  The electric field governing the dynamics of space charge produced by high
intensity femtosecond laser pulses focused on a copper surface is investigated
by time-resolved low-energy-electron-scattering. The pump-probe experiment has
a measured temporal resolution of better than 35 ps at 55 eV probe electron
energy. The probe electron acceleration due to space charge is reproduced
within a 3-dimensional non-relativistic model, which determines an effective
number of electrons in the space charge electron cloud and its initial
diameter. Comparison of the simulations with the experiments indicates a
Coulomb explosion, which is consistent with transients in the order of 1 ns,
the terminal kinetic energy of the cloud and the thermoemission currents
predicted by the Richardson-Dushman formula.
