Schittny R.,Karlsruhe Institute of Technology |
Kadic M.,Karlsruhe Institute of Technology |
Guenneau S.,Fresnel Institute |
Wegener M.,Karlsruhe Institute of Technology
Physical Review Letters | Year: 2013
It was recently shown theoretically that the time-dependent heat conduction equation is form invariant under curvilinear coordinate transformations. Thus, in analogy to transformation optics, fictitious transformed space can be mapped onto (meta)materials with spatially inhomogeneous and anisotropic heat-conductivity tensors in the laboratory space. On this basis, we design, fabricate, and characterize a microstructured thermal cloak that molds the flow of heat around an object in a metal plate. This allows for transient protection of the object from heating while maintaining the same downstream heat flow as without object and cloak. © 2013 American Physical Society.
Guenneau S.,Fresnel Institute |
Amra C.,Fresnel Institute |
Veynante D.,École Centrale Paris
Optics Express | Year: 2012
We adapt tools of transformation optics, governed by a (elliptic) wave equation, to thermodynamics, governed by the (parabolic) heat equation. We apply this new concept to an invibility cloak in order to thermally protect a region (a dead core) and to a concentrator to focus heat flux in a small region. We finally propose a multilayered cloak consisting of 20 homogeneous concentric layers with a piecewise constant isotropic diffusivity working over a finite time interval (homogenization approach). © 2012 Optical Society of America.
Jang M.,California Institute of Technology |
Sentenac A.,Fresnel Institute |
Yang C.,California Institute of Technology
Optics Express | Year: 2013
Isotropic optical focusing-the focusing of light with axial confinement that matches its lateral confinement, is important for a broad range of applications. Conventionally, such focusing is achieved by overlapping the focused beams from a pair of opposite-facing microscope objective lenses. However the exacting requirements for the alignment of the objective lenses and the method's relative intolerance to sample turbidity have significantly limited its utility. In this paper, we present an optical phase conjugation (OPC)-assisted isotropic focusing method that can address both challenges. We exploit the time-reversal nature of OPC playback to naturally guarantee the overlap of the two focused beams even when the objective lenses are significantly misaligned (up to 140 microns transversely and 80 microns axially demonstrated). The scattering correction capability of OPC also enabled us to accomplish isotropic focusing through thick scattering samples (demonstrated with samples of ∼7 scattering mean free paths). This method can potentially improve 4Pi microscopy and 3D microstructure patterning. © 2013 Optical Society of America.
Busson M.P.,ESPCI ParisTech |
Rolly B.,Fresnel Institute |
Stout B.,Fresnel Institute |
Bonod N.,Fresnel Institute |
Bidault S.,ESPCI ParisTech
Nature Communications | Year: 2012
A photon interacts efficiently with an atom when its frequency corresponds exactly to the energy between two eigenstates. But at the nanoscale, homogeneous and inhomogeneous broadenings strongly hinder the ability of solid-state systems to absorb, scatter or emit light. By compensating the impedance mismatch between visible wavelengths and nanometre-sized objects, optical antennas can enhance light-matter interactions over a broad frequency range. Here we use a DNA template to introduce a single dye molecule in gold particle dimers that act as antennas for light with spontaneous emission rates enhanced by up to two orders of magnitude and single photon emission statistics. Quantitative agreement between measured rate enhancements and theoretical calculations indicate a nanometre control over the emitter-particle position while 10 billion copies of the target geometry are synthesized in parallel. Optical antennas can thus tune efficiently the photo-physical properties of nano-objects by precisely engineering their electromagnetic environment. © 2012 Macmillan Publishers Limited. All rights reserved.
Durt T.,Fresnel Institute
International Journal of Modern Physics B | Year: 2013
The role played by time in the quantum theory is still mysterious by many aspects. In particular it is not clear today whether the distribution of decay times of unstable particles could be described by a time operator (TO). As we shall discuss, different approaches to this problem (one could say interpretations) can be found in the literature on the subject. As we shall show, it is possible to conceive crucial experiments aimed at distinguishing the different approaches, by measuring with accuracy the statistical distribution of decay times of entangled particles. Such experiments can be realized in principle with entangled kaon pairs. © 2013 World Scientific Publishing Company.
Gao L.,Fresnel Institute |
Lemarchand F.,Fresnel Institute |
Lequime M.,Fresnel Institute
Optics Express | Year: 2012
In the present paper we determine the optical constants and thicknesses of multilayer thin film stacks, in the visible and near infrared ranges. These parameters are derived from the transmittance and reflectance spectra measured by a spectrophotometer, for several angles of incidence. Several examples are studied, from a simple single layer structure up to a 22-layer dielectric filter. We show that the use of a large number of incidence angles is an effective means of reducing the number of mathematical solutions and converging on the correct physical solution when the number of layers increases. More specifically, we provide an indepth discussion of the approach used to extract the index and thickness of each layer, which is achieved by analysing the various mathematical solutions given by a global optimization procedure, based on as little as 6 and as many as 32 variable parameters. The results show that multiple incidences, lead to the true solution for a filter with a large number of layers. In the present study, a Clustering Global Optimization algorithm is used, and is shown to be efficient even for a high number of variable parameters. Our analysis allows the accuracy of the reverse engineering process to be estimated at approximately 1 nm for the thickness, and 2 10 -3 for the index of each layer in a 22-layer filter. © 2012 Optical Society of America.
Huck A.,Fresnel Institute |
Guillaume M.,Fresnel Institute |
Blanc-Talon J.,Office for Advanced Research and Innovation MRIS
IEEE Transactions on Geoscience and Remote Sensing | Year: 2010
This paper considers the problem of unsupervised spectral unmixing for hyperspectral image analysis. Each observed pixel is assumed to be a noisy linear mixture of pure material spectra, namely, endmembers. The mixing coefficients, usually called abundances, are constrained to positive and summed to unity. The proposed unmixing approach is based on the nonnegative matrix factorization (NMF) framework, which considers the physical constraints of the problem, including the positivity of the endmember spectra and abundances. However, the basic NMF formulation has degenerated solutions and suffers from nonconvexity limitations. We consider here a regularization function, called dispersion, which favors the solution such that the endmember spectra have minimum variances. Such a solution encourages the recovered spectra to be flat, preserving the possible spectral singularities (peaks and sharp variations). The regularized criterion is minimized with a projected gradient (PG) scheme, and we propose a new step-size estimation technique to fasten the PG convergence. The derived algorithm is called MiniDisCo, for minimum dispersion constrained NMF. We experimentally compare MiniDisCo with the recently proposed algorithm. It is shown to be particularly robust to the presence of flat spectra, to a possible a priori overestimation of the number of endmembers, or if the amount of observed spectral pixels is low. In addition, experiments show that the considered regularization correctly overcomes the degeneracy and nonconvexity problems, leading to satisfactory unmixing accuracy. We include a comparative analysis of a real-world scene. © 2006 IEEE.
Munhoz F.,Fresnel Institute |
Rigneault H.,Fresnel Institute |
Brasselet S.,Fresnel Institute
Physical Review Letters | Year: 2010
Polarization-resolved coherent anti-Stokes Raman scattering (CARS) is usually applied to measure the depolarization ratio in solutions or evidence orientation effects in anisotropic media. We present an extensive approach based on multiple-field polarization-resolved CARS, in order to unravel the complexity of vibrational resonances up to the fourth-order symmetry, at the microscopic scale in nonisotropic media. The CARS polarized signals measured under a continuous variation of the incident pump and/or Stokes excitation beams are analyzed using a full tensorial picture both in the nonresonant and resonant regimes. This method evidences the strong influence of vibrational symmetries on polarized CARS, and more specifically the occurrence of Kleinman symmetry deviations at the vicinity of the Raman lines frequencies. This technique, illustrated on a cubic symmetry crystal, is general and can be applied to other medium symmetries. © 2010 The American Physical Society.
Kadic M.,Fresnel Institute |
Guenneau S.,Fresnel Institute |
Enoch S.,Fresnel Institute
Optics Express | Year: 2010
We adapt tools of transformation optics to surface plasmon polaritons (SPPs) propagating at the interface between two anisotropic media of opposite permittivity sign. We identify the role played by entries of anisotropic heterogeneous tensors of permittivity and permeability -deduced from a coordinate transformation- in the dispersion relation governing propagation of SPPs. We apply this concept to an invisibility cloak, a concentrator and a rotator for SPPs. © 2010 Optical Society of America.
Baffou G.,Fresnel Institute |
Rigneault H.,Fresnel Institute
Physical Review B - Condensed Matter and Materials Physics | Year: 2011
We investigate theoretically and numerically the thermodynamics of gold nanoparticles immersed in water and illuminated by a femtosecond-pulsed laser at their plasmonic resonance. The spatiotemporal evolution of the temperature profile inside and outside is computed using a numerical framework based on a Runge-Kutta algorithm of the fourth order. The aim is to provide a comprehensive description of the physics of heat release of plasmonic nanoparticles under pulsed illumination, along with a simple and powerful numerical algorithm. In particular, we investigate the amplitude of the initial instantaneous temperature increase, the physical differences between pulsed and cw illuminations, the time scales governing the heat release into the surroundings, the spatial extension of the temperature distribution in the surrounding medium, the influence of a finite thermal conductivity of the gold/water interface, the influence of the pulse repetition rate of the laser, the validity of the uniform temperature approximation in the metal nanoparticle, and the optimum nanoparticle size (~40 nm) to achieve a maximum temperature increase. © 2011 American Physical Society.