arXiv subjects

Serge Meimon

Publications and source records attributed to Serge Meimon.

7 recordsLinked to original sources

arXiv2026

The vanishing distance: a practical range boundary for dynamic wavefront shaping

Wavefront shaping (WFS) is a powerful modern method to control light propagation through scattering media, with applications ranging from biomedical imaging via cryptography to free-space optical communication. While WFS has been highly successful in static or slowly evolving media, its practical relevance in dynamic and extended scattering environments remains difficult to assess. In particular, no simple criterion currently identifies the propagation distance beyond which the residual ballistic component is no longer distinguishable from the scattered background. Here, we introduce the vanishing distance, defined as the propagation length where the ballistic power equals that carried by a single diffuse mode. Unlike the transport mean free path, which characterizes angular randomization of the scattered field, the vanishing distance identifies the loss of the ballistic channel on a modal-power basis. Beyond this distance, transmission or imaging can no longer rely on the ballistic component and must instead exploit the scattered field. We present a simple semi-analytical model, validated against Monte Carlo simulations and experiments in both monodisperse and heterogeneous scattering media, allowing the vanishing distance and the associated minimum source power to be estimated. Across representative scattering environments, the transition is found to occur typically after about 30-40 scattering mean free paths. These results provide a simple guideline for assessing the practical relevance of dynamic wavefront shaping.

physics.optics↗

arXiv2026

Nanosecond wavefront shaping to focus through agitated turbid media

Multiple scattering rapidly scrambles optical fields in fog, snow and turbid water, causing op- timized wavefront corrections to become obsolete on microsecond timescales. Although wavefront shaping enables focusing through static scattering layers, closed-loop control in dynamically evolving media has remained experimentally challenging because the correction bandwidth must approach the intrinsic decorrelation rate of the speckle. Here, we demonstrate closed-loop wavefront shaping with 32 independent degrees of freedom in an agitated turbid medium exhibiting sub-microsecond decorrelation. The medium thickness exceeds the transport mean free path, meaning the far-field speckle autocorrelation is limited to a diffraction-sized grain. Despite the microsecond decorrelation and this multiple-scattering regime, stable focusing is maintained as the correction cycle approaches the intrinsic dynamics of the medium. These results establish an experimentally accessible regime for coherent wave control in rapidly evolving complex media.

physics.optics↗

arXiv2021

Partial-Field Illumination Ophthalmoscope: improving the contrast of a camera-based retinal imager

Effective and accurate in-vivo diagnosis of retinal pathologies requires high performance imaging devices, combining a large field of view and the ability to discriminate the ballistic signal from the diffuse background in order to provide a highly contrasted image of the retinal structures. Here, we have implemented the Partial-Field Illumination Ophthalmoscope, a patterned illumination modality, integrated on a high pixel rate adaptive optics full-field microscope. This non-invasive technique enables us to mitigate the low signal-to-noise ratio, intrinsic of full-field ophthalmoscopes, by partially illuminating the retina with complementary patterns to reconstruct a wide field image. This new modality provides an image contrast spanning from the full-field to the confocal contrast, depending on the pattern size. As a result, it offers various trade-offs in terms of contrast and acquisition speed, guiding the users towards the most efficient system for a particular clinical application.

physics.med-ph↗

arXiv2020

Super-resolution in vivo retinal imaging using structured illumination ophthalmoscopy

Structured illumination microscopy (SIM) is one of the most versatile super-resolution techniques. Yet, its application to live imaging has been so far mainly limited to fluorescent and stationary specimens. Here, we present advancements in SIM to jointly tackle all the challenges of imaging living samples, i.e., obtaining super-resolution over an undistorted wide-field while dealing with sample motion, scattering, sample-induced optical aberrations and low signal-to-noise ratio. By using adaptive optics to compensate for optical aberrations and a reconstruction algorithm tailored for a moving and thick tissue, we successfully applied SIM to in vivo retinal imaging and demonstrated structured illumination ophthalmoscopy for high contrast super-resolution in vivo imaging of the human retina.

physics.med-ph↗

arXiv2020

Optical Incoherence Tomography: a method to generate tomographic retinal cross-sections with non-interferometric imaging systems

Optical tomographic cross-sectional images of biological samples were made possible by interferometric imaging techniques such as Optical Coherence Tomography (OCT). Owing to its unprecedented view of the sample, OCT has become a gold standard, namely for human retinal imaging in the clinical environment. In this Letter, we present Optical Incoherence Tomography (OIT): a completely digital method extending the possibility to generate tomographic retinal cross-sections to non-interferometric imaging systems such as en-face AO-ophthalmoscopes. We demonstrate that OIT can be applied to different imaging modalities using back-scattered and multiply-scattered light including systems without inherent optical sectioning. We show that OIT can be further used to guide focus position when the user is "blind" focusing, allowing precise imaging of translucent retinal structures, the vascular plexuses and the retinal pigment epithelium using respectively split detection, motion contrast, and autofluorescence techniques.

physics.med-ph↗

arXiv2019

Jointly super-resolved and optically sectioned Bayesian reconstruction method for structured illumination microscopy

Structured Illumination Microscopy (SIM) is an imaging technique for achieving both super-resolution (SR) and optical sectioning (OS) in wide-field microscopy. It consists in illuminating the sample with periodic patterns at different orientations and positions. The resulting images are then processed to reconstruct the observed object with SR and/or OS. In this work, we present BOSSA-SIM, a general-purpose SIM reconstruction method, applicable to moving objects such as encountered in in vivo retinal imaging, that enables SR and OS jointly in a fully unsupervised Bayesian framework. By modeling a 2-layer object composed of an in-focus layer and a defocused layer, we show that BOSSA-SIM is able to jointly reconstruct them so as to get a super-resolved and optically sectioned in-focus layer. The achieved performance, assessed quantitatively by simulations for several noise levels, compares favorably with a state-of-the-art method. Finally, we validate our method on open-access experimental microscopy data.

physics.optics↗

arXiv2008

A self-calibration approach for optical long baseline interferometry imaging

Current optical interferometers are affected by unknown turbulent phases on each telescope. In the field of radio-interferometry, the self-calibration technique is a powerful tool to process interferometric data with missing phase information. This paper intends to revisit the application of self-calibration to Optical Long Baseline Interferometry (OLBI). We cast rigorously the OLBI data processing problem into the self-calibration framework and demonstrate the efficiency of the method on real astronomical OLBI dataset.

physics.optics↗