Generalization of the coupled dipole method to periodic structures

We present a generalization of the coupled dipole method to the scattering of light by arbitrary periodic structures. This new formulation of the coupled dipole method relies on the same direct-space discretization scheme that is widely used to study the scattering of light by finite objects. Therefore, all the knowledge acquired previously for finite systems can be transposed to the study of periodic structures.Comment: 5 pages, 2 figures, and 1 tabl

Selective nanomanipulation using optical forces

We present a detailed theoretical study of the recent proposal for selective nanomanipulation of nanometric particles above a substrate using near-field optical forces [Chaumet {\it et al.} Phys. Rev. Lett. {\bf 88}, 123601 (2002)]. Evanescent light scattering at the apex of an apertureless near-field probe is used to create an optical trap. The position of the trap is controlled on a nanometric scale via the probe and small objects can be selectively trapped and manipulated. We discuss the influence of the geometry of the particles and the probe on the efficiency of the trap. We also consider the influence of multiple scattering among the particles on the substrate and its effect on the robustness of the trap.Comment: 12 pages, 17 figure

Optical binding of magnetodielectric Rayleigh particles

We present a theoretical and numerical study of the optical binding and optical torque between two Rayleigh particles with arbitrary, complex, scalar dielectric permittivity and magnetic permeability. We use a computational approach based on the discrete dipole approximation to derive the optical force and torque experienced by the particles when illuminated by a linearly or circularly polarized plane wave. We show that optical binding between magnetodielectic particles is qualitatively different from the traditional case involving dielectric particles only. In particular, we show that for certain configurations, the system of two magnetodielectric particles will experience a long-range optical torque whose amplitude envelope does not decay with the separation between the particles. © 2013 American Physical Society

Optical binding of particles with or without the presence of a flat dielectric surface

Optical fields can induce forces between microscopic objects, thus giving rise to new structures of matter. We study theoretically these optical forces between two spheres, either isolated in water, or in presence of a flat dielectric surface. We observe different behavior in the binding force between particles at large and at small distances (in comparison with the wavelength) from each other. This is due to the great contribution of evanescent waves at short distances. We analyze how the optical binding depends of the size of the particles, the material composing them, the wavelength and, above all, on the polarization of the incident beam. We also show that depending on the polarization, the force between small particles at small distances changes its sign. Finally, the presence of a substrate surface is analyzed showing that it only slightly changes the magnitudes of the forces, but not their qualitative nature, except when one employs total internal reflection, case in which the particles are induced to move together along the surface.Comment: 8 pages, 9 figures, and 1 tabl

Coupled-dipole method in time domain

We present a time-domain formulation of electrodynamics based on the self-consistent derivation of the electromagnetic field in a linear, dispersive, lossy object via the coupled dipole method. © 2008 Optical Society of America

Discrete dipole approximation for time-domain computation of optical forces on magnetodielectric scatterers

We present a general approach, based on the discrete dipole approximation (DDA), for the computation of the exchange of momentum between light and a magnetodielectric, three-dimensional object with arbitrary geometry and linear permittivity and permeability tensors in time domain. The method can handle objects with an arbitrary shape, including objects with dispersive dielectric and/or magnetic material responses. © 2011 Optical Society of America

Invisibility and supervisibility: Radiation dynamics in a discrete electromagnetic cloak

We study the radiation dynamics of an electric dipole source placed near or inside a discrete invisibility cloak. We show that the main features of radiation dynamics can be understood in terms of the interaction of the source with a nonideal cloak in which local-field effects associated with the discrete geometry play a crucial role. As a result, radiation dynamics in a discrete cloak can differ drastically from what a source would experience in an ideal, continuous cloak. This can lead, for instance, to an enhancement of the emission by the cloak, thus making the source more visible to an outside observer than it would be without the cloak. The two main physical mechanisms for enhanced, or inhibited, radiation dynamics are the coupling of the source to leaky modes inside the cloak, and the coupling of the source with the lattice of the discrete cloak, via the local field. We also explore the robustness of the effect to material dispersion and losses

Discrete dipole approximation for the study of radiation dynamics in a magnetodielectric environment

We develop a general computational approach, based on the discrete dipole approximation, for the study of radiation dynamics near or inside an object with arbitrary linear dielectric permittivity, and magnetic permeability tensors. Our method can account for dispersion and losses and provides insight on the role of local-field corrections in discrete magnetodielectric structures. We illustrate our method in the case of a source inside a magneto-dielectric, isotropic sphere for which the spontaneous emission rate of a source can be computed analytically. We show that our approach is in excellent agreement with the exact result, providing an approach capable of handling both the electric and magnetic response of advanced metamaterials. © 2010 Optical Society of America

Webmapping, archéologie et Géoportail

The “Géoportail” is a French creation responding to the INSPIRE European directive; the website http://www.geoportail.fr/ is published by IGN (Institut Géographique National) and allows for easy and free or low cost access to many geographic reference data. IGN develops various kinds of services like visualisation, download, formats and coordinates transformation and API Géoportail; it publishes these services independently or in partnership with other public agencies, companies or associations. Archaeologists may use the API Géoportail to augment the value of their results or to show partial results on a public website http://www.geoportail.fr/

Optical binding of electrically small magnetodielectric particles

An ensemble of spherical particles with arbitrary dielectric permittivity and magnetic penneability was considered in the dipole approximation. Each particle was described by complex electric and magnetic polarizabilities. A computational approach based on the coupled dipole method, also called the discrete dipole approximation, was used to derive the optical force experienced by each particle due to an incident electromagnetiG..Ji.eld and the fields scattered by all other particles. This approach is general and can handle material dispersion and losses. In order to illustrate this approach, we studied the case of two spherical particles separated by a distance d, and illuminated by an incident plane wave whose wave vector is normal to the axis of the particles. We computed the optical force experienced by each particle in the direction of the beam (radiation pressure), and perpendicular to the beam (optical binding) for particles with positive and negative refractive indices. We also considered the effect of material losses