Retrieving time-dependent Green's functions in optics with low-coherence interferometry

We report on the passive measurement of time-dependent Green's functions in the optical frequency domain with low-coherence interferometry. Inspired by previous studies in acoustics and seismology, we show how the correlations of a broadband and incoherent wave-field can directly yield the Green's functions between scatterers of a complex medium. Both the ballistic and multiple scattering components of the Green's function are retrieved. This approach opens important perspectives for optical imaging and characterization in complex scattering media.Comment: 5 pages, 4 figure

A matrix approach for optical imaging in highly scattering media

L’objectif des travaux présentés dans cette thèse est d’étudier la propagation de la lumière dans les milieux inhomogènes afin de repousser les limites actuelles de l’imagerie : les aberrations et la diffusion multiple. Dans une première partie, nous avons associé les outils et le formalisme initialement développés pour les ondes ultrasonores aux techniques propres à l’optique. Grâce à un dispositif expérimental innovant, nous avons enregistré les réponses d’un milieu complexe pour une collection de champs incidents, formant ainsi une matrice de réflexion. Une étude des corrélations spatiales de cette matrice permet alors de séparer les contributions de diffusion simple et multiple. Alors que la première permet de former une image seulement limitée par la diffraction d’un objet enfoui au sein du milieu, la seconde permet de caractériser les paramètres de transport de la lumière dans le milieu.La seconde partie de ma thèse s’est intéressée à la possibilité d’extraire une information cohérente à partir d’un champ aléatoire. Il a été démontré, en acoustique et en sismologie notamment, que la corrélation d’un champ incohérent mesuré en deux points permettait d’estimer la réponse impulsionnelle entre ces deux mêmes points. Dans ma thèse, nous avons étendu cette approche aux ondes optiques. En particulier nous avons démontré la mesure de réponses impulsionnelles entre des diffuseurs individuels à l’aide d’une simple lampe halogène et d’un montage interférométrique. A la suite de cette preuve de principe, nous avons réalisé des estimations de paramètres de transport pour des milieux fortement diffusants.My thesis was devoted to the study of the propagation of optical waves in inhomogeneous media in an attempt to push back the fundamental limits of optical imaging: multiple scattering and aberrations. In a first part, we combined the tools and the formalism developed initially for acoustic waves with techniques peculiar to the field of optics. Thanks to a system that allows to both control and measure the optical field, we record the output responses of a scattering medium for a given set of input fields. This collection of input-output responses forms a matrix called the reflection matrix. We then exploit the spatial and temporal contents of this matrix to discriminate the ballistic and the multiple scattered light. The first contribution provides an image with a diffraction limited resolution of an object placed behind or embedded in a turbid medium, while the second contribution offers information on the transport of light in the diffusive regime.The second study was dedicated to the measurement of a coherent information from a totally incoherent source. It has been shown in acoustics and seismology that correlations of an In my thesis, we extended this property to optical waves. In particular, we demonstrated the measurement of an impulse response between individual scatterers with a femtosecond resolution using a simple halogen white light source. Following this proof of principle, the characterization of the transport properties of a medium was performed from a collection of impulse responses in the diffusive regime

Remote scanning for ultra-large field of view in wide-field microscopy and full-field OCT

Imaging specimens over large scales and with a sub-micron resolution is instrumental to biomedical research. Yet, the number of pixels to form such an image usually exceeds the number of pixels provided by conventional cameras. While most microscopes are equipped with a motorized stage to displace the specimen and acquire the image tile-by-tile, we propose an alternative strategy that does not require any moving part in the sample plane. We propose to add a scanning mechanism in the detection unit of the microscope to collect sequentially different sub-areas of the field of view. Our approach, called remote scanning, is compatible with all camera-based microscopes. We evaluate the performances in both wide-field microscopy and full-field optical coherence tomography and we show that a field of view of 2.2 mm with 1.1 micron resolution can be achieved. We finally demonstrate that the method is especially suited to image biological samples such as millimetric engineered tissues

Remote scanning for ultra-large field of view in wide-field microscopy and full-field OCT

Imaging specimens over large scales and with a sub-micron resolution is instrumental to biomedical research. Yet, the number of pixels to form such an image usually exceeds the number of pixels provided by conventional cameras. While most microscopes are equipped with a motorized stage to displace the specimen and acquire the image tile-by-tile, we propose an alternative strategy that does not require any moving part in the sample plane. We propose to add a scanning mechanism in the detection unit of the microscope to collect sequentially different sub-areas of the field of view. Our approach, called remote scanning, is compatible with all camera-based microscopes. We evaluate the performances in both wide-field microscopy and full-field optical coherence tomography and we show that a field of view of 2.2 mm with 1.1 micron resolution can be achieved. We finally demonstrate that the method is especially suited to image biological samples such as millimetric engineered tissues

Remote scanning for ultra-large field of view in wide-field microscopy and full-field OCT

Imaging specimens over large scales and with a sub-micron resolution is instrumental to biomedical research. Yet, the number of pixels to form such an image usually exceeds the number of pixels provided by conventional cameras. Although most microscopes are equipped with a motorized stage to displace the specimen and acquire the image tile-by-tile, we propose an alternative strategy that does not require to move any part in the sample plane. We propose to add a scanning mechanism in the detection unit of the microscope to collect sequentially different sub-areas of the field of view. Our approach, called remote scanning, is compatible with all camera-based microscopes. We evaluate the performances in both wide-field microscopy and full-field optical coherence tomography and we show that a field of view of 2.2 × 2.2 mm 2 with a 1.1 µm resolution can be acquired. We finally demonstrate that the method is especially suited to image motion-sensitive samples and large biological samples such as millimetric engineered tissues

Adaptive coherence volume in full-field optical coherence tomography

International audienc

Contribution a l'etude de la corrosion generalisee et de l'inhibition du cuivre et de l'acier doux dans les eaux de refroidissement cinetique de corrosion

CNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueSIGLEFRFranc