I. E. Psarobas

Phononic crystals with planar defects

We study the effect of planar defects in phononic crystals of spherical scatterers. It is shown that a plane of impurity spheres introduces modes of vibration of the elastic field localized on this plane at frequencies within a frequency gap of a pure phononic crystal; these show up as sharp resonances in the transmittance of elastic waves incident on a slab of the crystal. A periodic arrangement of impurity planes along a given direction creates narrow impurity bands with a width which depends on the position of these bands within the frequency gap of the pure crystal and on the separation between the impurity planes. We show how a slight deviation from periodicity (one impurity plane is different from the rest) reduces dramatically the transmittance of elastic waves incident on a slab of the crystal.

A layer-multiple-scattering method for phononic crystals and heterostructures of such☆

We present a computer program to calculate the frequency band structure of an infinite phononic crystal, and the transmission, reflection and absorption of elastic waves by a slab of this crystal. The crystal consists of a stack of identical slices parallel to a given surface; the slice may consist of multilayers of non-overlapping spheres of given periodicity parallel to the surface and homogeneous plates. The elastic coefficients of the various components of the crystal may be complex functions of the frequency.

Absolute spectral gaps for infrared light and hypersound in three-dimensional metallodielectric phoxonic crystals

The study of the propagation of waves in inhomogeneous media is a problem of wide interest because of its implications in technology and the broad view that can provide in understanding a large area of physical problems. 1 In particular, classical wave transport in periodic media can provide the means to control light, sound or both with the development of so-called classical spectral gap materials. One of the most important properties of such materials is the existence of frequency regions, the so-called band gaps, where propagation is not allowed and all waves are decaying. Such effects are established for both electromagnetic EMRefs. 2 and 3 and acoustic 4,5 fields. Photonic crystals with submicron periodicity have band gaps in the visible and near infrared part of the spectrum promising applications in optical sensors and telecommunications. Phononic crystals on the other hand are mainly studied in more macroscopic length scales in the order of millimeter. Only very recently, elastic composites with submicron periodicity were demonstrated with acoustic band gaps in the gigahertz range. 6,7 Tailoring both acoustic and optical properties on the same system can lead to applications which require better control of the acousto-optic interaction. 8 It was proposed that phoxonic crystals having dual spectral gaps for both photons and

Acoustic properties of colloidal crystals

We present a systematic study of the frequency band structure of acoustic waves in crystals consisting of nonoverlapping solid spheres in a fluid. We consider colloidal crystals consisting of polystyrene spheres in water,and an opal consisting of close-packed silica spheres in air. The opal exhibits an omnidirectional frequency gap of considerable width; the colloidal crystals do not. The physical origin of the bands are discussed for each case in some detail. We also present results on the transmittance of finite slabs of the above crystals.

Viscoelastic response of sonic band-gap materials

A brief report is presented on the effect of viscoelastic losses in a high density contrast sonic band-gap material of close-packed rubber spheres in air. The scattering properties of such a material are computed with an on-shell multiple scattering method, properties which are compared with the lossless case. The existence of an appreciable omnidirectional gap in the transmission spectrum, when losses are present, is also reported.

On wave propagation in inhomogeneous systems

Abstract We present a theory of electron, electromagnetic, and elastic wave propagation in systems consisting of non-overlapping scatterers in a host medium. The theory provides a framework for a unified description of wave propagation in three-dimensional periodic structures, finite slabs of layered structures, and systems with impurities: isolated impurities, impurity aggregates, or randomly distributed impurities. We point out the similarities and differences between the different cases considered, and discuss the numerical implementation of the formalism.We present a theory of electron, electromagnetic, and elastic wave propagation in systems consisting of non-overlapping scatterers in a host medium. The theory provides a framework for a unified description of wave propagation in three-dimensional periodic structures, finite slabs of layered structures, and systems with impurities: isolated impurities, impurity aggregates, or randomly distributed impurities. We point out the similarities and differences between the different cases considered, and discuss the numerical implementation of the formalism.

The layer multiple-scattering method applied to phononic crystals

Abstract After a brief description of the layer multiple scattering method as applied to phononic crystals, we present some results obtained by this method, relating to: crystals of polystyrene spheres in water; crystals of silica spheres in air; and crystals of steel spheres in polyester. We relate the transmission characteristics of slabs of these ma terials to the complex band structure of the corresponding infinite crystals. We emphasize aspects of the underlying physics which have not been discussed previously.

Photonic crystals of chiral spheres

We examined the properties of photonic crystals that consist of nonoverlapping chiral spheres in a dielectric medium. We considered the effect of the chiral property of the spheres on the frequency band structure of the electromagnetic field in the crystal and on the transmittance properties of a slab of the crystal, and we estimated the optical activity of the crystal.

Chiral phononic structures

A full elastodynamic multiple scattering approach is employed to investigate the behavior of nonreciprocal phononic structures consisting of periodic helical assemblies of spheres. We report on cases of dense and sparse helical chains, cases with size variation and low frequency behavior.

Dynamically tuned zero-gap phoXonic systems

A full electrodynamic and elastodynamic multiple scattering approach is employed to describe the optical and acoustic modes, and to account for their mutual interaction both in time and frequency domain in one-dimensional phoXonic crystal slabs. We report on the occurrence of nonlinear acousto-optic interactions and demonstrate the effect of the hypersonic tuning of photonic Dirac points in the optical and telecom frequencies. Potential sensing capabilities are examined under moderate acousto-optic interactions in the proximity of crossing photonic bands enabling light to slow down, stop or reverse. Quarter-wave stack arrangements are considered in the optical (polymeric-based slab) and IR (Si-based slab) frequencies. Such structures support two bands that cross symmetrically, without forming a photonic gap. In the vicinity of the Dirac point (crossing bands), dynamic tuning achieves efficient transfer of energy between the bands using weak and slow modulations of the wave velocity. Finally, through hypersonic light modulation, we may achieve efficient electromagnetic pulse reversal and switching.