Ondes, complexité et information (OCI)

Forêt de tiges : un modèle de diffusion multiple utrasonore

Responsable

Alexandre AUBRY

Tél. : 01 80 96 30 66

Co-responsable

Sébastien POPOFF

Tél. : 01 80 96 39 48

Membres permanents

Alexandre AUBRY

Tél. : 01 80 96 30 66

Julien DE ROSNY

Tél. : 01 80 96 30 52

Arnaud DERODE

Tél. : 01 80 96 30 67

Mathias FINK

Tél. : 01 80 96 30 69

Emmanuel FORT

Tél. : 01 80 96 30 35

Abdelwaheb OURIR

Tél. : 01 80 96 30 39

Sébastien POPOFF

Tél. : 01 80 96 39 48

Actualités

Sensitivity of Lamb waves in viscoelastic polymer plates to surface contamination Spytek, J., D. A. Kiefer, R. K. Ing, C. Prada, J. Grando, and J. De Rosny Ultrasonics 149, 107571 (2025) Résumé: Detecting surface contamination on thin thermoformed polymer plates is a critical issue for various industrial applications. Lamb waves offer a promising solution, though their effectiveness is challenged by the strong attenuation and anisotropy of the polymer plates. This issue is addressed in the context of a calcium carbonate (CaCO3) layer deposited on a polypropylene (PP) plate. First, the viscoelastic properties of the PP material are determined using a genetic algorithm inversion of data measured with a scanning laser vibrometer. Second, using a bi-layer plate model, the elastic properties and thickness of the CaCO3 layer are estimated. Based on the model, the sensitivity analysis is performed, demonstrating considerable effectiveness of the A1 Lamb mode in detecting thin layers of CaCO3 compared to Lamb modes A0 and S0. Finally, a direct application of this work is illustrated through in-situ monitoring of CaCO3 contaminants using a straightforward inter-transducer measurement.
Output control of dissipative nonlinear multimode amplifiers using spacetime symmetry mapping Chen, C. W., K. Wisal, M. Fink, A. D. Stone, and H. Cao Nature Physics (2025) Résumé: In many linear and nonlinear systems, time-reversal symmetry makes it possible to control the output waves by appropriately shaping the input waves. However, time-reversal symmetry is broken in systems with energy dissipation, necessitating a different approach for relating the input and output fields. We theoretically consider a saturated multimode fibre amplifier in which light generates a heat flow and suffers thermo-optical nonlinearity, thus breaking time-reversal symmetry. We identify a spacetime symmetry that maps the target output back to an input field. This spacetime symmetry mapping applies phase conjugation, gain and absorption substitution but not time reversal, and it holds in a steady state and for slowly varying inputs. Our approach enables coherent wavefront control of nonlinear dissipative systems.
Temporal chirp, temporal lensing, and temporal routing via space-time interfaces Pacheco-Peña, V., M. Fink, and N. Engheta Physical Review B 111, no. 10 (2025) Résumé: A time interface (a rapid change of the constitutive parameters of a material in time), applied within an unbounded medium where a wave travels, can enable frequency conversion and is considered the temporal analog of a spatial interface between two materials. Here, we study light-matter interactions in four dimensions, 4D (space, x,y,z, and time, t), by exploring the implications of applying time interfaces, not to the entire space where a wave travels, but to certain regions of space in order to create spatial interfaces in time. Different configurations such as induced perpendicular, parallel, and oblique spatial interfaces via a temporal interface are discussed. It is shown how such four-dimensional combination of temporal and spatial interfaces can enable interesting features such as the 4D generalized Snell's law and temporal chirp, temporal lensing, and temporal routing of electromagnetic waves. Such exotic possibilities may provide new ways to manipulate light-matter interactions via a combination of temporal and spatial interfaces.
Complementary Speckle Stimulated Emission Depletion Microscopy Arjmand, P., S. C. Thodika, H. Li, E. Bivas, M. Oheim, H. Yoshida, E. Brasselet, and M. Guillon ACS Photonics (2025) Résumé: Stimulated emission depletion (STED) microscopy has emerged as a powerful technique providing visualization of biological structures at the molecular level in living samples. In this technique, the diffraction limit is broken by selectively depleting the fluorophore’s excited state by stimulated emission, typically using a donut-shaped optical vortex beam. STED microscopy performs exceptionally well in degraded optical conditions, such as living tissues. Nevertheless, photobleaching and acquisition time are among the main challenges for imaging large volumetric fields of view. In this regard, random light beams such as speckle patterns have proved to be especially promising for three-dimensional imaging in compressed sensing schemes. Taking advantage of the high spatial density of intrinsic optical vortices in speckles─one of the most commonly used types of structured beams in STED microscopy─we propose here a novel scheme that employs speckles for performing STED microscopy. Two speckle patterns are generated at the excitation and the depletion wavelengths, respectively, exhibiting inverted intensity contrasts. We illustrate spatial resolution enhancement using complementary speckles as excitation and depletion beams on both fluorescent beads and biological samples. Our results establish a robust method for super-resolved three-dimensional imaging with promising perspectives in terms of temporal resolution and photobleaching.

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Présentation du thème

Les avancées technologiques et scientifiques des quinze dernières années, auxquelles l’Institut Langevin a contribué de manière pionnière, ont considérablement élargi notre capacité à contrôler les champs optiques, électromagnétiques et acoustiques avec une précision spatio-temporelle sans précédent. Grâce à ces progrès, il est désormais possible d’explorer et d’exploiter un nombre impressionnant de degrés de liberté, ouvrant ainsi des perspectives innovantes pour de nombreuses applications.

D’une part, les télécommunications bénéficient particulièrement de ces avancées, permettant des transmissions plus rapides, plus fiables et plus sécurisées. D’autre part, l’imagerie en milieux complexes profite largement de ces progrès grâce à une approche matricielle exhaustive, exploitant toute l’information disponible pour améliorer significativement la qualité et la précision des images obtenues.

En parallèle à ces travaux appliqués, des études plus fondamentales sont menées, notamment sur les ondes de gravité, qui sont particulièrement adaptées pour l’exploration des milieux dépendant du temps. Ces recherches fondamentales sont essentielles pour approfondir notre compréhension des phénomènes complexes et ouvrir de nouvelles voies de recherche.

Ainsi, la manipulation de l’information dans des milieux complexes devient plus sophistiquée et efficace, facilitant des développements dans divers secteurs tels que la médecine, les sciences de la terre, l’ingénierie, et bien d’autres.

En somme, les contributions de l’Institut Langevin jouent un rôle crucial dans la transformation de ces découvertes scientifiques en solutions pratiques et innovantes, redéfinissant ainsi les frontières de ce qui est possible.

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