Showing papers by "A. A. Maradudin published in 1988"

Bistability and switching in nonlinear prism coupling

Abstract: We demonstrate that when a nonlinear coupler is operated in the switching regime, small amounts of either nonlocality in the optically induced refractive index change or of longitudinal feedback can lead to optical bistability. Outside the switching regime, there is a threshold for the amount of nonlocality or feedback required for bistability. The diverse predictions of previous theoretical formulations are therefore reconciled.

Self-consistent-screening calculation of surface-phonon dispersion curves at the (110) surface of aluminum.

Abstract: We have calculated the dynamical matrix for an aluminum slab bounded by a pair of (110) surfaces using a self-consistent implementation of pseudopotential perturbation theory. The screening response of the conduction electrons to the field of the ions is obtained within the local-density approximation of density-functional theory. Both relaxed and unrelaxed geometries are treated. We present numerical results for the dispersion curves of surface phonons. Comparison is made with recent theoretical and experimental results.

Shear horizontal acoustic surface shape resonances.

Abstract: We have calculated the discrete frequencies of the elastic vibration modes localized in the vicinity of a rectangular ridge fabricated from one material that is bonded to the planar surface of a substrate of a second material. These acoustic surface shape resonances correspond to a displacement field that is polarized parallel to the ridge (i.e., it has shear horizontal polarization). The frequencies of these modes are complex because the range in which they occur overlaps the continuum of frequencies of the bulk and surface modes of the substrate, so that they can radiate energy into the latter. The modes are damped thereby, and this damping depends sensitively on the aspect ratio of the ridge and on the material parameters of the ridge and substrate.

k gaps for surface polaritons on gratings.

Abstract: On montre que des bandes interdites k peuvent apparaitre dans les courbes de dispersion des polaritons de surface sur des reseaux metalliques, ainsi que determine par des mesures de reflectivite en polarisation p. On presente des calculs exacts de la reflectivite d'une dent de scie symetrique sur Ag, et obtient des expressions analytiques expliquant le comportement observe

Molecular dynamics of Rayleigh waves in Lennard-Jones crystals.

Abstract: The frequency- and wave-vector-dependent spectral densities of the displacement correlation functions for atoms at the surface and at the midplane of a slab consisting of twenty-one (001) layers of an fcc crystal are calculated at two temperatures by means of a molecular-dynamics computer simulation. The atoms in the slab interact through Lennard-Jones (6-12) potentials, and anharmonic effects of all orders are taken into account. The dispersion and lifetimes of the Rayleigh waves on the surfaces of the slab are determined, as well as the changes in the interplanar spacings in the vicinity of the surfaces.

Self-Consistent Theory of Surface Phonon Dispersion Curves at the (110) Surface of Aluminum

Abstract: Considerable progress has been made in recent years in the experimental determination of surface phonon dispersion curves for metals by inelastic helium atom scattering [1] and by electron energy loss spectroscopy [2]. Relatively little progress has been made, however, in the first-principles calculation of surface phonon dispersion curves for metals. In the pseudopotential perturbation-theoretic calculations of CALANDRA et al.[3] for alkali metal surfaces, the ground state and response properties of the electronic subsystem were calculated using the infinite-barrier model (IBM) for the electron wave functions. Surface phonon dispersion curves were then calculated from the response function. Although this procedure is relatively simple, it does not provide a self-consistent treatment of the metal surface. In a different approach HO and BOHNEN [4] used the local density approximation (LDA) to density functional theory and the frozen-phonon method to calculate the surface phonon frequencies for Al(110) at a few high symmetry points on the boundary of the surface Brillouin zone. They then employed a force constant model to interpolate between these points and the origin and thus obtain surface phonon dispersion curves. Clearly, such a calculation is a hybrid and not a bona fide first-principles calculation of surface phonon dispersion curves.