Nanostructures produites par laser femtosecond pour des applications magnétiques, acoustiques et plasmoniques avancées

Femtosecond (fs) laser pulses have become a standard tool for the localized modification of materials, enabling surface functionalization, nanofabrication, and investigations of material properties through techniques like ultrafast laser spectroscopy. However, such studies are often conducted separately, limiting the discovery of intriguing physical properties in laser-fabricated materials.This thesis presents a comprehensive approach to all-optical investigations that integrate laser nanofabrication with advanced nano-optical techniques, including superresolution interferometry, ultrafast scanning acoustic microscopy, and magneto-plasmonic microscopy. At the heart of fs-laser modification are non-equilibrium thermal processes, which typically result in material destruction and removal through ablation. Remarkably, when applied to a complex compound like FeRh, fs-laser ablation was found to induce magnetic phase switching. This phenomenon was explored in detail using magneto-optical microscopy.For various applications, structures with predictable and finely tuned properties are crucial, necessitating nanometer precision and well-defined material characteristics. A non-destructive alternative to ablation is fs-laser spallation, which primarily operates through the generation of intense ultrafast acoustic pulses, which require significantly less energy for nanostructuring than ablation. Spallation leads to the separation or delamination of thin films from their substrate when the material is irradiated from the substrate side. In this work, fs-laser nanostructuring was applied to ferromagnetic layers and multilayers. To characterize the resulting structures, a superresolution interferometer was developed, reaching the Abbe diffraction limit. This setup allowed us to observe gaps ranging from nanometers to submicrometers on both sides of the fabricated structures without requiring their destruction.The fabricated structures were then subjected to further investigation to assess their properties. First, we examined the ultrafast acoustic dynamics in delaminated 100 nm thick Ni and Fe films. To achieve this, a custom optical setup was built, enabling the study of ultrafast acoustic dynamics with microscopic lateral resolution. The results revealed the confinement of acoustic pulses within the delaminated films, compared to the behavior in films still attached to the substrate. Separate acoustic modes were identified, with frequencies reaching 100–200 GHz.Another noteworthy application explored in this thesis is magneto-plasmonics. Laser-induced spallation creates a vacuum nanogap, transforming the thin film into an additional layer. This substrate-vacuum-film configuration was shown to excite surface plasmon-polaritons (SPPs) in an Otto configuration. Experimental results on a 100 nm Au / 200 nm Co bilayer with a 550 nm gap demonstrated the excitation of SPPs. A magneto-plasmonic microscope was developed for these measurements, revealing enhanced magneto-optical signals due to SPP excitation, with the data fitting well with theoretical predictions.As a result, this work demonstrates the feasibility of nondestructive fs-laser nanostructuring of ferromagnetic multilayers and highlights their potential applications in acousto-magneto-plasmonics via all-optical methods. These findings hold significant promise for advancing the field of magneto-acoustics, as freestanding delaminated films are expected to enhance magnon modes through phonon-magnon interactions reahing the THz frequency range. Additionally, the field of magnetism can benefit from structures designed for curvature magnetism, where laser spallation offers new possibilities in nanofabrication. Notably, fs-laser spallation is not limited to ferromagnetic or metallic materials; it can also be applied to semiconductors and 2D and 3D materials, expanding its potential for emerging applications.