Ultrafast investigation of Exciton-Photon systems under strong coupling regime

Light-matter interactions have been explored in the last decades to study the modification of the spontaneous emission rates of matter systems in a presence of a tailored electromagnetic field. The aim of this thesis is to explore the properties of light confinement and its coupling dynamics. In particular, it will be explored in two main frameworks: the coupling between an emitter and either a confined photon in an optical cavity (e.g. Fabry-Pérot cavity) or surface lattice resonances sustained by a plasmonic nanoparticle array. Specifically, the latter topic will be crucial for the argumentation of this thesis in terms of its advantages for light-matter coupling with respect to other photonic and plasmonic platforms. The strong coupling regime is achieved in ordered aluminum nanostructures arranged in three different lattice geometries and compared. These plasmonic platforms are hybridized with J-Aggregate organic molecule and studied in its transient dynamics while resonantly excited in the visible regime. Fast decays as well as largest Rabi splitting are obtained in the honeycomb-like nanodisks arrays coupled with J-aggregate organic dye. Our studies could open new routes toward the light-matter coupling investigation with expected high-impact benefits in many fields, such as photo(electro)catalysis and photochemistry.