An experiment has been performed with the LULI
Multi-TeraWatt Laser. The acceleration of electrons injected
in a plasma wave generated by the laser wakefield mechanism
has been observed with a maximum energy gain of 1.5 MeV.
It has been shown that the electrons deflected during the
interaction, could scatter on the walls of the experimental
chamber, and fake a high-energy signal. A special effort
has been given in the electron detection to separate the
accelerated electrons signal from the background noise.The
experimental results agree with theoretical predictions
and numerical simulations when 3D effects on the electron
beam are taken into account.