Ultrafast optoacoustics on multifunctional cavities

The ability to control magnetic order on ultrafast timescales is a central challenge for the development of next-generation data storage technologies. While current magnetic devices operate on nanosecond timescales, fundamental spin dynamics occur much faster, in the picosecond regime. Harnessing this intrinsic speed requires new approaches to manipulate magnetism beyond conventional electronic methods. This thesis explores the control of magnetic systems through lattice vibrations, focusing on the interaction between coherent acoustic phonons and spin dynamics in nanostructured materials. Using femtosecond pump–probe spectroscopy, we investigate the ultrafast acoustic response of metallic nanostructures excited by short laser pulses. Two model systems are studied: polycrystalline freestanding nickel cavities fabricated via laser delamination and metal–insulator–metal (MIM) cavities supporting optical epsilon-near-zero (ENZ) modes. In these platforms, optical excitation generates coherent GHz–THz acoustic phonons whose dynamics are analyzed through time-domain measurements, Fourier analysis, and numerical simulations. This approach enables the characterization of acoustic resonances, lifetimes, confinement mechanisms, and energy dissipation processes.