  This paper is concerned with a theoretical analysis of the behavior of
optically excited spin currents in bilayer and multilayer systems of
ferromagnetic and normal metals. As the propagation, control and manipulation
of the spin currents created in ferromagnets by femtosecond optical pulses is
of particular interest, we examine the influence of different thicknesses of
the constituent layers for the case of electrons excited several electronvolts
above the Fermi level. Using a Monte-Carlo simulation framework for such highly
excited electrons, we first examine the spatio-temporal characteristics of the
spin current density driven in a Fe layer, where the absorption profile of the
light pulses plays an important role. Further, we examine how the combination
of light absorption profiles, spin-dependent transmission probabilities, and
iron layer thicknesses affect spin current density in a Fe/Au bilayer system.
For high-energy electrons studied here, the interface and secondary electron
generation have a small influence on spin transport in the bilayer system.
However, we find that spin injection from one layer to another is most
effective within a certain range of iron layer thicknesses.
