fibre. Apart from time of flight, our set-up provides the intramodal dispersion of each mode (d² β/dω ²). To demonstrate, we have measured the modal dispersion difference between two tubular modes that were selectively excited in a multimode graded index fibre. For comparison, a theoretical expression has been derived, based on a ray optics approach.     

Omnidirectional and compact Tamm phonon-polaritons enhanced mid-infrared absorber

Narrow band mid-infrared (MIR) absorption is highly desired in thermal emitter and sensing applications. We theoretically demonstrate that the perfect absorption at infrared frequencies can be achieved and controlled around the surface phonon resonance frequency of silicon carbide (SiC). The photonic heterostructure is composed of a distributed Bragg reflector (DBR)/germanium (Ge) cavity/SiC on top of a Ge substrate. Full-wave simulation results illustrate that the Tamm phonon-polaritons electric field can locally concentrate between the Ge cavity and the SiC film, contributed to the improved light-phonon interactions with an enhancement of light absorption. The structure has planar geometry and does not require nano-patterning to achieve perfect absorption of both polarizations of the incident light in a wide range of incident angles. Their absorption lines are tunable via engineering of the photon band-structure of the dielectric photonic nanostructures to achieve reversal of the geometrical phase across the interface with the plasmonic absorber.     

Low-loss surface modes and lossy hybrid modes in metamaterial waveguides

We show that waveguides with a dielectric core and a lossy metamaterial cladding (metamaterial-dielectric guides) can support hybrid ordinary-surface modes previously only known for metal-dielectric waveguides. These hybrid modes are potentially useful for frequency filtering applications as sharp changes in field attenuation occur at tailorable frequencies. Our results also show that the surface modes of a metamaterial-dielectric waveguide with comparable electric and magnetic losses can be less lossy than the surface modes of an analogous metal-dielectric waveguide with electric losses alone. Through a characterization of both slab and cylindrical metamaterial-dielectric guides, we find that the surface modes of the cylindrical guides show promise as candidates for all-optical control of low-intensity pulses.     

Dispersion and angular analysis of acoustic modes in a shallow sea

An experiment that allowed constructing a pattern of mode signals radiated by a point source at the distances of 7 and 10 km has been staged in the Barents Sea. The image of mode signals focused by time reversal is obtained in the mode number-group delay coordinates. The used algorithm is based on the coincidence of frequency characteristics of modes of a real waveguide and an ideal waveguide in a shallow sea. A mechanism of the phenomenon that explains the observed results is proposed.     

Surface loving and surface avoiding modes

We theoretically study the propagation of sound waves in GaAs/AlAs superlattices focusing on periodic modes in the vicinity of the band gaps. Based on analytical and numerical calculations, we show that these modes are the product of a quickly oscillating function times a slowly varying envelope function. We carefully study the phase of the envelope function compared to the surface of a semi-infinite superlattice. Especially, the dephasing of the superlattice compared to its surface is a key parameter. We exhibit two kind of modes: Surface Avoiding and Surface Loving Modes whose envelope functions have their minima and respectively maxima in the vicinity of the surface. We finally consider the observability of such modes. While Surface Avoiding Modes have experimentally been observed [Phys. Rev. Lett. 97, 1224301 (2006)], we show that Surface Loving Modes are likely to be observable and we discuss the achievement of such experiments. The proposed approach could be easily transposed to other types of wave propagation in unidimensional semi-infinite periodic structures as photonic Bragg mirror.     

Dispersion of surface plasmons in InSb-gratings

The reflection of a monochromatic plane electromagnetic wave by a grating consisting of grooves in the surface of a semiconductor plasma (InSb) is investigated theoretically, in particular in that region of frequencies where the complex permittivity of the semiconductor plasma has a negative real part. From the numerically obtained reflection factor pertaining to anH-polarized incident wave, the excitation and the dispersion of surface plasmons at the boundary of the medium is discussed. The grating problem is rigorously formulated as a boundary value problem employing a Green's function technique. Numerical results pertaining to the reflection factor are presented for different grating parameters.     

Dispersion relation and surface gravity of universal horizons

In Einstein-aether theory,violating Lorentz invariance permits some super-luminal communications,and the universal horizon can trap excitations traveling at arbitrarily high velocities.To better understand the nature of these universal horizons,we first modify the ray tracing method,and then use it to study their surface gravity in charged Einstein-aether black hole spacetime.Instead of the previous result by Cropp et al.,our results show that the surface gravity of the universal horizon is dependent on the specific dispersion relation,k_(uh)-2(z-1)k_(uh)/z,where z denotes the power of the leading term in the superluminal dispersion relation,characterizing different species of particles.And the associated Hawking temperatures also are different with z.These findings,which coincide with those derived by the tunneling method,provide some full understanding of black hole thermodynamics in Lorentz-violating theories.     

Dispersion relations of the intercalate modes in graphite intercalation compounds

We study the dynamics of the charged intercalate molecules. The model for the intercalate is a two dimensional plasma with the appropriate screening due to the charge carriers in the graphite layers. The dependence of the dispersion relation on stage and charge transfer is discussed and the relation of these modes to conductivity is pointed out.     

Dispersion and lifetimes of electromagnetic modes attached to strongly textured slab waveguides

The influence of strong, two-dimensional (2D) periodic texture on the dispersion and lifetimes of resonant electromagnetic modes localized in the vicinity of thin (80 to 155 nm) GaAs membranes supported on thick (1 to 2 m) wet-oxidized AlAs cladding layers is reported. A method of extracting this information by fitting Fano-like features in broadband specular reflectivity spectra is described in detail, and applied to samples containing both triangular and square 2D lattices. A new and easier method of probing the properties of these modes is also demonstrated. It involves incorporating a superlattice of defects in the principal crystal lattice, and monitoring the defect diffraction spectrum, rather than the specular reflectivity.     

Dispersion curves for a viscoelastic Timoshenko beam with fractional derivatives

The Kramers–Kronig dispersion relation, often used as a viscoelastic constitutive law for polymeric materials, is based on purely mathematical properties of linearity, convergence of improper integrals, and causality; thus, it may also be valid as a viscoelastic constitutive law for general structural materials. Accordingly, the motion equation of a Timoshenko beam composed of conventional elastic structural materials is extended to one composed of viscoelastic materials. From the derived governing equation, a dispersive equation is derived for a viscoelastic Timoshenko beam. By plotting phase velocity curves and group velocity curves for a beam of solid circular cross-section composed of a viscoelastic material (polyvinyl chloride foam), the influence of the fractional order of viscoelasticity is examined. As a result, it is found that, in the high frequency range, only the first mode of a Timoshenko beam converged to the propagation velocity of the Rayleigh wave, which takes account of the fractional order of viscoelasticity. In addition, the phase velocity and the group velocity were found to increase as the fractional order approaches 0, and to decrease as the fractional order approaches 1. Furthermore, the rate of velocity change becomes greater as the fractional order approaches 0, and becomes smaller as the fractional order approaches 1.