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Due to the wide range of applications of discharges and plasmas, their characterizations have been receiving a revival of interest these last couple of years. Among all the relevant characteristics of a plasma, the spatial distribution and the temporal evolution its associated electric field (E-field) is a subject of major interest and one of the more critical parameters to be analyzed. Firstly, this thesis work concerns the non-invasive vector characterization of the electric field associated to cold plasmas (dielectric barrier discharge, atmospheric plasma jet, ...). The other part is devoted to the nonlinear interaction between a cold plasma and an optical pulse wave for the parametric generation of Terahertz (THz) waves. In both cases (plasma generated with a high voltage source and plasma due to air breakdown), we have detected an electric field (of the order of MV/m for plasma analysis and of a few V/m for high frequency generation) either with a pigtailed electro-optical probe, or by using an experimental free space EO bench (developped at IMEP-LAHC). We have carried out a complete polarimetric study of the E-field generated by electrodes or by ionization of a gas like helium. In particular, we have been interested in the polarization behavior of the observed phenomena. We also studied the possibility to improve the efficiency of the THz generation by adding a helium plasma jet or the gas alone. We have performed a complete characterization of the generated THz signal (in modulus and orientation). The obtained results are perfectly described by a model that we have developed. This model has been experimentally validated by a polarimetric study of the THz pulse using an innovative EO detection., En raison de la large gamme d'applications des décharges et des plasmas, leurs caractérisations ont reçu un regain d'intérêt ces dernières années. Parmi toutes les caractéristiques pertinentes d'un plasma, la distribution spatio-temporelle du champ électrique (E) qui leur est associé est un sujet d'intérêt majeur et l'un des paramètres critiques à analyser. Ce travail de thèse concerne d'abord la caractérisation vectorielle non invasive du champ électrique associé aux plasmas froids (décharge à barrière diélectrique, jet de plasma à pression atmosphérique, ...). L'autre partie est consacrée à l'interaction non linéaire entre un plasma froid et une onde impulsionnelle optique pour la génération paramétrique d'ondes Térahertz. Dans les deux cas (plasma généré avec une source haute tension et plasma dû à un claquage de l'air), nous avons détecté un champ électrique (de l'ordre du MV/m pour l'analyse du plasma et de quelques V/m pour la génération haute fréquence) soit avec une sonde électro-optique (EO) fibrée, soit en utilisant un banc expérimental en espace libre faisant appel là aussi à une détection EO (développé à l'IMEP-LAHC). Nous avons réalisé une étude polarimétrique complète du champ E généré par des électrodes ponctuelles ou par ionisation d'un gaz comme l'hélium. En particulier, nous nous sommes intéressés au comportement en polarisation des phénomènes observés. Nous avons également étudié la possibilité d'améliorer l'efficacité de génération d'une impulsion teraHertz (THz) par claquage dans l'air en ajoutant un jet de plasma d'hélium. Une étude complète du signal généré (en module et en orientation) a été menée, et les résultats obtenus sont parfaitement décrits par un modèle que nous avons développé. Ce modèle a été validé expérimentalement par une étude polarimétrique de l'impulsion THz en utilisant une détection EO innovante.

International audience; Two methods are described and compared to measure electric fields (EFs) in the plume of an atmospheric pressure plasma jet. The first one uses an electric-optical probe made of a BSO crystal. In this case, the measurement is based on Pockels effect. The second one is Stark spectroscopy of the Helium line at 492nm. From the results obtained, it appears that the presence of a dielectric target triggers an enhancement of the electric field in the plume near the target. Moreover, it will be shown that both techniques have their advantages and are complementary.

International audience; An organic tissue exposed to plasma experiences a highly reactive environment consisting of ions,electrons, free radicals, UV radiation, neutral molecules and electric field (EF). Of these activeagents, EF is one of the least investigated up to these days [1]. Nevertheless, EF can potentiallyplay a major role transiently increasing cell membrane permeability, a phenomenon commonlyknown as “electroporation” [2] and nowadays effectively used for several applications includinggene transfection and electrochemotherapy [3]. Thus, in the present work, we report the timeresolved measurement of the EF induced in a liquid medium within a typical electroporation setupby a plasma gun (PG) device. The results are compared with the values estimated for aconventional electroporation device (Cliniporator, IGEA SpA) in the perspective of a possibleimpact of plasma induced EF on biological targets. The comparison was done adopting a 4 wellμ-slide (Ibidi®) armed with two plane parallel electrodes used for in-vitro electroporation test andfilled with 500μl of the target liquid, being either SMEM culture medium or high purity water.Three different experimental cases were taken into account (Fig.1, left): 1) the plane electrodespowered by the Cliniporator; 2) the PG plume hitting on one plane electrode; 3) the PG plumehitting on the liquid with (3a) and without (3b) ground electrode. Despite the considerably highervoltage powering the plasma device, preliminary results show an EF on the target lower than theone applied by the electroporation system. This observation goes along with the recorded currentthat results in general one order of magnitude lower for the plasma system. Furthermore, resultsshow a key role played by the grounding of the liquid medium which can hinder the induction ofan EF by the plasma source. While still preliminary, presented results provide new insights on oneof the less investigated aspects of plasma and liquid target interaction, the induced EF.Fig. 1: (left) Photos and schematics of the experimental set up; voltage, current and EF waveformfor case 1 (center) and case 3b (right).This work and A.S. are supported by PLASCANCER project, INCa-PlanCancer-n°17CP087-00References[1] E. Robert, T. Darny, S. Dozias, S. Iseni, J. M. Pouvesle, Physics of Plasma, 22, 122007 (2015).[2] D. Miklavćić; M. Puc, Wiley Encyclopedia of Biomedical Engineering, 1 (2006).[3] L. M. Mir, European J. of Cancer Supplement, 4, 38-44 (2006)

International audience; Atmospheric pressure plasma jets have been extensively studied for several years as theyshowed very promising results in numerous fields such as material processing or plasma medicine.What makes cold plasma interesting is the presence of electrons, ions, reactive oxygen andnitrogen species, visible and UV light and high transient electric fields (EF). Even if the latter playa key role, from the production and propagation of the plasma to the efficiency of applications,they are far from being fully understood. This work focuses on the comparison of measurementsof EF produced by a Plasma Gun (PG) discharge with an electro-optic probe based on Pockelseffect [1] with 2D simulations of atmospheric pressure discharges propagating in a geometry closeto the Plasma Gun’s one. Plasma Gun consists in a vertically downward oriented capillary with aninner high-voltage electrode and an outer grounded one. Plasma is powered with μs-durationvoltage pulses from single shot to 4kHz.In [2] the electric field is evaluated by the simulations inside the capillary, in the glass andoutside. The aim of this work is to compare the radial profile of the electric field outside thecapillary between experiments and simulations to get information on the plasma inside it. Theelectro-optic probe was placed at different levels alongside the capillary and was getting far fromit. Measurements were executed every 5mm over 5cm. At the middle of the capillary a decreaseinversely proportional to the distance has been found. It reminds the shape of an EF produced byan infinite uniformly charged cylinder. 2D simulations were in a good agreement finding also thesame slope for EF. But simulations permit also to get information on the distribution of chargedensity and especially to know if the main contribution is from volume or surface charge density.Results show that the radial profile of EF outside the tube is mostly determined by the volumecharge density in positive polarity while in negative polarity the surface charge density isdominant. Simulations have provided values of average volume charge density in the order of 7.5nC/cm3 in positive polarity and of average surface charge density around 1nC/cm² in negativepolarity. Near the electrodes, a decrease inversely proportional to the square of the distance hasbeen found, showing that there is an axial position dependence. A time dependence investigationwill also be presented.X.D. acknowledges his grant funding Thermofisher Scientific INEL/Région Centre Val de Loire.References[1] G. Gaborit et al., IEEE Trans. Plasma Sci., 42 (2014).[2] P. Viegas, F. Pechereau and A. Bourdon, Plasma Source Science and Technology, in press(2018)

International audience; The EFILE diagnostic (Electric Field Induced Lyman-α Emission) aims to provide a non intrusive and precise measurement of the electric field in plasma, using a beam of hydrogen atoms prepared in the metastable 2s state. The metastable particles are obtained by means of a proton beam extracted from a hydrogen plasma source, and neutralised by interaction with vaporised caesium. When a 2s atom enters a region where an electric field is present, it undergoes a transition to the 2p state (Stark mixing). It then quickly decays to the ground level, emitting Lyman-α radiation, which is collected by a photomultiplier. The 2s → 2p transition rate is proportional to the square of the magnitude of the electric field, and depends on the field oscillation frequency (with peaks around 1 GHz). By measuring the intensity of the Lyman-α radiation emitted by the beam it is possible to determine the magnitude of the field in a defined region. In this work, an analysis of the behaviour of the diagnostic under static or radiofrequency electric field is presented. Electric field simulations obtained with a finite element solver of Maxwell equations, combined with theoretical calculations of the Stark mixing transition rate, are used to develop a model for the interpretation of photomultiplier data. This method shows good agreement with experimental results for the static field case, and allows to measure the field magnitude for the oscillating case.

Electro-optical microscopy is a micrometric quantitative mapping technique of electrical fields and of electro-optical tensor components in a medium. The set-up is a confocal microscope included in an interferometer with homodyne detection used to record and measure weak phase shifts due to Pockels effect. The sample must be transparent, quadratically nonlinear and submitted to an intrinsic or externally applied electric field. This doctoral dissertation introduce the concept of electro-optical microscopy. The realization of the microscope is then detailed. The two dimensionnal electro-optical mapping obtained in a polymer film is discussed. Finally, we demonstrate for the first time a Pockels effect induced phase shift in a doped phospholipidic membrane. Applications perpectives to biological transmembranar potentials are presented. In conclusion, technological difficulties of this application are detailled and solutions are suggested.; La microscopie électro-optique est une nouvelle technique de cartographie quantitative micrométrique des champs électriques et des composantes du tenseur électro-optique d'un milieu. Techniquement, il s'agit de mesurer le déphasage engendré par effet Pockels au moyen d'un microscope confocal inclus dans un interféromètre en détection homodyne. L'échantillon doit être transparent, non linéaire quadratique et soumis à un champ électrique, intrinsèque ou appliqué. Cette thèse présente tout d'abord une étude théorique de la microscopie électro-optique. On y décrit la réalisation pratique du microscope. Les résultats obtenus sur un premier échantillon en couche polymère sont ensuite étudiés et on présente la première mesure de déphasage par effet Pockels dans une membrane phospholipidique dopée. Les perspectives d'applications à des mesures de potentiels transmembranaires sont présentées. Les difficultés technologiques qui seront rencontrées sont détaillées et des solutions sont proposées.

Electro-optical microscopy is a micrometric quantitative mapping technique of electrical fields and of electro-optical tensor components in a medium. The set-up is a confocal microscope included in an interferometer with homodyne detection used to record and measure weak phase shifts due to Pockels effect. The sample must be transparent, quadratically nonlinear and submitted to an intrinsic or externally applied electric field. This doctoral dissertation introduce the concept of electro-optical microscopy. The realization of the microscope is then detailed. The two dimensionnal electro-optical mapping obtained in a polymer film is discussed. Finally, we demonstrate for the first time a Pockels effect induced phase shift in a doped phospholipidic membrane. Applications perpectives to biological transmembranar potentials are presented. In conclusion, technological difficulties of this application are detailled and solutions are suggested., La microscopie électro-optique est une nouvelle technique de cartographie quantitative micrométrique des champs électriques et des composantes du tenseur électro-optique d'un milieu. Techniquement, il s'agit de mesurer le déphasage engendré par effet Pockels au moyen d'un microscope confocal inclus dans un interféromètre en détection homodyne. L'échantillon doit être transparent, non linéaire quadratique et soumis à un champ électrique, intrinsèque ou appliqué. Cette thèse présente tout d'abord une étude théorique de la microscopie électro-optique. On y décrit la réalisation pratique du microscope. Les résultats obtenus sur un premier échantillon en couche polymère sont ensuite étudiés et on présente la première mesure de déphasage par effet Pockels dans une membrane phospholipidique dopée. Les perspectives d'applications à des mesures de potentiels transmembranaires sont présentées. Les difficultés technologiques qui seront rencontrées sont détaillées et des solutions sont proposées.

On decrit un nouvel appareil de mesure du champ electrique dans les dielectriques transparents. Son originalite reside dans le fait qu'il mesure a la fois l'amplitude et la direction du champ electrique aussi bien en regime statique qu'en regime variable. La methode est fondee sur la mesure ponctuelle de la birefringence induite par effet Kerr dans le dielectrique. La mesure de formes de lumiere variant rapidement dans le temps a ete rendue possible par l'utilisation, comme modulateur, d'une cellule de Kerr a champ electrique tournant utilisant un liquide nematogene. La resolution de l'appareil qui a ete realise est de 3 x 10-3 radian en dephasage optique et de 3 degres en direction a la frequence de 1 kHz.