  We use a hydrodynamic model to describe the relaxation of optically injected
currents in quantum wells on a picosecond time scale, numerically solving the
continuity and velocity evolution equations with the Hermite-Gaussian functions
employed as a basis. The interplay of the long-range Coulomb forces and
nonlinearity in the equations of motion leads to rather complex patterns of the
calculated charge and current densities. We find that the time dependence of
even the first moment of the electron density is sensitive to this complex
evolution.
