Search results for "nanotechnologies"
showing 10 items of 209 documents
Static chiral Willis continuum mechanics for three-dimensional chiral mechanical metamaterials
2019
International audience; Recent static experiments on twist effects in chiral three-dimensional mechanical metamaterials have been discussed in the context of micropolar Eringen continuum mechanics, which is a generalization of linear Cauchy elasticity. For cubic symmetry, Eringen elasticity comprises nine additional parameters with respect to linear Cauchy elasticity, of which three directly influence chiral effects. Here, we discuss the behavior of the static case of an alternative generalization of linear Cauchy elasticity, the Willis equations. We show that in the homogeneous static cubic case, only one additional parameter with respect to linear Cauchy elasticity results, which directly…
Resonance quality, radiative/ohmic losses and modal volume of Mie plasmons
2012
International audience; Molecular sytems are efficiently coupled to metal nanoparticles via the excitation of localized surface plasmons-polaritons (SPPs). The coupling strength between SPP and emitters can be estimated from the ratio Q/V where Q and V refer to the mode quality factor and effective volume, respectively. In this letter, we investigate in details the properties of Mie plasmons supported by a metallic nanosphere (Q-factor, radiative and ohmic losses, modal volume). We particularly focus on the difficulty to unambiguously define the modal volumes of localized SPPs. This leads us to propose two definitions; the first one is based on Purcell factor for a dipolar emitter in close …
Fluorescence relaxation in the near-field of a mesoscopic metallic particle : distance dependence and role of plasmon modes
2008
International audience; We analytically and numerically analyze the fluorescence decay rate of a quantum emitter placed in the vicinity of a spherical metallic particle of mesoscopic size (i.e with dimensions comparable to the emission wavelength). We discuss the efficiency of the radiative decay rate and non–radiative coupling to the particle as well as their distance dependence. The electromagnetic coupling mechanisms between the emitter and the particle are investigated by analyzing the role of the plasmon modes and their nature (dipole, multipole or interface mode). We demonstrate that near-field coupling can be expressed in a simple form verifying the optical theorem for each particle …
Surface-Wave Coupling to Single Phononic Subwavelength Resonators
2017
International audience; We propose to achieve manipulation of mechanical vibrations at the micron scale by exploiting the interaction of individual, isolated mechanical resonators with surface acoustic waves. We experimentally investigate a sample consisting of cylindrical pillars individually grown by focused-ion-beam-induced deposition on a piezoelectric substrate, exhibiting different geometrical parameters and excited by a long-wavelength surface elastic wave. The mechanical displacement is strongly confined in the resonators, as shown by field maps obtained by laser scanning interferometry. A tenfold displacement field enhancement compared to the vibration at the surface is obtained, r…
Purcell factor for a point-like dipolar emitter coupled to a two-dimensional plasmonic waveguide
2011
International audience; We theoretically investigate the spontaneous emission of a point-like dipolar emitter located near a two-dimensional plasmonic waveguide of arbitrary form. We invoke an explicit link with the density of modes of the waveguide describing the electromagnetic channels into which the emitter can couple. We obtain a closed form expression for the coupling to propagative plasmon, extending thus the Purcell factor to plasmonic configurations. Radiative and nonradiative contributions to the spontaneous emission are also discussed in detail.
Second order diffractive optical elements in a spatial light modulator with large phase dynamic range
2013
International audience; A study of the diffraction efficiency of a spatial light modulator with a large dynamic phase range is reported. We use a phase-only device that reaches 4π phase modulation depth for the wavelength of 454 nm. This allows operating phase-only diffractive optical elements in the second harmonic diffraction order, instead of in the usual first diffraction order. This type of implementation shows advantages in terms of resolution and diffraction efficiency. Experimental results are reported for blazed diffractive gratings and diffractive lenses.
Density-near-zero using the acoustically induced transparency of a Fano acoustic resonator
2016
International audience; We report experimental results of near-zero mass density involving an acoustic metamaterial supporting Fano resonance. For this, we designed and fabricated an acoustic resonator with two closely coupled modes and measured its transmission properties. Our study reveals that the phenomenon of acoustically induced transparency is accompanied by an effect of near-zero density. Indeed, the dynamic effective parameters obtained from experimental data show the presence of a frequency band where the effective mass density is close to zero, with high transmission levels reaching 0.7. Furthermore, we demonstrate that such effective parameters lead to wave guiding in a 90-degre…
Isotropic Chiral Acoustic Phonons in 3D Quasicrystalline Metamaterials.
2020
International audience; The elastic properties of three-dimensional (3D) crystalline mechanical metamaterials, unlike those of amorphous structures, are generally strongly anisotropic—even in the long-wavelength limit and for highly symmetric crystals. Aiming at isotropic linear elastic wave propagation, we therefore study 3D periodic approximants of 3D icosahedral quasicrystalline mechanical metamaterials consisting of uniaxial chiral metarods. Considering the increasing order of the approximants, we approach nearly isotropic effective speeds of sound and isotropic acoustical activity. The latter is directly connected to circularly polarized 3D metamaterial chiral acoustic phonons—for all …
Elastodynamic behavior of mechanical cloaks designed by direct lattice transformations
2020
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Elastic Metasurfaces for Deep and Robust Subwavelength Focusing and Imaging
2021
International audience; Metasurfaces are planar metamaterials with a flat surface and a subwavelength thickness that are able to shape arbitrary wave fronts such as focusing or imaging. There is a broad interest in the literature about subwavelength focusing and imaging based on bulk metamaterials while the utilization of metasurfaces for elastic waves has rarely been reported. Here, we present a type of elastic metasurface consisting of a line of gradient resonant pillars for robust deep subwavelength focusing and imaging of elastic waves in a plate. Numerical approaches supported by analytic Huygens-Fresnel demonstrations show that the subwavelength full width at half maximum (FWHM) behav…