Interface Of Free Space Research Articles

Dispersion analysis of grounded dielectric slab coated with double positive (DPS) / double negative (DNG) material

The present work investigates the dispersion characteristics both for TM and TE modes in a grounded dielectric slab coated with double positive (DPS) material and double negative (DNG) material. The outermost dielectric layer is assumed to be free space. By employing proper boundary conditions at interfaces, dispersion relations for the aforementioned structure for both TM and TE modes are derived. Additionally, surface waves at the interface of free space and DPS/DNG coating are investigated. Existence of mode degeneracy for DNG/DPS combination has been discussed based on dispersion analysis.

Resonant excitation of terahertz surface magnetoplasmons by optical rectification over a rippled surface of n-type indium antimonide

We analysed the excitation of a surface magnetoplasmon wave by the mode conversion of a p-polarized laser beam over a rippled semiconductor (n-type)-free space interface. The pump surface magnetoplasmon wave exerts a ponderomotive force on the free electrons in the semiconductor, imparting a linear oscillatory velocity at the laser modulation frequency to them. This linear oscillatory velocity couples with the modulated electron density to produce a current density, which develops a resonant surface magnetoplasmon wave in the terahertz region. The amplitude of the terahertz surface magnetoplasmon wave can be tuneable with an external magnetic field and the semiconductor's temperature.

Excitation of second harmonic terahertz surface magnetoplasmons over a rippled surface of n-InSb

We analyzed the excitation of second harmonic (SH) terahertz (THz) surface magnetoplasmons (SMPs) over a n-type semiconductor (n-InSb)-free space interface. P-polarized laser obliquely incidents on the magnetized rippled surface of semiconductor with frequency ω and wave number k0z and k0x and exerts a ponderomotive force on free electrons of semiconductor surface and imparts second harmonic oscillatory velocity v→2ω. Second harmonic oscillatory velocity v→2ω couples with modulated electron density nq of rippled surface to produce a second harmonic nonlinear current J→2ωnl, which resonantly derives SH THz SMPs with wave number k2z=2k0z+q and frequency 2ω. SH THz SMPs amplitude increases with applied external magnetic field as well as with incident angle and gets the maximum value then decreases further increase in the applied external magnetic field and incident angle. The conversion efficiency of SH THz SMPs amplitude is achieved up to 4.2%.

Parametric excitation of surface plasma waves over a metallic surface by laser in an external magnetic field

AbstractEffects of external static magnetic field (applied in$\hat y$-direction) on resonant excitation of surface plasma waves (SPW) have been investigated over the metal free space interface. The high power laser$({\rm \omega} _0,\;\vec k_{0z})$is incident over the metal surface and exerts a ponderomotive force on the metal electrons in the skin layer. The ponderomotive force disturbs the quasi-neutrality of plasma which results into the excitation of space charge field at the frequency 2ω0. The electron density perturbation at frequency 2ω0driven by self-consistent space charge potential couples with the oscillatory velocity due to the seed SPW$({\rm \omega}, \;\vec k_z)$and produces nonlinear current to drive another counter propagating SPW$({\rm \omega} _1,\;\vec k_{1z})$at the phase matching conditions of frequency ω = ω1− 2ω0and wavenumber$\vec k_z = \vec k_{1z} - 2\vec k{}_{0z}$(by feedback mechanism). The parametric process becomes resonant at 2ω0≈ ωpand the maximum growth rate is achieved for an incidence angle of laser θ = 40°. The growth rate of the process reduces to half on increasing the magnetic field from 0.49 to 2.45 MG. The present study may be significant to the laser absorption experiments where surface rippling can strongly affect the laser energy absorption.

Fractional space analysis of optical refraction in silver

Silver metal is known to share some of the peculiar features of metamaterials in optical frequency domain. In this article, we investigate the occurrence of negative and/or orthogonal phase velocity, negative refraction and counterposition phenomena in silver with fractional dimensions. For this purpose an interface of free space and silver metal is considered for various values of fractional dimensions of both the half spaces. The observed values of the refracted poynting vector relate to the occurrence of the above mentioned phenomena. It is noted that although the fractionality of either of the half space does not alter the occurrence of the said phenomena, the absolute values of the refracted poynting vector vary greatly with a change in the fractionality of dimensions, indicating a possible control of energy flow in refracted fields via fractional parameters.

Contactless power transmission for NFC antennas in credit‐card size format

Wireless energy transmission is a key element in Contactless HF Communication Technologies, such as radio frequency identification or near field communication (NFC). This power aspect differentiates the technology from conventional wireless communication. The authors consider the circuit model as a lumped-element description with a coupled-transformer field model to formulate a representation of the problem and include the orientation of the magnetic field in planar space. The authors propose a novel computational model to reveal the dynamics of energy transfer can be represented as a set of forces projected by the oscillator at the interface of free-space. Finally, a high-frequency finite-element simulation based on the authors' model is used to solve a practical problem of two coupled elliptical spiral-loop antennas of a credit-card size, where the authors consider their contribution in the context of NFC.

Dispersivity of Balanced Near-Zero Permittivity and Permeability (EMNZ) Medium

$\epsilon $ -near-zero (ENZ), $\mu $ -near-zero (MNZ), and $\epsilon $ -and- $\mu $ -near-zero (EMNZ) materials all exhibit the property of $n=\sqrt {\epsilon _{r}\mu _{r}}\approx 0$ . The wave impedance $Z=({\mu /{\epsilon }})^{1/2}$ , though, is different for the different materials. For the EMNZ, the impedance can remain finite, in contrast to the ENZ and MNZ materials. Therefore, the electric and magnetic fields within the EMNZ can remain coupled, unlike the ENZ and MNZ. This paper presents an analysis of dispersivity in an EMNZ layer under the condition of balance $\mu _{r}=\epsilon _{r}$ . One possible application for this condition is seen in the analysis of transmission and reflection from an EMNZ–free space interface, which reveals that a perfect match condition is possible for normal incidence, while for any other incidence angle, this interface is a perfect reflector.

Scattering of electromagnetic plane wave from a perfect electric conducting strip placed at free space–chiral interface

The scattering of electromagnetic plane wave from a perfect electric conducting strip of finite width is investigated in this study. The strip is placed at the planar interface of free space and chiral medium. The Kobayashi potential method is used to determine the scattering from the strip. The dual integral equations are acquired through the boundary conditions. These equations as well as the edge conditions are satisfied through the properties of Weber–Schafheitlin integrals and the Jacobi polynomials. The projection of the Jacobi polynomials is used to get the matrix equations which are solved numerically to determine the unknown coefficients. Monostatic and bistatic scattering widths are examined in the free space region of the geometry. The far-zone scattered fields are analyzed by changing the values of different parameters, i.e. chirality and incident angle.

Low optical-loss facet preparation for silica-on-silicon photonics using the ductile dicing regime

The efficient production of high-quality facets for low-loss coupling is a significant production issue in integrated optics, usually requiring time consuming and manually intensive lapping and polishing steps, which add considerably to device fabrication costs. The development of precision dicing saws with diamond impregnated blades has allowed optical grade surfaces to be machined in crystalline materials such as lithium niobate and garnets. In this report we investigate the optimization of dicing machine parameters to obtain optical quality surfaces in a silica-on-silicon planar device demonstrating high optical quality in a commercially important glassy material. We achieve a surface roughness of 4.9 nm (Sa) using the optimized dicing conditions. By machining a groove across a waveguide, using the optimized dicing parameters, a grating based loss measurement technique is used to measure precisely the average free space interface loss per facet caused by scattering as a consequence of surface roughness. The average interface loss per facet was calculated to be: −0.63 dB and −0.76 dB for the TE and TM polarizations, respectively.

Evaluation of Capacitance of Dielectric-Coated Metallic Parabolic and Spherical Bowls

Electrostatic modeling for the evaluation of the capacitance of the dielectric-coated metallic spherical and parabolic bowls is presented in this article using the method of moments with a pulse basis function and a delta matching. Two sets of integral equations are formed, relating the potential on the metallic surface and the charge density and the normal component of the displacement flux density at the metal–dielectric–free-space interface. A matrix equation is formed, which is solved for the unknown charge densities. Numerical data on the capacitance has been presented, and the validity of the analysis has been justified.

Resonant Terahertz Generation by Optical Rectification of an Amplitude Modulated Surface Plasma Wave

An amplitude modulated surface plasma wave, produced via mode conversion of a laser, is shown to resonantly excite a surface plasma wave at the modulation frequency over a rippled metal free space interface. The pump surface plasma wave (SPW) exerts a ponderomotive force on metal electrons, imparting them an oscillatory velocity at the modulation frequency. This velocity beats with the surface modulation to produce a nonlinear current driving the surface plasma wave at the modulation frequency which may be chosen in the terahertz range. The presence of surface modulation is essential for effective coupling of surface plasma wave to terahertz wave.

Laser mode conversion into a surface plasma wave in a metal coated optical fiber

An optical fiber, coated with thin metal film, supports two distinct kinds of waves, viz., body waves that propagate through the fiber as transverse magnetic (TM) and transverse electric modes, and surface plasma waves that propagate on metal free space interface. When the metal has a ripple of suitable wave number q, a body wave of frequency ω and propagation constant kz induces a current at ω,kz+q in the ripple region that resonantly derives a surface plasma wave. When the metal surface has metallic particles attached to it and molecules are adsorbed on them, the surface plasma wave undergoes surface enhanced Raman scattering with them. The scattered signals propagate backward as a TM body wave and can be detected.

Bandwidth limitations of impedance matched ideal dipoles

Using circuit theory and Chu's network representations of the wave impedance of the lowest spherical multipole field, the Ideal dipole, an explicit expression is derived for the upper limit for the impedance bandwidth obtainable for an ideal, lossless, linearly polarized antenna. The expression embodies the network character of an ideal antenna and its role in the guidance of energy between the feed point and the free-space interface, making it more appropriate as a reference than the theoretical radiation quality factor (Q). Moreover, practical antennas do not always manifest a clear single-pole behavior, undermining the basic assumption of a reciprocal relation between Q and the bandwidth.

Efficient finite-difference time-domain scheme for light scattering by dielectric particles: application to aerosols

We have examined the Maxwell-Garnett, inverted Maxwell-Garnett, and Bruggeman rules for evaluation of the mean permittivity involving partially empty cells at particle surface in conjunction with the finite-difference time-domain (FDTD) computation. Sensitivity studies show that the inverted Maxwell-Garnett rule is the most effective in reducing the staircasing effect. The discontinuity of permittivity at the interface of free space and the particle medium can be minimized by use of an effective permittivity at the cell edges determined by the average of the permittivity values associated with adjacent cells. The efficiency of the FDTD computational program is further improved by use of a perfectly matched layer absorbing boundary condition and the appropriate coding technique. The accuracy of the FDTD method is assessed on the basis of a comparison of the FDTD and the Mie calculations for ice spheres. This program is then applied to light scattering by convex and concave aerosol particles. Comparisons of the scattering phase function for these types of aerosol with those for spheres and spheroids show substantial differences in backscattering directions. Finally, we illustrate that the FDTD method is robust and flexible in computing the scattering properties of particles with complex morphological configurations.

A novel inverse scattering solution for a one-dimensional inhomogeneous medium using a microwave networking technique

For weak scatterers, simple relations have been discovered between physical properties and the Fourier transforms of their scattering fields, but they are invalid under strong-scattering conditions. In this paper, a microwave networking technique is used to investigate the one-dimensional inverse scattering problem, from which a novel inverse scattering solution for the permittivity profile is derived by considering the equivalent microwave network of the permittivity profile discontinuity at the interface of free space with the medium. This novel solution is essentially different from previous relations and is valid for both weak-scattering and strong-scattering conditions. Closed-form and numerical reconstruction examples show that the novel solution is accurate in comparison with exact theory and is applicable to both continuous and discontinuous permittivity profiles.

Nonlinear differential equation for the reflection coefficient of an inhomogeneous lossy medium and its inverse scattering solutions

Nonlinear differential equations for the reflection coefficients of an inhomogeneous lossy medium illuminated by both TE-polarized and TM-polarized electromagnetic plane waves are derived using a microwave networking technique, which can be approximately solved by a nonlinear renormalization method. Considering the equivalent microwave network of the permittivity profile discontinuity at the interface of free space with the medium, two novel inverse scattering solutions for the permittivity profile and the conductivity profile are further investigated in closed forms. Closed-form and numerical reconstruction examples show the availability of this scheme.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Millimeter wave twist reflector design aspects

A millimeter-wave twist reflector design procedure is described. An effective dielectric constant for capacitive susceptance correction for a unidirectional planar grating at the interface of free space and dielectric material in the twist reflector environment is introduced. The loss factor of the dielectric material is taken into account for the prediction of twist reflector performance. With the introduction of these corrections experimental results are found to be in close agreement with the theory. Normalized curves for the design of twist reflectors in terms of grating parameters, dielectric substrate relative permittivity, and dielectric material thickness are presented. Experimental results are given.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Nonlinear Cross Modulation in a Dispersive Magnetoplasm at Gyroresonance on Its Reflection from Free Space Interface

In this article expressions for the first and second order cross modulations (CM's) have been obtained when an amplitude-modulated electromagnetic wave (EMW) is reflected from the magneto-plasma free space interface in the presence of an external magnetic field at gyroresonance by the rigorous kinetic approach (Boltzmann equation). The expressions thus obtained have been used to study the variations of the first and second order CM's with various plasma parameters such as collision frequency, plasma frequency, and index of modulation.

Harmonic Components Reflected from a Plasma Free Space Interface around Plasma Resonance

Expressions for the magnitude of the second and third harmonic components of the electric vector in the reflected wave have been obtained for the case of normal incidence of an electromagnetic wave (having a frequency near plasma frequency) on a plasma free space interface.

NONLINEAR DEMODULATION OF AN AMPLITUDE-MODULATED ELECTROMAGNETIC WAVE IN A PLASMA

In this paper the authors have derived the expression for the electric vector when an amplitude-modulated electromagnetic wave propagates in a nonlinear dispersive medium. Demodulation is obtained in the case of a wave propagating in a nonlinear medium, whereas overmodulation has been obtained when the wave is reflected back in the free space from a plasma free-space interface. Some calculations have been performed in both cases and it has been found that the demodulation decreases with increasing electron density, with increasing index of modulation of the incident wave, and with increasing collision frequency. In the case of reflection the overmodulation is found to decrease with decreasing electron density, increasing index of modulation, and decreasing collision frequency inside the plasma. The calculated results have been presented in the form of tables in the Discussion.