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

Single-shot hyperspectral wavefront imaging Blochet, B., N. Lebas, P. Berto, D. Papadopoulos, and M. Guillon Nature Communications 17, no. 1 (2026) Résumé: Single-shot hyperspectral wavefront sensing is essential for applications like spatio-spectral coupling metrology in high-power laser or fast material dispersion imaging. Under broadband illumination, traditional wavefront sensors assume an achromatic wavefront, which makes them unsuitable. We introduce a hyperspectral wavefront sensing scheme based on the Hartmann wavefront sensing principles, employing a multicore fiber as a Hartmann mask to overcome these limitations. Our system leverages the angular memory effect and limited spectral correlation width of the multicore fiber, encoding wavefront gradients into displacements and the spectral information into uncorrelated speckle patterns. This method retains the simplicity, compactness, and single-shot capability of conventional wavefront sensors, with only a slight increase in computational complexity. It also allows a tunable trade-off between spatial and spectral resolution. We demonstrate its efficacy for recording the hyperspectral wavefront cube from single-pulse acquisitions at the Apollon multi-petawatt laser facility, and for performing multispectral microscopic imaging of dispersive phase objects.
Reconfigurable and active time-reversal metasurface turns walls into sound routers Dorlot, F., C. Bourdeloux, M. Fink, and F. Lemoult Communications Physics 8, no. 1 (2025) Résumé: Sound control in noisy or reverberant spaces is important for applications ranging from communication to immersive audio. However, existing methods often struggle to deliver sound selectively to specific listeners without interference. Here we show that an active acoustic metasurface, composed of programmable elements that both sense and re-emit sound, enables precise targeting of audio in complex environments. Each element processes signals in real time using convolution filtering, allowing us to exploit reciprocity and time-reversal symmetry in wave propagation. Experiments with audible sound in reverberant rooms demonstrate that this approach creates clear, individualized sound channels while suppressing unwanted noise. This research opens new possibilities for adaptive sound delivery in crowded or dynamic settings, with potential applications in conferencing, entertainment, and assistive listening technologies.
Fundamental bounds of wavefront shaping of spatially entangled photons Shekel, R., S. M. Popoff, and Y. Bromberg APL Photonics 10, no. 11, 110801 (2025) Résumé: Wavefront shaping enables control of classical light through scattering media. Extending these techniques to spatially entangled photons promises new quantum applications, but their fundamental limits, especially when both photons scatter, remain unclear. Here, we theoretically and numerically investigate the enhancement of two-photon correlations in two specific output modes through thick scattering media. We analyze three configurations: shaping one photon after the medium, shaping both photons before the medium, and shaping both photons after the medium. We show that each configuration yields fundamentally different enhancements compared to classical expectations. For a system with N modes, we show that shaping one photon yields the classical enhancement η ≈ (π/4)N, while shaping both photons before the medium reduces it to η ≈ (π/4)2N. However, in some symmetric detection schemes, when both photons are measured at the same mode, perfect correlations are restored with η ≈ N, resembling digital optical phase conjugation. Conversely, shaping both photons after the medium leads to a complex, NP-hard-like optimization problem, yet achieves superior enhancements, up to η ≈ 4.6N. These results reveal unique quantum effects in complex media and identify strategies for quantum imaging and communication through scattering environments. Mots-clés: entangled photons; wavefront shaping; focusing; complex media; multimode fiber; scattering media
Open Transmission Channels in Multimode Fiber Cavities with Random Mode Mixing Pelc, G., S. Guterman, R. Gutiérrez-Cuevas, A. Goetschy, S. M. Popoff, and Y. Bromberg Physical Review Letters 135, no. 17, 173801 (2025) Résumé: The transport of light in disordered media is governed by open transmission channels, which enable nearly complete transmission of the incident power, despite low average transmission. Extensively studied in diffusive media and chaotic cavities, open channels exhibit unique properties such as universal spatial structure and extended dwell times. However, their experimental study is challenging due to the large number of modes required for control and measurement. We propose a multimode fiber cavity (MMFC) as a platform to explore open channels. Leveraging mode confinement and finite angular spread, MMFCs enable a full control over all channels. This allowed us to achieve an 18-fold power enhancement by selectively exciting an open channel with a transmission rate of 0.90+/-0.04. By analyzing 100 transmission matrices of MMFC realizations, we observed a bimodal transmission eigenvalue distribution, indicating high channel control and low losses. The scalability of MMFCs, combined with long dwell times and potential for nonlinear phenomena, offers new opportunities for studying complex wave transport. Mots-clés: wavefront shaping; transmission matrix; multimode fiber; bimodal distribution; total transmission

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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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