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.
Attenuation and dispersion of coherent Rayleigh and head waves on the surface of a polycrystal Du Burck, C., and A. Derode The Journal of the Acoustical Society of America 159, no. 1, 955-973 (2026) Résumé: This work presents experimental and theoretical results concerning the dispersion and attenuation caused by scattering during the propagation of ultrasonic waves on the surface of a polycrystal. Rayleigh and head waves are measured in the case of two Inconel® 600 samples with different average grain sizes. The coherent, i.e., ensemble-averaged, waves are estimated, as well as their frequency-dependent phase velocities and scattering mean-free paths. The results obtained from a contactless laser setup are compared to those obtained from a transducer array placed on the surface of the sample. The influence of contact is highlighted, particularly at low frequency and in the small-grained sample, where the attenuation by scattering is lower. Moreover, the two-point correlation (TPC) functions of both samples are estimated, and it is shown that neither is exponential. Standard theoretical models are adapted to these particular TPCs and yield effective bulk wavenumbers, from which effective surface wavenumbers can be calculated via a simple and approximate method. The theoretical results are then compared to the experimental ones.
Hydrogel metapad with ultrasound transparency and broadband focusing for biomedical imaging Zhang, J., D. Yu, T. Zhang, C. Gao, E. Dong, Z. Song, C. Fan, Z. Han, F. Lemoult, M. Fink, Z. Wang, Y. Lin, and Y. Zhang National Science Review 13, no. 6 (2026) Résumé: Imparting broadband transparency and focusing on flexible ultrasound bioelectronics can significantly enhance the capabilities for precise evaluation of tissues and organs as well as treatment of diseases. While existing wearable ultrasound devices, whether rigid or stretchable, often merge rigid ultrasound element arrays with soft materials to achieve a reliable interface on the human skin, they lack controlled artificial microstructures, resulting in compromised ultrasound transparency and challenges in achieving broadband focusing. Here, we report a metapad made of hydrogel metamaterials with high ultrasound transparency and broadband focusing by controlling the hydrogel porosity at a sub-wavelength scale. The hydrogel metapad achieves near-perfect acoustic impedance matching with tissues, low attenuation loss, broadband transmission, and high focusing intensity gain. Ultrasound imaging simulations further show a significant improvement in imaging contrast near the focal region when using the hydrogel metapad. Practical applications demonstrate that it enhances the imaging capabilities of ultrasound probes for vital human organs, including blood vessels and the heart. Our hydrogel metapad holds great potential for advancing soft acoustic functional devices, capable of seamlessly interfacing with both biological tissues and aquatic environments.
Taking Advantage of Multiple Scattering for Optical Reflection Tomography Wasik, T., V. Barolle, A. Aubry, and J. Garnier IEEE Transactions on Computational Imaging 12, 533-547 (2025) Résumé: Optical Diffraction Tomography (ODT) is a powerful non-invasive imaging technique widely used in biological and medical applications. While significant progress has been made in transmission configuration, reflection ODT remains challenging due to the ill-posed nature of the inverse problem. We present a novel optimization algorithm for 3D refractive index (RI) reconstruction in reflection-mode microscopy. Our method takes advantage of the multiply-scattered waves that are reflected by uncontrolled background structures and that illuminate the foreground RI from behind. It tackles the ill-posed nature of the problem using weighted time loss, positivity constraints and Total Variation regularization. We have validated our method with data generated by detailed 2D and 3D simulations, demonstrating its performance under weak multiple scattering conditions and with simplified forward models used in the optimization routine for computational efficiency. In addition, we highlight the need for multi-wavelength analysis and the use of regularization to ensure the reconstruction of the low spatial frequencies of the foreground RI.

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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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