arXiv subjects

Antoine Hubert

Publications and source records attributed to Antoine Hubert.

5 recordsLinked to original sources

arXiv2025

Two-photon light-sheet live imaging at kilohertz frame rate using birefringence-based pulse splitting

Multiphoton microscopy is widely used for live imaging. However, its acquisition speed remains limited by fluorophore emission rates and photodamage. To increase the pixel rate of a two-photon microscope beyond a few megahertz (MHz), multi-point parallelized schemes have been proposed. Two-photon (2P) light-sheet microscopy emerges as an effective approach for high-speed multiphoton imaging of live specimens, as it enables parallelized excitation while minimizing the required laser power. However, optimizing the signal-to-photodamage ratio in 2P light-sheet microscopy requires to precisely control the illumination parameters, including both wavelength and pulse frequency. Since conventional femtosecond laser sources generally do not allow independent modulation of these parameters, the development of low-cost, efficient and robust strategies to modulate the temporal excitation profile is essential to fully exploit the advantages of 2P light-sheet microscopy. Here, we introduce a compact pulse splitting scheme that meets these criteria. We used cascaded birefringent crystals to convert each excitation laser pulse into an adjustable sequence of collinear sub-pulses. We demonstrate its effectiveness in optimizing 2P light-sheet imaging of live zebrafish embryos. We analyze the impact of pulse splitting on photobleaching, nonlinear photodamage, and imaging performance. Additionally, we demonstrate high-speed 2P imaging of the beating heart and brain calcium dynamics using red fluorophores in live embryos. We achieve kilohertz imaging frame rate, reaching more than 150 MHz pixel rates with fluorescent signal levels above 10 $photons.pixel^{-1}$ using a laser mean power and a peak intensity in the range of 100 mW and 0.1 $TW.cm^{-2}$ at the sample, respectively. This adjustable pulse-splitting scheme allows full advantage to be taken of light-sheet illumination for fast in vivo 2P imaging.

physics.optics↗

arXiv2025

Design and optimization of in situ self-functionalizing stress sensors

Mechanical contributions are crucial regulators of diverse biological processes, yet their \textit{in vivo} measurement remains challenging due to limitations of current techniques, that can be destructive or require complex dedicated setups. This study introduces a novel method to synthesize biocompatible, self-functionalizing stress sensors based on inverted emulsions, that can be used to probe stresses inside tissues but can also locally perturb the biological environment through specific binder presentation or drug delivery. We engineered an optimal design for these inverted emulsions, focusing on finding the balance between the two contradictory constraints: achieving low surface tension for deformability while maintaining emulsion instability for efficient self-functionalization and drug release. Proof-of-concept experiments in both agarose gels and complex biological systems, including brain organoids and zebrafish embryos, confirm the droplets ability to deform in response to mechanical stress applied within the tissue, to self-functionalize and to release encapsulated molecules locally. These versatile sensors offer a method for non-invasive stress measurements and targeted chemical delivery within living biological tissues, giving the potential to overcome current technical barriers in biophysical studies.

cond-mat.soft↗

arXiv2025

Thermal Lensing Effects in Two-Photon Light-Sheet Microscopy

In light-sheet fluorescence microscopy (LSFM), the axial resolution is governed by the illumination beam profile, motivating the development of advanced beam-shaping techniques to enhance imaging performance. Two-photon LSFM (2P-LSFM), in particular, improves the signal-to-background ratio by reducing laser scattering and distortion in biological specimens. However, we report a potentially detrimental thermal effect in 2P-LSFM: the high laser powers required for two-photon excitation induce localized heating, which alters the refractive index of the medium and effectively forms a divergent thermal lens in water. At 500 mW the light-sheet waist broadens by 25% and shifts by 300 $\mu$m before stabilizing several seconds after the laser shutter is opened. Both experiments and simulations reveal that this thermal lensing effect scales with laser power and the path length the beam travels through water. The resulting degradation in resolution and signal-to-noise ratio may compromise imaging applications that require high laser powers for rapid volumetric imaging of large specimens or functional brain imaging. This limitation is particularly critical in dynamic sample environments, such as during stepwise repositioning or flow-based delivery of chemical or hydrodynamic sensory stimuli, where changes occur on timescales comparable to the thermal settling time.

physics.optics↗

arXiv2022

Single-shot quantitative aberration and scattering length measurements in mouse brain tissues using an extended-source Shack-Hartmann wavefront sensor

Deep fluorescence imaging in mammalian brain tissues remains challenging due to scattering and optical aberration-induced loss in signal and resolution. Correction of aberrations using adaptive optics (AO) requires their reliable measurement in the tissues. Here, we show that an extended-source Shack-Hartmann wavefront sensor (ESSH) allows quantitative aberration measurements through fixed brain slices with a thickness up to four times their scattering length. We demonstrate in particular that this wavefront measurement method based on image correlation is more robust to scattering compared to the standard centroid-based approach. Finally, we obtain a measurement of the tissue scattering length taking advantage of the geometry of a Shack-Hartmann sensor.

physics.optics↗

arXiv2021

A conservative level set method for liquid-gas flows with application in liquid jet atomisation

In this paper, a methodology for modelling two-phase flows based on a conservative level set method in the framework of finite volume method is presented. The novelty of the interface capturing method used here lies on the advection of level set which is solved with a WENO scheme and is corrected with a novel re-initialisation method for retaining its signed distance function character. The coupling with the volume of fluid method is done with a simple algebraic approach and with the new algorithm the accumulated mass conservation errors remain reasonably low. The paper presents a unique coupling between the level set method and the Eulerian-Lagrangian-Spray-Atomisation approach for modelling spray dispersion in liquid atomisation systems. The method is shown to have good accuracy providing similar results to other numerical codes for the classical tests presented. Preliminary results are also shown for three-dimensional simulations of the primary break-up of a turbulent liquid jet obtaining results comparable to direct numerical simulations. Consequently, the coupled method can be used for simulating various two-phase flow applications offering an accurate representation of the interface dynamics.

physics.comp-ph↗