  We show experimentally that XUV radiation is produced when a laser pulse is
Thomson backscattered from sheets of relativistic electrons which are formed at
the rear-surface of a foil irradiated on its front side by a high-intensity
laser. An all-optical setup is realized using the Jena Titanium:Sapphire TW
laser system (JETI). The main pulse is split into two pulses: one to accelerate
electrons from thin aluminum foil targets to energies of the order of some MeV
and the other, counterpropagating probe pulse is Thomson-backscattered off
these electrons when they exit the target rear side. The process produced
photons within a wide spectral range of some tens of eV as a result of the
broad electron energy distribution. The highest scattering intensity is
observed when the probe pulse arrives at the target rear surface 100 fs after
the irradiation of the target front side by the pump pulse, corresponding to
the maximum flux of hot electrons at the interaction region. These results can
provide time-resolved information about the evolution of the rear-surface
electron sheath and hence about the dynamics of the electric fields responsible
for the acceleration of ions from the rear surface of thin, laser-irradiated
foils.
