  The kinetics of ultra-fast processes which leads to the thermalization
condition of a photo-excited plasma in semiconductor systems is studied
theoretically. We analyze the time evolution of a carrier population generated
by a finite optical pulse, from the beginning of the pulse until the time in
which the carrier population reaches a quasi-equilibrium condition. We
calculate the energy fluxes caused by the main interaction mechanisms along the
different stages the system passes through. Our analysis is done by using a set
of non-linear rate equations which govern the time evolution of the carrier
population in the energy space. We consider the main interaction mechanisms,
including dynamic screening and phonon population effects.
