Doppler holography is an emerging retinal imaging technique that captures the dynamic behavior of blood flow with high temporal resolution, enabling quantitative assessment of retinal hemodynamics. This requires accurate segmentation of retinal arteries and veins, but traditional segmentation methods focus solely on spatial information and overlook the temporal richness of holographic data. In this work, we propose a simple yet effective approach for artery-vein segmentation in temporal Doppler holograms using standard segmentation architectures. By incorporating features derived from a dedicated pulse analysis pipeline, our method allows conventional U-Nets to exploit temporal dynamics and achieve performance comparable to more complex attention- or iteration-based models. These findings demonstrate that time-resolved preprocessing can unlock the full potential of deep learning for Doppler holography, opening new perspectives for quantitative exploration of retinal hemodynamics. The dataset is publicly available at https://huggingface.co/datasets/DigitalHolography/
High-speed digital holography reveals local blood flow contrasts in the eye fundus through deterministic signal analysis, leveraging a forward scattering model of dynamically diffused light. This approach enables the estimation of absolute blood flow in primary in-plane retinal arteries.
We present an experimental and theoretical study of the influence of disorder correlations on the behavior of the ballistic coherent wave traveling through a strongly scattering medium. We considered two types of samples: on the one hand, a 3-D granular suspension of randomly packed submillimeter glass beads and, on the other hand, 2-D assemblies of randomly distributed millimeter copper rods immersed in water. In the 3-D case, for broadband emission in the MHz range, the transmitted signal exhibits strong dispersion, leading to a signal composed of a low-frequency ballistic wave (not observed in previous analogous experiments) followed by a higher-frequency multiply scattered wave, known as the Coda Wave. With increasing thickness, the Coda tends to disappear due to absorption, so that only the ballistic wave remains. Experiments on 2-D samples provide information on its origin: we compared the ballistic transmission through a dilute sample (well described in the ISA approximation) and through a compact stack of rods. A low-frequency ballistic wave only appears in the latter case. A parallel numerical study indicates that this effect does not require contact between the scatterers but appears at high surface fractions, typically of the order of 50% for which disorder correlations must be considered.
Light-matter interactions are frequently perceived as predominantly influenced by the electric optical field, with the magnetic component of light often overlooked. Nonetheless, the magnetic aspect plays a pivotal role in various optical processes, including chiral light-matter interactions, photon-avalanching, and forbidden photochemistry, underscoring the significance of manipulating magnetic processes in optical phenomena. Here, we explore the ability to control the magnetic light and matter interactions at the nanoscale. In particular, we demonstrate experimentally, using a plasmonic nanostructure, the transfer of energy from the optical magnetic field to a nanoparticle, thanks to the deep subwavelength magnetic confinement allowed by our nano-antenna. This control is made possible by the particular design of our plasmonic nanostructure, which has been optimized to spatially separate the electric and magnetic fields of the localized plasmon. Furthermore, by studying the spontaneous emission from the Lanthanide-ions doped nanoparticle, we observe that the optical field distributions are not spatially correlated with the electric and magnetic near-field quantum environments of this antenna, which seemingly contradicts the reciprocity theorem. We demonstrate that this counter-intuitive observation is in fact, the result of the different optical paths followed by the excitation and emission of the ions, which forbids a direct application of that theorem.
We present a physically intuitive matrix approach for quantitative imaging of complex media. While standard reflection imaging methods generally rely on confocal focusing operations, matrix imaging consists of decoupling the location of the incident and received focal spots [1]. Following this principle, a self-portrait of the focusing process can be obtained around each point of the medium. The Gouy phase shift exhibited by each focal spot can be leveraged to finely monitor the wave velocity distribution inside the medium [2]. A local multiple scattering rate can also be evaluated and its depth evolution can lead to a local measurement of the scattering mean free path, independently from absorption losses [3]. The approach is here demonstrated with ultrasound for a controllable phantom system before being applied in vivo to liver. The wave velocity and the scattering mean free path are quantitative markers for biomedical diagnosis but they are also important monitoring parameters for nondestructive testing and geophysical applications. This work thus opens important perspectives for quantitative imaging of heterogeneous media in all fields of acoustics. [1] W. Lambert etal., Phys. Rev. X 10, 021048 (2020). [2] F. Bureau et al., arXiv:2409.13901 (2024). [3] A. Goicoechea et al., Phys. Rev. Lett. 133, 176301 (2024).
