Single shot measurements of the E-field vector with pigtailed optical probes
Summary form only given. Over the variety of available sensors dedicated to electric (E)-field characterization, the use of antennas constitutes the most widespread technique. While such probes are convenient and provide a good sensitivity, they remain invasive and bandwidth limited. At the opposite, fibered electro-optic transducers1 are fully dielectric, millimeter sized and allow to perform measurements of the E-field vector from DC to several gigahertz and even up to terahertz frequencies using equivalent-time sampling. Furthermore, recent developments lead to a simultaneous characterization of 2 transverse E-field vector components with a single EO probe2. Based on polarization state modulation, the EO transducer is linked to a remote (up to 30 meters) optoelectronic set-up including a ultra low noise laser feeding the probe and a real time optical set-up to manage the modulation treatment. The automated and servo controlled measurement bench is temperature dependent free. The available measurement dynamics exceeds 100 dB, ranging from less than 1 V. m-1. Hz-1/2 up to the breakdown electric field in air.An exhaustive comparison between BO sensors and other technologies will be firstly given during the conference. This analysis will be based on intrinsic sensor properties, such as sensitivity, frequency bandwidth, vectorial selectivity, spatial resolution and induced perturbation on the field to be measured. After recalling the principles of the BO effect, the optical arrangement of the optical probes will be described. The characterization of the BO system will be presented together with experimental results illustrating the potentialities of BO sensors. Among these examples, measurements of pulsed B-field in air (pulsed power), water (specific absorption rate evaluation in pulsed regime) or in plasma (real time evolution of the electrical discharge associated B-field) will be shown.
Développement d'une sonde électro-optique dédiée à la mesure simultanée du champ électrique et de la température au sein des milieux biologiques
Le bioelectromagnetisme, domaine de recherche se situant au carrefour de la biologie et de l'electromagnetisme, s'interesse a l'etude des interactions entre les ondes electromagnetiques et le vivant. La finalite de ces travaux de these concerne le developpement d'un capteur optique dedie a la mesure simultanee du champ electrique et de la temperature au sein de milieux biologiques exposes a un rayonnement radiofrequence. Il s'agit donc, plus specifiquement, de realiser une sonde electro-optique repondant aux differents besoins metrologiques des applications dosimetriques et qui soit, de plus, compatible avec les milieux d'etude. Une campagne de mesure preliminaire a ete dediee a la caracterisation les proprietes optiques, thermo-optiques et electro-optiques des cristaux d'interet (elements de transduction de ces sondes). Un capteur fibre a ensuite ete realise. Ce dernier a permis d'effectuer des mesures simultanees de champ electrique et de temperature dans le cadre d'experimentations en dosimetrie radiofrequence, permettant ainsi une caracterisation duale inedite du Debit d'Absorption Specifique (DAS). Cette sonde, entierement dielectrique, a egalement rendu possible une premiere discrimination du profil temporel d'impulsions nanosecondes de fortes amplitudes au sein d'une solution biologique, dans le cadre d'experimentations en electroporation cellulaire.
Mass Loss History of Evolved Stars
We provide high-resolution maps of the circumstellar dust shells of several dozen Asymptotic Giant Branch (AGB) stars using data from the Spitzer space telescope Multiband Imaging Photometer (MIPS) imaged at 70μm. AGB stars are the major contributors of chemical elements such as carbon, oxygen and silicon, which are essential to the existence of life in the universe, through mass loss processes that take place at the surface of the star. We probe the spatial distribution of cold (∼40 K) dust grains in order to trace the history of mass loss from the observed radial density variation in these shells. Our images illustrate that different morphologies may evolve because AGB stars can already interact with the interstellar medium (ISM) that surrounds them even at these early stages of the AGB mass loss history. Relative motion of the star as well as the ISM with respect to the local environment may be of particular importance for shell structure evolution.