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Akhlesh Lakhtakia

Publications and source records attributed to Akhlesh Lakhtakia.

At least 163 records · Page 9Linked to original sources
arXiv2007

Scattering loss in electro-optic particulate composite materials

The effective permittivity dyadic of a composite material containing particulate constituent materials with one constituent having the ability to display the Pockels effect is computed, using an extended version of the strong-permittivity-fluctuation theory which takes account of both the distributional statistics of the constituent particles and their sizes. Scattering loss, thereby incorporated in the effective electromagnetic response of the homogenized composite material, is significantly affected by the application of a low-frequency (dc) electric field.

physics.optics↗
arXiv2006

On the Bergman-Milton bounds for the homogenization of dielectric composite materials

The Bergman-Milton bounds provide limits on the effective permittivity of a composite material comprising two isotropic dielectric materials. These provide tight bounds for composites arising from many conventional materials. We reconsider the Bergman-Milton bounds in light of the recent emergence of metamaterials, in which unconventional parameter ranges for relative permittivities are encountered. Specifically, it is demonstrated that: (a) for nondissipative materials the bounds may be unlimited if the constituent materials have relative permittivities of opposite signs; (b) for weakly dissipative materials characterized by relative permittivities with real parts of opposite signs, the bounds may be exceedingly large.

physics.optics↗
arXiv2006

Simultaneous negative- and positive-phase-velocity propagation in an isotropic chiral medium

The phase velocity of plane waves propagating in an isotropic chiral medium can be simultaneously positive for left-circularly polarized light and negative for right-circularly polarized light(or vice versa). The constitutive parameter regimes supporting this phenomenon are established for nondissipative and dissipative mediums. The boundary between positive and negative phase velocity is characterized by infinite phase velocity.

physics.optics↗
arXiv2006

Concealment by uniform motion

The perceived lateral position of a transmitted beam, upon propagating through a slab made of homogeneous, isotropic, dielectric material at an oblique angle, can be controlled through varying the velocity of the slab. In particular, by judiciously selecting the slab velocity, the transmitted beam can emerge from the slab with no lateral shift in position. Thereby, a degree of concealment can be achieved. This concealment is explored in numerical calculations based on a 2D Gaussian beam.

physics.optics↗
arXiv2006

Counterposition and negative refraction due to uniform motion

Refraction of obliquely incident plane waves due to the interface of a vacuous half-space and a half-space occupied by a simply moving, nondissipative, isotropic dielectric-magnetic medium is considered, when the medium's velocity lies parallel to the interface and in the plane of incidence. Counterposition of the refracted wavevector and time-averaged Poynting vector occurs when the medium's velocity is sufficiently large in magnitude and makes an obtuse angle with the incident wavevector. The counterposition induced by relative motion occurs whether the refraction is negative or positive when the medium is at rest.

physics.optics↗
arXiv2006

On electromagnetics of an isotropic chiral medium moving at constant velocity

A medium which is an isotropic chiral medium from the perspective of a co-moving observer is a Faraday chiral medium (FCM) from the perspective of a non-co-moving observer. The Tellegen constitutive relations for this FCM are established. By an extension of the Beltrami field concept, these constitutive relations are exploited to show that planewave propagation is characterized by four generally independent wavenumbers. This FCM can support negative phase velocity at certain translational velocities and with certain wavevectors, even though the corresponding isotropic chiral medium does not. The constitutive relations and Beltrami--like fields are also used to develop a convenient spectral representation of the dyadic Green functions for the FCM.

physics.optics↗
arXiv2006

Effect of charge on negative-phase-velocity propagation of electromagnetic waves in the ergosphere of a rotating black hole

The presence of charge promotes the propensity of a rotating black hole to support the propagation of electromagnetic plane waves with negative phase velocity (NPV) in its ergosphere, whether the Kerr-Newman or the Kerr-Sen metric descriptions of spacetime are considered. Striking differences in the NPV characteristics for the Kerr-Newman and Kerr-Sen metrics emerge from numerical studies, particularly close to the outer event horizon when the magnitude of the charge is large.

astro-ph↗
arXiv2006

Swamping of circular Bragg phenomenon and shaping of videopulses

We studied the durations and average speeds of videopulses transmitted through chiral sculptured thin films using a finite-difference algorithm. The chiral STF was either linear or possessed an intensity-dependent permittivity. Videopulse durations tended to decrease with increasing carrier wavelength and to increase, for given carrier wavelength and polarization state, when the chiral STF was nonlinear with intensity-dependent permittivity. The rate of decrease in durations with wavelength was less than that for longer-duration pulses. The effect of the circular Bragg phenomenon was swamped by the wide bandwidth possessed by videopulses. Two measures of videopulse average speed did not change much with carrier wavelength, and decreased slightly, for a given carrier wavelength and polarization state, in the nonlinear case. The other measure of average speed tended to increase with increasing carrier wavelength, and decrease, for a given carrier wavelength and polarization state, in the nonlinear case.

physics.optics↗
arXiv2006

Electrical control of the linear optical properties of particulate composite materials

The Bruggeman formalism for the homogenization of particulate composite materials is used to predict the effective permittivity dyadic of a two-constituent composite material with one constituent having the ability to display the Pockels effect. Scenarios wherein the constituent particles are randomly oriented, oriented spheres, and oriented spheroids are numerically explored. Thereby, homogenized composite materials (HCMs) are envisaged whose constitutive parameters may be continuously varied through the application of a low-frequency (dc) electric field. The greatest degree of control over the HCM constitutive parameters is achievable when the constituents comprise oriented and highly aspherical particles and have high electro-optic coefficients.

physics.optics↗
arXiv2006

Narrowband and ultranarrowband filters with electro-optic structurally chiral materials

When a circularly polarized plane wave is normally incident on a slab of a structurally chiral material with local $\bar{4}2m$ point group symmetry and a central twist defect, the slab can function as either a narrowband reflection hole filter for co-handed plane waves or an ultranarrowband transmission hole filter for cross-handed plane waves, depending on its thickness and the magnitude of the applied dc electric field. Exploitation of the Pockels effect significantly reduces the thickness of the slab.

physics.optics↗
arXiv2006

Correlation length and negative phase velocity in isotropic dielectric-magnetic materials

A composite material comprising randomly distributed spherical particles of two different isotropic dielectric-magnetic materials is homogenized using the second-order strong-property-fluctuation theory in the long-wavelength approximation. Whereas neither of the two constituent materials by itself supports planewave propagation with negative phase velocity (NPV), the homogenized composite material (HCM) can. The propensity of the HCM to support NPV propagation is sensitive to the distributional statistics of the constituent material particles, as characterized by a two--point covariance function and its associated correlation length. The scope for NPV propagation diminishes as the correlation length increases.

physics.optics↗
arXiv2005

Positive-, negative-, and orthogonal-phase-velocity propagation of electromagnetic plane waves in a simply moving medium

Planewave propagation in a simply moving, dielectric-magnetic medium that is isotropic in the co-moving reference frame, is classified into three different categories: positive-, negative-, and orthogonal-phase-velocity (PPV, NPV, and OPV). Calculations from the perspective of an observer located in a non-co-moving reference frame show that, whether the nature of planewave propagation is PPV or NPV (or OPV in the case of nondissipative mediums) depends strongly upon the magnitude and direction of that observer's velocity relative to the medium. PPV propagation is characterized by a positive real wavenumber, NPV propagation by a negative real wavenumber. OPV propagation only occurs for nondissipative mediums, but weakly dissipative mediums can support nearly OPV propagation.

physics.optics↗
arXiv2005

Orthogonal-Phase-Velocity Propagation of Electromagnetic Plane Waves

In an isotropic, homogeneous, nondissipative, dielectric-magnetic medium that is simply moving with respect to an inertial reference frame, planewave solutions of the Maxwell curl postulates can be such that the phase velocity and the time-averaged Poynting vector are mutually orthogonal. Orthogonal-phase-velocity propagation thus adds to the conventional positive-phase-velocity propagation and the recently discovered negative-phase-velocity propagation that is associated with the phenomenon of negative refraction.

physics.optics↗
arXiv2005

A Map of the Nanoworld: Sizing up the Science, Politics, and Business of the Infinitesimal

Mapping out the eight main nodes of nanotechnology discourse that have emerged in the past decade, we explore how various scientific, social, and ethical islands of discussion have developed, been recognized, and are being continually renegotiated. We do so by (1) identifying the ways in which scientists, policy makers, entrepreneurs, educators, and environmental groups have drawn boundaries on issues relating to nanotechnology; (2) describing concisely the perspectives from which these boundaries are drawn; and (3) exploring how boundaries on nanotechnology are marked and negotiated by various nodes of nanotechnology discourse.

physics.soc-ph↗
arXiv2005

Correlation length facilitates Voigt wave propagation

Under certain circumstances, Voigt waves can propagate in a biaxial composite medium even though the component material phases individually do not support Voigt wave propagation. This phenomenon is considered within the context of the strong--permittivity--fluctuation theory. A generalized implementation of the theory is developed in order to explore the propagation of Voigt waves in any direction. It is shown that the correlation length--a parameter characterizing the distributional statistics of the component material phases--plays a crucial role in facilitating the propagation of Voigt waves in the homogenized composite medium.

physics.optics↗