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Anna G.,CNRS Charles Fabry Laboratory | Goudail F.,CNRS Charles Fabry Laboratory | Dolfi D.,Thales Alenia
Journal of the Optical Society of America A: Optics and Image Science, and Vision | Year: 2012

In active polarization imaging, one frequently needs to be insensitive to noninformative spatial intensity fluctuations. We investigate a way of solving this issue with general state contrast (GSC) imaging. It consists in acquiring two scalar polarimetric images with optimized illumination and analysis polarization states, then forming a ratio. We propose a method for maximizing the discrimination ability between a target and a background in GSC images by determining the optimal illumination and analysis states. A further advantage of this approach is to provide an objective way of quantifying the performance improvement obtained by increasing the number of degrees of freedom of a GSC imager. The efficiency of this approach is demonstrated on simulated and real-world images. © 2012 Optical Society of America.


Lozan O.,French National Center for Scientific Research | Perrin M.,French National Center for Scientific Research | Ea-Kim B.,CNRS Charles Fabry Laboratory | Rampnoux J.M.,French National Center for Scientific Research | And 2 more authors.
Physical Review Letters | Year: 2014

In this Letter, we study the heat dissipated at metal surfaces by the electromagnetic field scattered by isolated subwavelength apertures in metal screens. In contrast to the common belief that the intensity of waves created by local sources should decrease with the distance from the sources, we reveal that the dissipated heat at the surface remains constant over a broad spatial interval. This behavior that occurs for noble metals at near infrared wavelengths is observed with nonintrusive thermoreflectance measurements and is explained with an analytical model, which underlines the intricate role played by quasicylindrical waves in the phenomenon. Additionally, we show that, by monitoring the phase of the quasicylindrical waves, the total heat dissipated at the metal surface can be rendered substantially smaller than the heat dissipated by the launched plasmon. This interesting property offers an alternative to amplification for overcoming the loss issue in miniaturized plasmonic devices. © 2014 American Physical Society.


Nosal S.,ETH Zurich | Soudais P.,Dassault Aviation | Greffet J.-J.,CNRS Charles Fabry Laboratory
IEEE Transactions on Antennas and Propagation | Year: 2012

A surface integral equation modeling is described for complex doubly periodic structures. To avoid long computations of the slowly convergent pseudoperiodic Green's function, fictitious surfaces between translated unit cells are set in order to bound regions of the structure within the symmetry cell and use the free-space Green's function. The integral operators on top and bottom surfaces are computed with an algorithm originally used for planar frequency-selective surfaces. This approach uses a unique periodic PMCHWT formulation in all the regions, with two different kinds of Green's function. The method and its advantages are illustrated by two cases in the near-IR domain and in the radar domain. A frequency selective structure is studied, that shows a large flat-top bandwidth under oblique incidence and TM polarization. © 2006 IEEE.


Awada C.,CEA Saclay Nuclear Research Center | Barbillon G.,CNRS Charles Fabry Laboratory | Charra F.,CEA Saclay Nuclear Research Center | Douillard L.,CEA Saclay Nuclear Research Center | Greffet J.-J.,CNRS Charles Fabry Laboratory
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

In this paper, an experimental study of hot spots in gold/dielectric films using photoemission electron microscopy is reported. This technique allows a characterization of the statistical optical properties with unprecedented accuracy in the 800- to 1040-nm range. Theoretical predictions of the scaling theory on the number and intensity wavelength dependences of hot spots in the near-infrared are confirmed. Statistical properties of the intensity distribution, spectral behavior, and spatial localization of the hot spots are reported. © 2012 American Physical Society.


Armijo J.,CNRS Charles Fabry Laboratory | Jacqmin T.,CNRS Charles Fabry Laboratory | Kheruntsyan K.V.,University of Queensland | Bouchoule I.,CNRS Charles Fabry Laboratory
Physical Review Letters | Year: 2010

We perform measurements of the third moment of atom number fluctuations in small slices of a very elongated weakly interacting degenerate Bose gas. We find a positive skewness of the atom number distribution in the ideal gas regime and a reduced skewness compatible with zero in the quasicondensate regime. For our parameters, the third moment is a thermodynamic quantity whose measurement constitutes a sensitive test of the equation of state, and our results are in agreement with a modified Yang-Yang thermodynamic prediction. Moreover, we show that the measured skewness reveals the presence of true three-body correlations in the system. © 2010 The American Physical Society.


Armijo J.,CNRS Charles Fabry Laboratory | Jacqmin T.,CNRS Charles Fabry Laboratory | Kheruntsyan K.,University of Queensland | Bouchoule I.,CNRS Charles Fabry Laboratory
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2011

By measuring the density fluctuations in a highly elongated weakly interacting Bose gas, we observe and quantify the transition from the ideal gas to a quasicondensate regime throughout the dimensional crossover from a purely one-dimensional (1D) to an almost three-dimensional (3D) gas. We show that that the entire transition region and the dimensional crossover are described surprisingly well by the modified Yang-Yang model. Furthermore, we find that at low temperatures the linear density at the quasicondensate transition scales according to an interaction-driven scenario of a longitudinally uniform 1D Bose gas, whereas at high temperatures it scales according to the degeneracy-driven critical scenario of transverse condensation of a 3D ideal gas. © 2011 American Physical Society.


Armijo J.,CNRS Charles Fabry Laboratory | Garrido Alzar C.L.,CNRS Charles Fabry Laboratory | Bouchoule I.,CNRS Charles Fabry Laboratory
European Physical Journal D | Year: 2010

We have studied the thermal properties of atom chips consisting of high thermal conductivity aluminum nitride (AlN) substrates on which gold microwires are directly deposited. We have measured the heating of wires of several widths and with different thermal couplings to the copper mount holding the chip. The results are in good agreement with a theoretical model where the copper mount is treated as a heat sink and the thermal interface resistance between the wire and the substrate is vanishing. We give analytical formulas describing the different transient heating regimes and the steady state. We identify criteria to optimize the design of a chip as well as the maximal currents Ic that can be fed in the wires. For a 600 μm thick-chip glued on a copper block with Epotek H77, we find Ic = 16 A for a 3 μm high, 200 μm wide-wire. © 2009 EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg.


Ravets S.,CNRS Charles Fabry Laboratory | Labuhn H.,CNRS Charles Fabry Laboratory | Barredo D.,CNRS Charles Fabry Laboratory | Beguin L.,CNRS Charles Fabry Laboratory | And 2 more authors.
Nature Physics | Year: 2014

Resonant energy transfers, the non-radiative redistribution of an electronic excitation between two particles coupled by the dipole-dipole interaction, lie at the heart of a variety of phenomena1, notably photosynthesis. In 1948, Förster established the theory of fluorescence resonant energy transfer (FRET) between broadband, nearly-resonant donors and acceptors2. The 1/R6 scaling of the energy transfer rate, where R is the distance between particles, enabled widespread use of FRET as a 'spectroscopic ruler' for determining nanometric distances in biomolecules. The underlying mechanism is a coherent dipolar coupling between particles, as recognized in the early days of quantum mechanics4, but this coherence has not been directly observed so far. Here we study, spectroscopically and in the time domain, the coherent, dipolar-induced exchange of excitations between two Rydberg atoms separated by up to 15 μm, and brought into resonance by applying an electric field. Coherent oscillation of the system between two degenerate pair states then occurs at a frequency scaling as 1/R3, the hallmark of resonant dipole-dipole interactions5. Our results not only demonstrate, at the fundamental level of two atoms, the basic mechanism underlying FRET, but also open exciting prospects for active tuning of strong, coherent interactions in quantum many-body systems. © 2014 Macmillan Publishers Limited. All rights reserved.


Federici A.,CNRS Charles Fabry Laboratory | Dubois A.,CNRS Charles Fabry Laboratory
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

Full-field optical coherence microscopy (FF-OCM) is an established optical technology based on low-coherence interference microscopy for high-resolution non-invasive three-dimensional imaging of semi-transparent samples. We present an extension of the technique setting up an achromatic imaging system over a spectral range extending from 530 nm to 1700 nm, to provide tomographic images in three distinct bands centered at 635 nm, 870 nm and 1170 nm. Image contrast enhancement as well as sample characterization is performed using the conventional RGB color channel representation. Light is emitted by a halogen lamp and then separates into two arms of a Linnik-type interferometer with microscope objectives placed in each arm. The images are projected onto a visible to short-wavelength infrared detector based on an InGaAs photodiode array. Enface oriented tomographic images are obtained by arithmetic combination of four phase-shifted interferometric images. Great care was taken to reach similar performances in the three bands. An axial resolution of ~1.9μm and a transverse resolution of ~2.4μm are achieved in the three bands. A dynamic dispersion compensation system is set up to preserve axial resolution and signal intensity level when the imaging depth is varied. Images of biological samples revealing their spectral properties are shown as illustration of improved detection capability with enhanced contrast. © 2014 SPIE.


Dubois A.,CNRS Charles Fabry Laboratory
AIP Conference Proceedings | Year: 2013

Full-field optical coherence microscopy (FF-OCM) is a recent optical technology based on low-coherence interference microscopy for semi-transparent sample imaging with ∼ 1 μm spatial resolution. FF-OCM has been successfully applied to three-dimensional imaging of various biological tissues at cellular-level resolution. The contrast of FF-OCM images results from the intensity of light backscattered by the sample microstructures. This contrast mechanism, based on refractive index changes, provides information on the internal architectural morphology of the sample. In this paper, we present a multimodal FF-OCM system, capable of measuring simultaneously the intensity, the power spectrum and the phase-retardation of light backscattered by the sample being imaged. Tomographic fluorescence-based images can also be produced by coupling to the FF-OCM set-up a fluorescence microscopy system with structured illumination. Fluorescence targeted probes can be used to identify molecular components of subcellular scattering structures. Compared to conventional FF-OCM, this multimodal system provides enhanced imaging contrasts at the price of a moderate increase in experimental complexity and cost. © 2013 AIP Publishing LLC.

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