Searcharxiv⌕ Search

arXiv subjects

A. Lakhtakia

Publications and source records attributed to A. Lakhtakia.

At least 19 recordsLinked to original sources
arXiv2019

Plane-wave scattering by an ellipsoid composed of an orthorhombic dielectric-magnetic material with arbitrarily oriented constitutive principal axes

The extended boundary condition method can be formulated to study plane-wave scattering by an ellipsoid composed of an orthorhombic dielectric-magnetic material whose relative permittivity dyadic is a scalar multiple of its relative permeability dyadic, when the constitutive principal axes are arbitrarily oriented with respect to the shape principal axes. Known vector spherical wavefunctions are used to represent the fields in the surrounding matter-free space. After deriving closed-form expressions for the vector spherical wavefunctions for the scattering material, the internal fields are represented as superpositions of those vector spherical wavefunctions. The unknown scattered-field coefficients are related to the known incident-field coefficients by a transition matrix. The total scattering and absorption efficiencies are highly affected by the orientation of the constitutive principal axes relative to the shape principal axes, and the effect of the orientational mismatch between the two sets of principal axes is more pronounced as the electrical size increases. The dependence of the total scattering efficiency, but not of the absorption efficiency, on the angle of rotation about a shape principal axis can be predicted qualitatively from the variation of a scalar function with respect to the angle of rotation. The total scattering and absorption efficiencies do not depend on the polarization state of incident plane wave when the scattering material is impedance-matched to free space. The polarization state of the incident plane wave has a more discernible effect on the total scattering and absorption efficiencies for ellipsoids compared to spheres.

physics.optics↗
arXiv2011

Vector solitons in nonlinear isotropic chiral metamaterials

Starting from the Maxwell equations, we used the reductive perturbation method to derive a system of two coupled nonlinear Schrödinger (NLS) equations for the two Beltrami components of the electromagnetic field propagating along a fixed direction in an isotropic nonlinear chiral metamaterial. With single-resonance Lorentz models for the permittivity and permeability and a Condon model for the chirality parameter, in certain spectral regimes, one of the two Beltrami components exhibits a negative real refractive index when nonlinearity is ignored and the chirality parameter is sufficiently large.We found that, inside such a spectral regime, there may exist a subregime wherein the system of the NLS equations can be approximated by the Manakov system. Bright-bright, dark-dark, and dark-bright vector solitons can be formed in that spectral subregime.

nlin.PS↗
arXiv2010

Spontaneous decay of an emitter's excited state near a finite-length metallic carbon nanotube

The spontaneous decay of an excited state of an emitter placed in the vicinity of a metallic single-wall carbon nanotube (SWNT) was examined theoretically. The emitter-SWNT coupling strongly depends on the position of the emitter relative to the SWNT, the length of the SWNT, the dipole transition frequency and the orientation of the emitter. In the high-frequency regime, dips in the spectrum of the spontaneous decay rate exist at the resonance frequencies in the spectrum of the SWNT conductivity. In the intermediate-frequency regime, the SWNT conductivity is very low, and the spontaneous decay rate is practically unaffected by the SWNT. In the low-frequency regime, the spectrum of the spontaneous decay rate contains resonances at the antennas resonance frequencies for surface-wave propagation in the SWNT. Enhancement of both the total and radiative spontaneous decay rates by several orders in magnitude is predicted at these resonance frequencies. The strong emitter-field coupling is achieved, in spite of the low Q factor of the antenna resonances, due to the very high magnitude of the electromagnetic field in the near-field zone. The vacuum Rabi oscillations of the population of the excited emitter state are exhibited when the emitter is coupled to an antenna resonance of the SWNT.

cond-mat.mes-hall↗
arXiv2008

Constraints on effective constitutive parameters of certain bianisotropic laminated composite materials

When the electrically thin unit cell of a laminated composite material is made of two bianisotropic sheets whose constitutive properties in the thickness direction are decoupled from the constitutive properties in the interfacial planes, the laminated composite material can be homogenized into a material not all of whose constitutive parameters are independent of each other. This non-independence of the constitutive dyadics of the constituent materials and the homogenized composite material is captured by two simple constraints, which may not hold if even one of the two constituent materials has more complicated constitutive properties than stated above.

physics.optics↗
arXiv2008

Analysis of Multiwalled Carbon Nanotubes as Waveguides and Antennas in the Infrared and the Visible Regimes

The propagation of azimuthally symmetric guided waves in multiwalled carbon nanotubes (MWCNTs) was analyzed theoretically in the mid-infrared and the visible regimes. The MWCNTs were modeled as ensembles of concentric, cylindrical, conducting shells. Slightly attenuated guided waves and antenna resonances due to the edge effect exist for not-too-thick MWCNTs in the far- and mid-infrared regimes. Interband transitions hinder the propagation of guided waves and have a deleterious effect on the performance of a finite-length MWCNT as an antenna. Propagation of surface-plasmon waves along an MWCNT with a gold core was also analyzed. In the near-infrared and the visible regimes, the shells behave effectively as lossy dielectrics suppressing surface-plasmon-wave propagation along the gold core.

cond-mat.mtrl-sci↗
arXiv2008

On widening the angular existence domain for Dyakonov surface waves using the Pockels effect

The propagation of Dyakonov surface waves (DSWs) at the planar interface between an isotropic material and a linear electro-optic birefringent material can be dynamically controlled using the Pockels effect. The range of directions for DSW propagation has been previously found to be rather narrow. By careful choice of various parameters, this range of directions can be increased by more than an order of magnitude.

physics.optics↗
arXiv2008

Polarization--universal rejection filtering by ambichiral structures made of indefinite dielectric--magnetic materials

An ambichiral structure comprising sheets of an anisotropic dielectric material rejects normally incident plane waves of one circular polarization (CP) state but not of the other CP state, in its fundamental Bragg regime. However, if the same structure is made of an dielectric--magnetic material with indefinite permittivity and permeability dyadics, it may function as a polarization--universal rejection filter because two of the four planewave components of the electromagnetic field phasors in each sheet are of the positive--phase--velocity type and two are of the negative--phase--velocity type.

physics.optics↗
arXiv2008

Sculptured-thin-film plasmonic-polaritonics

The solution of a boundary--value problem formulated for the Kretschmann configuration shows that the phase speed of a surface--plasmon--polariton (SPP) wave guided by the planar interface of a sufficiently thin metal film and a sculptured thin film (STF) depends on the vapor incidence angle used while fabricating the STF by physical vapor deposition. Furthermore, it may be possible to engineer the phase speed by periodically varying the vapor incidence angle. The phase speed of the SPP wave can be set by selecting higher mean value and/or the modulation amplitude of the vapor incidence angle.

physics.optics↗
arXiv2007

Electrical control of surface-wave propagation at the planar interface of a linear electro-optic materials and an isotropic dielectric material

Surface waves can propagate on the planar interface of a linear electro-optic (EO) material and an isotropic dielectric material, for restricted ranges of the orientation angles of the EO material and the refractive index of the isotropic material. These ranges can be controlled by the application of a dc electric field, and depend on both the magnitude and the direction of the dc field. Thus, surface-wave propagation can be electrically controlled by exploiting the Pockels effect.

physics.optics↗
arXiv2007

Electromagnetic wave propagation in an almost circular bundle of closely packed, metallic, carbon nanotubes

An equivalent-multishell approach for the approximate calculation of the characteristics of electromagnetic waves propagating in almost circular (azimuthally symmetric), closely packed bundles of parallel, identical, and metallic carbon nanotubes (CNTs) yields results in reasonably good agreement with a many-body technique, for infinitely long bundles when the number of CNTs is moderately high. The slow-wave coefficients for azimunthally symmetric guided waves increase with the number of metallic CNTs in the bundle, tending for thick bundles to unity, which is characteristic of macroscopic metallic wires. The existence of an azimuthally nonsymmetric guided wave at low frequencies in a bundle of a large number of finite-length CNTs stands in contrast to the characteristics of guided-wave propagation in a single CNT. The equivalent-multishell approach yields the polarizability scalar and the antenna efficiency of a bundle of finite-length CNTs in the long-wavelength regime over a wide frequency range spanning the terahertz and the near-infrared regimes. Edge effects give rise to geometric resonances in such bundles. The antenna efficiency of a CNT bundle at the first resonance can exceed that of a single CNT by four orders of magnitude, which is promising for the design and development of CNT-bundle antennas and composite materials containing CNT-bundles as inclusions.

cond-mat.mtrl-sci↗
arXiv2006

Theory of electrically controlled exhibition of circular Bragg phenomenon by an obliquely excited structurally chiral material. Part 2: arbitrary dc electric field

Numerical examination of the solution of the boundary--value problem of the reflection and transmission of a plane wave due to a slab of an electro--optic structurally chiral material (SCM) indicates that the exhibition of the circular Bragg phenomenon by the SCM can be controlled not only by the sign and the magnitude of a dc electric field but also by its orientation in relation to axis of helicoidal nonhomogeneity of the SCM. Thereby, the possibility of electrical control of circular--polarization filters has been extended.

physics.optics↗
arXiv2006

Theory of electrically controlled exhibition of circular Bragg phenomenon by an obliquely excited structurally chiral material

The boundary-value problem of the reflection and transmission of a plane wave due to a slab of an electro-optic structurally chiral material (SCM) is formulated in terms of a 4x4 matrix ordinary differential equation. The SCM slab can be locally endowed with one of 20 classes of point group symmetry, and is subjected to a dc voltage across its thickness. The enhancement (and, in some cases, the production) of the circular Bragg phenomenon (CBP) by the application of the dc voltage has either switching or circular-polarization-rejection applications in optics. The twin possibilities of thinner filters and electrical manipulation of the CBP, depending on the local crystallographic class as well as the constitutive parameters of the SCM, emerge.

physics.optics↗
arXiv2006

Quantification of optical pulsed-plane-wave-shaping by chiral sculptured thin films

The durations and average speeds of ultrashort optical pulses transmitted through chiral sculptured thin films (STFs) were calculated using a finite-difference time-domain algorithm. Chiral STFs are a class of nanoengineered materials whose microstructure comprises parallel helicoidal nanowires grown normal to a substrate. The nanowires are $\sim$10-300 nm in diameter and $\sim1-10 μ$m in length. Durations of transmitted pulses tend to increase with decreasing (free-space) wavelength of the carrier plane wave, while average speeds tend to increase with increasing wavelength. An increase in nonlinearity, as manifested by an intensity-dependent refractive index in the frequency domain, tends to increase durations of transmitted pulses and decrease average speeds. The circular Bragg phenomenon exhibited by a chiral STFs manifests itself in the frequency domain as high reflectivity for normally incident carrier plane waves whose circular polarization state is matched to the structural handedness of the film and whose wavelength falls in a range known as the Bragg regime; films of the opposite structural handedness reflect such plane waves little. This effect tends to distort the shapes of transmitted pulses with respect to the incident pulses, and such shaping can cause sharp changes in some measures of average speed with respect to carrier wavelength. A local maximum in the variation of one measure of the pulse duration with respect to wavelength is noted and attributed to the circular Bragg phenomenon. Several of these effects are explained via frequency-domain arguments. The presented results serve as a foundation for future theoretical and experimental studies of optical pulse propagation through causal, nonlinear, nonhomogeneous, and anisotropic materials.

physics.optics↗
arXiv2006

Scattering by a nihility sphere

On interrogation by a plane wave, the back-scattering efficiency of a nihility sphere is identically zero, and its extinction and forward-scattering efficiencies are higher than those of a perfectly conducting sphere.

physics.optics↗
arXiv2006

Scattering by a nihility cylinder

The total scattering and the extinction efficiencies of a nihility cylinder of infinite length and circular cross--section are identical and independent of the polarization state of a normally incident plane wave.

physics.optics↗
arXiv2004

On Onsager Relations and Linear Electromagnetic Materials

We investigated the Onsager relations in the context of electromagnetic constitutive relations of linear, homogeneous materials. We determined that application of the Onsager relations to the constitutive equations relating $#P$ and $#M$ to both $#E$ and $#B$ is in accord with Lorentz reciprocity as well as the Post constraint.

physics.optics↗
arXiv2004

Size-Dependent Bruggeman Approach for Dielectric-Magnetic Composite Materials

Expressions arising from the Bruggeman approach for the homogenization of dielectric-magnetic composite materials, without ignoring the sizes of the spherical particles, are presented. These expressions exhibit the proper limit behavior. The incorporation of size dependence is directly responsible for the emergence of dielectric-magnetic coupling in the estimated relative permittivity and permeability of the homogenized composite material.

physics.class-ph↗