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The topic of the thesis I investigated since November 2017 (ANR project) is called: « Optical & Terahertz signature of vegetal, study at the sunflower leaf scale ». In a whole world climate changing context, we focus on varietal selection of food plants issue facing water stress conditions. In the near future, lack of water resources in several places all around the world will oblige us to improve deeply agronomic yield efficiency. This could be improved by new technologies and technics based on physic principles. For few decades now, numerous works mixing these two domains has been performed and published. They allowed to develop new kind of agronomy, more precise and effective. Study we present in this work has been performed in this state of mind. However, contrary to the new optical agronomic tools, we investigated at the sunflower leaf scale. The opto-geometricals properties could bring relevant information with respect to this topic. The first step would be to get more familiar with the vegetal living tissue we work with. Different well-known technics have been used to probe the leaf like spectroscopy, Scanning Electron Microscopy (SEM), angular scattering, classic microscopy and speckle pattern study. Next step of this work is about numerical reconstruction of the internal architecture of a leaf. As a dicotyledonous plant, thickness of a leaf is organized as a stack of layers. Each layer has its own physiologic and morphologic properties linked with their functionality. In order to probe this structure, we enlightened it with Terahertz pulse which contains large wavelengths and allows measurements to avoid scattering phenomenon. Hence, we have been able to rebuilt the internal leaf structure by analyzing the Terahertz light deformations in time domain thanks to a reverse engineering technique. The results emphasize for the first time and in a non-destructive way, the internal geometry and the optical indices of the layers composing the leaf structure (trichomes, cuticles, mesophyll). These first unpublished results which need to be reinforced by larger measurements campaign, promote to continue in this way. Such fast parameters estimation of an internal leaf organization could lead to new techniques and may strongly interest agronomists. Therefore, this work offers a real potential research direction since it provides new observable containing information which could be crucial for phenotyping., Le sujet de thèse que j'ai investi dans le cadre du projet OptiPAG depuis novembre 2017 (projet ANR) s'intitule : « Signature optique et terahertz des végétaux, étude à l'échelle de la feuille de tournesol ». Plus précisément, dans un contexte de changement climatique à grande échelle, on s'intéresse à la problématique de la sélection variétale des espèces végétales alimentaires vis-à-vis de leur résistance au stress hydrique. Dans un futur proche, le manque local de ressources en eau dans certaines régions du globe nous obligera à améliorer considérablement l'efficacité des rendements agricoles et ceci notamment par le biais de nouvelles techniques de phénotypage basées sur des principes optiques/physiques. Depuis quelques décennies maintenant, de nombreuses études à cheval entre ces deux domaines ont été publiées et ont permis de développer une agronomie plus précise et plus efficace. Les travaux que nous avons menés ont été réalisés dans cet état d'esprit. Cependant, contrairement aux nouveaux outils d'agronomie de précision, nous avons souhaité ici nous intéresser aux observables d'une feuille de tournesol, mesures optiques à l'échelle d'une feuille de tournesol en imaginant que ses propriétés opto-géométriques puissent véhiculer de l'information pertinente et robuste au regard de cette problématique. Il s'agit donc dans un premier temps de se familiariser suffisamment avec le matériel végétal en le soumettant à des mesures optiques classiques telles que la spectrométrie, l'imagerie MEB et microscopique, l'analyse de diffusion angulaire, l'imagerie et l'étude statistique du speckle ... La deuxième partie de ce travail s'intéresse à la reconstruction numérique de l'architecture interne d'une feuille. En tant que plante dicotylédone, l'épaisseur d'une feuille de tournesol est composée d'un empilement de couches dont les propriétés physiologiques et morphologiques varient. Afin de sonder cette structure organisée, nous l'avons soumise à un rayonnement THz dont les dimensions en longueurs d'onde, de l'ordre de grandeur des épaisseurs des couches, permettent de limiter le phénomène de diffusion. Ainsi, à partir de l'analyse de la déformation d'un pulse de lumière THz, il a été possible de reconstruire, par reverse engineering, une formule d'empilement cohérente avec l'observation et les a priori dont nous disposons. Ceci donne accès, pour la première fois, à une analyse précise et non destructrice de la géométrie interne des feuilles de végétaux, analyse qui consigne les indices complexes et les épaisseurs de chacune des couches de la feuille (trichomes, cuticules, mésophylles). Ces premiers résultats inédits, qui méritent d'être appuyés par des campagnes systématiques de mesure, encouragent évidemment à poursuivre dans cette direction. Estimer rapidement un ensemble de paramètres optiques et morphologiques traduisant la structure d'une coupe transversale de feuille pourrait particulièrement intéresser les agronomes. Ce travail ouvre donc une direction de recherche à fort potentiel puisqu'il propose de fournir de nouvelles observables physiques susceptibles de transporter de l'information déterminante dans le cadre d'un phénotypage.

International audience; We analyze the multilayer structure of sunflower leaves from Terahertz data measured in the time-domain at a ps scale. Thin film reverse engineering techniques are applied to the Fourier amplitude of the reflected and transmitted signals in the frequency range f < 1.5 Terahertz (THz). Validation is first performed with success on etalon samples. The optimal structure of the leaf is found to be a 8-layer stack, in good agreement with microscopy investigations. Results may open the door to a complementary classification of leaves.

International audience; Wavefront sensors encode phase information of an incoming wavefront into an intensity pattern that can be measured on a camera. Several kinds of wavefront sensors (WFS) are used in astronomical adaptive optics. Amongst them, Fourier-based wavefront sensors perform a filtering operation on the wavefront in the focal plane. The most well known example of a WFS of this kind is the Zernike wavefront sensor, and the pyramid wavefront sensor (PWFS) also belongs to this class. Based on this same principle, new WFSs can be proposed such as the n-faced pyramid (which ultimately becomes an axicone) or the flattened pyramid, depending on whether the image formation is incoherent or coherent. In order to test such novel concepts, the LOOPS adaptive optics testbed hosted at the Laboratoire d'Astrophysique de Marseille has been upgraded by adding a Spatial Light Modulator (SLM). This device, placed in a focal plane produces high-definition phase masks that mimic otherwise bulk optic devices. In this paper, we first present the optical design and upgrades made to the experimental setup of the LOOPS bench. Then, we focus on the generation of the phase masks with the SLM and the implications of having such a device in a focal plane. Finally, we present the first closed-loop results in either static or dynamic mode with different WFS applied on the SLM.

Wavefront sensors encode phase information of an incoming wavefront into an intensity pattern that can be measured on a camera. Several kinds of wavefront sensors (WFS) are used in astronomical adaptive optics. Amongst them, Fourier-based wavefront sensors perform a filtering operation on the wavefront in the focal plane. The most well known example of a WFS of this kind is the Zernike wavefront sensor, and the pyramid wavefront sensor (PWFS) also belongs to this class. Based on this same principle, new WFSs can be proposed such as the n-faced pyramid (which ultimately becomes an axicone) or the flattened pyramid, depending on whether the image formation is incoherent or coherent. In order to test such novel concepts, the LOOPS adaptive optics testbed hosted at the Laboratoire d'Astrophysique de Marseille has been upgraded by adding a Spatial Light Modulator (SLM). This device, placed in a focal plane produces high-definition phase masks that mimic otherwise bulk optic devices. In this paper, we first present the optical design and upgrades made to the experimental setup of the LOOPS bench. Then, we focus on the generation of the phase masks with the SLM and the implications of having such a device in a focal plane. Finally, we present the first closed-loop results in either static or dynamic mode with different WFS applied on the SLM., 14 pages, 9 figures, submitted to JATIS