Abstract : This PhD work is in the context of research into fusion by inertial confinement. It concerns more particularly the scheme of fast ignition, which provides for the use of ultra-intense laser pulses to initiate nuclear reactions in the fuel. Until now, the feasibility of this scenario has not been proved. It depends on many fundamental aspects of physics into play, which are not yet completely under control. In this work, we proposed to study experimentally a fundamental aspect of this new schema: the transport of energy by the relativistic electrons created by a laser beam ultra-intense.