Sibased nanostructures for enhanced nonlinear interactions, ultracompact
diffractive optics, and light localization in multifractal landscapes Luca Dal Negro (Boston University, USA) mercredi 19 juillet 2023, 14:00, Salle 310
Résumé: The ability to manipulate wave transport phenomena and to enhance lightmatter
interactions using siliconcompatible, dispersionengineered materials, epsilonnearzero
(ENZ) platforms, and complex photonic media with desired radiation properties is at the
heart of current nanophotonics and metamaterials technologies. For example, the dramatic
enhancement of the nonlinear optical interactions of transparent conductive oxides (TCOs)
provides unique opportunities to engineer novel optoelectronic devices with orderofunity
(nonperturbative) refractive index changes on subpicosecond time scales for dynamically
tunable metasurfaces, broadband optical modulators, optical switching, and timevarying
photonics applications on the chip. Moreover, recent progress in the theory, inversedesign,
fabrication, and characterization of highrefractive index, lowloss, diffractive optical
elements and dielectric nanostructures with tailored disorder and hyperuniform geometries
established novel strategies to engineer ultracompact imaging devices and nanostructures
with desired wave transport and localization properties over targeted spectral and spatial
frequency bandwidths.
In this talk, I will discuss our work on the design, fabrication, and characterization of highly
nonlinear Sicompatible materials and nanostructures based on the indium tin oxide (ITO)
platform with tunable ENZ responses across the nearinfrared spectral range. In particular, I
will address the nonperturbative Kerrtype optical nonlinearity of fabricated materials and
resonant devices driven by the excitation of optical Tamm states. Building on this platform, I
will illustrate the potential of topologically optimized highQ nonlinear dielectric nanocavities
for extreme subwavelength field confinement potentially enabling photonblockade and
strongcoupling effects. Next, I will present our recent work on the inversedesign of ultra
compact and multifunctional spectroscopic imaging devices based on diffractive optical
networks (aDONs) and the adjoint optimization of highrefractive index functionalized
scattering arrays for imaging and radiation engineering on the chip. Finally, I will provide a
perspective on anomalous diffusion and light localization in multifractal photonic
environments that encode the characteristic multiscale complexity of numbertheoretic
sequences and algebraic number fields beyond random lasing device applications.
A. Capretti, Y. Wang, N. Engheta, L. Dal Negro “Enhanced thirdharmonic generation in Sicompatible
epsilonnearzero indium tin oxide nanolayers”, Opt. Lett., Vol. 40, Issue 7, 15001503, (2015)
2) W. Britton, F. Sgrignuoli, L. Dal Negro, “Structuredependent optical nonlinearity of indium tin oxide”, Appl.
Phys. Lett. 120, 101901 (2022)
3) W. Britton, Y. Chen, F. Sgrignuoli, L. Dal Negro, “PhaseModulated Axilenses As Ultracompact
Spectroscopic Tools”, ACS Photonics, 7, 10, 2731–2738 (2020)
4) W. Britton, Y. Chen, F. Sgrignuoli, L. Dal Negro, “Compact DualBand MultiFocal Diffractive Lenses”, Laser
Photonics Rev. 15, 2000207 (2021)
5) Y. Chen, Y. Zhu, W. A. Britton, and L. Dal Negro, “Inverse design of ultracompact multifocal optical devices
by diffractive neural networks”, Opt. Lett., Vol. 47, No. 11, 28422845, (2022).
6) Y. Zhu, Y. Chen, and L. Dal Negro, “Design of ultracompact broadband focusing spectrometers based on
diffractive optical networks”, Opt. Lett., Vol. 47, No. 24, 63096312, (2022).
7) S. Gorsky; W. A. Britton; Y. Chen, J. Montaner; A. Lenef, M. Raukas, L. Dal Negro, “Engineered
hyperuniformity for directional light extraction”, APL Photonics 4, 110801 (2019)
8) F. Sgrignuoli, S. Gorsky, W. A. Britton, R. Zhang, F. Riboli, and L. Dal Negro, “Multifractality of light in
photonic arrays based on algebraic number theory” Communications Physics, 3, 106 (2020).
9) Y. Chen, F. Sgrignuoli, Y. Zhu, T. Shubitidze, and L. Dal Negro, “Enhanced wave localization in multifractal
scattering media”, Phys. Rev. B 107, 054201 (2023).
10) L. Dal Negro, “Waves in Complex Media”, Cambridge University Press (2022).

Experimental investigations of one and twodimensional optical
Anderson localization systems Sushil Mujumdar (Tata Institute of Fundamental Research, Mumbai, INDIA) lundi 17 juillet 2023, 11:00, Amphithéâtre
Résumé: Light transport in disordered media involves multiple scattering of
light waves and their selfinterference, which realizes some very
exotic phenomena such as Anderson localization. In this talk, after a
very brief introduction to this field, we will discuss some of our
experimental investigations in low dimensional systems. We will first
discuss the experimental demonstration of lasing over onedimensional
Andersonlocalized modes. Subsequently, we will demonstrate anomalous
transport and exceptional points in nonHermitian localizing
structures. Finally, we will discuss the experimental measurement of
Thouless conductance in twodimensional open systems.
PRL, 111, 233903 (2013); PRL. 124, 123901 (2020); arXiv:2301.06532
(2023); PRB 100, 060201(R) (2019) Eds' Sugg.

Multichannel optics: from deeptissue imaging to fast solvers and inverse design Chia Wei (Wade) Hsu (University of Southern California) mardi 20 juin 2023, 11:00, Amphitheatre
Résumé: Light scattering couples the many degrees of freedom in the electromagnetic fields. In this talk, I will present recent work in our group in three directions: 1) compensating light scattering to image deeper inside biological tissue, 2) developing fast solvers to compute the multichannel response of complex optical systems, and 3) designing highperformance multichannel nanophotonic structures. All of them concern the scattering matrix of the system, which relates the incident wavefront to the outgoing wavefront. On the imaging part, we develop a scheme that uses the measured scattering matrix to digitally perform spatiotemporal focusing, guidestarfree input/output wavefront correction, and dispersion compensation through numerically optimizing an image quality metric. Doing so enables noninvasive volumetric imaging with onemicron isotropic resolution at one millimeter beneath mouse brain tissue; the depthoverresolution ratio exceeds 900. On the fast solver, we present a fullwave simulation method called "augmented partial factorization" (APF). By augmenting the Maxwell operator with the input and output profiles, APF computes the scattering matrix without solving for the internal field and without looping over the inputs, achieving 3 to 7 orders of magnitude speedup compared to existing frequencydomain solvers. We made this code opensource and use it to demonstrate twophoton coherent backscattering from disorder and open channels for 3D vectorial waves. In the last part, we use APF to realize the inverse design of nonlocal metasurfaces.

Séminaire Doctorants (Institut Langevin, ESPCI Paris  PSL, France) mardi 23 mai 2023, 11:00, Amphithéâtre

Earthquake magnitude distribution and aftershocks: A statistical geometry explanation François Petrelis (LPENS, ENS Paris  PSL, France) mardi 16 mai 2023, 11:00, Amphitheatre
Résumé:
Earthquakes in nature follow several statistical properties. In particular, the distribution of energy released by an earthquake (GutenbergRichter's law) and the frequency of aftershocks after a large event (Omori's law) are both powerlaws.
By studying several earthquake models, we show that these properties result from the spatial distribution of the stress field. This field can be described as a random curve for onedimensional models and a random surface for twodimensional models. Using this analogy, a series of predictions is made that includes the GutenbergRichter law, the bvalue, and, for twodimensional models, the existence of aftershocks and their temporal distribution following Omori's law.

Séminaire Doctorants (Institut Langevin, ESPCI Paris  PSL, France) mardi 18 avril 2023, 11:00, Amphithéâtre

Imaging acoustic waves in 2D confined by hook or by crook Oliver B. Wright (Hokkaido University, Sapporo, Japan ) vendredi 07 avril 2023, 11:00, Amphitheatre
Résumé: This talk describes experiments and simulations on two different ways to confine surface acoustic waves in twodimensions on microscopic scales: by the use of a surface phononic crystal cavity [1] or by the use of zerogroupvelocity waves in a thin plate [2]. In the former case, a quasihexagonal cavity in a honeycomblattice surface phononic crystal formed in crystalline silicon is imaged by means of an ultrafast technique, and the acoustic energy confinement is quantified. In the latter case, Lamb waves are similarly imaged in a micronscale thickness siliconnitride plate coated with a titanium film. We discuss the dispersion relations and spatial localization in detail in these two cases. Applications include sensing and the testing of bonded nanostructures.
[1] P. H. Otsuka, R. Chinbe, M. Tomoda, O. Matsuda, Y. Tanaka, D. M. Profunser, S. Kim, H. Jeon, I. A. Veres, A. A. Maznev and O. B. Wright, (Photoacoustics, in press) 
[2] Q. Xie, S. Mezil, P. H. Otsuka, M. Tomoda, J. Laurent, O. Matsuda, Z. Shen and O. B. Wright, Nat. Comm. 10, 2228 (2019).

Defect reconstruction in waveguides using cutoff frequencies Angèle Niclas (Ecole Polytechnique, France) mardi 04 avril 2023, 11:00, Amphitheatre
Résumé: This talk aims at introducing a new theoretical multifrequency method to reconstruct width defects in waveguides and plates. Using cutoff frequencies of the structure, we can provide a stable inverse method that proves very robust to noised data. I will start by describing this method in the simplest case of a scalar waveguide. Then, I will provide theoretical tools to extend this method to elastic plates using Lamb modes. I will then focus on ZGV frequencies and show numerical reconstructions of width defects obtained with this method.

Mueller polarimetric imaging for biomedical diagnostics Angelo Pierangelo (Polytechnique, France) mardi 28 mars 2023, 11:00, Amphitheatre
Résumé: Improving the health of populations has always been a major concern of advanced human societies. Since the beginning of the 20th century, considerable efforts have been made to improve disease prevention and access to quality care. In particular, the considerable development of biomedical imaging has led to significant improvements in the detection and treatment of many types of pathologies, including cancer. Indeed, several imaging techniques (CTscan, PETscan, magnetic resonance, etc.) are commonly used in medical practice for this purpose.
In addition, new optical techniques (fluorescence, second harmonic generation, optical coherent tomography, etc.) have been tested for a decade to develop new imaging systems able to detect diseases at an early stage or to improve the definition of surgical resection margins of pathological areas. Among all these optical techniques, polarimetric imaging has shown great promise for biomedical diagnosis. Indeed, it has been extensively tested for the examination of biological tissues, optically very complex systems where strong scattering and anisotropy effects can occur simultaneously.
In particular, Mueller polarimetric imaging allows the complete polarimetric characterization of biological tissues, providing unique information on their microstructure, which can greatly improve the diagnosis of many diseases. Indeed, this technique has proven to be very sensitive for detecting changes in cell structure and density, as well as in the organization of extracellular matrix fibers, such as collagen, due to the development of a disease, even at an early stage. Furthermore, it is a noncontact technique that can be implemented with a macroscopic field of view (several tens of cm²), while providing sensitive contrasts to the sample microstructure at a scale smaller than the actual spatial resolution of the image. In addition, it uses conventional light sources (LED, halogen lamps and others) and relatively inexpensive optics. However, although Mueller polarimetric imaging has shown great potential for improving the analysis of biological tissues, the implementation of this technique in vivo is considered extremely difficult for all research groups working in this field and most studies have been conducted ex vivo.
In this talk, I will present the main results and future perspectives of my research activity, whose main objective is the design, fabrication and implementation of innovative Mueller polarimetric imaging systems with unmatched performance for ex vivo and in vivo exploration of biological tissues. After a description of the main scientific and societal challenges of this research activity, an overview of the different imaging systems developed will be presented as well as the main results obtained in different biomedical applications ranging from gynecology to neurosurgery. These systems can represent a significant advance in the early and reliable detection of various pathologies, paving the way for more effective patient management strategies.

Reflectionless scattering in complex media Matthieu Davy (IETR, Rennes) mardi 21 mars 2023, 11:00, Amphitheatre

Séminaire Doctorants (Institut Langevin, ESPCI Paris  PSL, France) mardi 14 mars 2023, 11:00, Amphithéâtre

Photosynthesis: a lesson in light harvesting from nature Sébastien Bidault (Institut Langevin, Paris, France) mardi 07 mars 2023, 10:30, Amphitheatre

Characterization of thinwalled structures using local measurement of Lamb waves Jakub Spytek ( Institut Langevin, Paris, France) mardi 28 février 2023, 11:00, Amphitheatre
Résumé: Fullfield imaging of Lamb waves is a technique used for the nondestructive evaluation of engineered thinwalled structures. It involves the excitation of Lamb waves (usually at a single point) and then measuring the time histories of propagating Lamb waves at multiple spatial points using noncontact vibration sensors, such as laser vibrometers or aircoupled transducers. With the use of signal processing techniques, it is possible to estimate the properties of the measured waves, such as energy or wavenumber. Based on these properties, it is possible to detect and characterize damage in the structure, as well as estimate the elastic properties of the material. During this seminar, I will present the principles of fullfield imaging of Lamb waves and their application for the nondestructive evaluation of thinwalled samples. I will also discuss the possibility of using fullfield imaging for quantifying the effect of surface contamination on the propagating Lamb waves.

Vibrations and Heat Transfers in Amorphous Materials and in GlassCeramics Anne Tanguy ( INSA Lyon, France) mardi 21 février 2023, 11:00
Résumé: Amorphous materials have high heat capacity but low thermal conductivity compared to crystals with the same composition. The understanding of these properties is based on the study of acoustic attenuation and more generally on the specific vibrational properties of glasses. After a general description of the vibrational eigenmodes in disordered materials, we will show the link between the dynamics of vibrational wave packets and the expression of thermal conductivity at the atomic scale. We will then discuss the different acoustic attenuation mechanisms and their expression at different scales: from the atomic scale to the continuous scale. Finally, we will focus on the effect of crystal/amorphous interfaces on the thermal properties of nanostructured materials such as glassceramics. We will show how the presence of amorphous parts reinforces the diffusive contribution to heat transport, and allows controlling not only the orientation, but also the direction of the heat flux.
[1] Y. Beltukov, D. A. Parshin, V.M. Giordano and A. Tanguy Physical Review E 98 023005 (2018): Propagative and diffusive regimes of acoustic damping in bulk amorphous material.
[2] P. Desmarchelier, A. Carré, K. Termentzidis and A. Tanguy Nanomaterials 11, 1982 (2021): Heat Transport in Nanocomposite: The Role of the Shape and Interconnection of Nanoinclusions
[3] H. Luo, V.M. Giordano, A. Gravouil and A. Tanguy Journal of NonCrystalline Solids 583, 121472 (2022): A continuum model reproducing the multiple frequency crossovers in acoustic attenuation in glasses
place=Amphithéâtre

Compressive and multiplexed imaging using complex media Marc Guillon (Université ParisCité, France) vendredi 17 février 2023, 10:00, Amphitheatre
Résumé: Compressed imaging aims at maximizing the amount of collected information while minimizing the number of measurements, relying on some samplebased priors. The main advantages of this approach can be to speed up the acquisition rate, allow single shot measurements, improve resolution or the signal to noise ratio, gathering multimodal contrasts, minmizing the invasiveness of potentially phototoxic probing beams etc. To achieve so, it turns out that random functions are almost ideal to probe samples. Light speckles have then been extensively used to provide compressed and multiplexed images, in particular using scattering samples.
In this seminar, I will present our contribution to compressive imaging through superresolution microscopy as well as wavefront sensing. We investigated 3D superresolution fluorescence microscopy both by saturating fluorescence excitation and performing stimulated emission with speckles. I will also show our results about highresolution multiplexed, multispectral and polarimetric wavefront imaging and their future application to optical metrology and bioimaging.

Deterministic and statistical characterisation of rough and porous media from acoustic scattering Jacques Cuenca (Siemens Industry Software, Leuven, Belgium) mardi 14 février 2023, 11:00, Amphitheatre
Résumé: The purpose of this seminar is to show a model inversion framework for the estimation of material properties from acoustic measurements. Two applications are presented, namely the reconstruction of rough surfaces from sound scattering and the estimation of porous material properties from sound reflection. In the case of rough surface characterisation, the property of interest is the depth profile of the surface, and the measurement consists of scattered sound pressure retrieved at a microphone array. The application to porous material characterisation aims at determining the transport properties of a homogeneous porous sample from its sound absorption spectrum. The first step of the methodology is a deterministic model inversion, which is formulated as a nonlinear optimisation problem and provides an initial estimate of the unknown model parameters. The inverse problem is then formulated in a statistical sense and solved using Bayesian inference, which enables the estimation of credible intervals on the unknowns. It is shown that the sequential use of deterministic and statistical inversion allows to reduce computational time while yielding a feasible solution and its uncertainty range.

Closedaperture unbounded acoustics experimentation using multidimensional deconvolution Jack Li ( ETH, Zurich, Switzerland) mardi 07 février 2023, 11:00, Amphitheatre
Résumé: In physical acoustic laboratories, wave propagation experiments often suffer from unwanted reflections at the boundaries of the experimental setup. We propose using multidimensional deconvolution (MDD) to postprocess recorded experimental data such that the scattering imprint related to the domain boundary is completely removed and only the Green's functions associated with a scattering object of interest are obtained. The MDD results consist of the Green's functions between any pair of points on the closed recording surface, fully sampling the scattered field. We apply the MDD algorithm to postprocess laboratory data acquired in a 2D acoustic waveguide to characterize the wavefield scattering related to a rigid steel block while removing the scattering imprint of the domain boundary. The experimental results corroborate that MDD is an effective and general method to obtain the experimentally desired Green's functions for arbitrary inhomogeneous scatterers.

Séminaire Doctorants (Institut Langevin, ESPCI Paris  PSL, France) mardi 17 janvier 2023, 11:00, Amphithéâtre

Surface PhononPolaritons as Efficient Heat Carriers Sebastian Volz (LIMMS, Tokyo, Japan) jeudi 05 janvier 2023, 15:00, Amphitheatre
Résumé: Recent studies showed that surface phononpolaritons, i.e. evanescent electromagnetic waves propagating along the surface of polar dielectric materials [1] [2], may potentially serve as novel heat carriers to enhance the thermal performance in micro and nanoscale devices.
This seminar will expose the significant contribution of these carriers to thermal conductivity in ultrathin (below 100nm) films [3], but also to radiation, yielding SuperPlanckian emission and absorption between surfaces of larger scales (10mm).
[1] D.Z Chen, A. Narayanaswamy, and G. Chen, Phys. Rev. B 72, 155435 (2005).
[2]J. OrdonezMiranda, L. Tranchant, T. Tokunaga, B. Kim, B Palpant, Y. Chalopin, T. Antoni, and S. Volz, J. Appl. Phys. 113, 084311 (2013).
[3] Y. Wu, J. OrdonezMiranda, S. Gluchko, R. Anufriev, D. De Sousa Meneses, L. Del Campo, S. Volz, and M. Nomura, Science Advances 6(40):eabb4461, (2020).

Scaling Theory of Wave Confinement in Classical and Quantum Periodic Systems Marek Kozon (University of Twente, Nederlands) jeudi 15 décembre 2022, 11:00, Amphitheatre

Séminaire Doctorants : (Institut Langevin, ESPCI Paris  PSL, France) mardi 13 décembre 2022, 11:00, Amphithéâtre

Shaping light interaction with finitesize matter Ad Lagendijk (University of Twente, Nederlands) mardi 06 décembre 2022, 11:00, Amphitheatre

Séminaire Doctorants : (Institut Langevin, ESPCI Paris  PSL, France) mardi 15 novembre 2022, 11:00, Amphithéâtre

Willem Vos (University of Twente, Nederlands) mardi 18 octobre 2022, 11:00, Amphitheatre

Séminaire Doctorants : (Institut Langevin, ESPCI Paris  PSL, France) mardi 11 octobre 2022, 11:00, Amphithéâtre

Study of light transport in 𝝌(𝟐)nonlinear complex media: From few
particles system to 3D disorder Rabisankar Samanta (Tata Institute of Fundamental Research, Mumbai, India) mercredi 27 juillet 2022, 11:00, room 310
Résumé: Light diffusion in a complex medium is a ubiquitous phenomenon in nature.
The transport of photons becomes fascinating when the medium has χ(2) 
nonlinearity. In this type of medium, fundamental light gets multiply
scattered and subsequently generates second harmonic (SH) light. Again,
these SH photons undergo multiple scattering events before coming out of the
sample. In this talk, I will be discussing different aspects of secondharmonic
generation in complex media which span from a few particles system to 3D
disorder. With outofplane imaging, we show interference in the SH light
among the submicron size harmonic particles. In a quasi3D disordered
medium, we have studied intensitydependent speckle decorrelation in the
fundamental and SH light. Further, the spatial and temporal diffusion of both
the harmonics in a finite, 3D complex medium will be discussed. Finally, I
will conclude my talk with the possible applications and future directions in
this field.

Interférométrie Sismique appliquée aux données de la mission NASA Discovery InSight sur Mars : Structure crustale et suivi temporel Nicolas Compaire (ISTERRE, Grenoble,France) mardi 19 juillet 2022, 11:00, Amphitheatre

DEconstrained and largescale optimization in nanophotonics Raphael Pestourie (MIT, Boston, USA) mardi 12 juillet 2022, 11:00, Amphitheatre
Résumé: Optical metasurfaces are thin largearea structures with aperiodic subwavelength patterns, designed for focusing light and a variety of other wave transformation. Because of their irregularity and large scale, they are one of the most challenging tasks for computational design. This talk will present ways to harness the full computational power of modern largescale optimization in order to design metasurfaces with thousands or millions of free parameters. To that end, we exploit domaindecomposition approximations and “surrogate” models. We will also review some traditional techniques such as adjoint simulations and the principle of equivalence. We will also present some recent experimental results on lenses. Finally, if time permits, we will discuss recent progress combining traditional numerical methods and machine learning for dataefficient surrogate models and how they will impact inverse design in nanophotonics and beyond.

Analyseur de spectre RF ultra large bande à creusement spectral dans un cristal Tm :YAG : de la démonstration en laboratoire aux essais opérationnels Perrine Berger (Thales) mardi 21 juin 2022, 11:00, Amphitheatre
Résumé: Les propriétés de creusement de trou spectral (Spectral Hole Burning, SHB) rendent les ions de terres rares particulièrement attractifs pour le traitement large bande de signaux RF et les mémoires quantiques. Ces applications exploitent en effet les longs temps de cohérence des transitions optiques de ces systèmes lorsqu’ils sont refroidis à température cryogénique (3K). Nous démontrons ainsi un analyseur de spectre de radiofréquence (RF) avec une bande passante instantanée de plusieurs dizaines de gigahertz.
Nous avons implémenté l'architecture dite « arcenciel », dans laquelle les composantes spectrales RF portées optiquement subissent une dispersion angulaire géante (6 rad / nm) dans le cristal. Cette dispersion gigantesque est obtenue en stockant un motif spectrospatial dans les sousniveaux Zeeman de l'état fondamental 3H6 de Tm: YAG avec deux faisceaux laser périodiquement balayés en fréquence et angulairement balayés. La bande passante hyperfréquence d'intérêt étant alors étalée sur plus de 200 milliradians, elle peut être imagée et acquise avec un photodétecteur pixélisé à haut débit. Les techniques optiques (balayages et stabilités de fréquence laser, optomécanique) ont été maitrisées pour réaliser des essais opérationnels hors laboratoire. Ce démonstrateur permet d’obtenir le spectre de signaux microondes complexes sur une bande passante instantanée de 40 GHz, avec une résolution temporelle de l'ordre du µs, une résolution de fréquence adaptable jusqu'au MHz, sur une grande plage de dynamique multisignaux. L'analyse est continue, conduisant à une probabilité de 100% d'interception des signaux RF, qu’ils soient continus, modulés en fréquence, courts ou impulsionnels, et ceci est réalisé avec une faible latence. Cette architecture ne nécessite pas de conversion analogiquenumérique avec une dynamique élevée, ni d’imposants calculs de densité spectrale de puissance, qui sont les principaux goulots d'étranglement dans les techniques d'analyse spectrale ultralarge bande standard.

Single spin magnetic resonance by microwave fluorescence detection Patrice Bertet (CEA, Université Paris/Saclay, France) mardi 14 juin 2022, 11:00, amphithéâtre
Résumé: We report a new method for electron spin detection at millikelvin temperatures. Analogous to the optical fluorescence detection of atoms or molecule, the method consists in detecting the microwave photons spontaneously emitted by the spins when they relax radiatively to their equilibrium ground state after being excited by a pulse (ie, their microwave fluorescence) [1]. To enhance the radiative relaxation rate [2], the spins are inductively coupled to a smallmodevolume, highqualityfactor, superconducting resonator patterned on top of the sample. The microwave fluorescence photons are then routed towards a singlemicrowavephoton detector [3] based on a superconducting qubit.
The method applies to all paramagnetic species with sufficiently low nonradiative decay rate. Here, we report the detection of rareearthion spins (Er3+ in a scheelite CaWO4 host matrix) by their microwave fluorescence. We perform a complete spectroscopic characterization of a small erbium ensemble. We also report the first microwave detection of individual erbium ion spins, and their coherent manipulation [4].
[1] E. Albertinale et al., Nature 600, 434 (2021) 
[2] A. Bienfait et al., Nature 531, 74 (2016) 
[3] R. Lescanne et al., Phys. Rev. X 10, 021038 (2020) 
[4] Z. Wang et al., in preparation (2022)

Designer Nucleic Acid Architectures for Programmable Selfassembly Hao Yan (Center for Molecular Design and Biomimetics, Biodesign Institute & School of Molecular Sciences, Arizona State University) mardi 07 juin 2022, 11:00, Amphitheatre
Résumé: DNA and RNA has emerged as an exceptional molecular building block for nanoconstruction due to its predictable conformation and programmable intra and intermolecular base pairing interactions. A variety of convenient design rules and reliable assembly methods have been developed to engineer DNA nanostructures of increasing complexity. The ability to create designer DNA architectures with accurate spatial control has allowed researchers to explore novel applications in many directions, such as directed material assembly, structural biology, biocatalysis, DNA computing, nanorobotics, disease diagnosis, and drug delivery. In this talk I will discuss some of our work in the field of structural nucleic acid nanotechnology, and present some of the challenges and opportunities that exist in DNA and RNA based molecular design and programming. Specifically, I will discuss some of the new designs for 3D DNA crystals and the use of the crystals as host to organize guest molecules and visualize their atomic level structures. I will discuss the use of DNA template to organize dye molecules for long range energy transfer over submicron distances for potential light harvesting applications. I will also discuss our progress in using DNA and RNA nanotechnology for biomedical applications.

Séminaire Doctorants : Zosia BRATASZ and Guyu ZHOU (Institut Langevin, ESPCI Paris  PSL, France) mardi 31 mai 2022, 11:00, Amphithéâtre

Emergence of homochirality in large molecular systems Davide Lacoste (Gulliver, ESPCI Paris  PSL, France) mardi 24 mai 2022, 11:00, Amphithéâtre
Résumé: The question of the origin of homochirality of living matter, or the
dominance of one handedness for all molecules of life
across the entire biosphere, is a longstanding puzzle in the research
on the Origin of Life. In the fifties, Frank proposed
a mechanism to explain homochirality based on properties of
simple autocatalytic networks containing only a few
chemical species. Following this work, chemists struggled to find
experimental realizations of this model, possibly due
to a lack of proper methods to identify autocatalysis [1]. In any
case, a model based on a few chemical species seems rather
limited, because prebiotic earth is likely to have consisted of
complex ‘soups’ of chemicals.
To include this aspect of the problem, we recently proposed a
mechanism based on properties of large outofequilibrium chemical
networks [2]. We showed that a homochiral phase transition is
likely to occur as the number of chiral species in the system becomes large
or as the amount of free energy injected into the system increases.
Our approach, based on random matrix theory,
can account for the sparsity of chemical networks, and
points towards a robust mechanism for the emergence
of homochirality. Furthermore, the chiral symmetry of the relevant matrices
has implications for the various conventions used to measure chirality and
for the relative chiral signs adopted by different groups of
molecules in prebiotic chemistry [3].
References:
[1] A. Blokhuis, D. Lacoste, and P. Nghe, PNAS (2020), 117, 25230.
[2] G. Laurent, D. Lacoste, and P. Gaspard, PNAS (2021) 118 (3) e2012741118.
[3] G. Laurent, D. Lacoste, and P. Gaspard, Proc. R. Soc. A 478:20210590 (2022).

Homogenization of thin dielectric and plasmonic metasurfaces Nicolas Lebbe (Institut Langevin, ESPCI Paris  PSL, France) mardi 17 mai 2022, 11:00, Salle 310
Résumé: Electromagnetic metasurfaces are smartly engineered
twodimensional microstructures made of many subwavelength elements
called metaatoms designed to control the flow of light. To simplify their
study and numerical simulation, many methods have been developed to reduce
the geometrical complexity of metaatoms into effective material
properties. Unfortunately, these effective properties are often limited to
a small spectrum or small variations of the angle of incidence.
In this presentation, we will present new results of surface
homogenization which allows the modeling of electromagnetic metasurfaces
with equivalent transition conditions and effective electromagnetic
surface susceptibilities. We will insist on the case of plasmonic
metasurfaces for which we have recently shown that the effective
parameters can be obtained by solving a single generalized eigenvalue
problem. Once solved, it allows to analytically compute the transmission
and reflection through the metasurface for any wavelength, incidence angle
and material constituting the metaatoms.

Acoustic evaluation of material parameters, stresses, and strains in soft materials Michel Destrade (NUI Galway, Ireland) mardi 10 mai 2022, 11:00, Amphithéâtre
Résumé: This talk discusses two goals that can be achieved with elastic waves travelling in soft materials.
First, we see how tracking the changes in wave speed with stress or strain gives access to linear and nonlinear material parameters in a nondestructive manner. These can then be used to design biomaterials or to create meaningful Finite Element simulations. Examples include brain matter, muscles, and stretched soft plates.
Then, we find that the state of stress and strain existing in a loaded material can be accessed directly from wave speed measurements, without having to determine, or even know, its material properties beyond its mass density and geometry. These techniques are expected to have important applications in health monitoring of loaded structures. Examples include stressed rail steel, the human skin in situ, and thin membranes such as a stretched rubber sheet, a piece of cling film (~10 μm thick) and the animal skin of a bodhrán, a traditional Irish drum.

Séminaire Doctorants (Institut Langevin, ESPCI Paris  PSL, France) mardi 26 avril 2022, 11:00, Amphithéâtre

Assessment of human exposure to radiofrequency waves. From deterministic approaches to stochastic methods Joe Wiart (LTCI, Telecom Paris, Institut Polytechnique de Paris, Institut Mines Telecom, France ) mardi 19 avril 2022, 11:00, Amphithéâtre / En ligne
Résumé: With the increasing use of wireless communications, exposure to electromagnetic waves has become a perennial concern where the risk or the perception of risk are omnipresent. With each new technological development, the possible health effects are analyzed and challenged as well as the associated levels of protection. The 5G debate is a telling example. In this approach, tools to measure or calculate exposure to electromagnetic waves are essential. For nearly 30 years, the tools used to measure or calculate exposure levels have evolved and adapted to new protocols, new frequencies and new uses. The deterministic, experimental or numerical methods used in dosimetry have been confronted with the complexity and versatility of the systems. Stochastic approaches and artificial intelligence have supplemented deterministic approaches in dosimetry. The challenges and different methods used will be developed in this presentation.

Refractive Acoustooptics Maxim Cherkashin (University College London, UK) mercredi 13 avril 2022, 11:00
Résumé: Contrary to the more widespread acoustooptic devices, based on diffraction of light, last years seen increased interest in their refraction based counterparts. In this talk I will discuss the recent developments in this field and highlight the newly opened capabilities of such devices. Namely, light focusing, focus translation and light waveguiding inside scattering media by tailored ultrasonic fields will be highlighted.

There is plenty of room at the nanoscale;
emission control beyond the spherical cow Margoth CórdovaCastro (Institut Langevin, ESPCI Paris  PSL, France) mardi 12 avril 2022, 11:00, Amphithéâtre

From the reality of Climate Change to the imperative of a low carbon transition Benoît Lebot (NégaWatt, France) mardi 05 avril 2022, 11:00, Amphithéâtre

Séminaire Doctorants (Institut Langevin, ESPCI Paris  PSL, France) mardi 29 mars 2022, 11:00, Amphithéâtre

Alloptical interrogation of brain circuits using optogenetics and holographic light shaping Valentina Emiliani (Institut de la Vision, Paris, France) mardi 22 mars 2022, 11:00, Amphithéâtre
Résumé: Genetic targeting of neuronal cells with activity reporters (calcium or voltage indicators) has initiated the paradigmatic transition whereby photons have replaced electrons for reading largescale brain activities at cellular resolution. In parallel, optogenetics has demonstrated that targeting neuronal cells with photosensitive microbial opsins, enables the transduction of photons into electrical currents of opposite polarities thus writing, through activation or inhibition, neuronal signals in a noninvasive way.
These progresses have in turn stimulated the development of sophisticated optical methods to enable “all optical” in depth brain circuits interrogation with high spatial and temporal resolution on large volumes.
Here, we will review the most significant breakthroughs of the past years, which enable reading and writing neuronal activity at the relevant spatiotemporal scale for brain circuits manipulation, with particular emphasis on the most recent advances in what we named circuit optogenetics: a combination of approaches including holographic light illumination, temporal focusing, opsins engineering and laser development for the control of single or multiple targets independently in space and time with singleneuron and singlespike precision, at large depths.

Buckling instability and swimming of elastic spherical shells (from beach balls to microswimmers) Gwennou Coupier (LiPhy, Université Grenoble Alpes, France) mardi 15 mars 2022, 11:00, Amphithéâtre
Résumé: Buckling of elastic structures is an effective way to produce rapid motion in a fluid at any scale. Encapsulated microbubbles, which are currently used as ultrasound contrast agents, can deform and collapse under an external load from an acoustic wave. They reinflate when the pressure decreases. The shape hysteresis associated with this deformation cycle makes this simple object a good candidate to become an ultrasound controlled microswimmer.
I will explore this possibility through experiments at macro and micro scales and numerical simulations. The coupling between the acoustic wave and the selfoscillation of the deformed shell leads to complex  sometimes chaotic  dynamics with direct consequences on the direction and efficiency of the swimming.

FibroScan : le produit qui a transformé le quotidien des hépatologues Laurent Sandrin (Echosens, Paris, France) mardi 08 mars 2022, 11:00, Salle 310

Cristaux phononiques piézoélectriques Bertrand Dubus (IEMN, Lille, France) mardi 01 mars 2022, 11:00, Amphithéâtre

Séminaire Doctorants (Institut Langevin, ESPCI Paris  PSL, France) mardi 22 février 2022, 11:00, Amphithéâtre

Quantum calculus. An example through Shor's algorithm Ahmed Ben Aissa (Institut Langevin, ESPCI Paris  PSL, France) mardi 08 février 2022, 11:00, Amphithéâtre
Résumé: This presentation will explore some basic concepts and
principles in quantum computing, from quantum gates to the Quantum Fourier
Transform (QFT). Shor's algorithm, a polynomialtime algorithm for integer
factorization, will be presented, alongside a detailed study of its
stepbystep implementation on a multiqubit machine. Finally, an indepth
look at the computational complexity of this implementation, as well as
simulation results, will be presented.

Probing chiral metamaterials with waves packets: experiments and theory Marcelo Guzman (ENS Lyon, Lyon, France) mardi 01 février 2022, 11:00, Amphithéâtre
Résumé: In less than a decade, topological phase physics has spread frantically over all fields of physics. Among the rich class of topological phases, of particular interest are chiral phases. Chiral symmetry, although originally introduced in quantum mechanical systems, is naturally found at the macroscale, in systems as diverse as photonic arrays, acoustic metamaterials, and mechanical networks.
In this talk, using mechanics as a guiding line, I will lay out a generic framework to characterise chiral metamaterials. I will first introduce the concept of chiral polarization, a material property that distinguishes distinct topological phases. Combining theory, simulations and experiments, I will show how to measure the chiral polarization and thereby detect zero energy excitations in chiral structures. I will in particular stress on a practical method based on local excitations, which provides a quantitative and local probe of topological excitations in periodic and amorphous metastructures.
I will close my talk by generalising our results to the flourishing field of higherorder topological insulators. I will show how to detect and design zeroenergy corner states without relying on any apriori modelling of a mechanical, photonic or acoustic metamaterial.

Making ensembles of semiconducting nanocrystals emit complex forms of light Aloyse Degiron (Laboratoire Matériaux et Phénomènes Quantiques, Université de Paris, Paris, France) mardi 25 janvier 2022, 11:00, Amphithéâtre
Résumé: How far can we go in shaping the random spontaneous emission of quantum emitters? The designs rules that have been established over the years are based on leveraging the Purcell effect—the dependence of the fluorescence rate of pointsource emitters to their surrounding environment. Here, we experimentally show that this framework is not necessarily relevant for ensembles of interacting emitters and that a different rule governs their interactions with their environment—the local Kirchhoff law recently introduced by Greffet et al, which arises when the carriers are in a thermodynamic quasiequilibrium.
We discuss the specificities of this regime by considering assemblies of PbS nanocrystals in direct contact with metal nanostructures. We illustrate the new opportunities of these findings by showing: (i) that the emitters are not quenched by the metal, even if the latter is a very lossy material. In fact, the radiation efficiency is maximum when the emitters are touching the metal. (ii) that the carrier quasiequilibrium imprints its signature in the photoluminescence and electroluminescence spectra. (iii) that the isotropic and unpolarised luminescence of the PbS nanocrystals can be turned into vector beams and other nontrivial light forms associated with fruitful developments in fluorescence imaging, optical trapping, highspeed telecommunications and quantum technologies.

Séminaire Doctorants (Institut Langevin, ESPCI Paris  PSL, France) mardi 18 janvier 2022, 11:00, Salle 310

Fluidcoupled mechanical waveguides for ultrasonic sensing Daniel Kiefer (Institut Langevin, ESPCI Paris  PSL, France) mardi 11 janvier 2022, 11:00, Salle 310
Résumé: Transittime ultrasonic flow meters measure the fluid flow rate through a pipe by exploiting the nonreciprocity due to flow. Robust operation in a wide temperature range from 0°C to 100°C is, thereby, a major practical challenge. A second difficulty arises when conveniently insonifying the pipe's interior from the outside, in which case the pipe wall acts as a mechanical waveguide. The interaction with the fluid medium results in quasiguided (leaky and trapped) waves in the sense that their energy is no longer strictly confined within the pipe wall – an effect that is desired in this context. These quasiguided waves are described by an intricate nonlinear eigenvalue problem. From a theoretical point of view, I will outline a procedure to reliably obtain the full set of solutions. Although the obtained waves are very convenient conceptually, their physical nature is – to date – not fully understood. From a more practical point of view, I will present how these waves can be used to conveniently model transittime ultrasonic flow sensors, thereby including the effect of temperature. Compared to conventional meters, we find that the time of flight of guided wave based sensors exhibits a decreased crosssensitivity to temperature. This is a consequence of the temperaturedependent radiation angle of leaky waves, which tends to compensate corresponding changes of the fluid wave speed. Finally, I will give an overview of accompanying projects: Schlieren photography of ultrasound, electromagneticacoustic transducers for waveguide excitation, a dipstick sensor for fluid characterization and ultrasonic holography.

Probe coupled to a Gaussian field: effective dynamics and nonlinear
memory Vincent Démery (Gulliver, ESPCI Paris  PSL, France) mardi 07 décembre 2021, 11:00, Salle 310
Résumé: The effective dynamics of a probe coupled to its environment can be
quite complex: it often becomes nonMarkovian, its longtime diffusion
coefficient can be reduced or increased, depending on whether the system
is at equilibrium or not, and it may acquire a confinement dependent
effective memory. I will first introduce typical effects induced by the
environment. I will then introduce the general model of a probe linearly
coupled to a Gaussian field, and the systems that it may represent. I
will determine the effective dynamics of the probe and show how to
compute the key observables perturbatively. Last, I will discuss how our
results shed light on the usual modeling of complex fluids with a linear
memory kernel.

Waves at the surface of soft elastic gels Pierre Chantelot (Physics of Fluids, University of Twente, Nederlands) mardi 30 novembre 2021, 11:00, Amphithéâtre
Résumé: Wave propagation at the surface of soft elastic solids brings up questions about the existence of forces able to compete with bulk elasticity. I will discuss the interplay between elastic, capillary and gravity forces on surface and guided waves, and how wave propagation measurements could reveal the nature of the interface of soft solids. I will show that for guided waves, capillary effects become visible by affecting the balance of inplane and outofplane displacements at the interface and that they are enhanced for small thicknesses. I will also discuss how using gravity as a destabilising force enables us to dramatically affect the elastogravity wave dispersion relation.

MicroNano structured materials in 3D Arturo Susarrey Arce (Mesoscale Chemical Systems research group, University of Twente, Nederlands) lundi 29 novembre 2021, 14:30, Amphithéâtre
Résumé: There is a latent need for more refined threedimensional elements in optics, electronics, energy, and health. In this seminar, micro(nano)fabrication approaches for the production of threedimensional structures are explored. Applications in the field of (i) Optoelectronics and energy with the fabrication of 3D luminescent materials using twophoton lithography and electrospinning, (ii) the use of nanolithography for the fabrication of 3D plasmonic materials, and (iii) the usage of 3D structures for the growth of spheroids will be provided. At the end of the seminar, a reflection on what more 3D MicroNano structured materials have to offer will be covered.

Séminaire Doctorants (Institut Langevin, ESPCI Paris  PSL, France) mardi 23 novembre 2021, 11:00, Amphithéâtre

Séminaire Doctorants (Institut Langevin, ESPCI Paris  PSL, France) mardi 26 octobre 2021, 11:00, Amphithéâtre

Nonthermal electrons in metal nanostructures – “reality” or “fake news”? Yonatan Sivan (Ben Gurion University, Israël) vendredi 15 octobre 2021, 11:00, Amphithéâtre
Résumé: We present a selfconsistent theory of the steadystate electron distribution in metals under continuouswave illumination which treats, for the first time, both thermal and nonthermal effects on the same footing. We show the number of nonthermal electrons (i.e., the deviation from thermal equilibrium) is very small, so that the power that ends up generating these nonthermal electrons is many orders of magnitude smaller than the amount of power that leads to regular heating.
Using this theory, we reexamine the exciting claims on the possibility to enhance chemical reactions with these nonthermal electrons. We identify a series of rather astounding errors in the temperature measurements in some of the most famous papers on the topic which led their authors to underestimate regular heating effects. As an alternative, we show that a very simple 19th century theory, based on just simple heating, can explain the published experimental data with excellent accuracy.

Artificial graphenes: Dirac matter beyond condensed matter Gilles Montambaux (Laboratoire de Physique des Solides, Université ParisSaclay, France) mardi 28 septembre 2021, 11:00, Amphithéâtre
Résumé: After the discovery of graphene and its so many fascinating properties, there has been a growing interest for the study of “artificial graphenes”. These are totally different and novel systems which bear exciting similarities with graphene. Among them are lattices of ultracold atoms, microwave or photonic lattices, “molecular graphene”, or phosphorene. The advantage of these structures is that they serve as new playgrounds for measuring and testing physical phenomena which may not be reachable in graphene, in particular: the possibility of controlling the existence of Dirac points (or Dirac cones) existing in the electronic spectrum of graphene, of performing interference experiments in reciprocal space, of probing geometrical properties of the wave functions, of manipulating edge states, etc.
These cones, which describe the band structure in the vicinity of the two connected energy bands, are characterized by a topological “charge”. They can be moved in reciprocal space by appropriate modification of external parameters (pressure, twist, sliding, stress, etc.). They can be manipulated, created or suppressed under the condition that the total topological charge be conserved. The merging between two Dirac cones is thus a topological transition that may be described by two distinct universality classes, according to whether the two cones have opposite or like topological charges.
In this presentation, I will discuss several aspects of the scenarios of merging or emergence of Dirac points as well as the experimental investigations of these scenarios in condensed matter and beyond.

Développement au c2rmf et dans le cadre du projet Espadon des techniques de tomographie appliquées aux sciences du patrimoine Vincent Detalle (Ministère de la Culture et de la Communication, France) mardi 21 septembre 2021, 11:00, Amphithéâtre

Séminaire Doctorants (Institut Langevin, ESPCI Paris  PSL, France) mardi 14 septembre 2021, 11:00, Amphithéâtre

Noninvasive fluorescence imaging deep in scattering media Sylvain Gigan (KastlerBrossel Laboratory, ENS  PSL, Sorbonne U., CNRS, Collège de France, France) mardi 15 juin 2021, 11:00, Amphithéâtre

InceGauss Modes of Aberrated Cavities as Emulators of ManyBody Topological Transitions Rodrigo GutierrezCuevas (Institut Fresnel, Marseille, France) mardi 08 juin 2021, 11:00, En ligne
Résumé: Here, we show that the wellknown and simple system of a resonant cavity with slightly aberrated curved mirrors is analogous to a BoseHubbard dimer, a wellknown model in condensed matter physics. The modes of the aberrated cavity, namely the InceGauss beams, present two topologically distinct regimes: the HGlike regime where astigmatism dominates, and the LGlike regime where spherical aberration dominates. These are analogous to the Rabi and Fock regimes of the BoseHubbard system. By considering the rayoptical limit, we further show that, as the ratio between the two aberrations changes, the ray structure undergoes a topological transition. This transition can be visualized in the Poincaré/Bloch sphere where the ray structure goes from being describable in terms of a single loop to splitting into two loops. Additionally, we derive and model the dynamical behavior in the ray limit, where we show that the evolution of a ray inside the aberrated cavity follows the meanfield twomode GrossPitaevskii equation. We also consider the wave model and show that the aberrated cavity can emulate pure quantum behavior such as the squeezing of a coherent state.

Novel Imaging Techniques in Laser Ultrasonic at Micrometer Scale Sylvain Mezyl (Institut Langevin, ESPCI Paris  PSL, France) mardi 01 juin 2021, 11:00
Résumé: In this talk, I will discuss some of the works I conducted in my last two postdoctoral positions.
In a first part, I will present a novel method in laser ultrasonic using ultrashort pulses that allows to image any arbitrary frequency at GHz frequency by intensitymodulating the pump beam. WhisperingGallery Modes and ZeroGroup Velocity Modes are tracked and imaged.
In a second part, I will describe a microendoscope, with a 125x250 µm2 footprint, and performing photoacoustic and fluorescent imaging through a multimode fibre using wavefront shaping.
Finally, I will present experimental evidences of a novel memory effect in peculiar multimode fibres. A simple model is associated to interpret this phenomenon.

Séminaire des doctorants mardi 25 mai 2021, 11:00

Carbon nanostructures as quantumlight sources Christophe Voisin (LPENS, ENS  PSL, Paris, France) mardi 18 mai 2021, 11:00
Résumé: Singlephoton sources are a key building block for secured quantum telecommunications. In view of integration in long range telecommunication networks nearinfrared emission and room temperature operation are current challenges.
Carbon nanostructures and especially carbon nanotubes have strong assets in this perspective. They can be operated as high quality singlephoton emitters. In addition, their emission wavelength can be chosen over a wide range using the variety of their geometry (the chiral family) or external chemical functionalization. Nevertheless, the reported brightness is consistently small and the spectral purity is not well controlled. Moreover, the origin of the photon antibunching (usually a fingerprint of atomlike emitters) in this 1D system has long been controversial. We address this issue using hyperspectral superresolution techniques inspired by bioimaging.
These key properties can be drastically improved by coupling the nanostructure to a small volume, highfinesse optical cavity through the socalled Purcell effect. In fact, lightmatter interaction at the scale of a single emitter can be strongly modified when the electromagnetic field in confined to volumes of the order of lambda^3 , which is the realm of cavity quantum electrodynamics. Originating from atomic physics, this field has become technologically relevant when solid state emitters (quantum wells, quantum dots…) were first coupled to integrated microcavities. Here, we used an original tunable cavity design using a scanning optical fiber in order to tackle the spatial and spectral mode matching issues. We show that the emission rate of the nanotube can be enhanced by a factor 60 leading to an effective brightness of about 0.4 and a coupling factor close to 100%.
Furthermore, our original design brings a wide tuning range for the singlephoton source by exploiting indirect emission processes assisted by acoustic phonons. This new feature is very attractive for multiplexing approaches or for indistinguishability engineering from remote nanosources for quantum information processing.

Ultrasound for the brain: new tools for reading and writing in the neural circuits Charlie Demené (Physics for Medecine, ESPCI Paris  PSL, France) mardi 04 mai 2021, 11:00

Séminaire des doctorants mardi 27 avril 2021, 11:00, Salle 310

Multiple scattering of ultrasonic waves in complex media: applications in fisheries acoustics. Benoît Tallon (ISTERRE, Grenoble, France) mardi 20 avril 2021, 11:00, En ligne
Résumé: Wave transport in complex media is widely studied through calibrated model systems ranging from nanopowder (in optics) to millimetric beads aggregates (in acoustics). Those samples are designed to strongly scatter waves and achieve complex transport phenomena such as wave subdiffusion. In this seminar, I will show how model systems achieved by millifluidics are good candidates to study such phenomena with ultrasounds. Then, we will see how similar observations can be done in a natural disordered system namely: a shoal of fish. The parallel between laboratory and in situ experiments gives i) new characterization tools for fisheries acoustics and ii) leads for the bioinspired design of disordered systems.

Nonlinear MetaOptics Giuseppe Leo (Laboratoire Matériaux et Phénomènes Quantiques, Université de Paris, France) mardi 06 avril 2021, 11:00
Résumé: Alldielectric nonlinear metasurfaces have recently brought harmonic generation to subwavelength level, with spectral and polarization control unachievable in bulk crystals. Not only does metaoptics define a field for investigating nonlinear physics at the nanoscale, but it also opens promising application perspectives. Compared to plasmonics, where the electric field is strongly confined close to the metal surface, the electric field of the resonant modes in dielectric nanoparticles penetrates deep inside their nondissipative volume, enhancing intracavity lightmatter interactions and their nonlinear optical response.
In this seminar, I will briefly review the fundamentals of this new research field, from modeling to technology and experimental techniques, with a focus on χ(2) nonlinear nanoantennas and metasurfaces. Then I will comparatively discuss the use of quasinormalmode formalism and multipolar expansion of the scattering efficiency to describe nonlinear frequency conversion at the nanoscale. Finally, based on the χ(2) fully tensorial features of AlGaAs metasurfaces, I will present our recent demonstration of 02π phase control on an harmonic field, generated for the first time with a sufficient efficiency for practical purposes.

Séminaire des doctorants mardi 23 mars 2021, 11:00, Salle 310

Moving needles in moving haystacks: probing material failure at the microscale Stefano Aime (C3M, ESPCI Paris  PSL, France) mardi 16 mars 2021, 11:00, Webinar / En ligne
Résumé: The failure of materials under load is widespread, occurring from geological scales, as in earthquakes, to biological and softmatter systems, with huge implications to everyday life and material science. Despite consistent efforts in this field, failure is very often undesired and unpredicted: surprisingly, or maybe unsurprisingly, it turns out that what is so common in our daily experience is based on profound science that is not yet fully understood.
In this talk I will discuss experiments in which we investigate the microscopic signature of failure in various soft materials, by simultaneously measuring their mechanical response and microscopic dynamics. Our experiments show that material failure is associated with qualitative and quantitative changes of the dynamics, from reversible particle displacements to bursts of irreversible plastic rearrangements.

2D IIVI semiconductor nanoparticles: controlling the heterostructures and surface chemistry for band engineering Sandrine Ithurria (LPEM, ESPCI Paris  PSL, France) mardi 02 mars 2021, 11:00

Séminaire des doctorants mardi 23 février 2021, 11:00, Salle 310

Anderson localization of ultrasound in disordered anisotropic media Antton Goicoechea (Institut Langevin, Paris, France) mardi 02 février 2021, 11:00, Webinar
Résumé: The effects of structural anisotropy on wave transport can be quite intriguing. I will show that, in a disordered anisotropic material, anisotropy in the propagation of multiply scattered waves is significantly reduced and may even vanish as the Anderson localization transition is approached, by capitalizing on advantages of ultrasonic experiments. Initial results using a random matrix approach to describe wave transport in an anisotropic system also support this experimental observation. These findings are expected to be very general, as the underlying physics is relevant to all types of waves (electrons, matter waves, and optical and acoustic waves), and they also resolve a puzzling question raised by previous conflicting theoretical predictions.

Séminaires des doctorants mardi 26 janvier 2021, 11:00

La vaccination et le vaccin anticovid: questionsréponses Martine Boccara (Institut de Biologie de l'École Normale Supérieure, Paris, France) mardi 19 janvier 2021, 11:00, En ligne

Time reversal of optical waves Joel Carpenter (University of Queensland, Brisbane, Australia) mardi 12 janvier 2021, 11:00, En ligne
Résumé: Lossless linear wave propagation is symmetric in time, a principle which can be used to create time reversed waves. Such waves are special “prescattered” spatiotemporal fields, which propagate through a complex medium as if observing a scattering process in reverse, entering the medium as a complicated spatiotemporal field and arriving after propagation as a desired target field, such as a spatiotemporal focus. Time reversed waves have previously been demonstrated for relatively low frequency phenomena such as acoustics, water waves and microwaves. Many attempts have been made to extend these techniques into optics. However, the much higher frequencies of optics make for very different requirements. A fully time reversed wave is a volumetric field with arbitrary amplitude, phase and polarisation at every point in space and time. The creation of such fields has not previously been possible in optics. We demonstrate time reversed optical waves with a device capable of independently controlling all of light’s classical degrees of freedom simultaneously. Such a class of ultrafast wavefront shaper is capable of generating a sequence of arbitrary 2D spatial/polarisation wavefronts at a bandwidth limited rate of 4.4 THz. This ability to manipulate the full field of an optical beam could be used to control both linear and nonlinear optical phenomena.

Unconventional optical wavefront shaping and imaging Pascal Berto (Institut de la vision, Paris) mardi 08 décembre 2020, 11:00, Webinar
Résumé: In recent decades, the advent of spatiallyresolved techniques to control and image the phase of light waves has profoundly transformed photonics, enabling major advances in several fields, including microscopy. In this talk, I will first present a wavefront shaping concept in which the phase of the transmitted light is shaped at the microscale by using the thermooptical effect. By engineering the temperature landscape in a thermooptical material, one forms a distribution of refractive index associated to a desired microoptical element (lens, axicon, etc.), with an electricallytuneable amplitude. I will explain how this simple and compact concept could complement the existing optical shaping toolbox by offering lowchromaticaberration, polarizationinsensitive and transmissionmode microcomponents. In the second part of this talk, dedicated to phase imaging, I will describe how a broadband and costeffective wavefront sensor (WFS) can be simply implemented by placing a thin diffuser in the close vicinity of a camera. For such a diffuser, a local wavefront gradient yields a local translation of the speckle pattern, a property ensured by the socalled “memory effect”. After describing the WFS itself, I will discuss the potential of the technique for quantitative phase imaging of biological samples and for 3D nanoparticle superlocalization and tracking. Finally, we will see that the unique signature of the speckle patterns allows to multiplex several wavefronts incoming at various angles.

Singlemolecule studies of transcription elongation and pausing by RNA polymerase Antony Lee (LP2N, Institut d’Optique, Bordeaux) mardi 24 novembre 2020, 11:00, webinar
Résumé: Transcription by RNA polymerase (RNAP) is interspersed with sequencedependent pausing. The processes through which paused states are accessed and stabilized occur at spatiotemporal scales beyond the resolution of previous methods, and are poorly understood. Here, we combine highresolution optical trapping with improved data analysis methods to investigate the formation of paused states at enhanced temporal resolution. We find that pause sites reduce the forward transcription rate of nearly all RNAP molecules, rather than just affecting the subset of molecules that enter longlived pauses. We propose that the reduced rates at pause sites allow time for the elongation complex to undergo conformational changes required to enter longlived pauses. We also find that backtracking occurs stepwise, with states backtracked by at most one base pair forming quickly, and further backtracking occurring slowly. Finally, we find that nascent RNA structures act as modulators that either enhance or attenuate pausing, depending on the sequence context.

Superresolution microscopy at visible and nearinfrared wavelengths: from nanomaterials to deep tissue imaging Laurent Cognet (LP2N, Institut d’Optique, Bordeaux) mardi 17 novembre 2020, 11:00, webinar
Résumé: Singlemolecule localization microscopy (SMLM) is a key approach to study structural and dynamic arrangements of the matter at the nanoscale in a wide range of applications. As a member of the “superresolution microscopy” family SMLM indeed provides optical images with resolutions well beyond the diffraction limit. Yet, it remains challenging to study more complex systems than isolated nanostructures or isolated living cells in biology with such approaches. For instance, SMLM in thick and intact brain tissues is penalized by the limited brightness of fluorescent emitters, the optical aberrations induced by the samples and/or the poor penetration of the light into biological tissue at visible wavelengths.
To circumvent these limitations and push the applicability of SMLM, we recently proposed several new schemes. I will first present SELFI, an original strategy to superlocalise single emitters in 3D at unprecedented depths inside a biological tissue and thus allow 3D superresolution microscopy in such complex systems. I will then present another approach based on single carbon nanotube tracking in the nearinfrared to obtain superresolved maps of the extracellular space within intact live brain tissues and in the context of neurodegenerative diseases. Finally, I will show that a novel family of single molecule nanoprobes can be engineered for SMLM in the nearinfrared through the creation of photoswitchable carbon nanotube and ultrashort carbon nanotube displaying localized emission centers that could be reveal by superresolution microscopy of the nanotube themselves.

Cavities with tunable boundaries : from wave chaos to applications with microwave cavities JeanBaptiste Gros (Institut Langevin) mardi 10 novembre 2020, 11:00, webinar
Résumé: For decades, wave chaos has been an attractive field of fundamental research concerning a wide variety of physical systems such as quantum physics , room acoustics or ocean acoustics, elastodynamics, guidedwave optics, microwave cavities. The success of wave chaos is mainly due to its ability to describe such a variety of complex systems through a unique formalism, the socalled random matrix theory (RMT), which permits us to derive a universal statistical behaviour. More recently, chaotic cavities have been involved in a large variety of applications ranging from computational imaging to electromagnetic (EM) compatibility testing, as well as wavefront shaping for telecommunication or wavebased analog computation. Among all the universal statistics of chaotic cavities, the most important one for these applications is field ergodicity meaning that the fields in chaotic systems are statistically equivalent to an appropriate random superposition of plane waves.
To implement a wave chaotic system experimentally, traditionally cavities of elaborate geometries (bowtie shapes, truncated circles, parallelepipeds with hemispheres) are employed because the geometry dictates the wave field’s characteristics. In the first part of this talk, I will present a radically different paradigm: a cavity of regular geometry with tunable boundary conditions, experimentally implemented by leveraging electronically reconfigurable metasurfaces (ERM) developed by GreenerWave. The latter are able to locally imposed a πphase shift on the reflected field. In a way, the ERMs are EM equivalent of Spatial Light Modulators used in optics or Schroeder's diffusers used in room acoustics with the difference in this case that the ERM are reconfigurable at will.
In the second part of this talk, I will present three applications using reconfigurable cavity.

Light interaction with nanoresonators Philippe Lalanne (LP2N, Institut d'Optique d'Aquitaine) mardi 03 novembre 2020, 11:00, Webinar
Résumé: Resonators are triggering the development of various applications in nanooptics, from quantum information processing, plasmonassisted lasing, to nanosensing of biomolecules. The properties of cavities, of any kind, are due to their intrinsic natural resonance modes. Because of dissipation, either by absorption or leakage in the open space, the modes have a finite lifetime. They are eigenstates of a nonHermitian operator, here the Maxwell’s equations.
Two characteristic parameters, which figure prominently in the physics and device applications of cavities, quantify the capability of cavity modes to boost lightmatter interactions, the quality factor Q and the mode volume V.
It is therefore important to be familiar with the modes, their Qs, their Vs, their excitation rate by plane waves or nearfield sources, their perturbation by tiny objects ... Usually, all these concepts are well comprehended in the limit of Hermitian physics. We will revisit them substantially in the framework of nonHermitian physics, trying to answer questions such as: how we partition the LDOS between V and Q? Is it simply Q/V? Is the definition of Q so evident? Why V should be complex valued? What is the signification of Im(V)?

Séminaires des doctorants mardi 27 octobre 2020, 11:00, Salle 310

Phase behavior and dynamics of nonequilibrium particulate systems: from granular gases to selfpropelled colloids Nariaki Sakai (Institut Langevin, Paris) mardi 20 octobre 2020, 11:00, Salle 310
Résumé: Granular material has been a model experimental system to probe to what extent standard statistical mechanics apply to outof equilibrium systems. Grains are characterized by a negligible thermal fluctuations and dissipative interparticle interactions. Thus, static steady states are necessarily at rest, and any dynamical steady state like granular gases necessarily involves injection of energy, and this flow of energy shifts the material towards an outof equilibrium steady state. On the contrary, colloidal suspensions are subject to thermal fluctuations and evolve at equilibrium similarly to molecular fluids, but it is also possible to make it out of equilibrium by driving externally the material e.g. shear or under any external potential energy field, or internally like in active matter or selfpropelled particles. These systems have focused the attention of many researchers, in particular because it can mimick collective behaviours we can observe in living systems, like swarming of bacteria, or flock of birds.
In this talk, I will briefly present my background and the context of the experimental work I did during my PhD on driven granular suspensions. Then I will present in more detail the work of my former postdoc on imaging of 3d dense suspension of selfpropelled colloidal particles. Finally, I will shift towards the work I am currently doing in the Institute with Xiaoping Jia and Arnaud Tourin on wave propagation in a disordered elastic lattice  a numerical toy model to understand sound propagation in granular media. I will especially present some preliminary results concerning the relation that can exist between open and close eigenchannels of a disordered medium  obtained from its scattering matrix  and its structure e.g. the vibrational modes.

Coupling supercritical angle fluorescence with superlocalization microscopy unlocks unbiased, reproducible 3D bioimaging Clément Cabriel (Institut Langevin, Paris) mardi 13 octobre 2020, 11:00, Salle 310
Résumé: Among fluorescence microscopy techniques, single molecule localization microscopy (SMLM) is a powerful high resolution tool commonly used in biology for both structural and functional imaging. Provided samples are adequately labelled, multiple proteins can be imaged down to the 10nm scale. Most 3D SMLM strategies resort to Point Spread Function (PSF) shaping to encode the axial information in the shapes of the PSFs. Although they are relatively straightforward to implement and offer a good compromise between precision and capture range, these approaches not only rely on a critical calibration step, but also share a common drawback—the axial information retrieved in relative to the focal plane. As such, they suffer from many experimental nonidealities, which include axial drift, axial chromatic aberration and sample tilt. This lack of reliability has hindered wider use of 3D SMLM.
Here, we propose to exploit the nearfield part of the fluorescence emission, which yields intrinsic information about the absolute axial position of emitters in the sample. Indeed, at the biological sample/glass coverslip interface, the index mismatch causes a part of the evanescent emission of the molecules to become coupled into propagative waves as they reach the interface. This fluorescence component consequently propagates above the critical angle, and is called Supercritical Angle Fluorescence (SAF). It can be collected through a high numerical aperture objective, and pupil plane filtering allows its extraction from the rest of fluorescence. As the SAF intensity decays with the distance from the emitter to the coverslip, its axial position can be obtained independently from the position of the focal plane.
While this detection modality has a shallow capture range (~200 nm), it can be used as a complementary absolute reference in PSF shapingbased SMLM. We use a crosscorrelation algorithm that takes both the SAF and PSF shaping axial positions of each molecule as inputs to determine the position of the focal plane and correct the 3D SMLM data. Characterization of the results evidences the efficient correction of chromatic aberration, axial drift and sample tilt. Finally, we provide examples of biological applications to multicolor cytoskeleton, neurons and bacteria samples imaging.

Séminaires des doctorants mardi 06 octobre 2020, 11:00, Salle 310

Wavefront sensing with a thin diffuser: principle and its applications Tengfei Wu (Institut de la vision, Paris) mardi 22 septembre 2020, 11:00, Salle 310
Résumé: Using the “memory effect”, we propose and implement a broadband, compact, and costeffective Wavefront Sensing scheme with a simple thin diffuser. We experimentally demonstrate its various capabilities to provide quantitative phase imaging, nanoparticle tracking and superlocalization.

Séminaires des doctorants mardi 30 juin 2020, 11:00, En ligne

Séminaires des doctorants mardi 26 mai 2020, 11:00, En ligne

Pascal Berto (Institut de la vision, Paris) mardi 19 mai 2020, 11:00, Salle 310 [ANNULÉ]

Philippe Lalanne (Institut d'Optique, Bordeaux) mardi 12 mai 2020, 11:00, Salle 310 [ANNULÉ]

Séminaires des doctorants mardi 28 avril 2020, 11:00, Salle 310 [ANNULÉ]

Laurent Cognet (LP2N, Institut d’Optique, Bordeaux) mardi 14 avril 2020, 11:00, Amphi IPGP [ANNULÉ]

Arnaud Brignon (Thales, Paris) mardi 31 mars 2020, 11:00, Amphi IPGP [ANNULÉ]

Juanjo Saenz (DIPC, San Sebastian) jeudi 26 mars 2020, 11:00, Salle 310 [ANNULÉ]

Christophe Moser (Laboratory of Applied Photonics Devices, EPFL) mardi 24 mars 2020, 11:00, Salle 310 [ANNULÉ]

Ludovic Margerin (IRAP Observatoire MidiPyrénées, Toulouse) mardi 17 mars 2020, 11:00, Amphi IPGP [ANNULÉ]

Improvement of Central SNR and Transmit Coverage of a Human Head Phased Array at UltraHigh Field Using Dipole Antennas Nikolai Avdievitch (Max Planck Institute for Biological Cybernetics, Tübingen, Germany) mardi 25 février 2020, 11:00, Amphi IPGP
Résumé: The first part of the presentation deals with an improvement of the central SNR of human head array at ultrahigh magnetic fields (UHF, > 7T). Increasing the number of surface loops in a human head receive (Rx) array improves the peripheral signaltonoise ratio (SNR), while SNR near the brain center doesn’t substantially change. Recent theoretical works demonstrated that an optimal central SNR at UHF requires contribution of two current patterns associated with a combination of surface loops and dipole antennas. Use of various dipole antennas as MRI RF detectors has been recently introduced and successfully implemented mostly for imaging human body sized objects. In this work, we evaluated and compared several Rx dipolelike elements for use within human head UHF Rxarray. We constructed and characterized novel singlerow and doublerow phased arrays, which consisted of transceiver (TxRx) surface loops and Rxdipoles. We demonstrated that combining surface loops and dipolelike elements substantially (> 30%) improve SNR near the brain center as compare to arrays consisted of surface loops only. The second part of the presentation discusses an improvement of the transmit (Tx) coverage of the human head array coils. Due to a substantial shortening of the RF wave length (below 15 cm at 7 T), RF magnetic field at UHF has a specific Tx excitation pattern with strongly decreased (more than 2 times) values at the periphery of a human head. This effect is seen not only in the transversal slice but also in the coronal and sagittal slices, which considerably limits the longitudinal Txcoverage (along the magnet’s axis) of conventional surface loop head arrays. In this work, we developed a novel human head UHF array consisted of 8 TxRx foldedend dipole antennas circumscribing a head. Due to an asymmetrical shape of dipole elements, the array couples to the intrinsic “dielectric resonance” mode of the head. Due to this interaction, firstly, the new array provides for a simple way of minimizing the maximum local SAR. Secondly, it provides for a longitudinal coverage better than that achieved by a similar array consisted of unfolded dipoles as well as by an 8element singlerow and 16element doublerow surface loop arrays.

Fluid dynamics in zebrafish embryos Olivier Thouvenin (Institut Langevin) mardi 18 février 2020, 11:00, Amphi IPGP
Résumé: During this seminar, I will describe and explain a set of surprising observations made a few years ago in zebrafish embryos. The cerebrospinal fluid (CSF) was found to flow bidirectionally in a single channel in the center of the spinal cord, and to form several vortices, despite the small Reynolds number. In this work, we combined biology experiments with modeling and simulations to explain the origin of this flow and predict its impact on zebrafish embryogenesis.
We demonstrated that CSF flow is established thanks to an active force, generated by small motile cilia beating only on one side of the channel. We found that this active force imposes a pressure gradient inside the channel that probably help to maintain the channel structure. We also demonstrate that the bidirectional flow accelerates the transport of particles in the CSF via a coupled convectivediffusive transport process, in a regime similar to the TaylorAris diffusion.
Finally, I will turn to some (more) biology, and show how CSF circulation contributes to body axis formation and brain development. We now have several clues that pathological CSF circulation can lead to various diseases such as idiopathic scoliosis or meningitis.

Les vortex acoustiques, concept et applications Régis Marchiano (Institut Jean le Rond d'Alembert, Paris) mardi 04 février 2020, 11:00, Amphi IPGP
Résumé: Une onde peut être caractérisée par son amplitude, sa phase et parfois sa polarisation. Il arrive qu'une de ces quantités devienne singulière. L'exemple le plus connu est celui des caustiques, qui sont des singularités d'amplitude (en optique les exemples sont nombreux : caustique de la tasse à café, arcenciel...). Un autre type de singularité moins connu est la singularité de phase qui correspond à une onde dont la phase n'est pas définie en un ou plusieurs points de l'espace. En acoustique, ces singularités existent aussi : les vortex acoustiques sont un exemple de singularité de phase, ils sont caractérisés par un front d'onde hélicoïdal. La phase s'enroule alors autour de l'axe de propagation le long duquel elle n'est pas définie. Cette structure de phase s’accompagne d’un zéro d'amplitude le long de l'axe de propagation. Loin d’être une simple curiosité théorique, ce type d’ondes est de plus en plus étudié car il possède de nombreuses propriétés intéressantes pouvant être mises à profit dans des applications. La première partie de l’exposé sera consacrée à la présentation de ces ondes : leur structure et leurs principales propriétés (généricité, stabilité, conservation de la charge topologique, effet paramétrique, onde de choc azimutale). Puis, dans une deuxième partie, trois applications récentes basées sur ces ondes seront présentées. D’abord, l’alignement sousmarin qui consiste à utiliser la singularité de phase comme un traceur spatial. Ensuite la manipulation 3D sans contact qui est basée sur le fait qu’un vortex acoustique exerce une force (grâce à l’effet de pression de radiation) avec un point d’équilibre stable. Enfin, la caractérisation de matériaux et la rhéologie qui peuvent tirer parti du couple qu’exerce un vortex acoustique lors de son interaction avec un objet.

Multiple light scattering as a probe of local dynamics in liquid foams Sylvie CohenAddad (Institut des NanoSciences de Paris, Sorbonne Université) mardi 28 janvier 2020, 11:00, Amphi IPGP
Résumé: Liquid foams, i.e. aqueous foams or concentrated emulsions, are made of a dense packing of soft particles in a surfactant solution. These structures are intrinsically unstable and age with time via intermittent local particle reorganisations. Besides, their mechanical response goes from solidlike to liquidlike when the applied load is large enough to trigger particle rearrangements. Local structural changes are thus the keyprocesses underlying both the ageing and the mechanical behaviour.
Foams strongly scatter light and tend to be opaque, which prevents direct observations of internal rearrangements. However, multiple light scattering can be turned into benefit to design new noninvasive probes. I will present studies that illustrate how coarsening or strain induced local dynamics in liquid foams can be investigated using dedicated coherent light scattering experiments.

Advancing tools for fast and sensitive volumetric single molecule imaging in cells Bassam Haaj (Laboratoire Physico Chimie, Institut Curie) mardi 21 janvier 2020, 11:00, Amphi IPGP
Résumé: Single molecule imaging is becoming inevitable in many biophysical studies of cell processes. Cells are however threedimensional objects and intracellular events are typically not constrained to one focal plane, thus, the conventional single plane microscopy is inadequate for detailed studies of fast single molecule dynamics in three dimensions. In addition, the focal plane may frequently be at the wrong place at the wrong time, thereby missing important aspects of dynamic events.
I will present multifocus microscopy technique (MFM) that allows to image up to 9 focal planes in parallel on the same camera. Thanks to diffraction elements positioned at the emission path of a conventional widefield microscope it is possible to acquire an imaging volume of 20x20x4um with speeds of up to 200 volumes per second when bright particles are used. The advantage of MFM will be highlighted with example studies in yeast and mammalian cells. I will show how MFM can be tailored for multicolor imaging. Recent efforts for combining MFM with selective plane illumination will be exposed with examples of single molecule imaging inside the nucleus of living cells. I will also present a new software in virtual reality to visualize and interact with multidimensional pointcloud (single molecule) data.

Willis coupling in acoustic metamaterials and beyond its passivity bound Jensen Li (Hong Kong University of Science and Technology) mardi 17 décembre 2019, 11:00, Salle 310
Résumé: Here, we report our recent progress on acoustic and elastic Willis media, achieving the analogy of bianisotorpy in electromagnetism. We have demonstrated Willis coupling on a structured beam with resonating cantilever structures and its resultant asymmetric propagation of flexural waves on such a beam. Next, we experimentally demonstrate how the passive bound of Willis coupling can be surpassed by going to an active Willis medium.

Evolutionary Photonics: Structure, Function, Development and Biomimetics of Selfassembled Organismal Photonic Nanostructures Vinod Kumar Saranathan (NUS, Singapore) mardi 10 décembre 2019, 11:00, Amphi IPGP
Résumé: Colors in Nature can be produced either chemically, by the selective light absorption by pigments, or physically, by light interference from biophotonic nanostructures. Intriguingly, there are almost no known violet, blue or green pigments in animals. And yet these structurally produced colors are ubiquitous in nature and constitute an important aspect of the overall appearance of organisms, as they are frequently used in camouflage, and in social and sexual communication. As the underlying biophotonic nanostructures are overwhelmingly diverse in form and function, their structural and optical characterization has hitherto remained challenging despite centuries of research, which is where I have made rapid and significant contributions. Although there is a burgeoning interest on structural colors from biologists, physicists and engineers, we currently lack an explicit comparative framework, which is essential to understand how these biological signals function, and evolve in organisms. Moreover, the mechanisms controlling the morphogenesis of these complex, biologically patterned nanostructures are much too large to be described by conventional cell or molecular biology, and much too small to be captured by traditional developmental biology. As a consequence, we know very little about the development of photonic nanostructures within cells, beyond the realisation that they are selfassembled intracellularly by mechanobiological, phase separation and microphase separation like processes. Biophotonic nanostructures are also of broader interest to materials science and engineering, since the facile synthetic fabrication of threedimensional photonic nanostructures at these rather large optical length scales (200500 nm) is challenging. Organismal structural colors that have evolved over millions of years to function in a variety of signalling contexts are an ideal source to look for naturally optimized solutions to technological problems in sensing, photonics, etc. In this talk, I will summarise our current knowledge about the structure, function and morphogenesis of biophotonic nanostructures and how this can be leveraged for the biomimetic or bioinspired synthesis of next generation photonic metamaterials and devices.

Control and emergence of collective order in complex photonic and phononic media Nicolas Bachelard (TU Vienna) mardi 03 décembre 2019, 11:00, Amphi IPGP
Résumé: In wave physics, random media are characterized by the existence of multiple degrees of freedom as well as a subsequent multiplicity of configurations. In this talk, I will present different approaches that I developed to harness the versatility of disordered systems and force the emergence of collective order out of random ensembles.
First, I will consider the case of strongly scattering media filled with optical gain that create random lasing emissions (and are referred to as random lasers). While the spectrum of random lasers is typically multimode—composed of many frequencies, here I will demonstrate that the interaction amongst modes can be controlled through wavefrontshaping technique in order to collectively buildup a singlemode emission at tunable frequency.
Then, I will show that random populations of mobile particles can be driven to selforganize into outofthermodynamicequilibrium crystalline structures through the controlled dissipation of coherent energy. The elements individually synchronize their responses to dynamically develop collective properties such as resiliency abilities or the selfadaptation to the environment.

Séminaires des doctorants mardi 19 novembre 2019, 11:00, Salle 310

Developing new tools to achieve highresolution in the living human retina: imaging and surgical applications Pedro Baraçal de Mecê (Institut Langevin) mardi 12 novembre 2019, 11:00, Amphi IPGP
Résumé: The retina is the innermost, lightsensitive tissue of the eye which translates the image of the visual world into electrical neural impulses to the brain to create visual perception. Imaging the retina with a cellular resolution allows an additional inside of the visual perception process, ophthalmic pathologies, but also to neurodegenerative diseases since the retina is an optical window to the brain. However, the desired cellular resolution is hardly achievable mainly because of the ocular aberrations induced by the eye’s optics. Here, we present different strategies to achieve highresolution in the retina using fullfield imaging techniques. These strategies include the use of adaptive optics, darkfield illumination, structured illumination, and spatially incoherence light source combined with optical coherence tomography (OCT). We show how these different strategies could be used to guide retinal laser surgery and to study important retinal features in the living human eye such as neurons and vasculature, helping early disease diagnosis and monitoring of disease evolution.

Séminaires des doctorants mardi 05 novembre 2019, 11:00, Amphi IPGP

Direct reconstruction method in linear elastography with internal data Pierre Milien (Institut Langevin) mardi 22 octobre 2019, 11:00, Salle 310
Résumé: We present a new method to solve the linear elasticity inverse problem, i.e to reconstruct the Lamé parameters from the measurement of the displacement field in a medium. We will show why this method allows for stable inversion, then show how it can be numerically implemented and how it performs on simulated and experimental data.

Séminaires des doctorants mardi 17 septembre 2019, 11:00, Salle 310

Waveinduced softening and postdisturbance relaxation in dense granular matter through flow heterogeneities Charles Lieou (Center for Nonlinear Studies  Solid Earth Geophyics Group, Los Alamos National Laboratory) mardi 10 septembre 2019, 11:00, Amphi IPGP
Résumé: We report a series of experiments on the softening and volumetric compaction of a dense granular pack through acoustic pressure and shear waves. Softening is manifested by a reduction of standingwave resonance frequency, and of the travelingwave speed, as the amplitude of the disturbance increases beyond some threshold. We explain these observations using a theoretical model, based on shear transformation zones (STZs), that directly attributes these observations to dynamical heterogeneities and slipping contacts in the granular pack. We also discuss the slow relaxation in granular matter after the cessation of wave disturbance, and attribute the aging process to a broad spectrum of time scales and barrier heights in the STZ dynamics. In so doing, we demonstrate the fundamental connection between nonaffine granular rearrangements, mesoscopic glassy dynamics, jamming and unjamming, and matterwave interactions.

Séminaires des doctorants mardi 02 juillet 2019, 11:00, Salle 310

Generating entangled photons with tailored spatial correlations. Yaron Bromberg (Hebrew Univesity of Jerusalem) vendredi 28 juin 2019, 11:00, Amphi 45B, Rdc tour 45, Jussieu
Résumé: Quantum technologies hold great promise for revolutionizing photonic applications such as cryptography and imaging. Yet their implementation in realworld scenarios is held back, mostly due to sensitivity of quantum states of light to scattering. Recent developments in shaping of single photons introduce new ways to control scattering of quantum light. Here we cancel scattering of entangled photons, by shaping the classical laser beam that stimulates their creation. We show that when the laser beam and the entangled photons pass through the same diffuser, focusing the laser using classical wavefront shaping recovers the unique correlations of entangled photons, which were scrambled by scattering. Since the shaping is done exclusively on the classical laser beam, it does not introduce loss to the entangled photons, and it is not limited by the low signaltonoise ratios associated with quantum light.

Séminaire des doctorants mardi 18 juin 2019, 11:00, Salle 310

Superresolution photoacoustic imaging Sergey Vilov (Liphy, Grenoble) mardi 11 juin 2019, 11:00, Salle 310
Résumé: Acousticresolution photoacoustics (ARPA) permits spectralsensitive imaging in deep tissues by detecting acoustic waves resulting from light absorption.
The resolution in ARPA has been so far limited by acoustic diffraction. Inspired by superresolution methods introduced in optics, such as PALM, STORM and STED,
we seek to overcome the diffraction limit in ARPA. We demonstrate experimentally in vitro that superresolution in ARPA is achievable by such methods as
superlocalisation, fluctuationbased imaging, and modelbased reconstruction. In addition, we show that modelbased reconstruction can lead to
superresolution in sparsearray photoacoustic or ultrasound imaging. At the end, we determine strong and weak points of each method and
provide an outlook for superresolution photoacoustic imaging.

Fast, volumetric imaging with microscopes Jérome Mertz (Department of Biomedical Engineering, Boston University) mardi 28 mai 2019, 11:00, Amphi IPGP
Résumé: Fast, volumetric imaging over large scales has been a longstanding challenge in biological microscopy. Camerabased microscopes are typically hampered by the problem of outoffocus background which undermines image contrast. This background must be reduced, or eliminated, to achieve volumetric imaging. Alternatively, scanning techniques such as confocal and multiphoton microscopy can provide high contrast and high speed, but their generalization to volumetric imaging requires an axial scanning mechanism, which, in general, drastically reduces speed. I will describe a variety of strategies we have developed to enable fast, highcontrast, volumetric imaging over large length scales. These strategies include targetedillumination widefield microscopy, multiz confocal microscopy and reverberation multiphoton microscopy. I will discuss the principles of these strategies and present experimental validations.

Hyperbolic Plasmonic Materials R. Margoth CórdovaCastro (King's College, London) mercredi 22 mai 2019, 15:00, Salle 310
Résumé: Hyperbolic materials are anisotropic media which exhibit metallic or dielectric behaviour depending on polarisation. Natural hyperbolic materials as well as hyperbolic metamaterials, composites with engineered optical properties that opened up new avenues for light manipulation, have an unprecedented ability to concentrate light on deeply subwavelength scales which promises a wide variety of new applications in nanophotonic technologies.
I developed three new material platforms for the realisation and control of hyperbolic dispersion and described their optical properties. These include a metamaterial based on an array of plasmonic nanocones, heterostructured metamaterial based on AuZnOAu metaatoms and a natural hyperbolic material CuS. A combined experimental and theoretical study of the optical properties of CuS colloidal nanocrystals show that they exhibit anisotropic plasmonic behaviour in the infrared and support optical modes with hyperbolic dispersion in the visible spectral range. Heterostructured, layered AuZnOAu nanorod metamaterials
supporting guided modes were developed with the introduction of a nanoscale dielectric gap in the the metaatoms.
The role of the shape of metaatoms forming the array has been studied on the example of transformation of nanorods forming the metamaterial into nanocones. The plasmonic mode structure of the individual nanocones and pronounced coupling effects between them provide multiple degrees of freedom to engineer both the field enhancement and the optical properties of the metamaterials. These metamaterials are the first socalled gradient refractive index metamaterials that behave as a medium with elliptic optical dispersion in the region of the nanocone apexes and hyperbolic optical dispersion in the region of the bases. A scalable manufacturing process for these metamaterials allowing massproduction at the centimeter scales has been proposed and developed. The introduced natural and engineered plasmonic hyperbolic materials bring about new opportunities for future exploration and applications of these unusual systems in nanophotonics for linear and nonlinear light manipulation, fluorescence control, surface enhanced Raman spectroscopy as well as hotcarrier plasmonics and photocatalysis.

Séminaire des doctorants mardi 14 mai 2019, 11:00, Salle 310

Wireless Contact Lens Eye Tracker (WIRCLEY), the first bioembedded eye tracker JeanLouis de Bougrenet de la Tocnaye (IMT Atlantique) mardi 07 mai 2019, 11:00, Amphi IPGP
Résumé: A wireless contact lens, incorporating various functions such as data transfer, energy collection, eye movement extraction, is presented. It measures the direction of gaze, vergence, blinks and jerks, combining optical and RF technologies. Their implementation is discussed from flexible substrates, encapsulable in scleral lenses, such as microbatteries and graphenebased biofuel cells. Preliminary results will be presented.

Simulating articial graphene with superconducting
resonators Alexis Morvan (LPS, Orsay) mardi 30 avril 2019, 11:00, Salle 310
Résumé: We present the study of honeycomb lattice realized with superconducting circuit. Thanks
to a laser scanning microscopy, we are able to measure the weight of a mode on each
site of the lattice and thus observe the delocalization of states over the entire lattice. In
addition to mode labelling, this imaging allows to reconstruct the band structure using
a Fourier transformation. We have also developed an ab initio method to calculate this
band structure using electromagnetic simulation at a few network sites. This method
gives us a quantitative way to predict the band structure of the superconductor circuit
array.
The use of an articial platform such as superconducting circuits allows great versatility in
the parameters of the systems studied. This high tunability makes it possible to observe
phenomena that are dicult to access for 2D materials. With superconducting circuits,
we were able to design arrays to observe graphene edge modes as well as topological
edge modes at the interface between two graphenes with a bandgap. The latter presents
a manifestation of the topological charge present in each valley of a gapped Graphene.

The WignerSmith operator: timedelay, wavefront shaping and micromanipulation Stefan Rotter (TU Wien) vendredi 19 avril 2019, 11:00, Amphi IPGP
Résumé: In this talk I will speak about the WignerSmith timedelay operator and its multiple applications in complex scattering problems. In particular, I will focus on wave propagation through disordered media, where this operator can be used to derive an interesting mean pathlength invariance or for focusing waves on a target embedded inside the disorde. Finally, I will report on recent progress in using a suitably modified WignerSmith operator for the creation of scattering states that feature an optimal performance for micromanipulation.

Séminaire des doctorants mardi 16 avril 2019, 11:00, Salle 310

The physics of exceptional points Stefan Rotter (TU Wien) vendredi 12 avril 2019, 11:00, Amphi IPGP
Résumé: I will discuss here the recent exciting developments associated with nonHermitian degeneracies, also known as “exceptional points”. After having been studied mostly in the domain of mathematical physics, quite a number of experiments have recently demonstrated how the presence of exceptional points leads to very counterintuitive effects, such as lossinduced lasing, chiral field modes, topological energy transfer etc. I will try to provide an introduction to this topic as well as an overview of the many different areas of physics in which exceptional points are meanwhile being explored.

Reconfigurable Radiation Pattern Antennas for Spatial Modulation MIMO Communications and A Brief Introduction to the Backscatter Communications Kammel Rachedi (Institut Langevin) mardi 09 avril 2019, 11:00, Amphi IPGP
Résumé: Spatial Modulation Multiple Input Multiple Output (SMMIMO) appeared to address both the needs of growing data rate and energyefficient of smart devices for InternetofThings (IoT) and wireless networks (5G, WiFi, etc.…) applications. In the first part of the presentation, we propose to take benefit of coupling effects between resonators to generate different radiation patterns that stand for SMMIMO symbols. The first reconfigurable antenna results from the coupling of meander monopoles and Lshaped resonators are discussed. The experimental prototype generates efficiently between 4 and 8 patterns. The concept of spatial diversity that is a key feature in SMMIMO is discussed. The second reconfigurable antenna is a metamateriallike structure based on split ring resonators (SRR). A semianalytic model that describes the magnetoelectric coupling between SRR is developed in agreement with the numerical and experimental results proposed model. In a close collaboration with IETR, these antennas have been successfully implemented in a SMMIMO device to transmit information.
Most of the wireless communication devices used an active antenna to transmit information. However, researchers have been investigating the potential of backscatter communications to take the benefit of the ambient electromagnetic waves by modulating them with a backscatterer to a reader. This technique allows to lower down the power consumption just by recycling the ambient electric fields (DVBT, 4G, etc…). In the second part of the presentation, we show how the modulated field is strongly sensitive of interference effects between the direct path and the scattered one. Within a collaboration with Orange Labs, we propose a systematic survey of this effect of interferences. Fading patterns are observed even in a Line of Sight (LOS) configuration. Experimental results are validated by an analytical model. Finally, it is demonstrated that the Binary Error Rate (BER) is directly driven by these interferences.

Ultranarrow spectral filter for acoustooptic imaging for medical applications Caroline Venet (Institut Langevin) mardi 26 mars 2019, 11:00, Salle 310
Résumé: Acoustooptic imaging coupled with ultrasound modality would be able to discriminate between healthy or diseased biological tissues thanks to the additional optical contrast. Acoustooptic imaging is a multiwave technique which localizes light in very scattering media with acoustic waves. The main issue is the detection of the localized light. In this presentation the investigated solution is the use of a spectral filter based on spectral hole burning. The goal is to use a YAG crystal doped with thulium ions under a magnetic field, which increases the lifetime of the spectral hole from 10ms to longer than a minute.
In this presentation I will first give an overview of the context of my work. Then I will present the acoustooptic images achieved with a longlived spectral filter in Tm:YAG, in a scattering medium. Lastly, I will also raise the subject of the challenges specific to the addition of magnetic field to my setup.

Séminaire des doctorants jeudi 14 mars 2019, 11:00, Salle 310

Micromanipulation in disordered media with the generalized WignerSmith Operator Andre Brandstötter (Institute for Theoretical Physics, Vienna University of Technology) mardi 12 mars 2019, 11:00, Salle 310
Résumé: We utilize a generalization of the WignerSmith timedelay operator to manipulate a target embedded inside a disordered structure by shaping the incident wavefront. Such a manipulation involves, e.g., applying a welldefined torque onto the target or strongly focusing onto it. Our technique relies on the generalization of the WignerSmith timedelay operator and was successfully tested in a microwave setup featuring a waveguide containing a disordered medium.

Building Deep Learning Models: Bricks / Architectures / Applications Alexandre Popoff (Medisys Lab, Philips Research France) mardi 05 mars 2019, 11:00, Amphi IPGP
Résumé: Since 2012, the field of deep learning has seen numerous advances in various domains
(computer vision, speech recognition, natural language processing, etc.), often at a fast pace.
These evolutions often originate from paradigmatic developments in new neural network
architectures and layers. The purpose of this presentation is to give an overview of the
recent developments in deep learning by focusing on their constitutive bricks,
i.e. the layers, and the way they are assembled in various models.
As a concrete example of deep learning model building, we will study the recent participation of
Philips Research France (Medisys Lab) to the JFR (Journées Francophones de Radiologie) 2018 challenge on knee meniscus.
The goal of this challenge was to detect and classify tears in knee meniscii on MRI images.
The retained solution, which brought the first place to the Philips/Hospices Civils de Lyon team,
is a combination of image segmentation and classification models, with the addition of special image preprocessing.

Séminaire des doctorants mardi 19 février 2019, 11:00, Salle 310

Séminaire des doctorants mardi 29 janvier 2019, 11:00, Salle 310

Lightningfast solution of scattering problems in nanophotonics: an effortless modal approach Parry Yu Chen (Ben Gurion University ) mardi 15 janvier 2019, 11:00, Amphi IPGP
Résumé: Nanophotonic structures are capable of generating field hotspots, which can enhance quantum lightmatter interactions by many orders of magnitude. However, numerical simulations for applications such as radiative heat transfer, electron energy loss spectroscopy, van der Waals forces, Purcell factor throughout a volume, and many others are challenging and often computationally prohibitive. Common to these simulations is that the Green’s function or local photonic density of states must be known at each point across a volume of space, necessitating the solution of Maxwell’s equations perhaps many thousands of times.
We propose a modal solution, which requires just a single simulation to find the modes of the nanophotonic system, from which we immediately obtain the Green’s function everywhere in space. This not only reduces simulation time by approximately 2 orders of magnitude, but also offers ready physical insight into the spatial variation of Green’s function. Modal methods have long been used for closed systems, where the formulation is exceedingly simple. We have generalized modal methods to open systems while maintaining this simplicity, catering to the explosion of research interest in nanophotonics. We furthermore present a highlyefficient exponentiallyconvergent method of generating the modes themselves.

Chiral lightmatter coupling at nanophotonic interfaces Mihail Petrov (ITMO University, Saint Petersburg) mercredi 05 décembre 2018, 11:00, Amphi IPGP
Résumé: Nanophotonic systems offer unique opportunities for controlling and stimulating lightmatter coupling. One of the important topics which drag the interest of the researchers is artificial chirality in quantum sources in interaction with surface photonic or plasmonic modes. The presence of the transverse optical spin component of guided modes opens a possibility to control their direction of propagation by means of the so called spinlocking effect. The atom transition with nonzero spin moment can excite surface modes in preferable direction, or, on the contrary, the scattering of surface mode is very sensitive to chirality of atomic transitions.
In this work we present a brief overview of our recent theoretical results on coupling of chiral atoms with surface guiding modes. In particular, we demonstrate that the scattering of nonfiber guided mode on ensemble of atoms with chiral transitions, and show how the spin of nanofiber modes governs the scattering spectrum. Moreover, we propose a model of atomic ensemble of chiral atoms with perfect unidirectional coupling, and suggest a rigorous solution in such system, which demonstrate the main features of unidirectional coupling. Such system can be implemented with a simple metal nanowire, where the spinlocking effect is extremely strong. Finally, we will discuss the effect of quantum anisotropy, which allows coupling of orthogonal quantum states close to a nanophotonics systems. We show by using anisotropic metasurfaces one can couple two atomic levels with chiral transition, which may results in noninverse Rabi oscillation between two quantum states in a single atom.

Coherent control of light transport in a dense atomic medium Alexandra Sheremet (LKB, Paris) jeudi 22 novembre 2018, 11:00, Salle 310
Résumé: Lightmatter interfaces play a crucial role in the context of quantum information
networks, enabling for instance the reversible mapping of quantum state of light onto
quantum states of matter. A promising approach for the realization of such interfaces is
based on ensemble of neutral atoms. A critical figure of merit of such interfaces is the
overall storageandretrieval efficiency, which is mainly determined by technical losses and
atomic decoherence, and depends on the storage mechanism and matter properties.
Collective and cooperative effects manifistable in an atomic ensemble could provide
essential enhancement of the coupling strength between the light and atomic systems. In this
context, one of the strongest requirements to obtain a high efficiency is a large optical
depth, which can be achieved by increasing the size of the atomic system or atomic density
in the system. Moreover, recent experimental advances in the trapping technique have made
it possible to create 1D, 2D or 3D spatially ordered atomic configurations, where the
collective effects play a very important role. In addition, the interaction between light and
atoms can be enhanced by trapping atoms in the vicinity of a nanoscale waveguide due to
strong confinement of the light.
In this context, in this talk I will discuss light propagation in a spatially dense atomic
ensemble, where the average distance between atoms is comparable with the resonant
wavelength. In such dense atomic configurations dipoledipole interaction play an important
role and can lead to manifestation of super and subradiance effects. I will consider the light
propagation in both free space and trapped near nanofiber surface atomic ensembles. The
light scattering in such dense atomic configuration is described in terms of microscopic
approach based on the standard scattering matrix and Resolvent operator formalism. We
show theoretically and experimentally that spatially dense atomic ensembles allow
obtaining effective lightmatter interface and reliable light storage with essentially fewer
atoms than it can be achieved in dilute gases. Furthermore, we show that the presence of an
optical nanofiber modifies the character of atomic interaction and results in longrange
dipoledipole coupling between atoms not only via the free space, but also through the
waveguide mode.

Limiting amplitude principle for Maxwell’s equations at the
interface of a metamaterial Maxence Cassier (Institut Fresnel) mardi 20 novembre 2018, 11:00, Salle 310
Résumé: In this talk, we are interested in a transmission problem between a dielectric and a metamaterial.
The question we consider is the following: does the limiting amplitude principle hold in such a
medium? This principle defines the stationary regime as the large time asymptotic behavior of a
system subject to a periodic excitation.
An answer is proposed here in the case of a twolayered medium composed of a dielectric and
a particular metamaterial (Drude model). In this context, we reformulate the timedependent
Maxwell’s equations as a conservative Schr¨odinger equation and perform its complete spectral
analysis. This permits a quasiexplicit representation of the solution via the ”generalized diagonalization”
of the associated unbounded selfadjoint operator. As an application of this study,
we show finally that the limiting amplitude principle holds except for a particular fequency, called
the plasmonic frequency, characterized by a ratio of permittivities and permeabilities equal to − 1
across the interface. This frequency is a resonance of the system and the response to this excitation
blows up linearly in time.

Bright squeezed vacuum of light :
interferometric measurements and nonlinear optics Mathieu Manceau (Laboratoire de Physique des Lasers, Université Paris 13) mardi 13 novembre 2018, 11:00, Amphi IPGP
Résumé: Bright squeezed vacuum (BSV) is a quantum state of light that can be produced from a strongly pumped unseeded parametric amplifier, its brightness can be comparable with lasers (more than 10 trillion photons per mode). In this seminar I will present two applications of bright squeezed light. First I will report on interferometric measurements beyond the shot noise limit using a socalled SU(1,1) interferometer. I will then describe experiments using bright squeezed light as a pump to generate nonlinear effects. The sensitivity of an interferometric measurement on a phase shift depends on the state of light used as a probe and the measurement scheme. A ‘standard’ precision is provided by a coherent state fed into a MachZender interferometer, the socalled shot noise limit (SNL). A measurement beating this limit is said to be supersensitive. In order to make supersensitive phase measurements, quantum resources can be used. For example, squeezed light is now implemented in gravitational wave detectors. Besides the input state and the detection scheme, one can also modify the interferometer. Two optical parametric amplifiers (OPAs) can be used instead of the passive beamsplitters of conventional interferometric setups to form an SU(1,1) interferometer, the phase sensitive response of the OPAs giving rise to interference patterns. Using this interferometer, we demonstrate a phase sensitivity overcoming the shot noise limit by 2.3 dB and show the remarkable robustness of this scheme against detection losses.
I will then show that BSV, i.e. amplified quantum fluctuations, turns out to be very useful for pumping multiphoton effects despite the common opinion that large intensity noise is detrimental for any applications. In particular, BSV can be used to enhance the occurence of extreme events and rogue waves in nonlinear optics and to create states with exotic photon statistics.

Late time behavior of disordered elastic systems Douglas Photiadis (U.S. Naval Research Laboratory, Washington) mardi 06 novembre 2018, 11:00, Amphi IPGP
Résumé: The late time behavior of disordered wave bearing systems, acoustic, elastic or optical, has been of great interest in recent years. From a practical perspective, late time measurements correspond to large distances in a disordered system, and are thus relevant in many imaging or nondestructive
evaluation applications. From a basic science perspective, late time ob
servations can reveal interference behavior resulting from the approach to
the Anderson transition, and offer the prospect of observing classical wave
systems in a localized phase. While the Anderson transition has been the
oretically predicted to occur in such systems for some time, clear evidence
of a localized phase has unexpectedly been quite difficult to find. Our theo
retical understanding of the current status is still incomplete, with continu
ing efforts employing direct numerical simulations, selfconsistent, multiple
scattering models, and field theoretic methods. Of these, direct numerical
simulations and field theoretic methods enable a description of the local
ized phase. Direct numerical simulations, particularly those based on a
monopole or dipole scattering approximation, have achieved some promis
ing results but still describe highly idealized systems, and require substan
tial computational resources to describe systems substantially larger than a
mean free path. Field theoretic methods on the other hand, while yielding
semianalytic results, have in the past been restricted to even more idealized
systems. We discuss recent results in these areas, particularly with a view of
moving towards a more realistic description of disordered, elastic systems.

Glassy dynamics in granular matter through flow heterogeneities: ShearTransformationZone theory and applications in granular flow and nonlinear acoustics Charles Lieou (Center for Nonlinear Studies  Solid Earth Geophyics Group, Los Alamos National Laboratory) mardi 16 octobre 2018, 11:00, Salle 310
Résumé:
Granular matter display both solidlike and fluidlike properties, and are ubiquitous in nature and industrial applications. A variety of phenomena observed in driven granular matter can be attributed to glassy dynamics  namely, local contact changes and rearrangements at loose spots. In this talk, I present an overview of the ShearTransformationZone (STZ) theory, a statistical description of granular flow and the dynamics of flow heterogeneities in unconsolidated granular matter, consistent with the principles of nonequilibrium thermodynamics. The propensity for flow heterogeneities or "shear transformation zones" to rearrange and produce nonaffine strain is given by a thermodynamicallydefined structural effective temperature known as the compactivity. I will discuss applications of the STZ theory in describing stickslip instabiltiies in granular flow, and resonance shifts in nonlinear acoustic experiments. If time permits, I will also discuss an STZ description of relaxation in a granular glass bead pack.

A rational framework for dynamic homogenization at finite wavelengths and frequencies Bojan Guzina (University of Minnesota) mardi 19 juin 2018, 11:00, Salle 310
Résumé: In this study, we establish an inclusive paradigm for the homogenization of scalar wave motion in periodic media (with or without the source term) at finite frequencies and wavelengths spanning the first Brioullin zone. We take the eigenvalue problem for the unit cell of periodicity as a point of departure, and we consider the projection of germane Bloch wave function onto a suitable eigenfunction as descriptor of effective wave motion. For generality the finite wavenumber, finite frequency (FWFF) homogenization is pursued in Rd via secondorder asymptotic expansion about the apexes of “wavenumber quadrants” comprising the first Brioullin zone, at frequencies near given (optical) dispersion branch. We also consider the degenerate situations of crossing or merging dispersion branches with arbitrary multiplicity, where the effective description of wave motion reveals several distinct asymptotic regimes depending on the symmetries of the eigenfunction basis affiliated with a repeated eigenvalue. One of these regimes – for whose occurrence we expose a sufficient condition – is shown to describe the socalled Dirac points, i.e. conical contacts between dispersion surfaces, that are relevant to the phenomenon of topological insulation. For all cases considered, the effective description turns out to admit the same general framework, with differences largely being limited to (i) the basis eigenfunction, (ii) the reference cell of medium periodicity, and (iii) the wavenumberfrequency scaling law underpinning the asymptotic expansion. We illustrate the utility of our analysis by several examples, including an asymptotic description of the Green’s function near the edge of a band gap.

Semiconductor Lasers and the Butterfly effect: what and why ? Frédéric Grillot (Laboratoire Traitement et Communication de l'Information, Télécom ParisTech) mardi 12 juin 2018, 11:00, Salle 310
Résumé: Semiconductor lasers invented in 1962 are vital to our modern daily life. For example, they generate the optical impulses that carry evergreater amounts of information in fiberoptic networks over great distances. The emergence of irregular and unpredictable pulsations and dynamical instabilities from a laser were first noted during the very early stages of the development of lasers. Pulses with amplitude varying in an erratic manner were reported in the output of the ruby solidstate laser. However, the lack of knowledge of what would later be termed butterfly effect i.e. deterministic chaos resulted in these initial observations being either left unexplained or wrongly attributed to noise. This presentation will highlight the fundamental physics underpinning the butterfly effect in semiconductor lasers and also the opportunities in harnessing it for potential applications.

Numerical simulations of dry and wet granular media in shear reversal flow and its constitutive modelling with fabric evolution Jin Sun (University of Edinburgh) lundi 11 juin 2018, 15:00, Salle 310
Résumé: Granular media exhibit significant dependence on its flow history. This behaviour has, however, not been sufficiently studied or considered in constitutive models. In this talk, I will present numerical results from discrete element simulations of dry granular materials and granular suspensions under simple shear flow. Unsteady flow is introduced through a reversal of shear direction after the flow reaches steady state. The bulk stresses display striking evolution following reversal at a strain scale of unity or larger. This largescale evolution is common to both dry and wet flows, and related to the reorientation of the anisotropic microstructure. When hydrodynamic interactions are included, however, a dramatic response in hydrodynamic stress occurs at very a small strain scale, which is controlled by the nonhydrodynamic surface interactions. We further established a constitutive model to describe such unsteady flows in the rateindependent regime. The model consists of a stress equation and an evolution equation of a secondorder fabric tensor, the second invariant of which is used to characterise the microstructure anisotropy and the trace is the coordination number. The pressure and a scalar viscosity are modelled as functions of the fabric tensor. Even with this relatively basic incorporation of fabric (without resorting to a fourthorder viscosity tensor), the model is shown to be able to capture well the stress evolution in shear reversal and predict more complex flows under cyclic loading.

From computational imaging to optical computing Laurent Daudet (Professor at Paris Diderot University / CTO and cofounder at LightOn) mardi 15 mai 2018, 09:30, Salle 310
Résumé: Multiple diffusion resulting from the propagation of waves in disordered environments, such as light passing through biological tissues or a fine layer of paint, is an extremely complex process but remains linear. In fact, with spatially discrete inputs and outputs, it can perform the equivalent of a random projection, i.e. the multiplication of the input vector by an iid random matrix. In this context, we have shown that these environments act precisely as "compressed sensing" model systems, allowing signal acquisition with a number of measurements driven by the actual amount of information. Conversely, one can see this physical system as an optimal mixer of information, performing instantaneously in the (physical) analog domain an elementary computation brick of many Machine Learning schemes. We will present a series of proof of concept experiments in Machine Learning, and discuss recent technological developments of optical coprocessors within the startup LightOn, cofounded with Igor Carron, Sylvain Gigan & Florent Krzakala.

Photoacoustic microscopy combined with nonlinear optics Yoshihisa Yamaoka (Saga University, Kyushu, Japan) vendredi 27 avril 2018, 11:00, Salle 310
Résumé: Recently, photoacoustic microscopy (PAM) has attracted
attention to visualize deep structures in living tissues. However, it is
difficult to improve the spatial resolution of PAM without using
highfrequency components of photoacoustic waves, which are not suitable
for deep imaging. To overcome this drawback, we have developed
twophoton absorptioninduced photoacoustic microscopy (TPPAM). The
spatial resolution in TPPAM is determined by twophoton absorption
(TPA). The use of lowfrequency ultrasonic components generated by TPA
enables PAM to visualize deeper structures while preserving the high
spatial resolution.

Contrôle de la propagation des ondes acoustiques : Architectures non réciproques et transmission extraordinaire Thibaut Devaux (Université de Hokkaido, Sapporo, Japan) jeudi 19 avril 2018, 11:00, Amphithéatre
Résumé: Maîtriser la propagation des ondes acoustiques dans l’espace est un récent enjeu scientifique. Avec l’avènement des métamatériaux, de nombreuses architectures ont été proposées ces dernières années pour briser le principe de réciprocité ou pour permettre la focalisation spatiale de l’énergie acoustique dans des régions de taille inférieure à la longueur d’onde. Ce séminaire propose de présenter les dernières avancées sur ces sujets effectuées à l’Université du Mans en France ainsi qu’à l’Université de Hokkaido au Japon.
Après un bref rappel des travaux existants et des perspectives envisagées pour la propagation asymétrique des ondes acoustique, la première partie présente un concept de rectificateur acoustique s’appuyant sur une structure composée d’un partie sélectionnante composée d’un cristal phononique et d’une partie convertissante basée sur le phénomène nonlinéaire d’autodémodulation d’un milieu granulaire non consolidé.
La seconde partie de ce séminaire est dévouée au principe de la transmission extraordinaire des ondes acoustiques (EAT) qui permet de concentrer l’énergie dans une région de taille sublongueur d’onde avec une quantité d’énergie transmise supérieure à celle attendue par les seules considérations géométriques. Une architecture est proposée afin de montrer la possibilité d’obtenir cet effet pour des ondes de volumes à des régimes de l’ordre du GHz en couplant les résonances acoustiques de FabryPérot à l’intérieur d’un tube de taille nanométrique avec une structure rainurée permettant la conversion des ondes longitudinales en ondes de surface.

Propagation of THz radiation in scattering medium for imaging in brownout condition Clotilde Prophete (Institut Langevin) mardi 17 avril 2018, 11:00, Salle 310
Résumé: Helicopters face huge risks when landing or takingoff in arid area: the rotor airflow stirs up the sand grains and create sand clouds, called brownout, that can annul the pilot's visibility. We study a solution to avoid accidents that may occur: an active THz imaging system to image through the brownout. My work is composed of two parts. On the one hand, we offer an analytical model to evaluate the performance of the imaging system. On the other hand, we evaluate experimentally the propagation of THz radiation through sand clouds.

Electricallydriven optical antennas for novel light emission processes Claire Deeb (C2N, Orsay) jeudi 12 avril 2018, 11:00, salle 310
Résumé: Gaps formed between metal surfaces control the coupling of localized plasmons, thus allowing gaptuning targeted to exploit the enhanced optical fields for different applications. Classical electrodynamics fails to describe this coupling across subnm gaps, where quantum effects
become important owing to nonlocal screening and spillout of electrons. The advantages of narrow gap antennas have mostly been demonstrated for processes like SERS that are excited optically, but promising new phenomena appear when such antennas are fed by electric generators. However, the extreme difficulty of engineering and probing an electrically driven optical nanogap antenna has limited experimental investigations of physical concepts at stake in these conditions. The feasibility of structuring electronfed antennas as nanolight sources has been recently demonstrated; however, the suggested configuration remains very limited: too much power was lost as heat when operating the optical antenna, and the antenna operation time was limited by the structure lifetime to sustain a bias voltage for a few hours. The innovative structure that I propose in my talk will cope with all these limitations: ALD dielectric materials substitute the air
gap to improve the antenna stability; a quantum efficiency of 0.1 is targeted owing to a significantly efficient antenna (2 orders of magnitude higher field enhancement). The resulting source will operate at room temperature and have a tunable spectral response (ranging from
visible frequencies to THz regime) defined by the antenna geometry and the applied bias. Also, this source will be compact, Sicompatible, and will not request specific emitting materials (e.g. IIIV semiconductors) to operate.

Fluids of light in semiconductor lattice Jacqueline Bloch (C2N, Marcoussis) mardi 10 avril 2018, 11:00, Amphi IPGP
Résumé: When confining photons in semiconductor lattices, it is possible deeply modifying their physical properties. Photons can behave as finite or even infinite mass particles, photons can propagate along edge states without back scattering, photons can become superfluid, photons can behave as interacting particles. These are just a few examples of properties that can be imprinted into fluids of light in semiconductor lattices. Such manipulation of light present not only potential for applications in photonics, but great promise for fundamental studies. One can invent artificial media with very exotic physical properties at the single particle level or even more interestingly when many body interactions are considered. During the talk, I will illustrate the variety of physical systems we can emulate with fluids of light by presenting a few recent experiments. Perspectives in terms of quantum simulation will be discussed.

Optics of resonantly coupled subwavelength particles Nick Schilder (Amolf, Amsterdam) jeudi 05 avril 2018, 11:00, Salle 310
Résumé: In this talk I present two different systems that are built up of resonantly coupled subwavelength particles. The first system is a disordered cloud of cold atoms, whereas the second system is a hexagonal array of silicon nanopillars. In both cases the individual entities are resonantly coupled to each other, which leads to an interaction with light that is different than the sum of individual particles. In a wavelengthsized cloud of cold atoms we theoretically show that this disordered system actually shows order in its optical response by the presence of some particular collective modes. We also predict a special regime of light scattering from dense, subwavelengthsized clouds of atoms. The ensemble of atoms scatters less light than a single atom does, precisely due to their strong nearfield interactions. In the second part of my talk, I focus on hexagonal lattices of silicon nanopillars. These arrays show collective modes which we can this time experimentally visualize with 10 nm resolution thanks to cathodoluminescence spectroscopy. With this technique, we focus a 30keV electron beam on the sample. The electrons have a strong electric field surrounding them and serve as a localized coherent broadband optical excitation source that excites modes inside the nanopillars at the nanometer scale. The periodic repetition of a resonant nanopillar leads to the creation of a band diagram; it is a photonic crystal slab. With angleresolved cathodoluminescence spectroscopy we have access to that band diagram in a single measurement. We found experimental evidence of the existence of modes with an effective refractive index very close to one.

Adaptive quantum optics with spatially entangled photon pairs Hugo Defienne (Princeton University) mardi 27 mars 2018, 11:00, Salle 310
Résumé: Light shaping is an established division of modern optics, at the origin of many applications for communication, computing and imaging. In this work, we generalize light shaping to the quantum domain. We show that patterns of phase modulation for classical laser light can also shape higher orders of spatial coherence, allowing deterministic tailoring of highdimensional entanglement. By modulating spatially entangled photon pairs, we create periodic, topological, and random structures of quantum illumination, without effect on intensity. We then structure the quantum illumination to simultaneously compensate for entanglement that has been randomized by a scattering medium and to characterize the medium's properties via a quantum measurement of the optical memory effect. The results demonstrate fundamental aspects of spatial coherence and open the field of adaptive quantum optics.

Combining retinal birefringence scanning with long working distance OCT for pediatric applications – challenges and solutions Boris Gramatikov (Wilmer Eye Institute, Johns Hopkins University School of Medicine) lundi 26 mars 2018, 11:00, Salle 310
Résumé: Optical coherence tomography (OCT) enables volumetric rendering and the generation of fundus images that precisely register OCT images to fundus features. Yet, there is little data about how a child’s retina develops. This limits our knowledge of how diseases affect a child’s vision early in life and makes diagnosis of these diseases more difficult. The introduction of OCT to pediatric applications has been impeded by several factors, among them limited speed of data acquisition and analysis, difficulty in attaining stable fixation of the pediatric patient on a target over a period of time long enough to allow reliable analysis, short working distance, etc. The system described here integrates three major components: a) a computercontrolled video player that plays attention attracting movies and directs the subject’s fixation to a central point target, b) a retinal birefringence scanning (RBS) subsystem for fast detection of central fixation by detecting the position of the fovea, and c) a longworkingdistance optical coherence tomography subsystem for acquiring 3D images from the retina. Significant issues need to be resolved. These include separating the two systems spectrally, presenting suitable visual targets on a small LCD screen, communication between the two systems in real time, precise alignment, simultaneous aiming of the two systems, etc. Of particular importance is the fact that most optical components in the combined path can also affect the polarization state of light in the RBS path, as does the human cornea. To address this issue, a computer model was employed, to optimize system performance. The hybrid system integrating OCT and RBS acquires and analyzes data only during moments of central fixation. This is expected to significantly reduce the image processing time and shorten overall exam duration.

The Radiative Transfer Equation: a versatile tool to model light propagation through random media Ugo Tricoli (Institut Langevin) mardi 20 mars 2018, 11:00, Salle 310
Résumé: The presentation will start with a brief introduction to the Radiative Transfer Equation (RTE) and its numerical solution with the Monte Carlo method. Firstly, applications of the RTE to the Earth's atmosphere will be considered, in particular for the detection of small nonspherical ice particles in optically thin cirrus. Then, in the context of biomedical optics, the RTE is applied to model light propagation in biological tissues. Using the reciprocity relation for the vector RTE, the benefits of the use of polarized light are demonstrated for diffuse optical tomography. These results are extended through a perturbative approach to consider temporal correlations in media with moving particles undergoing Brownian motion. As a result, applications of the RTE to diffuse correlation tomography and speckle contrast optical tomography are presented. In the last part, the RTE is used to simulate the coherent wave nature of the electromagnetic field. In particular, the propagation of partially coherent beams through random particulate media is considered.

Contrôle de la dispersion spatiale et temporelle dans les cristaux photoniques mésoscopiques et les structures plasmoniques périodiques Giovanni Magno (C2N, Marcoussis) mardi 13 mars 2018, 11:00, Salle 310
Résumé: La manipulation de la lumière à l’échelle de la longueur d’onde (et sublongueur d’onde) a été repensée par l’introduction des milieux périodiques tels que les cristaux photoniques et plus récemment les métamatériaux. La dispersion spatiale et temporelle est ici présentée en tant qu’élément de contrôle de la lumière, qui permet d’atteindre des fonctionnalités nontriviales dans les dispositifs nano photoniques basés sur des milieux périodiques. En particulier, dans le cadre de ce séminaire, seront discutées : la mise en forme spatiale et temporelle des faisceaux autocollimatés dans des directions arbitraires dans les cristaux photoniques mésoscopiques (composés par différentes périodes), la gestion de l’adaptation d’impédance, et la réalisation de guides, miroirs et cavités avec des interfaces planaires. La caractérisation expérimentale de ces cavités et la possibilité de les exploiter pour la réalisation de capteurs et de pince optiques innovants seront également présentées. La conception de pinces optiques plasmoniques en champ proche et ultracompactes sera finalement exposée.

Modeling and inverse problems in tumor growth Annabelle Collin (EnserbMatmeca, Bordeaux) mardi 13 février 2018, 11:00, Salle 310
Résumé: Recently, mathematical modeling of cancer started drawing great interest from the medical community. Indeed, developing models able to describe accurately tumor growth may help monitoring the disease evolution or even predicting the efficacy of different therapeutic strategies. Such applications are made possible through the routine monitoring of patients with imaging devices. This offers a consistent amount of valuable data to elaborate and validate the mathematical models. The aim of my talk is to present a quick overview of the strategies that we have recently developed in our team at Bordeaux.
In a first part, I will quickly present a simple tumor growth model based on a mechanistic description of the healthy and tumor cell densities evolution over time. This model is valid for example for meningiomas or for some lung metastases, i.e. when there is no treatment (only the growth is considered) and when the shape is approximatively the same over time. This model presents both the interest to be parametrizable  using the tumor volumes at 2 times and the initial shape tumor  for each considered patient and to produce reliable predictions and 3D extension simulation within a reasonable computing timescale. The parameters estimation strategy based on a reduced 0Dmodel and on stochastic methods (MonteCarlolike methods) will be presented.
When we consider treatments (tumour decay) or/and timeevolving shapes, more complex models  with different tumour cell densities  have to be written and more information  issued from medical imaging  is necessary to parametrize them. In a second part of my talk, I will introduce these complex models and I will present the information that can be extracted from medical imaging such as textures or shapes of the lesions. I will show why the parameter estimation approach used for the simple model is not anymore available and I will propose a new strategy based on data assimilation strategy. I will present a Luenberger  also called nudging  state observer coupled with a parameter Kalmanbased observer to perform a joint state and parameter estimation. I will illustrate my results with synthetic and real data.

DNAOrigami for nanophotonic applications Guillermo Acuna (Technische Universität Braunschweig) mardi 23 janvier 2018, 11:00, Amphi IPGP
Résumé: This contribution will start with a brief introduction to nanophotonics and plasmonics. In this context, different
nanofabrication techniques will be discussed with an emphasis on the DNAOrigami approach. In particular, we employ this technique as a platform where metallic nanoparticles as well as single organic fluorophores can be organized with nanometer precision in three dimensions. With these hybrid structures we initially study the nanoparticlefluorophore interaction in terms of the distancedependent fluorescence quenching and angular dependence around the nanoparticle. Based on these findings, we build highly efficient nanoantennas based on 100 nm gold dimers which are able to strongly focus light into the subwavelength region where the fluorophore is positioned and produce a fluorescence enhancement of more than three orders of magnitude. Using this highly confined excitation field we were able to perform single molecule measurements in solution at concentrations as high as 25 µM in the biologically relevant range ( larger than 1µM). Additionally, we report on a controlled increment of the radiative rate of organic dyes in the vicinity of gold nanoparticles with the consequent increment in the number of total emitted photons. We also employ the nanoantennas to mediate the fluorophore emission and thus to shift the apparent emission origin: A single molecule mirage. We will discuss how DNAOrigami can also improve the occupation of other photonic structures, the zeromode waveguides (ZMWs). These structures, which consist of small holes in aluminum films can serve as ultrasmall observation volumes for singlemolecule spectroscopy at high, biologically relevant concentrations and are commercially used for realtime DNA sequencing. To benefit from the singlemolecule approach, each ZMW should be filled with one target molecule which is not possible with stochastic immobilization schemes by adapting the concentration and incubation time. We present DNA origami nanoadapters that by size exclusion allow placing of exactly one molecule per ZMW. The DNA origami nanoadapters thus overcome Poissonian statistics of molecule positioning and furthermore improve the photophysical homogeneity of the immobilized fluorescent dyes. Finally, we will discuss future potential applications of this technology on smartphonebased point of care diagnostic platforms and diagnostics.

De l’imagerie par conjugaison de phase ultrasonore à la réalisation d'une caméra acoustique aérienne de mouvement de surface Pavel Shirkovkiy (Institut Langevin) mardi 16 janvier 2018, 11:00, Amphi IPGP
Résumé: Les méthodes de diagnostic ultrasonore sont largement développées aujourd'hui et sont appliquées avec succès en géophysique, en médecine et dans l’industrie pour le contrôle nondestructif. Les méthodes modernes d’imagerie ultrasonore utilisent de nouveaux procédés tels que retournement temporel ou l’interaction des ondes ultrasonores dans le milieu de propagation ainsi que l’interaction avec des champs de diverses natures. Le développement de nouveaux moyens de mesure sans contact suscite toujours le plus grand intérêt. L’introduction du contrôle ultrasonore sans contact et sans milieu couplant intéresse un nombre croissant de personnes dans le domaine du contrôle non destructif et ouvre la voie à des applications qu’il n’était pas possible d’envisager avec les techniques traditionnelles. Dans cet exposé, nous verrons la présentation d’une technique de conjugaison de phase magnétoacoustique pour des applications en vélocimétrie des écoulements développée pendant ma thèse. Dans un deuxième temps, je présenterai mon travail actuel dans le groupe de Ros Kiri Ing, à l’Institut Langevin. L’objectif principal du projet est de développer un outil de diagnostic in vivo basé sur les procédés avancés pour l’observation à distance des vibrations en surface du corps humain. La conception d’un dispositif médical innovant sera présentée sous la forme d’un imageur acoustique, non invasif et non intrusif qui fonctionne dans l’air pour des applications potentielles en sismocardiographie, pneumologie et en élastographie cornéenne.

Traitement de signaux avec un processeur atomique programmable Anne Chauvet (Laboratoire Aimé Cotton) mardi 09 janvier 2018, 11:00, Amphi IPGP
Résumé: Les signaux RF sont omniprésents aujourd'hui dans les domaines de la télédétection, de la communication, et de la guerre électronique. En particulier dans le domaine radar, le traitement des signaux détectés doit alors se faire instantanément, ce qui requiert des performances en termes de bande passante, de temps d'analyse et de dynamique que les technologies purement électroniques peinent à satisfaire. En particulier, l'étape de conversion analogiquenumérique fait appel à de nombreuses étapes de transposition, amplification, filtrage, multiplexage, qui dégradent les performances du traitement de signaux très large bande. Des solutions alternatives doivent être recherchées. Une voie prometteuse est celle du traitement analogique de signaux placés sur porteuse optique.
Dans ce contexte, les cristaux dopés aux ions de terre rare offrent des propriétés remarquables lorsqu'ils sont refroidis à la température de l'hélium liquide. Combinant une largeur inhomogène de plusieurs dizaines de GHz et une résolution spectrale en général très inférieure à 1 MHz, capables par ailleurs de mémoriser à l'échelle de la microseconde un profil spectral pendant des temps qui peuvent atteindre plusieurs jours, ces matériaux peuvent être utilisés comme processeurs optiques programmables, basés sur le phénomène de creusement spectral ou "spectral hole burning" (SHB).
Dans ce séminaire je présenterai 3 architectures utilisant le SHB, appliquées à différents enjeux de traitement du signal. Je commencerai par le plus abouti: l'analyseur spectral large bande "arcenciel", conçu au Laboratoire Aimé Cotton et à présent en cours de transfert technologique à Thales Research&Technology. Ce dispositif est basé sur la programmation de réseaux de diffraction dans le cristal. Puis je décrirai la première réalisations d'un processeur de renversement temporel, dans lequel une ligne dispersive est programmée. Enfin, je présenterai comment utiliser le SHB pour l'imagerie acoustooptique en milieu diffusant à l'aide d'un processeur basé sur la programmation d'un filtre passebande.

De la génération d’harmoniques sur miroir plasma à l’imagerie acoustooptique en milieu complexe Maimouna Bocoum (Institut Langevin, Paris) mardi 05 décembre 2017, 11:00, Salle 310
Résumé: Les technologies laser actuelles permettent de générer des impulsions de quelques cycles optiques dans le domaine visible procheInfrarouge (IR), limitant les durées de ces impulsions à quelques femtosecondes. En faisant interagir très non linéairement ces impulsions avec un plasma de densité solide, on génère un rayonnement cohérent dans l’XUV, de plusieurs centaines d’attosecondes. Toutefois, l’efficacité de la génération dépend des propriétés spatiotemporelles du champ IR générateur, et nécessite par ailleurs un contrôle de la surface du plasma à l’échelle du nanomètre. Dans cette présentation, nous verrons (i) la présentation d’une technique de mesure d’expansion du plasma développée pendant ma thèse (ii) la mise évidence expérimentale du lien entre la dynamique du plasma subfs et les propriétés spatiospectrales du champ XUV généré.
Dans un deuxième temps, je présenterai mon travail actuel dans le groupe de François Ramaz, à l’Institut Langevin. Les techniques d’imageries conventionnelles utilisant des lasers dans l’Infrarouge (IR) pour sonder les milieux biologiques sont limitées à quelques mm de profondeur à cause de la diffusion multiple. En modulant localement l’indice du milieu à quelques MHz avec une onde acoustique de quelques cycles, on crée, par effet « acoustooptique », un « shift » local de la fréquence laser égal à la fréquence ultrasonore. Les ultrasons se propageant de manière balistique, une image héritant des propriétés spatiales de l’onde acoustique et optiquement contrastée peut être obtenue en filtrant les photons marqués. Il devient ainsi possible d’imager à plusieurs centimètres dans des milieux fortement diffusants.

Enhancing spontaneous emission and absorption with plasmonic nanoantennas: What are the limits of the playground? Christophe Sauvan (Laboratoire Charles Fabry, Institut d'Optique, Paris) mardi 28 novembre 2017, 11:00, Salle 310
Résumé: The development of micro‐ and nanotechnologies has recently opened a wide range of possibilities for controlling light at the wavelength scale or below. A fine control of the light (emission, transport and detection) in small volumes is at the heart of various applications. Most of these applications rely on the use of optical resonances, which can be either localized in small volumes or delocalized over the system.
Plasmonic nanoantennas (or nanoresonators) are able to confine light in extremely small volume of the order of 1/10,000 of a cubic wavelength, i.e., well below the diffraction limit. Light confinement is associated with large field exaltations that can be used to enhance non‐linearities, spontaneous emission, or absorption. In the context of spontaneous emission, these properties lead to huge enhancement factors. Unfortunately, very large enhancement factors usually correspond to emitters located only a few nanometers away from a metal surface. As a consequence, quenching through non‐radiative energy transfer to the nearby metal constitutes the dominant relaxation process. The resulting radiative efficiency is extremely low and it is thus often thought that very large spontaneous decay rates in plasmonic nanoantennas are not of practical interest. However, recent experimental demonstrations have shown that it is possible to obtain large enhancement factors (typically above 1000) with non‐negligible radiative efficiencies (a few tenths of percent).
We have developed an electromagnetic theory that is able to unravel the interplay between the decay into the antenna mode and the quenching. The theory that is valid for any plasmonic nanoantenna relies on a modal formalism recently developed for photonic and plasmonic nanoresonators. In particular, we have shown that overcoming the quenching is possible in different types of metallo‐dielectric nanoantennas. Such an in‐depth quantitative analysis has allowed us to provide guidelines to design plasmonic nanoantennas that are able to overcome quenching and provide both large spontaneous decay rates and large radiative efficiencies.

Some biomedical applications of diamond nanocrystals François Treussart (ENS Paris Saclay) mardi 03 octobre 2017, 11:00, Salle 310
Résumé: Nanoparticles have significant advantages for biomedical applications, especially for the vectorization (possibly traceable) of active biomolecules, for labeling, or even as probes of some physicochemical parameters at the nanoscale.
The diamond nanocrystal (nanodiamond) is a remarkable system with intrinsic properties allowing all these applications simultaneously. We will show that nanodiamonds rendered fluorescent by the creation of embedded color centers, can be used to measure the intraneuronal transport parameters in cultured neurons.
Thanks to the high brightness and the excellent stability of nanodiamond photoluminescence we were able to correlate intraneuronal transport abnormalities to subtle genetic alterations found in neuropsychiatric disorders, and modeled in transgenic mices. Such an approach could provide an unbiased diagnosis of these complex diseases.
In an other biomedical application, still in cultured cells, we used nanodiamond coated with cationic polymer to transport therapeutic oligonucleotides (siRNA) against the sequence of a junction oncogene responsible for Ewing sarcoma (a rare bone cancer). Compared to a conventional approach, the vectorization of the interfering RNA by the nanodiamond lead to a stronger inhibition of the oncogene responsible of cell proliferation.
We will conclude by in vivo prospects of these two applications (intraneuronal transport and nanomedicine), introducing an alternative nanolabel, the silicon carbide nanocrystal, that offers nearinfrared responses (fluorescence and secondharmonic generation), in the transparency spectral range of tissues.

Nanophotonics and electronics for bright singlephoton sources based on color centers in diamond Mario Agio (Laboratory of NanoOptics, University of Siegen (Germany) & National Institute of Optics, Florence (Italy)) mardi 19 septembre 2017, 11:00, Amphi IPGP
Résumé: Singlephoton sources are crucial to a number of applications that take advantage of the exotic phenomena stemming from the laws of quantum physics. Color centers in diamond have gained much attention in this context, essentially for their unique optical properties at room temperature, but a substantial basic research effort in nanophotonics and electronics is still required.
In my seminar I will introduce nanooptical concepts to largely improve singlephoton sources and the work that we have recently undertaken towards obtaining highly efficient singlephoton sources based on the siliconvacancy color center in diamond. I will present results pertaining to diamond implantation and characterization as well as on the design of antenna configurations that can significantly improve the outcoupling efficiency and the emission rate. I will also discuss some ideas on the possibility of electrical pumping and the expected performances.

Topology optimization for multiphysics system Gil Ho Yoon (Hanyang University, Korea) vendredi 25 août 2017, 11:00, Amphi IPGP
Résumé: Topology optimization is one of structural optimization methods that
optimizes material layout within a given design domain for a given set of
loads, boundary conditions and constraint maximizing the performance of the
system. Currently, engineers use topology optimization at the conceptual
level in design process. In this talk, the application of topology
optimization for multiphysics system will be given. The multiphysics systems
such as acousticstructure interaction, fluidstructure interaction,
fluidthermal and porousacoustic coupling are hard to design by the
imagination of engineers. Therefore, topology optimization method plays an
important role. In the applications, the conventional analysis theories are
hard to apply because not only material properties but also governing
equations should be interpolated. Therefore some novel analysis approaches
should be developed. The author has researched on these subjects for the
last several years. This presentation introduces the concept of topology
optimization and shows several works in multiphysics system. Furthermore, a
new research towards metasurface and metamaterials is presented.

Granular dynamics: From radar particle tracking to cohesion mediated collective motion Kai Huang (University of Bayreuth) vendredi 30 juin 2017, 11:00, Salle 310
Résumé: From sand dunes to Faraday crispations, granular materials, i.e., large agglomeration of macroscopic particles, are ubiquitous in nature, industry and our daily lives with widespread applications ranging from the prediction of natural disasters (e.g. snow avalanches and debris flows) through the enhancement of energy efficiency in industries (e.g. mining, civil engineering) to emerging new technologies (e.g. powder based additive manufacturing). Due to the energy dissipation at the individual particle level, granular systems are highly dissipative and consequently their stationary states are typically far from thermodynamic equilibrium. Therefore, understanding how the mobility of individual particles influences the collective behavior is crucial in describing granular materials as a continuum.
At the `microscopic' level of individual particles, I will introduce a recently developed microwave radar system that is capable of tracking a metallic particle continuously in three dimensions and discuss its advantages and limitations in comparison to other particle imaging approaches. At the `macroscopic' level of collective motion, I will talk about the pattern forming scenario of partially wet granular materials (e.g., wet sand on the beach) with a focus on how liquid mediated particleparticle interactions influence the collective behavior. In particularly, I will focus on the formation of densitywave fronts in an oscillated wet granular layer undergoing a gasliquidlike transition and discuss how the emerging time and length scales are associated with the competition between the time scale for the collapse of particles due to short ranged attractive interactions and that of the energy injection resisting this process.

Networks theory: how things are connected Gabriel Cwilich (Yeshiva University, New York) mardi 23 mai 2017, 11:00, Salle 310
Résumé: In this seminar I will present some of the basic ideas of networks’ theory and their areas of current application in different fields of science, with emphasis in the new field of complex networks. I will present some of main theoretical models of networks and of network formation and , and I will discuss some applications to robustness and resilience, and to spreading and diffusion of processes in networks.

Using full optical phase information in retinal optical coherence tomography Gereon Hüttmann (University of Lübeck, Germany) lundi 22 mai 2017, 15:00, Salle 310

Plasmonics for infrared detection and imaging Riad Haidar (ONERA, Palaiseau) mardi 02 mai 2017, 11:00, Amphi IPGP
Résumé: The current trend towards compact, costeffective and multipurpose infrared optoelectronic systems brings the need for new conception tools and technological means. In this frame, subwavelength and plasmonic concepts open promising avenues: at a first level, for the conception of highefficiency and compact optical elements arrays (i.e., polarizer, filter, or lens arrays) that can be brought in the vicinity of focal plane arrays, inside the confined volume of the camera; at a second level, for the integration of optical functions within the pixel of detection; and at a third level, for the enhancement of the optoelectronic properties of the elementary infrared detector. I will draw an overview of recent advances and realizations done in our lab.

Extreme events in nature, rogue wave in optics John Dudley (Institut FEMTOST, Université de FrancheComté) mardi 28 mars 2017, 11:00, Amphi IPGP
Résumé: A central challenge in understanding extreme events in physics is to develop rigorous models linking the complex generation dynamics and the associated statistical behaviour. Quantitative studies of extreme phenomena, however, are often hampered in two ways: (i) the intrinsic scarcity of the events under study and (ii) the fact that such events often appear in environments where measurements are difficult. A particular case of interest concerns the infamous oceanic rogue or freak waves that have been associated with many catastrophic maritime disasters. Studying rogue waves under controlled conditions is problematic, and the phenomenon remains a subject of intensive research. On the other hand, there are many qualitative and quantitative links between wave propagation in optics and in hydrodynamics, because a nonlinearlyinduced refractive index perturbation to an optical material behaves like a moving fluid and is described mathematically by the same propagation equation as nonlinear waves on deep water. In this context, significant experiments have been reported in optics over the last two years, where advanced measurement techniques have been used to quantify the appearance of extreme localised optical fields that have been termed "optical rogue waves". The analogy between the appearance of localized structures in optics and the rogue waves on the ocean’s surface is both intriguing and attractive, as it opens up possibilities to explore the extreme value dynamics in a convenient benchtop optical environment. The purpose of this talk will be to discuss these results that have been obtained in optics, and to consider both the similarities and the differences with oceanic rogue wave counterparts.

Nanoantennas for light emission and molecular detection Florian Bigourdan (Institut Langevin) mardi 21 mars 2017, 11:00, Salle 310
Résumé: The purpose of this talk is to introduce to a broad audience a few
applications of antenna concepts for the manipulation of light.
In the optical range, surface modes called surface plasmon polaritons take
place in the vicinity of metallic antennas, enabling a strong light/matter
interaction within highly confined volumes. In order to take advantage
of this property, three applications of plasmonic antennas will be
investigated.
First, in the case of singlephoton sources, both theoretical and
experimental studies of singleemitters performance when coupled to a
planar metallic antenna will be presented. A strategy to enhance its
performance will be studied theoretically.
Then, in the case of electrical generation of light by inelastic
electron tunneling, we will analyse the modification of radiation
properties close to a metallic nanorod. This analysis paves the way
towards the design of integrated, compact electrical sources of surface
plasmons.
Finally, in the case of detecting a weak quantity of molecules, the
interaction between an infrared light beam and a subnanometric layer of
resonant molecules deposited on a nanostructured metallic mirror will be
studied.

Seismological imaging using surface wave focal spots Gregor Hillers (ISTERRE, Grenoble) mercredi 08 mars 2017, 11:00, Salle 310
Résumé: Modern dense seismological deployments consisting of many hundreds of sensors allow the reconstruction of the seismic wavefield in the nearfield from noise crosscorrelations. The correlation approach makes it thus feasible to resolve the focus or focal spot, which is a characteristic feature of the crosscorrelation wavefield at zero lag time. Based on the equivalence of timereversal and crosscorrelation, applications in acoustics, nondestructive testing, and medical imaging have long been relying on focal spot properties. I introduce focal spot based imaging in seismology on two (very) different scales using data from two dense arrays, each consisting of 1000 stations, that cover a ~1 km2 area and half of the United States, respectively. In the presentation I will provide a brief history of refocusing in seismology, before discussing aspects of focal spot based imaging that arise in the seismological surface wave context, and that have not been at the center of research in acoustics or elastography. These aspects include the relation to Aki's 1957 spatial autocorrelation method; the shape of the surface wave focal spot depending on horizontal and vertical motion; interference of surface wave fields and body wave fields, effects on the focal spot, and strategies for wave field separation; and the resolution of anisotropy. I will emphasize implications for spatial resolution with an outlook to a transfer of the superresolution concept to seismology.

The Anderson mobility gap and dynamic coherent backscattering of ultrasound Laura Cobus (Institut Langevin) mardi 24 janvier 2017, 11:00, Amphi IPGP
Résumé: Anderson localization can be described as the inhibition of wave propagation due to strong disorder. For threedimensional (3D) systems, there exists a true phase transition between the localized and diffuse regimes. For an electronic system this transition occurs when the energy distribution of sites reaches a critical disorder, or equivalently when electron energy is above some critical value for a fixed disorder strength. In contrast, localization of classical waves in 3D can only occur in a finite band of energy (or frequency), leading to a socalled a mobility gap: a localization regime bounded by a lower and upper transition towards diffuse behaviour. I will present an experimental investigation of a complete mobility gap in 3D, using observations of the dynamic coherent backscattering effect for ultrasonic waves. This method is free of both absorption and any nonlinear effects, thereby sidestepping two of the major historical roadblocks in the study of localization, and in some cases can present an advantage over analogous transmission measurements. We fit our data with the selfconsistent theory of localization, which has successfully described localized ultrasound in past transmission experiments. Through this technique, we were able to measure the localization length as a function of frequency all the way through the mobility gap.

High resolution in the human retina Serge Meimon (ONERA, Chatillon) mardi 17 janvier 2017, 11:00, Amphi IPGP
Résumé: The eye is the only optical window to a neurovascular network in our body, located in the retina. Probing this retinal network at the scale of optical wavelengths (typically a micron) provides insight not only on the major eye diseases (Agerelated Macular Degeneration, Glaucoma, Diabetic retinopathy), but also on the state of the brain neurovascular network and on the related pathologies (Alzheimer, Parkinson, Traumatic brain injuries).
These developments have been triggered by the adaptation of adaptive optics to ophthalmology since 1997. I started to work on the subject more than 10 years after. Before building yet another adaptive optics ophthalmoscope, I decided to investigate the optical properties of the eye, and of the aberrations the adaptive optics was to correct for. Indeed, unlike in astronomy, no reliable statistical model of eye motion and aberration dynamics was available.
I will present the results of an aberrometry campaign on 50 eyes, and discuss the link between motion and aberration. Then, I will show the latest retinal imaging results we obtained with the ECUROeil adaptive optics ophthalmoscope, a system we built and designed based on the aberrometry results. These images reveal blood flow in arteries and capilaries at 200Hz, as well as the fine structure of the optic nerve head. Some of these images prompted us to design novel imaging instruments, using high resolution structured illumination.

Experimental control of the propagation of hydroelastic waves Lucie Domino (PMMH, ESPCI Paris) mardi 10 janvier 2017, 11:00, Amphi IPGP
Résumé: Hydroelastic waves appear at very large scale in the marginal ice zone where the ocean is covered by a thin layer of ice. The physics of these surface waves is dominated by the bending elasticity of the thin sheet covering the liquid, but their propagation is much slower than plate (Lamb) waves thanks to the fluid inertia. In this seminar, I will describe our experimental approach of hydroelastic waves. I will first focus on the typical parameter range in which they can be observed at the laboratory scale. In a second step I will show that these waves open promising possibilities for wave control. In particular, I will present experimental configurations that allow for building hydroelastic waves based "optics", revisiting Snell's law, geometrical optics and Fourier optics in an hydrodynamics experiment. We also investigate the properties of resonators for our system, created using simple perforations in our elastic cover.

Modélisation mathématique des résonances plasmoniques de nanoparticules Pierre Millien (Institut Langevin) mardi 03 janvier 2017, 11:00, Amphi IPGP
Résumé: On étudie les résonances plasmoniques de particules métalliques isolées à l'aide de techniques d'équations intégrales. On effectue un développement asymptotique des champs électromagnétiques par rapport au volume de la particule et on évalue les sections efficaces d'absorption et de diffusion.

Modelbased inverse problem for the ultrasonic characterization of complex materials: An overview of potential applications to composites, cortical bone and bonded layers. Nicolas Bochud (Institut Langevin) lundi 19 décembre 2016, 11:00, Amphi IPGP
Résumé: Ultrasonic nondestructive evaluation (NDE) is an emerging technology that enables to raise the remaining life and reliability of nowadays structures, as well as to characterize pathologies in medical science. Typically, four levels of NDE are considered: (1) the detection of the presence of a damage, (2) the localization of that damage, (3) the identification and quantification of that damage, and (4) its influence on the remaining life of the structure. The concept of damage/pathology is here understood in a broad sense, which ranges from defects in a structural material to consistency changes in a biological materials.
For competitive damage assessment and quality control, quantitative NDE techniques based on the use of theoretical models of the ultrasonic wave propagation have been developed to extract additional information from experimental measurements. Despite the structural complexity of the considered materials (e.g., spatial heterogeneity of the mechanical properties, multiple damage mechanisms, dispersion, porosity, attenuation), relative simple models are required for efficient and realtime monitoring of the structure. Indeed, the complexity of the recorded signals suggests to directly compare the experimental measurements with theoretical results, with the purpose of extracting quantitative information from damage or pathology. A possible approach to solve this problem is provided by the modelbased inverse problem (IP) framework. The solution of an IP identification approach is commonly defined in terms of the minimization of an objective function consisting in the discrepancy between the experimental observations and the numerically predicted results.
The purpose of this talk is to present three potential applications of such modelbased inverse problems, namely (1) the characterization of CFRP plates subjected to postimpact fatigue damage using an ultrasonic throughtransmission setup; (2) cortical bone assessment using ultrasonic guided waves; and (3) the investigation of interfacial stiffnesses of a trilayer using zerogroup velocity Lamb modes.

Critical properties of the Anderson transition through the lookingglass of the CBS and CFS peaks Christian Miniatura (Centre for Quantum Technologies, Singapore) mercredi 14 décembre 2016, 11:00, Salle 310
Résumé: In disordered media, the absence of diffusion arising from the spatial localization of singleparticle states is known as Anderson localisation (AL). In three dimensions, AL manifests itself as a phase transition which occurs at a critical energy or at a critical disorder strength (the mobility edge) separating a metallic phase where states are spatially extended, from an insulating one where states are localized. Theoretically, much efforts have been devoted to the study of the critical properties of the Anderson transition (AT), such as wavefunction multifractality or critical exponents. In practice however, only a handful of experiments have found evidence for the 3D Anderson transition, among them cold atoms, and even fewer have investigated its critical features (mostly in the context of quantumchaotic dynamical localization). In addition to the intrinsic difficulty of achieving wave localization in three dimensions, one reason for the rareness of experimental characterizations of the Anderson transition is the lack of easily measurable observables displaying criticality. In this talk, I will show that the critical properties of the AT are encoded in two emblematic interference effects observed in momentum space: the coherent backscattering (CBS) and the coherent forward scattering (CFS) peaks, the latter being an effective ``order parameter’’ of the transition. By a finite time scaling analysis of the CBS width and of the CFS contrast temporal dynamics, one can extract accurate values of the mobility edge and critical exponents of the transition in agreement with their best known values to this date.

Wavefront shaped focusing in Nanophotonics and in Scattering media Bergin Gjonaj (TECHNION, Haifa) mardi 13 décembre 2016, 16:00, Amphi IPGP
Résumé: Wavefront shaping is the capability to control the incident light towards optimal coupling with a complex system. Applying wavefront shaping in Nanohotonics allowed us to focus light in the nanoscale and the capability to achieve superresolution imaging. Similarly, we could focus light in space and time at the location of target particles embedded in random scattering media. The outlook for both scenarios is to deliver highly concentrated optical energy in a local and controllable way so as to address with high sigbnaltonoise ration relevant problems in biomedical imaging, sensing and therapy.

A head full of waves: Imaging motion and mechanical deformations for neurosciences Olivier Thouvenin (Institut Langevin) jeudi 24 novembre 2016, 14:00, Salle 310
Résumé: During this seminar, I will show you that Michelson interferometers ae not only complicated experiments to scare students during their bachelor, but can also be of crucial importance for some researchers, as they enable the detection of subwavelength mechanical vibrations, even “deep” inside biological tissues. I will present our development of different optical microscopes, based on interferometry that can simultaneously measure some mechanical and biochemical information in various biological samples. We could notably demonstrate that subcellular mechanical fluctuations depend on cellular metabolic activity, offering us an original contrast to detect cells and their pathologies. Finally, I will also present our attempt to detect an electromechanical coupling in mammalian neurons with our microscopes, in order to demonstrate more complete theories explaining how information propagates in the brain.

A Potpourri of Rough Surface Scattering Phenomena Ingve Simonsen (Norwegian University of Sciences and Technology, Trondheim) mardi 15 novembre 2016, 11:00, Amphi IPGP
Résumé: The aim of this talk is to give a pedagogical introduction to light scattering from random and ordered rough surface. This will be done by presenting a collection ("a potpourri") of rough surface scattering phenomena. We will discuss what characterize them, under what conditions they occur, and what is their physical origin. Some of the phenomena we will present are enhanced back and forward scattering; satellite peaks; the Brewster scattering phenomenon; optical Yoneda peaks; Rayleigh and Wood anomalies; and Mueller matrices and depolarization.

Optical Tools for High Resolution Imaging of Cerebral Blood Flow and Microvasculature Andrew K. Dunn (Biomedical Engineering Department, University of Texas at Austin) mardi 08 novembre 2016, 11:00, Amphi IPGP
Résumé: Many optical techniques have been developed for realtime imaging of blood flow. Laser speckle contrast imaging has become one of the most widely used techniques due to its simple instrumentation and its ability to visualize blood flow over a wide range of spatial scales. However, obtaining quantitative blood flow information remains a challenge for laser speckle imaging. Recently, an extension to laser speckle imaging, called MultiExposure Speckle Imaging (MESI), was introduced that increases the quantitative accuracy of CBF images. This talk will describe technical developments in laser speckle imaging as well as new methods for threedimensional visualization of blood vessels that can be used to improve our understanding of blood flow measures inferred from speckle images.

Granular friction: from building the pyramids to the anatomy of individual contacts at the nanoscale Daniel Bonn (van der WaalsZeeman Institute, University of Amsterdam) mardi 11 octobre 2016, 11:00, Salle 310
Résumé: I will discuss the rheology and mechanical properties of wet granular materials, and show why the behavior can be very subtle. Once one understands the mechanical properties, I will show that one can use this knowledge to construct the perfect sandcastle, or to understand why the ancient Egyptians wetted the desert sand with water before sliding heavy stones over it.
I will then go on to show some new results on friction at the microscopic scale, between 2 grains. Amonton’s famous friction law states that the friction force is proportional to the normal force since both are proportional to the area of contact. However for spherical grains, the contact area is not proportional to the normal force, as shown by Hertz long ago. We use a new fluorescence technique that allows us to probe the real area of contact between 2 rough surfaces. In our case, we conclude that important deviations from Amonton’s law are observed.

SpaceTime Causality, Spatial NonLocality and Negative Refraction Davide Forcella (Institut Langevin) mercredi 21 septembre 2016, 17:00, Salle 310
Résumé: I will present a first principles analysis of the electromagnetic response of homogeneous and isotropic media.
Using such analysis I will show that spacetime causality defines necessary and sufficient conditions for negative refraction. In particular no real stable media can support negative refraction in absence of spatial nonlocality and
dissipation, while a generic first order correction to local dissipative response is sufficient to have negative
refraction. Such results provide a sound answer to the longstanding discussion on the conditions for negative refraction, and they open the way to the classification of media with negative refraction. We see many possible extensions and applications of our anlysis to other domains: such as nonhomogeneus or non  isotropic material, surface waves, sound waves, etc. with both theoretical and experimental implications.
We look forward to discuss together possible applications of such formalism and results.

Transfert radiatif de chaleur en présence de gradients de température :
nouvelles lois asymptotiques et couplage avec conduction Riccardo Messina (Laboratoire Charles Coulomb, Université de Montpellier, UMR 5221, Montpellier) mardi 20 septembre 2016, 11:00, Amphi IPGP
Résumé: Deux corps à températures différentes et séparés d’un espace vide échangent énergie par l’in
termédiaire du champ électromagnétique. En champ lointain, pour des distances grandes devant la
longueur d’onde thermique λT = h̄c/kB T (8 μm à température ambiante), ce transfert radiatif est
limité par la loi de Stefan–Boltzmann. La situation change drastiquement en champ proche, où le
flux diverge en d<sup>−2</sup> pour d → 0, pouvant donc dépasser de plusieurs ordres de grandeur cette limite.
Dans cette présentation je discute une approche théorique récemment développée pour l’étude
du flux de chaleur entre deux couches planaires caractérisées par un profil de température arbitraire.
Cette théorie est basée sur la connaissance des coéfficients de réflexion et transmission des couches.
Dans la premiére partie de ma présentation, je montre que le comportement dans la limite d → 0
dépend fortement du profil de température. Selon les propriétés de ce profil à proximité de l’interface
couches–vide, le flux peut diverger en d<sup>−2</sup>, d<sup>−1</sup> , log(d), ou tendre vers une constante.
Je discute ensuite le problème couplé conduction–radiation pour un système de deux couches
planaires, en montrant que pour certaines matériaux et distances d’accès expérimental (pouvant
aller jusqu’à des dizaines de nanometres) un profil de température peut naturellement apparaı̂tre, en
modifiant qualitativement le comportement du flux radiatif calculé en l’absence de couplage. Plus
spécifiquement, ce couplage implique toujours une limite finie du flux pour d → 0. Je discute enfin
cet effet dans le cas des matériaux typiquement utilisés dans les expériences, en montrant aussi que
la saturation du flux déjà observée dans une expérience récente pourrait être due à l’effet ici présenté.

Multimode fibers with random mode mixing: physics and applications Yaron Bromberg (The Hebrew University of Jerusalem) jeudi 15 septembre 2016, 11:00, Amphi IPGP
Résumé: Random mode mixing in multimode optical fibers has long been
considered a nuisance that should be circumvented. However, it was
recently realized that fibers with strong mode mixing provide
outstanding opportunities for studying the transport of light in
disordered media, as they exhibit two unique advantages over
scattering samples. First, the transmission through fibers is
extremely high, even in the presence of strong mode mixing, and thus
information of the input state of the light is only scrambled but not
lost. Second, unlike random scattering samples, fibers allow to fully
control the coupling of the input light to all the guided modes,
thanks to their finite numerical aperture. We have recently used these
properties of multimode fibers to study new features of coherent
backscattering, also known as weak localization of light. By utilizing
a magnetooptical effect, we controlled the interference between
timereversed paths inside a multimode fiber with strong mode mixing,
observed for the first time the optical analogue of weak
antilocalization, and realized a continuous transition from weak
localization to antilocalization [1].
Surprisingly, the chaoticlike dynamics of light in multimode fiber
and the extreme sensitivity to external perturbations, open the door
for new types of applications. We have recently shown that multimode
fibers can be used to generate and distribute secure keys for optical
encryption [2]. The fast fluctuations in the fiber mode mixing provide
the source of randomness for the key generation, and the optical
reciprocity principle guarantees that the keys at the two ends of the
fiber are identical. We experimentally demonstrated the scheme using
classical light and offtheshelf components, paving the way towards
cost‑effective key establishment at the physicallayer of fiberoptic
networks.
[1] Y. Bromberg, B. Redding, S. M. Popoff, and H. Cao, Control of
coherent backscattering by breaking optical reciprocity, Phys. Rev. A
93, 023826 (2016)
[2] Y. Bromberg, B. Redding, S. M. Popoff, and H. Cao, Remote key
establishment by mode mixing in multimode fibers and optical
reciprocity, arXiv:1506.07892

Optical Coherence Tomography: a tool to visualize the human brain architecture Caroline Magnain (Harvard Medical School  USA) mardi 05 juillet 2016, 11:00, Amphi IPGP

Imagerie acoustooptique: les challenges de l'imagerie in vivo JeanBaptiste Laudereau (Institut Langevin) mardi 21 juin 2016, 11:00, Salle 310
Résumé: Biological tissues are very strong lightscattering media. As a consequence, current medical imaging devices do not allow deep optical imaging unless invasive techniques are used. Acoustooptic (AO) imaging is a lightultrasound coupling technique that takes advantage of the ballistic propagation of ultrasound in biological tissues to access optical contrast with a millimeter resolution. Coupled to commercial ultrasound (US) scanners, it could add useful information to increase US specificity. Thanks to photorefractive crystals, we developed a bimodal AO/US imaging setup based on wavefront adaptive holography that recently showed promising ex vivo results on tumors for which acoustical contrast were not significant. However, before any clinical applications can be thought of, two major issues of in vivo imaging have to be addressed.
The first one concerns current AO sequences that take several tens of seconds to form an image, far too slow for clinical imaging. The second issue concerns in vivo speckle decorrelation that occurs over less than 1 ms, too fast for photorefractive crystals. In this talk, I will present a new US sequence that allows increasing the framerate of at least one order of magnitude and an alternative light detection scheme based on spectral holeburning in rareearth doped crystals that allows beating speckle decorrelation as first steps toward in vivo imaging.

Temporal Equivalent of a Mirror (and of a Bragg Mirror) Vincent Bacot (Institut Langevin) mardi 31 mai 2016, 11:00, Amphi IPGP
Résumé:
What would be the equivalent of looking into a glass mirror in time? Might we go through such a looking glass? These questions which seem to originate directly from a character in Alice in Wonderland entail fundamental interrogations about time reversible systems. Time and space play a similar role in (whatever) wave propagation (optical, acoustical, matter, water, ... waves). Wave control is usually performed by spatially engineering the properties of a medium but temporally manipulating these properties constitute a complementary approach. We demonstrate the relevance of this approach by introducing the concept of Instantaneous Time Mirror (ITM). When a wave propagates in a medium which undergoes at once a strong and brief change of its effective propagation properties, a time reversed, backpropagating wave instantly generated. The effect in the time domain of this disruption on the initial wave is the same as the effect in space of a (standard) mirror.
The ITM concept is general and may be applied to any type of wave. We validated this new instantaneous method of time reversal experimentally with water waves. A disruption is obtained by "shaking" abruptly the liquid in order to modify the effective gravity. This experiment is a first realization of the Gedankenexperiment imagined by Loschmidt in a famous dispute with Boltzmann about the time reversibility of the dynamics of gases.
The principle of the ITM will be extended to a periodic time modulation of the medium. The waves existing in this time crystal (or time Bragg mirror) feature peculiar properties. The similarities and differences with their spatial counterpart will be addressed and we will show that it allows us to bring together in a single general concept phenomena as apparently different as phase conjugation (in optics) and the hydrodynamic Faraday instability.

Liens statistiques entre l’intensité transmise et réfléchie par un milieu diffusant Nikos Fayard (Institut Langevin) mardi 17 mai 2016, 11:00, Amphi IPGP

Sound Field Recording and Reproduction and Its Extension to Superresolution Shoichi Koyama (Institut Langevin) mardi 10 mai 2016, 11:00, Amphi IPGP

Approche Matricielle de la propagation des ondes lumineuses en milieu diffusant : détection et imagerie Amaury Badon (Institut Langevin) mardi 03 mai 2016, 11:00, Amphi IPGP

Towards integrated optics at the nanoscale: plasmonemitter coupling using plasmonic structures Nancy Rahbany (Charles Delaunay Institute, University of Technology of Troyes) mardi 19 avril 2016, 11:00, Salle 310
Résumé: There is a growing interest nowadays in the study of strong lightmatter interaction at the nanoscale, specifically between plasmons and emitters. Researchers in the fields of plasmonics, nanooptics and nanophotonics are constantly exploring new ways to control and enhance surface plasmon launching, propagation, and localization. Moreover, emitters placed in the vicinity of metallic nanoantennas exhibit a fluorescence rate enhancement due to the increase in the electromagnetic field confinement. However, numerous applications such as optical electronics, nanofabrication and sensing devices require a very high optical resolution which is limited by the diffraction limit.
Targeting this problem, we introduce a novel plasmonic structure consisting of nanoantennas integrated in the center of ring diffraction gratings. Propagating surface plasmon polaritons (SPPs) are generated by the ring grating and couple with localized surface plasmons (LSPs) at the nanoantennas exciting emitters placed in the gap. We provide a thorough characterization of the optical properties of the simple ring grating structure, the double bowtie nanoantenna, and the integrated ring grating/nanoantenna structure, and study the coupling with an ensemble of molecules as well as single SiV centers in diamond. The combination of the subwavelength confinement of LSPs and the high energy of SPPs in our structure leads to precise nanofocusing at the nanoscale, which can be implemented to study plasmonemitter coupling in the weak and strong coupling regimes.

Manipulation, contrôle et guidage d’ondes élastiques en milieux complexes Benoît Gérardin (Institut Langevin) mardi 12 avril 2016, 11:00, Amphi IPGP

Spatial nonlocality and Negative Refraction: Electromagnetic properties of viscous charged fluids Davide Forcella (Institut Langevin) mardi 29 mars 2016, 11:00, Amphi IPGP
Résumé: In the seminar I will discuss some of the elctromagnetic properties of viscous charged fluids. In particular I will show how the viscosity and the charge density of such media conspire to generate a negative refractive index for frequency below a certain characteristic frequency, for all hydrodynamic charged systems. I will then discuss possible application of this result for actual experimental setups, focusing on the case of electrons in in metals. I will provide for them a phenomenological model based on the idea of viscous, chardged dissipative fluid. The analysis of this model will confirm that finite viscosity leads to multiple modes of evanescent electromagnetic waves at a given frequency, one of which is characterized by a negative index of refraction. Bulding on this result I will discuss how optical spectroscopy can be used to probe the viscosity of electrons in metals, a concept very rarely discussed in theory and not measured yet in experiments. I will then show that finite viscosity lead to decrease the reflectivity of a metallic surface, and it provides charactristic sharp signatures in the reflection, refraction and transmission of electromagnetics waves through metallic samples. I will conclude commenting on the experiments that are presetly trying to probe negative refraction and viscosity in metallic samples. I will moreover provides some comments on possible underlying reasons why such general group of materials manifest negative refraction, and argue about the importance of spatial nonlocality for this to happen.

TimeReversal Optical Focusing Changhuei Yang (California Institute of Technology) jeudi 24 mars 2016, 11:00, Amphi IPGP
Résumé: We appear opaque because our tissues scatter light very strongly. Traditionally, focusing of light in biological tissues is confounded by the extreme scattering nature of tissues. Interestingly, optical scattering is timesymmetric and we can exploit optical phase conjugation methods to null out scattering effects. I will discuss our recent results in using different types of guidestar methods in combination with digital optical phase conjugation to tightly focus light deep within biological tissues. These technologies can potentially enable incisionless laser surgery, targeted optogenetic activation, highresolution biochemical tissue imaging and more.
Fourier Ptychography  Microscopes are complex and fussy creatures that are capable of delivering limited image information. This is because physical optical lenses are intrinsically imperfect. The perfect lenses we draw in high school ray diagrams simply do not exist. I will discuss our recent work on Fourier Ptychographic Microscopy  a computational microscopy method that enables a standard microscope to push past its physical optical limitations to provide gigapixel imaging ability.

Fano Imaging at the nanoscale: from photonic crystals to disordered photonics Massimo Gurioli (LENS, Florence, Italie) mardi 08 mars 2016, 11:00, Amphi IPGP
Résumé: The tremendous progress in designing and tailoring the electric field in nanoresonators requires an investigation tool that is able to access the detailed features of the optical localized resonant modes with deepsubwavelength spatial resolution. This scenario has motivated the development of different nanoscale imaging techniques. Scanning nearfield optical microscopy (SNOM) photoluminescence is proven to be a powerful technique. However it cannot be used for phase mapping and it is hard to be extended to silicon or polymer photonics
Here, we show that a technique involving the combination of scanning nearfield optical microscopy with resonant scattering spectroscopy enables imaging the electric field in nanoresonators with outstanding spatial resolution (λ/19) by means of a pure optical method based on light scattering. By exploiting the Fano line shape, we can locally measure the phase modulation of the resonant modes without the need of external heterodyne detection. Also vectorial mapping is demonstrated. Finally we apply the method to the study of disorderd photonic system where ligth localization is directly imaged at the nanoscale.

Séminaire des doctorants Institut Langevin mardi 01 mars 2016, 11:00, Amphi IPGP

Comment la physique contribue à la métaphysique de la causalité Maximilian Kistler (Institut d’histoire et de philosophie des sciences et des techniques, Paris) mardi 23 février 2016, 11:00, Amphi IPGP

Acoustic waves in complex media: from perfect absorption (waveguides with resonators) to shocklike superdiffusion (granular media) Georgios Theocharis (Laboratoire d'Acoustique de l'Université du Maine, Le Mans) mardi 09 février 2016, 11:00, Amphi IPGP
Résumé:
The efficient absorption of audible sound takes an important position since excessive noise exposure becomes a major
public health concern. Thus, thin and lightweight absorbers that are both easily installed and capable to absorb sound over a wide
frequency range are strongly desired. In the first part of this seminar, I will present some of our recent activities in this field focusing
on the perfect acoustic absorption through the interplay of the inherent losses and transparent modes with high Q factor.
These modes are generated in a twoport, onedimensional waveguide, which is sideloaded by isolated resonators of moderate Q factor.
In asymmetric structures, near perfect onesided absorption has been observed (96%) with deep subwavelength samples.
Granular media are the second most manipulated material by man. However, the propagation of sound in granular solids remains a challenging scientific task. Important features of these media are: (i) the disorder in their packing and (ii) their nonlinear response.
In the second part of this seminar, I will present our investigations about energy transport in polydisperse granular chains.
After establishing the regime of sufficiently strong disorder, we focus our studies on the role of nonlinearity as this is desribed by Hertzian
contact mechanics. By increasing the initial excitation amplitudes we are able to identify three distinct dynamical regimes with different energy transport properties: a near linear, a weakly nonlinear and a highly nonlinear regime. We demonstrate that in the highly nonlinear regime, the
the energy is almost ballistically transported through shocklike excitations.

Wave mixing of short optical pulses of different spatiotemporal extents using transient Bragg gratings Yonatan Sivan (BenGurion University, Israel) mardi 26 janvier 2016, 11:00, Amphi IPGP
Résumé: Wave mixing is one of the most basic nonlinear optical processes. In the vast majority of cases, it is studied for one or more interacting quasimonochromatic waves, where all temporal and spatial scales are large and similar. In contrast, there are very few studies of the mixing of wave packets having different wavelengths, spectra, and temporal and spatial profiles. Indeed, these configurations involve rather a complicated and nonintuitive wave mixing process such that it is difficult to assess, a priory, what would be the final spatial length, temporal duration and spectral width of the pulses generated by the interaction.
In this talk, I will describe one of the first thorough studies of such complex configurations, and present a systematic way to predict and interpret the wave mixing process in terms of exchange of spectral and spatial Fourier components between the interacting pulses. I will focus on a simple example where an intense short pump pulse is periodicallypatterned such that it induces a transient Bragg grating (TBG) whose stop gap matches the frequency of an incoming long signal pulse.
I will demonstrate the validity of our interpretation using exact numerical simulations as well as a novel derivation of coupled mode theory for pulses propagating in timevarying media. Unlike previous attempts to derive such a model, our approach involves no approximation, and does not impose any restriction on the spatiotemporal profile. Moreover, the effect of modal dispersion on mode evolution and on the coupling to other modes is fully taken into account. It also avoids various artifacts of previous derivations by introducing the correct form of the solution, and can be applied to any other wave system.
I will then discuss the advantages and limitations of the proposed approach and demonstrate it for generating, switching and reversing ultrashort pulses propagating in several material platforms, such as silica fibers, semiconductor waveguides and plasmonic waveguides.

Comment le traitement du signal peut aider à optimiser les systèmes d'imagerie polarimétriques François Goudail (Laboratoire Charles Fabry, Institut d'Optique) mardi 19 janvier 2016, 11:00, Amphi IPGP
Résumé: Les systèmes d'imagerie polarimétrique permettent de révéler des contrastes qui n'apparaissent pas dans les images classiques. Ils disposent d'un certain nombre de degrés de liberté qui permettent de d'optimiser l'information apportée par ces images. Cette optimisation utilise des critères issus de la théorie du traitement du signal, qui sont différents selon le type d'information recherché dans l'image, par exemple : estimation d'un état de polarisation ou mise en évidence d'un contraste.
Je présenterai quelques exemples d'optimisation d'information polarimétrique pour différentes applications, en m'appuyant sur des systèmes d'imagerie polarimétriques adaptatifs que nous avons construits.

Discovering fUS imaging data structure using unsupervised learning methods Kristof Giber (Institut Langevin) mardi 12 janvier 2016, 11:00, Amphi IPGP
Résumé: Functional ultrasound imaging (US) has the potential to provide a high resolution image of the brain. However, finding functionally relevant structures can draw limitations to this resolution if we rely on matched anatomical atlases. Those limitations can arise from the amount of regional variations across individuals (this is large in human brain and not so large in rodent brain). They can also come from the way those atlases were produced, ie. based on anatomical markers or functional observations that are not relevant to the functions we investigate. Thus, to fully benefit from our resolution and achieve a relevant functional mapping, we need to apply data driven analysis and unsupervised learning methods such as Independent Component Analysis (ICA) and Deep Neural Networks (DNN). One way to go is to identify independent signal sources in each experiment and the corresponding activations. ICA is commonly used in fMRI and here I'll show that it's equally beneficial in fUS. Resting state activity was recorded in rodents during anaesthesia. Cortical and subcortical areas were reproducibly delineated at a fine scale at group level and backprojected to individual level. Correlation maps across areas delineated with ICASSO method reveal a strong correlation in the midline as well as local and contralateral connections. Using sparse autoencoders and DNNs with stacked layer configurations resulted in improved quality maps. The latter method was able to distinguish individual barrel activations in a whisker stimulation paradigm. The technique provides access to analysis at higher resolution and in paradigms when one cannot estimate the timing of the studied activations.

Superfluid Nanomechanical Resonators in Confined Geometries Xavier Rojas (Royal Holloway University of London) mardi 15 décembre 2015, 11:00, Amphi IPGP
Résumé: At low temperature, liquid He transitions into a superfluid state as a result of macroscopic quantum coherence. By confining liquid 4He in welldefined structures of size comparable with the coherence length, nonbulk phenomena can be revealed. For instance, nanofluidic confinement has allowed the study of finitesize effects near the superfluid transition, realizing the most precise test of scaling laws to date. In order to study the thermodynamic properties of confined liquid 4He, we have developed a new set of measurements based upon superfluid nanomechanical resonators. We made an ultrasonic analog of the FabryPerot resonator to measure the sound velocity of liquid 4He in a few micron gap, and a superfluid Helmholtz resonator to measure the superfluid fraction and the onset of quantum turbulence in nanofluidic channels. In addition, at very low temperature (T ∼ 10 mK) where the normal component is negligible, the mechanical quality factor of superfluid resonators can be extremely large (Q > 10 billions), which makes nanomechanical superfluid resonators very promising systems for the field of optomechanics and quantum information.

Acoustic array processing: New methods for sound field reconstruction and analysis Efren FernandezGrande (DTU, Denmark) mardi 08 décembre 2015, 11:00, Amphi IPGP
Résumé: Acoustic imaging methods are useful in order to localize sound sources, examine how these radiate sound, characterize the acoustic properties of materials, and analyze complex sound fields. These methods typically rely on measurements with an array of microphones in order to characterize thespatiotemporal properties of the sound field under study. This talk has an emphasis on spherical array processing and sparsity promoting methods based on Compressive Sensing (CS). CS constitutes an interesting alternative to classical leastsquares approaches. We will discuss applications where these techniques can be useful, such as sound source localization, sound absorption estimation, and sound field visualization in enclosures.

The geometric phases of polarized waves Vincent Rossetto (LPMMC, Unversité Joseph Fourier, Grenoble) mardi 01 décembre 2015, 11:00, Amphi IPGP
Résumé: The geometric phase is a general concept appearing in several domains in Physics. In wave physics, one can observe their existence in polarization, but they exist also for oscillatory mechanical systems or in quantum mechanics. During this seminar, we will present some geometric phase examples and discuss about the general conditions for their existence. We will then address the geometric phase of polarized waves in scattering media and discuss their relation with anisotropies.

The haircell bundle as a mechanosensor and amplifier for hearing Pascal Martin (Institut Curie) lundi 30 novembre 2015, 14:30, Amphi IPGP
Résumé: The ear works as a remarkable sound detector. Hearing can indeed operate over six orders of magnitudes of soundpressure levels, with exquisite sensitivity and sharp frequency selectivity to weak sound stimuli. Curiously, the ear does not work as a highfidelity sound receiver, introducing in the auditory percept “phantom” tones that are not present in the sound input. In this talk, I will present micromechanical experiments at the level of the cellular microphone of the inner ear – the hair cell – whose function is to transduce soundevoked vibrations into electrical nervous signals. I will discuss the origin of stiffness and drag of the mechanoreceptive hair bundle, a tuft of cylindrical protrusions that protrudes from the apical surface of each cell, and show that hair cells can power spontaneous oscillations of their hair bundles. Oscillations are thought to result from a dynamical interplay between mechanosensitive ion channels, molecular motors, and calcium feedback. We find that oscillations of the hair bundle allow the hair cell to actively resonate with its mechanical input at the expense of distortions with properties that are characteristic of hearing. Our results promote a general principle of sound detection that is based on nonlinear amplification by selfsustained “critical” oscillators in the inner ear, i.e. active dynamical systems that operate on the brink of an oscillatory instability called a Hopf bifurcation.

Imaging atherosclerosis with light and sound Gijs van Soest (Erasmus MC, Rotterdam) mardi 24 novembre 2015, 11:00, Amphi IPGP
Résumé: Atherosclerosis is one of the most deadly diseases in the world, killing about 17 million people each year by its sequelae, myocardial infarction
and stroke. Atherosclerotic plaques are complex, heterogeneous structures and it is difficult to predict which lesion will precipitate a clinical event.
Patient and lesionspecific assessment of the disease could provide better
guidance to therapeutic interventions, mechanical or pharmaceutical. In this talk, I will present some of our recent work on the development of new
technologies for imaging coronary and carotid atherosclerosis, based on
catheterbased optical coherence tomography at 5600 frames per second,
intravascular and noninvasive photoacoustic imaging, and imaging
submicron displacements with ultrasound.

Topological states in microwave resonator lattices Fabrice Mortessagne (LPMC, Université Nice Sophia Antipolis & CNRS) mardi 17 novembre 2015, 11:00, Amphi IPGP
Résumé: The recent realization of topological phases in insulators and superconductors has given incentive to explore analogous realizations. Propagation of microwaves in an array of dielectric ceramic cylinders constitutes a flexible experimental platform to investigate properties of topological states. I will show how a defect state in a dimerized chain of resonators can be topologically protected against structural disorder and how this state can be selectively enhanced by combining topological protection with nonhermitian symmetries. Our microwaves experiment contributed to create the active field of `artificial graphene'. I will present results related to the topological phase transition experiences by a honeycomb lattice under uniaxial strain: The gap opening and, depending of the boundary shape, the emergence of specific edges states.

Analyseur spectral RF haute cadence avec 20 GHz de bande passante instantanée Perrine Berger (Thales Research and Technology) mardi 10 novembre 2015, 11:00, Amphi IPGP
Résumé: Les ions de terre rare en matrice cristalline, bien connus comme matériaux à gain pour les lasers, offrent, lorsqu'ils sont refroidis à la température de l’hélium liquide, des propriétés prometteuses pour le traitement d’information classique ou quantique transposée sur porteuse optique.
Combinant une largeur inhomogène de plusieurs dizaines de GHz et une résolution spectrale en général très inférieure à 1MHz lorsqu'ils sont refroidis à basse température (<5K), et capables par ailleurs de mémoriser un profil spectral pendant des temps qui parfois atteignent plusieurs jours, ces matériaux peuvent être utilisés comme processeurs optiques programmables pour une grande variété d’applications. L’intérêt pour de tels processeurs analogiques dans les domaines du radar et de la guerre électronique vient des limites rencontrées par le traitement toutélectronique en régime très large bande (plusieurs GHz). En effet, l’acquisition des signaux et leur conversion dans le domaine numérique présente de sévères limites de performances dès que les fréquences et bandes passantes dépassent quelques GHz. De plus, les débits de données deviennent extrêmement important (jusqu'à plusieurs Tb/s), et nécessitent des puissances de calcul considérables (plusieurs Tflop/s), difficiles voire impossible à implémenter dans des systèmes, en particulier embarqués. Une autre approche consiste à implémenter des prétraitements analogiques, qui vont réduire en amont le débit de données numériques et donc la puissance de calcul requise. Les ions de terre rare en matrice cristalline sont de très bons candidats pour implémenter ces traitements.
Nous avons récemment réalisé une analyse spectrale RF avec 20 GHz de bande passante instantanée, et une cadence de rafraichissement de spectre supérieure à 10 kHz, obtenus grâce à une architecture dite « arcenciel » qui utilise les propriétés spectrales des ions de terre rare en matrice cristalline refroidis à <4 K. Le démonstrateur, réalisé avec des composants optoélectroniques commerciaux et un cryostat à circuit fermé, montre des performances proches de celles requises par les systèmes pour l’analyse du spectre électromagnétique.

Physique de transformation et métamatériaux Muamer Kadic (Institute of Applied Physics, Karlsruhe Institute of Technology) mercredi 04 novembre 2015, 10:30, Amphi IPGP
Résumé: En 2006, la proposition faite par John Pendry et Ulf Leonhard de mettre au point une cape d'invisibilité a connu un important retentissement médiatique. Cette dernière est basée sur l'optique transformationnelle. Fondée sur l'invariance des équations fondamentales de l'électromagnétisme par rapport aux déformations de l'espace, elle ouvre une voie novatrice pour la conception des dispositifs nanotechnologiques en optique. Ainsi, une déformation de l'espace peut être traduite sous forme de relations constitutives de milieux équivalents. La noninvariance des équations de l'élastodynamique dans le cas le plus général s'ajoute aux contraintes usuelles de fabrication. Les applications potentielles restent les plus utiles (capes sismiques, capes sonores pour les sousmarins). Une étude par Milton et al. met en œuvre la possibilité de contrôle d'ondes mécaniques dans un type de solide bien particulier : les milieux pentamodes (Métafluides ou métamatériaux ne pouvant encaisser que la contrainte hydrostatique). Leur tenseur d’élasticité se résume au module de compressibilité comme dans le cas d’un fluide.
Nous avons cherché à fabriquer ce type de matériaux ainsi qu'à les intégrer dans le dispositif de capes d'invisibilité. L'anisotropie, la clé de la réussite, a été particulièrement étudiée. Nous avons montré non seulement la possibilité de fabriquer des pentamodes mais également leur utilité plus large dans l'élastodynamique.
Le contrôle des propriétés effectives telles que les vitesses d'ondes ou la densité sera également présentée. Enfin nous verrons un exemple de cape d’invisibilité pour la mécanique basé sur le principe de l’inclusion neutre ainsi que sur la transformation directe de mailles.
La seconde partie de la présentation sera consacrée à la conception de capes d’invisibilité en milieu diffusif (thermique et optique) et nous parlerons enfin des métamateriaux pour le magnétotransport avec comme application des sondes à effet Hall.

Wavefront shaping and nonlinear optics in the transverse localization regime Marco Leonetti (Center for Life Nano Science@Sapienza) mardi 03 novembre 2015, 11:00, Salle 3000
Résumé: Transverse Anderson localization is the trapping of waves due a disordered potential which is invariant along propagation direction, canceling the effects of diffraction. It has recently been demonstrated that such form of wave trapping may be exploited to fabricate a novel generation of optical fibers which may either be obtained in plastic or in glass.
Here we report the effects of nonlinearity in disordered optical fibers supporting transverse Anderson localization. The presence of localization alters the response of a disordered plastic material turning a selfdefocusing behavior into a self focusing one. At high optical power, modes are found reduced in extension and multiple optical beams inside this nonlocal disordered medium are subject to a form of long range interaction.
Moreover, we performed wavefront shaping experiments in disordered optical fibers in the transverse Anderson localization regime. By wavefront shaping and optimization, we observed the generation of a propagationinvariant beam, where light is trapped transversally by disorder. These localized states can be excited by extended speckled beams, and activated at a user defined target position, with a higher efficiency with respect to homogeneous (non disordered) systems.

Optical transmission matrix for rabbit imaging and fast quantum calculation Thomas Chaigne & Hugo Defienne (Laboratoire Kastler Brossel) mardi 27 octobre 2015, 11:00, Amphi IPGP
Résumé: In complex media such as white paint or biological tissue, light encounters nanoscale refractiveindex inhomogeneities that cause multiple scattering. It has been considered for a long time as a serious hitch to perform microscopy at depth, as traditional techniques rely on ballistic photons (which intensity exponentially decreases with depth).
In the last decade though, wavefront shaping emerged as a powerful tool to overcome this limitation. By controlling the phase pattern of the incident beam, one has been able to focus light through such an opaque highly scattering sample. Applications in imaging as well as in multimode fiber transmission control thus arose in the past few years.
After presenting the basics of light scattering and wavefront shaping, we will focus on two (very) different applications. We will first present how the propagation of non classical photon light can be manipulated in such scattering media. Then we will present how to improve imaging depth in biological samples.

?? Tuan VoDinh (Duke university) lundi 26 octobre 2015, 11:00, Salle 3000

Making Waves in Amsterdam Rudolf Sprik (Van der WaalsZeeman Institute, Amsterdam) mardi 13 octobre 2015, 11:00, salle 3000

Détection et localisation de microbulles par ultrasons Yann Desailly (Institut Langevin) mardi 29 septembre 2015, 11:00, Amphi IPGP

Integrated in silico and in vivo approaches in the development of neuromodulation protocols in epilepsy Julien Modolo (Laboratoire de Traitement du Signal et de l'Image (LTSI), Université de Rennes 1) mardi 22 septembre 2015, 11:00, Amphi IPGP
Résumé: Neuromodulation, or the alteration of neuronal activity using electric, magnetic or chemical means, is becoming a therapy of growing importance in the treatment of neurological disorders. Parkinson’s disease is the best example of success of neuromodulation therapy, with over 100,000 patients implanted worldwide with a deep brain stimulation (DBS) device. In the field of epilepsy, neuromodulation therapy holds great promise for the symptomatic treatment of epilepsy, with encouraging results from studies conducted in epileptic patients using a chronically implanted device (RNS, Neuropace, USA) resulting in a mean decrease of 50% of seizures in 50% of patients. However, the mechanisms of action are still elusive, and there is still room for optimization of neuromodulation therapy in epilepsy. In order to address these issues, we are presenting an integrated approach combining electrophysiological and metabolic recordings in a mice model of epilepsy (kainate model) on the one hand, and in silico biophysical model of interictal and ictal activity on the other hand. We present experimental results on local electrical stimulation of the brain in epileptic mice, which suggest a possible decrease of pathological hyperexcitability of brain tissue. We then explore possible biological mechanisms using an in silico model of neuronal activity, which provides further insights in our experimental results. The perspectives of this work in terms of therapeutic potential and disease prevention will be presented.

Microélastographie : caractérisation mécanique de la cellule par ondes élastiques Gabrielle LaloyBorgna (LABTAU, Inserm  Université Lyon 1, France) Amphithéâtre

Rhéologie et acoustique dans des milieux divisés denses : des propriétés de contacts au comportement mécanique macroscopique Adrien Izzet (CBI, ESPCI Paris  PSL, France) Amphitheatre
