arXiv subjects

Thomas Chaigne

Publications and source records attributed to Thomas Chaigne.

14 recordsLinked to original sources

arXiv2026

Real time monitoring of pressure-induced deformation of PDMS to evaluate pressure distribution in microfluidic channels

Accurate pressure measurements in micrometric channels are essential for a wide range of microfluidic applications. Existing approaches rely on a variety of sensing mechanisms, but generally require the integration of additional probes or sensing elements during or after chip fabrication. Here, we introduce a pressure sensing approach based on quantitative phase imaging of the deformation of compliant microfluidic channels. We demonstrate real-time measurements of channel deformation over a large field of view with high sensitivity, without the need for embedded components or modifications of the microfluidic device.

physics.optics↗

arXiv2026

A depth-dependent, transverse shift-invariant operator for fast iterative 3D photoacoustic tomography in planar geometry

Iterative model-based image reconstruction in photoacoustic tomography (PAT) enables principled incorporation of detector physics, object-related priors, and complex acquisition strategies. However, for three-dimensional (3D) imaging scenario, the computational cost is often dominated by repeatedly solving wave equations. We propose a fast forward model for planar detection geometries that exploits transverse shift invariance. This symmetry enables to compute the full acoustic field from a 3D object, as a result of a set of 2D convolutions with depth-dependent impulse responses. This formulation yields a FFT-based forward operator and its corresponding discrete adjoint operator, making iterative reconstruction faster without calling partial differential equation (PDE) solvers at each iteration. We validate the model against commonly used PDE solver under matched discretization and boundary settings, and demonstrate accelerations of up to 2 orders of magnitude for iterative reconstructions from experimental all-optical photoacoustic datasets.

physics.optics↗

arXiv2025

Real-Time Electro-Optic Dual Comb Detection of Ultrasound Waves

High-resolution ultrasound based imaging techniques like photoacoustic (PA) imaging that require fast detection of acoustic waves, are often coupled with an opto-mechanical sensor like a Fabry-Perot cavity (FPC) for enhanced sensitivity at high frequency. Due to the inherent inhomogeneity of the FPC thickness, the resonance of the cavity can exhibit a spatial distribution, requiring dynamic adjustment of the interrogation wavelength when raster-scanning the sensor with a probe beam. To avoid this, we propose in this work the use of an electro-optically modulated dual-comb light source for rapid acoustic wave sensing within a specified bandwidth. Utilizing a dual-comb vibrometry approach, we demonstrated a proof-of-principle of the technique, with real-time detection of 10 MHz acoustic waves simultaneously with three different teeth (separated by 10 GHz) of the dual-frequency comb, achieving a 20 ns temporal resolution. We also investigated the system's sensitivity limit in terms of the strength of the detected acoustic waves, opening new possibilities for ultrafast PA imaging modalities.

physics.optics↗

arXiv2024

Optical wavefront shaping in deep tissue using photoacoustic feedback

Over the past decade, optical wavefront shaping has been developed to focus light through highly opaque scattering layers, opening new possibilities for biomedical applications. To probe light intensity deep inside soft scattering media such as biological tissues, internal guide-stars are required. Here, we give an overview of the main principles and describe in depth the use of a photoacoustic feedback signal for this purpose. We further present first principles calculations and simulations to estimate important experimental parameters, and detailed instructions on designing and conducting these experiments. Finally, we provide guidance towards selecting suitable equipment for building a typical experimental setup, paving the way for further innovative biomedical imaging and therapy applications.

physics.optics↗

arXiv2022

Fast interrogation wavelength tuning for all-optical photoacoustic imaging

Optical detection of ultrasound for photoacoustic imaging provides large bandwidth and high sensitivity at high acoustic frequencies. Higher spatial resolutions can therefore be achieved using Fabry-P\'erot cavity sensors, as compared to conventional piezoelectric detection. However, fabrication constraints during deposition of the sensing polymer layer require a precise control of the interrogation beam wavelength to provide optimal sensitivity. This is commonly achieved by employing slowly tunable narrowband lasers as interrogation sources, hence limiting the acquisition speed. We propose instead to use a broadband source and a fast tunable acousto-optic filter to adjust the interrogation wavelength at each pixel within a few microseconds. We demonstrate the validity of this approach by performing photoacoustic imaging with a highly inhomogeneous Fabry-P\'erot sensor.

physics.optics↗

arXiv2021

Roadmap on Wavefront Shaping and deep imaging in complex media

The last decade has seen the development of a wide set of tools, such as wavefront shaping, computational or fundamental methods, that allow to understand and control light propagation in a complex medium, such as biological tissues or multimode fibers. A vibrant and diverse community is now working on this field, that has revolutionized the prospect of diffraction-limited imaging at depth in tissues. This roadmap highlights several key aspects of this fast developing field, and some of the challenges and opportunities ahead.

physics.optics↗

arXiv2020

Reproducing Fresnel-Arago historical experiment: a visual illustration of the main concepts of physical optics

Many concepts of physical optics can be visually illustrated on a relatively simple optical setup in a table-top format, not requiring any very specific equipment. Diffraction, interferences, speckle, image formation, Fourier optics, strioscopy are among the many themes to be shown using the demonstration system described here. This short letter describes how to reproduce the setup and prepare the samples. It also gives a brief description of the experiments that can be performed to illustrate the main concepts of physical optics (except coherence). Its content should be of interest to the teachers and students at high school and early years of university.

physics.ed-ph↗

arXiv2019

Photoacoustic imaging beyond the acoustic diffraction-limit with dynamic speckle illumination and sparse joint support recovery

In deep tissue photoacoustic imaging the spatial resolution is inherently limited by the acoustic wavelength. Recently, it was demonstrated that it is possible to surpass the acoustic diffraction limit by analyzing fluctuations in a set of photoacoustic images obtained under unknown speckle illumination patterns. Here, we purpose an approach to boost reconstruction fidelity and resolution, while reducing the number of acquired images by utilizing a compressed sensing computational reconstruction framework. The approach takes into account prior knowledge of the system response and sparsity of the target structure. We provide proof of principle experiments of the approach and demonstrate that improved performance is obtained when both speckle fluctuations and object priors are used. We numerically study the expected performance as a function of the measurements signal to noise ratio and sample spatial-sparsity. The presented reconstruction framework can be applied to analyze existing photoacoustic experimental datasets containing dynamic fluctuations.

physics.optics↗

arXiv2017

Scattering correlations of time-gated light

Manipulating the propagation of light through scattering media remains a major challenge for many applications, including astronomy, biomedical imaging and colloidal optics. Wavefront shaping is one of the most promising ways to mitigate scattering and focus through inhomogeneous samples. However, wavefront correction remains accurate over only a limited spatial extent within the scattering medium - a correlation range referred to as the optical memory effect. Here, by selecting only the weakly scattered light for wavefront shaping, we show that the addition of temporal degrees of freedom enhances this correlation range. We investigate spatial scattering correlations by digitally time-gating the early arriving light in the spectral domain. We demonstrate that the range of the translational memory effect for the early arriving light is increased almost fourfold, paving the way for a range of scattering media imaging applications.

physics.optics↗

arXiv2017

Super-resolution photoacoustic imaging via flow induced absorption fluctuations

In deep tissue photoacoustic imaging the spatial resolution is inherently limited by the acoustic wavelength. We present an approach for surpassing the acoustic diffraction limit by exploiting temporal fluctuations in the sample absorption distribution, such as those induced by flowing particles. In addition to enhanced resolution, our approach inherently provides background reduction, and can be implemented with any conventional photoacoustic imaging system. The considerable resolution increase is made possible by adapting notions from super-resolution optical fluctuations imaging (SOFI) developed for blinking fluorescent molecules, to flowing acoustic emitters. By generalizing SOFI mathematical analysis to complex valued signals, we demonstrate super-resolved photoacoustic images that are free from oscillations caused by band-limited detection. The presented technique holds potential for contrast-agent free micro-vessels imaging, as red blood cells provide a strong endogenous source of naturally fluctuating absorption.

physics.optics↗

arXiv2015

Super-resolution photoacoustic fluctuation imaging with multiple speckle illumination

In deep tissue photoacoustic imaging, the spatial resolution is inherently limited by acoustic diffraction. Moreover, as the ultrasound attenuation increases with frequency, resolution is often traded-off for penetration depth. Here we report on super-resolution photoacoustic imaging by use of multiple speckle illumination. Specifically, we show that the analysis of second-order fluctuations of the photoacoustic images combined with image deconvolution enables resolving optically absorbing structures beyond the acoustic diffraction limit. A resolution increase of almost a factor 2 is demonstrated experimentally. Our method introduces a new framework that could potentially lead to deep tissue photoacoustic imaging with sub-acoustic resolution.

physics.optics↗

arXiv2014

Light Focusing and Two-Dimensional Imaging Through Scattering Media using the Photoacoustic Transmission-Matrix with an Ultrasound Array

We implement the photoacoustic transmission-matrix approach on a two-dimensional photoacoustic imaging system, using a 15 MHz linear ultrasound array. Using a black leaf skeleton as a complex absorbing structure, we demonstrate that the photoacoustic transmission-matrix approach allows to reveal structural features that are invisible in conventional photoacoustic images, as well as to selectively control light focusing on absorbing targets, leading to a local enhancement of the photoacoustic signal.

physics.optics↗

arXiv2013

Improving visibility in photoacoustic imaging using dynamic speckle illumination

In high-frequency photoacoustic imaging with uniform illumination, homogeneous photo-absorbing structures may be invisible because of their large size or limited-view issues. Here we show that, by exploiting dynamic speckle illumination, it is possible to reveal features which are normally invisible with a photoacoustic system comprised of a 20MHz linear ultrasound array. We demonstrate imaging of a 5 mm diameter absorbing cylinder and a 30 micrometer black thread arranged in a complex shape. The hidden structures are directly retrieved from photoacoustic images recorded for different random speckle illuminations of the phantoms by assessing the variation in the value of each pixel over the illumination patterns.

physics.optics↗

arXiv2013

Improving Photoacoustic-guided Focusing in Scattering Media by Spectrally Filtered Detection

We experimentally and numerically study the potential of photoacoustic-guiding for light focusing through scattering samples via wavefront-shaping and iterative optimization. We experimentally demonstrate that the focusing efficiency on an extended absorber can be improved by iterative optimization of the high frequency components of the broadband photoacoustic signal detected with a spherically focused transducer. We demonstrate more than 8-fold increase in the photoacoustic signal generated by a 30 microns wire using a narrow frequency band around 60MHz. We numerically confirm that such optimization leads to a smaller optical focus than using the low frequency content of the photoacoustic feedback.

physics.optics↗