Computation of leaky waves in layered structures coupled to unbounded media by exploiting multiparameter eigenvalue problems
Gravenkamp, H., B. Plestenjak, D. A. Kiefer, and E. Jarlebring
Journal of Sound and Vibration 596 (2025)
Résumé: We present a semi-analytical approach to compute quasi-guided elastic wave modes in horizontally layered structures radiating into unbounded fluid or solid media. This problem is of relevance, e.g., for the simulation of guided ultrasound in embedded plate structures or seismic waves in soil layers over an elastic half-space. We employ a semi-analytical formulation to describe the layers, thus discretizing the thickness direction by means of finite elements. For a free layer, this technique leads to a well-known quadratic eigenvalue problem for the mode shapes and corresponding horizontal wavenumbers. Incorporating the coupling conditions to account for the adjacent half-spaces gives rise to additional terms that are nonlinear in the wavenumber. We show that the resulting nonlinear eigenvalue problem can be cast in the form of a multiparameter eigenvalue problem whose solutions represent the wave numbers in the plate and in the half-spaces. The multiparameter eigenvalue problem is solved numerically using recently developed algorithms. Matlab implementations of the proposed methods are publicly available.
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Techniques for imaging optic disc vasculature in glaucomatous optic neuropathy: A review of the literature
Aubert, T., R. Lecoge, P. Bastelica, M. Atlan, M. Paques, P. Hamard, C. Baudouin, and A. Labbé
Journal Francais d'Ophtalmologie 48, no. 2, 104369 (2025)
Résumé: The anatomy and vasculature of the optic nerve head are complex and subject to numerous variations. The main risk factor for glaucomatous optic neuropathy is elevated intraocular pressure, but many other factors have been identified. A vascular component seems to play an important role in the pathogenesis and/or progression of glaucomatous optic neuropathy, either under the influence of ocular hypertension or as an independent risk factor, particularly as in normal tension glaucoma (NTG). Reduced ocular blood flow has been identified as a risk factor for glaucoma. Numerous instruments have therefore been developed to explore the vasculature of the optic nerve head and to try to better understand the changes in blood flow in the optic nerve in glaucomatous optic neuropathy. In this review, we provide an update on the various means of imaging the vasculature of the optic nerve head, from angiography to the most modern techniques with angiographic OCT and laser Doppler holography. Using the results found in glaucomatous optic neuropathies, we will explore the close link between reduced ocular blood flow and the development or progression of glaucoma. A better understanding of this pathophysiology opens the door to improved management of our glaucoma patients.
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Single-emitter super-resolved imaging of radiative decay rate enhancement in dielectric gap nanoantennas
Córdova-Castro, R. M., B. Van Dam, A. Lauri, S. A. Maier, R. Sapienza, Y. De Wilde, I. Izeddin, and V. Krachmalnicoff
Light: Science and Applications 13, no. 1 (2024)
Résumé: High refractive index dielectric nanoantennas strongly modify the decay rate via the Purcell effect through the design of radiative channels. Due to their dielectric nature, the field is mainly confined inside the nanostructure and in the gap, which is hard to probe with scanning probe techniques. Here we use single-molecule fluorescence lifetime imaging microscopy (smFLIM) to map the decay rate enhancement in dielectric GaP nanoantenna dimers with a median localization precision of 14 nm. We measure, in the gap of the nanoantenna, decay rates that are almost 30 times larger than on a glass substrate. By comparing experimental results with numerical simulations we show that this large enhancement is essentially radiative, contrary to the case of plasmonic nanoantennas, and therefore has great potential for applications such as quantum optics and biosensing.
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Regular sloshing modes in irregular cavities using metabathymetry
Anglart, A., A. Maurel, P. Petitjeans, and V. Pagneux
Applied Physics Letters 125, no. 21 (2024)
Résumé: We present a comprehensive investigation, combining numerical simulations and experimental measurements, into the manipulation of water waves and resonance characteristics within closed cavities utilizing anisotropic metamaterials. We engineer the anisotropic media with subwavelength-scale layered bathymetry through the application of coordinate transformation theory and the homogenization technique to a fully three-dimensional linear water wave problem. Experimental and numerical analyses of deformed cavities employing anisotropic metamaterial bathymetry demonstrate regular sloshing mode patterns and eigenfrequencies akin to those observed in rectangular reference cavities with flat bathymetry. Our study underscores the potential of water wave metamaterials for establishing robust anisotropic metabathymetry for the precise control of sloshing modes.
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Experimental demonstration of negative refraction of water waves using metamaterials with hyperbolic dispersion
Euvé, L.-P., K. Pham, P. Petitjeans, V. Pagneux, and A. Maurel
Physical Review Fluids 9, no. 11 (2024)
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Reflection Measurement of the Scattering Mean Free Path at the Onset of Multiple Scattering
Goïcoechea, A., C. Brütt, A. Le Ber, F. Bureau, W. Lambert, C. Prada, A. Derode, and A. Aubry
Physical Review Letters 133, no. 17 (2024)
Résumé: Multiple scattering of waves presents challenges for imaging complex media but offers potential for their characterization. Its onset is actually governed by the scattering mean free path ℓs that provides crucial information on the medium microarchitecture. Here, we introduce a reflection matrix method designed to estimate this parameter from the time decay of the single scattering rate. Our method is first validated by an ultrasound experiment on a tissue-mimicking phantom before being applied in vivo to a human liver. This Letter opens important perspectives for quantitative imaging of heterogeneous media with waves, whether it be for nondestructive testing, biomedical, or geophysical applications.
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