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A. Lakhtakia

Publications and source records attributed to A. Lakhtakia.

29 records · Page 2Linked to original sources
arXiv2004

Planewave diffraction at the periodically corrugated boundary of vacuum and a negative phase-velocity material

Considering the diffraction of a plane wave by a periodically corrugated half-space, we show that the transformation of the refracting medium from positive/negative phase-velocity to negative/positive phase-velocity type has an influence on the diffraction efficiencies. This effect increases with increasing corrugation depth, owing to the presence of evanescent waves in the troughs of the corrugated interface.

physics.optics↗
arXiv2004

Plane waves with negative phase velocity in Faraday chiral mediums

The propagation of plane waves in a Faraday chiral medium is investigated. Conditions for the phase velocity to be directed opposite to the direction of power flow are derived for propagation in an arbitrary direction; simplified conditions which apply to propagation parallel to the distinguished axis are also established. These negative phase-velocity conditions are explored numerically using a representative Faraday chiral medium, arising from the homogenization of an isotropic chiral medium and a magnetically biased ferrite. It is demonstrated that the phase velocity may be directed opposite to power flow, provided that the gyrotropic parameter of the ferrite component medium is sufficiently large compared with the corresponding nongyrotropic permeability parameters.

physics.optics↗
arXiv2004

Enhanced group velocity in metamaterials

The Bruggeman formalism is implemented to estimate the refractive index of an isotropic, dielectric, homogenized composite medium (HCM). Invoking the well--known Hashin--Shtrikman bounds, we demonstrate that the group velocity in certain HCMs can exceed the group velocities in their component materials. Such HCMs should therefore be considered as metamaterials.

physics.optics↗
arXiv2004

A limitation of the Bruggeman formalism for homogenization

The Bruggeman formalism provides an estimate of the effective permittivity of a particulate composite medium comprising two component mediums. The Bruggeman estimate is required to lie within the Wiener bounds and the Hashin-Shtrikman bounds. Considering the homogenization of weakly dissipative component mediums characterized by relative permittivities with real parts of opposite signs, we show that the Bruggeman estimate may not be not physically reasonable when the component mediums are weakly dissipative; furthermore, both the Wiener bounds and the Hashin-Shtrikman bounds exhibit strong resonances.

physics.optics↗
arXiv2003

A Conjugation Symmetry in Linear Electromagnetism, in Extension of Materials with Negative Real Permittivity and Permeability Scalars

If all space is occupied by a linear bianisotropic material--whether homogeneous or not--then the concurrent replacements of the permittivity and the impermeability tensors by the negatives of their respective complex conjugates and of the magnetoelectric tensors by their respective complex conjugates (in the Boys-Post representation) imply the conjugation of both E and H, in the absence of externally impressed sources. This conjugation symmetry in linear electromagnetism has observable consequences when the linear bianisotropic material occupies a bounded region.

physics.optics↗
arXiv2003

Restricted equivalence of paired epsilon-negative and mu-negative layers to a negative phase-velocity material ({\em alias} left-handed material)

The time-harmonic electromagnetic responses of (a) a bilayer made of an epsilon-negative layer and a mu-negative layer, and (b) a single layer of a negative phase-velocity material are compared. Provided all layers are electrically thin, a restricted equivalence between (a) and (b) exists. The restricted equivalence depends on the linear polarization state and the transverse wavenumber. Implications for perfect lenses and parallel-plate waveguides are considered.

physics.class-ph↗
arXiv2003

Positive and Negative Goos-Hanchen Shifts and Negative Phase--Velocity Mediums (alias Left-Handed Materials)

On total reflection from a half-space filled with an isotropic, homogeneous, weakly dissipative, dielectric-magnetic medium with negative phase-velocity (NPV) characteristics, it is shown here that a linearly polarized beam can experience either a negative or a positive Goos-Hanchen shift. The sign of the shift depends on the polarization state of the beam as well as on the signs of the real parts of the permittivity and the permeability of the NPV medium.

physics.optics↗
arXiv2002

The negative index of refraction demystified

We study electromagnetic wave propagation in mediums in which the effective relative permittivity and the effective relative permeability are allowed to take any value in the upper half of the complex plane. A general condition is derived for the phase velocity to be oppositely directed to the power flow. That extends the recently studied case of propagation in mediums for which the relative permittivity and relative permeability are both simultaneously negative, to include dissipation as well. An illustrative case study demonstrates that in general the spectrum divides into five distinct regions.

physics.class-ph↗
arXiv2002

On planewave remittances and Goos-Haenchen shifts of planar slabs with negative real permittivity and permeability

Two results about the planewave response of an isotropic, dielectric--magnetic, homogeneous, planar slab are deduced when the real parts of both the permittivity and the permeability are altered from positive to negative. First, the reflection and the transmission coefficients suffer phase reversals without change in their respective magnitudes. Second, the Goos-Haenchen shifts experienced by beams on total reflection reverse their directions.

physics.class-ph↗