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Imagerie de contraste ionique térahertz Physique statistique des plasmons polaritons de surface.

Abstract : The understanding of neuron physiology and functioning still presents challenges whose resolution lie at the interface between physics and biology. Such is the case for all cells presenting an important molarity difference between their distinct membrane bound compartments. Therefore, controlling water exchanges between these compartments during neuronal activity could drastically change the accuracy of the model used to describe action potential propagation. In order to investigate these issues a new method has been designed: Ionic contrast terahertz microscopy. It is based on the high sensitivity of terahertz radiation to ions in water solutions. Therefore a system of terahertz generation with semi-conductor antennas has been designed. The diffraction limit challenge, which reduces resolution to 300 µm in the terahertz range, has been overcome by the combination of near field imaging with aperture and a new technique of analysis that allows detecting spatial variation with a resolution better than ?/100. This analysis technique which is also an experimental configuration was named contrast near field. Ionic contrast terahertz microscopy allowed confirming that water is implied in most biological activity of neurons. Furthermore, it allowed us to quantify these water exchanges. One of the main consequences is that water may no longer be neglected in all modelization of neuron activity. Finally, this technique was also adapted to record cardiac cell activity with time resolution. Energy associated to the terahertz spectrum allows the investigation of large motion in biological molecules. However, the signal must be enhanced in order to have analyzable results. Thus plasmonics was investigated. The lack of specific activity of most metals in the terahertz range, leads to the conclusion that materials with subwavelength structures may be necessary to these studies. Ebbesen's subwavelength hole arrays were the center of the study. Experiments and modelization were focused on these arrays. A modified Fano model was designed and was found to be able to describe the transmission of the arrays. It was also able to model the evolution f the signal with the size and shape of holes. Furthermore, interaction between plasmon polaritons was investigated. Finally, unusual modelizations designed to describe experiments lead to a model based on phase transition and stochastic resonances. Results of these investigations show that there are many new questions arising and that the physics of the interactions between light and subwavelength hole arrays remains not understood.
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Submitted on : Tuesday, July 27, 2010 - 10:46:26 AM
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Jean-Baptiste Masson. Imagerie de contraste ionique térahertz Physique statistique des plasmons polaritons de surface.. Physique [physics]. Ecole Polytechnique X, 2007. Français. ⟨pastel-00002917⟩

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