This document presents a study of relaxation mechanisms of fullerenes induced by photoexcitation. We have investigated ionization and fragmentation processes of these model systems under irradiation by various light sources: femtosecond pulse, free electron laser (far IR) and Synchrotron (XUV). To study these mechanisms, we use the velocity map imaging technique which allows us to follow the evolution of the angular distribution and velocity of the emitted particles. The nature of the relaxation mechanisms changes drastically (statistical mechanisms, coherent ionization in strong field, autoionization of plasmons, etc.) depending on the pulse duration, its intensity and the wavelength. Several theoretical approaches have been used including a Weisskopf modelling for the statistical processes and direct treatment of the time dependant Schrödinger equation for the coherent processes. This study allows us building bridges between the relaxation mechanisms occurring on various scales of time
