Mathias FINK - Institut d'études scientifiques de Cargèse (IESC)

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performing any calculations. Pr. John H. Page Anderson Localization of Ultrasound in Three-Dimensional Mesoglasses The question of whether or not the Anderson localization of classical waves can really occur in three-dimensional disordered materials has intrigued physicists for many years. Recently there has been considerable progress in answering this question, with the most direct demonstration of 3D Anderson localization being first established in acoustics, through measurements of the dynamic transverse confinement of energy in a “mesoglass” consisting of a disordered elastic network of aluminum beads [1]. In this approach, an incident ultrasonic point source is used, and the spatial extent of the transmitted intensity is measured as a function of time on the opposite side of the sample. For diffuse waves, the spatial intensity profile on the sample surface is Gaussian, and the width squared grows linearly with time. For localized waves, the transverse spreading of the intensity is cut off, and the width saturates at long propagation times, giving information on the localization length. Thus, measurements of this dynamic transverse width provide a very direct way, which is independent of absorption, of distinguishing between diffusive and localized states [1]. After reviewing our initial experiments and their successful interpretation using the self-consistent theory of localization [2], I will show how the transverse width evolves with time as frequency is varied, and a mobility edge, separating extended from localized waves, is crossed. This work is enabling us to study aspects of classical wave localization near the Anderson transition that have not been amenable to experimental investigation previously, such as the multifractal spatial structure of localized wavefunctions [3], long-range and even infinite-range correlations of the intensity with position and frequency [4], and dynamic backscattering phenomena that reveal, in addition to the effects of localization on time-dependent coherent backscattering, a surprisingly large recurrent scattering contribution. [1] H. Hu, A. Strybulevych, J.H. Page, S.E. Skipetrov and B.A. van Tiggelen, Nature Phys. 4, 945-8 (2008). [2] N. Cherroret, S.E Skipetrov, and B.A van Tiggelen, Phys. Rev. E 82, 056603 (2010). [3] S. Faez, Anatoliy Strybulevych, J.H. Page, A. Lagendijk and B.A. van Tiggelen, Phys. Rev. Lett. 103, 155703 (2009). [4] W.K. Hildebrand, A. Strybulevych, S.E. Skipetrov, B.A. van Tiggelen, and J.H. Page, arXiv:1303.7042. Pr. Morchedaï Segev Anderson Localization of Light and Beyond Anderson Localization is one of the most basic concepts in solid-state physics. However, experiments with electronic systems have eluded scientists for many decades. Three decades after Anderson’s prediction, the concept has been extended to optics, and in 2007, our group has made the first demonstration of Anderson localization in its original context, where random fluctuations superimposed upon a periodic structure bring transport to a halt. Many experimental works have followed, in optics and matter-waves. But can disorder work to increase transport beyond diffusion, and perhaps even beyond ballistic transport ? The talk will review the recent progress on Anderson localization of light, and will describe experiments and theory demonstrating disordered–enhanced transport in photonic quasicrystals, and hyper-transport of light in photonic media with evolving disorder : a new regime of transport in which an arbitrary wavepacket expands at a rate faster than ballistic. Pr. Lihong Wang Synergy between light and sound : photoacoustic tomography and TRUE optical focusing
Photoacoustic tomography (PAT), combining optical and ultrasonic waves via the photoacoustic effect, provides in vivo multiscale non-ionizing functional and molecular imaging. PAT is the only modality capable of imaging across the length scales of organelles, cells, tissues, and organs with consistent contrast. PAT has the potential to empower multiscale systems biology and accelerate translation from microscopic laboratory discoveries to macroscopic clinical practice. PAT may also hold the key to the earliest detection of cancer by in vivo label-free quantification of hypermetabolism, the quintessential hallmark of cancer. Time-reversed ultrasonically encoded (TRUE) optical focusing is based on ultrasonic modulation of coherence light propagating in scattering tissue followed by time reversal of the ultrasonically encoded light component. TRUE focusing can noninvasively deliver light to a dynamically defined focus deep in a scattering medium. This technology opens the door to an even greater paradigm-shifting opportunity—one that controls the photon paths to minimize transmission loss in tissue. Pr. Martin Wegener Transformation materials for optics, elastodynamics, and thermodynamics I review our experimental efforts regarding implementing the ideas of transformation optics in the areas of optics, mechanics, and thermodynamics. This requires designing and fabricating artificial materials with intentionally spatially inhomogeneous and/or anisotropic effective material properties. In optics, visible-frequency broadband polarization-independent three-dimensional carpet cloaks have become possible. In mechanics, broadband two-dimensional free-space cloaks have been demonstrated and pentamode metamaterials for three-dimensional architectures are emerging. In thermodynamics, two-dimensional free-space cloaks have recently become possible - bringing us back to the beginnings of the field, i.e., to the Calderon tomography problem. Pr. Nikolay Zheludev What’s matter with meta matter ? We report on recent developments in metamaterials and nanophotonics research. Out particular focus will be on coherent control of signals with metamaterials, generation of vector potential fields with toroidal structures and using photonic network as oracle for solving complex decision problems. Pr. Claude Boccara Random behavior in optical coherence The randomness of the refractive index and/or the position of the scatterers blur the images in biological tissues. OCT by selecting singly backscattered photons is a first approach that allows overcoming this problem. Even with incoherent sources the OCT signal exhibits a speckle distribution. Despite of the speckle in the images the Full Field OCT (FFOCT) approach that we have developed allows to reveal the tissue morphology at the micron scale and starts to be a valuable tool in intra operative surgery. Sometimes the morphology is not enough to characterize the tissue, so we will examine the basic nature of the signal and what kind of supplementary information can be extracted from the OCT data such as local refractive index, density of scatterers and elasticity map. Finally (because we are in Cargese !) I will shows how FFOCT is used to count and characterize, through their Brownian trajectories, viruses in see water. Pr. Rémi Carminati Weak and strong coupling regimes of light-matter interaction in nanoscale disordered media The interplay between multiple scattering, near-field interactions and material resonances in
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Mathias FINK - Institut d'études scientifiques de Cargèse (IESC)

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