Masson, Jean-Baptiste (2007) Ionic contrast terahertz imaging Surface Plasmons polaritons statistical physics. PhD thesis LOB, EP - LOB Laboratoire d'Optique et Biosciences, EP/X p.209.

Alternative Locations: http://www.imprimerie.polytechnique.fr/Theses/Files/Masson2.pdf

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.

Table of content

Introduction 7
1 Optique térahertz 11
1.1 Le système expérimental - 12
1.1.1 Ordres de grandeur - 12
1.1.2 Présentation du système expérimental - 12
1.2 Éléments d’optiques et de méthodologie - 22
1.2.1 La polarimétrie térahertz - 22
1.2.2 Le dichroïsme circulaire - 23
1.2.3 La programmation en éléments finis - 28
1.2.4 Aspects théoriques de la transmission à travers un trou de taille inférieure
à la longueur d’onde - 34
2 Imagerie de contraste ionique térahertz 41
2.1 Introduction - 41
2.2 Spectroscopie térahertz des ions en solution - 42
2.2.1 Les cuves à ions - 44
2.3 Champ proche et contraste de champ proche - 48
2.3.1 Petit modèle et idées - 48
2.3.2 Simulations et résultats - 48
2.4 Imagerie d’axones et imagerie des flux d’eau - 54
2.4.1 Introduction - 54
2.4.2 La méthodologie - 56
2.4.3 La validité de cette imagerie - 57
2.4.4 Les résultats - 59
4 TABLE DES MATIÈRES
2.4.5 Conclusion - 63
2.5 Imagerie des flux ioniques dans du muscle cardiaque - 63
2.5.1 Introduction - 63
2.5.2 L’expérience - 64
2.5.3 Les résultats - 64
2.5.4 Remarques, perspectives et considérations - 67
2.5.5 Conclusion - 70
3 Physique statistique des plasmons 73
3.1 Introduction - 73
3.2 État de l’art et problématiques - 75
3.3 Modèle de Fano étendu - 79
3.3.1 L’expérience - 79
3.3.2 Le modèle - 79
3.3.3 Conclusion - 83
3.4 Interaction entre plasmons polaritons - 83
3.4.1 L’expérience - 85
3.4.2 La modélisation numérique - 86
3.4.3 Le modèle - 89
3.4.4 Conclusion - 91
3.5 Transition de phase de plasmon polaritons de surface - 91
3.5.1 Cas limites - 91
3.5.2 Les expériences - 92
3.5.3 Les premières bases du modèle - 94
3.5.4 Le modèle - 98
3.6 Résonance stochastique de plasmon polariton de surface - 102
3.6.1 Cas limites - 103
3.6.2 L’expérience - 103
3.6.3 La modélisation - 104
3.6.4 Remarques, perspectives et considérations - 108
3.6.5 Conclusion - 111
Conclusion 113
TABLE DES MATIÈRES 5
A La mesure des ions en biologie 117
A.1 Le dosage - 117
A.1.1 La colorimétrie - 117
A.1.2 Par précipité - 117
A.1.3 Par conductimétrie - 118
A.2 Sonde de Castaing - 118
A.3 Les sondes fluorescentes ions-dépendantes - 119
A.4 Les électrodes invasives et le patch-clamp - 120
A.4.1 Les électrodes invasives - 120
A.4.2 Le patch-clamp - 120
A.4.3 La sonde vibrante spécifique à un ion - 121
A.4.4 Mesure d’un flux ionique - 121
A.4.5 Mesure de flux ionique membranaire - 121
A.4.6 Mesure spatio-temporelle d’un flux ionique - 122
B Modèle de Fano 123
C Généralités sur les transitions de phase 127
D La percolation 129
Bibliographie 133
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