1,721,044 research outputs found
Anisotropic beam spreading in uniaxial crystals
No full textThe anisotropic spreading of a paraxial beam propagating orthogonally to the optical axis inside a uniaxial crystal is
investigated. The lack of rotational invariance around the propagation direction suggests to consider the mean square
width (MSW) of the beam in any transverse direction, which turn out to be a quadratic form of the unit vector associated
with the considered direction and to depend quadratically on the propagation distance z. The z-evolution of the
MSW is compared with its standard evolution in vacuum. A simple connection is establish, for cylindrically symmetric
input fields, between the anisotropic and the free space MSW, which in particular allows us to easily picture the
spreading of the beam by means of a simple geometrical construction. The particular case of an astigmatic Gaussian
beam is analytically carried out
Nonlocal homogenization theory in metamaterials: Effective electromagnetic spatial dispersion and artificial chirality
No full textWe develop, from first principles, a general and compact formalism for predicting the electromagnetic response of a metamaterial with nonmagnetic inclusions in the long-wavelength limit, including spatial dispersion up to the second order. Specifically, by resorting to a suitable multiscale technique, we show that the effective medium permittivity tensor and the first- and second-order tensors describing spatial dispersion can be evaluated by averaging suitable spatially rapidly varying fields, each satisfying electrostatic-like equations within the metamaterial unit cell. For metamaterials with negligible second-order spatial dispersion, we exploit the equivalence of first-order spatial dispersion and reciprocal bianisotropic electromagnetic response to deduce a simple expression for the metamaterial chirality tensor. Such an expression allows us to systematically analyze the effect of the composite spatial symmetry properties on electromagnetic chirality. We find that even if a metamaterial is geometrically achiral, i.e., it is indistinguishable from its mirror image, it shows pseudo-chiral-omega electromagnetic chirality if the rotation needed to restore the dielectric profile after the reflection is either a 0 degrees or 90 degrees rotation around an axis orthogonal to the reflection plane. These two symmetric situations encompass two-dimensional and one-dimensional metamaterials with chiral response. As an example admitting full analytical description, we discuss one-dimensional metamaterials whose single chirality parameter is shown to be directly related to the metamaterial dielectric profile by quadratures
Kapitza homogenization of deep gratings for designing dielectric metamaterials
No full textWe theoretically investigate the homogenization of the dielectric response to transverse electric waves of a transverse grating characterized by the Kapitza condition; i.e., the permittivity is rapidly modulated with a modulation depth scaling as the large wavelength-to-modulation-period ratio. We show that the resulting effective dielectric permittivity, in addition to the standard average of the underlying dielectric profile, has a further contribution arising from the fast and deep dielectric modulation. Such a contribution turns out to be comparable with the other one and hence can provide an additional method for designing dielectric metamaterials. As an example, we discuss an effective metal-to-dielectric transition produced by the Kapitza contribution obtained by changing the grating depth, a remarkable result for applications involving epsilon-near-zero metamaterial design. (C) 2013 Optical Society of Americ
Effective medium theory for kapitza stratified media: Diffractionless propagation
No full textWe show that in the presence of a rapidly modulated dielectric permittivity with a large modulation depth (Kapitza medium) a novel and robust regime of diffractionless electromagnetic propagation occurs. This happens when the mean value to depth ratio of the dielectric profile is comparable to the small ratio between the modulation period and the wavelength. We show that the standard effective medium theory is inadequate to describe the proposed regime and that its occurrence is not substantially hampered by medium losses. We check the feasibility of the proposed regime by means of a large modulation depth metal-dielectric layered medium whose electromagnetic behavior is analytically investigated. DOI: 10.1103/PhysRevLett.110.14390
Harnessing quadratic optical response of two-dimensional materials through active microcavities
No full textWe propose a method for efficiently harnessing the quadratic optical response of two-dimensional graphenelike materials by theoretically investigating second-harmonic generation from a current biased sheet placed within a planar active microcavity. We show that, by tuning the cavity to resonate at the second-harmonic frequency, a highly efficient frequency doubling process is achieved (several orders of magnitude more efficient than the free-standing sheet). The efficiency of the process is not due to phase matching, which is forbidden by the localization of the nonlinear quadratic response on the two-dimensional atomic layered material, but stems from the interplay between the two-dimensional planar geometry of the nonlinear medium and the field oscillation within the active cavity near its threshold. The suggested method can easily be extended to different wave interactions and nonlinearities, and therefore it can represent a basic tool for efficiently exploiting nonlinear optical properties of two-dimensional materials
Graphene-nonlinearity unleashing at lasing threshold in graphene-assisted cavities
No full textWe investigate the nonlinear optical features of a graphene sheet embedded in an active cavity and we show that, when tuned near its lasing threshold, the cavity is able to isolate the spatially localized graphene nonlinearity thus producing a very strong nonlinear device response with multivalued features. As opposed to standard situations where the small thickness of the graphene sheet hampers its remarkable nonlinear optical properties to be exploited, in our scheme the strong nonlinear optical regime is mainly triggered by the very intrinsic planar localization of graphene nonlinearity. The proposed strategy for exploiting graphene nonlinearity through its unleashing could open novel routes for conceiving ultraefficient nonlinear photonic devices
Kapitza dielectric metamaterials
No full textWe theoretically investigate the homogenization of the dielectric response of Kapitza dielectric metamaterials, i.e. materials hosting a subwavelength periodic grating whose depth scales as the large wavelength to modulation period ratio. We show that the standard effective medium theory is inadequate to describe the propagation in the considered metamaterials and, most importantly, a novel regime of diffractionless propagation occurs for transverse magnetic waves
Ciattoni A. et Veyret Y. (dir.), Les fondamentaux de la géographie
No full textBoyer Jean-Claude. Ciattoni A. et Veyret Y. (dir.), Les fondamentaux de la géographie. In: Annales de Géographie, t. 113, n°637, 2004. p. 332
Electric Directional Steering of Cathodoluminescence from Graphene-Based Hybrid Nanostructures
No full textControlling directional emission of nanophotonic radiation sources is fundamental to tailor radiation-matter interaction and to conceive highly efficient nanophotonic devices for on-chip wireless communication and information processing. Nanoantennas coupled to quantum emitters have proven to be very efficient radiation routers, while electrical control of unidirectional emission has been achieved through inelastic tunneling of electrons. Here we prove that the radiation emitted from the interaction of a high-energy electron with a graphene-nanoparticle composite has beams in directions that can be made to continuously span the full azimuthal circle even through small variations of the graphene Fermi energy. Emission directionality stems from the interference between the double-cone-shaped electron transition radiation and the nanoparticle dipolar diffraction radiation. Tunability is enabled since the composite hybrid plasmonic resonances and the graphene plasmon polariton phase drive the nanoparticle dipole moment, thus providing an effective electrical reorientation of the nanoantenna. The flexibility of our method provides a way to exploit graphene plasmon physics to conceive nanosources with ultrafast reconfigurability
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