Thèses

Lundi 5 Février 2024 à 10h15.

Light scattering investigation on amorphous optical coatings : Analysis of experimental issues

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Directeur de thèse / thesis director : Gianpietro Cagnoli et Valérie Martinez

Membres du jury / jury members :

FORET Marie, Rapporteure, Professeure des Universités, Université de Montpellier
TRAPANANTI Angela, Rapporteure, Professeure Associée Habilitée, Université de Camerino (Italie)
DUJARDIN Christophe, Examinateur, Professeur des Universités, Université Claude Bernard Lyon 1
LEMAITRE Anaël, Examinateur, Professeur des Universités, Ecole des ponts ParisTech
MARGUERITAT Jérémie, Examinateur, Chargé de Recherche, Université Claude Bernard Lyon 1
OLLIER Nadège, Examinatrice, Directrice de Recherche, CEA Saclay
CAGNOLI Gianpietro, Directeur de thèse, Professeur des Universités, Université Claude Bernard Lyon 1
MARTINEZ Valérie, Co-Directrice de thèse, Maître de Conférences, Université Claude Bernard Lyon 1

Résumé / Abstract :

This thesis is part of the analysis of the structural properties of low thermal noise amorphous materials that make up the Bragg mirrors of gravitational wave detectors. Reducing the thermal noise of the thin films used in the mirrors of these detectors is crucial to increase their sensitivity and look further into the universe. Annealing is applied to these out-of-equilibrium amorphous materials to reduce their thermal noise by tending their structure towards a more stable atomic arrangement. These structural modifications are probed using light scattering. However, optical thin films are deposited on a substrate, and the problem of extracting the single spectrum of the film arises. This is because optical interference within the thin film spectrally modifies the amplitude of the scattered light, preventing the quantification of structural modifications. A model based on optical interference and the transmission of light through an optical thin film on a substrate was developed in order to spectrally correct the amplitude of the light scattered by the substrate in order to extract the spectrum from the film.
In addition, an innovative experimental setup using the analysis of low-frequency scattered light was built in order to visualise the structural relaxations in amorphous materials that cause the thermal noise at the origin of energy dissipation.
Finally, a Raman analysis was carried out on the influence of heat treatment below the crystallisation temperature of tantalum pentoxide thin films currently used in gravitational wave detectors.
Other promising materials for new generations of these detectors were also studied using Raman spectroscopy.

Key-words:
light scattering, amorphous optical thin films, spectral filtering, gravitational waves.

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