Carrier-carrier interaction and ultrashort pulse propagation in a highly excited semiconductor laser amplifier beyond the rate equation limit

The influence of carrier correlation processes on the interaction and propagation of femtosecond optical pulses in an inverted semiconductor is theoretically investigated. Microscopically treated Coulomb scattering described from a first-principles theory, including both diagonal and nondiagonal dephasing, is seen to cause considerably different behavior on the dynamics than that modeled by employing a rate-equation approximation. Semiconductor intrinsic optical nonlinearities such as gain saturation and adiabatic following, controlled by microscopic dephasing and relaxation mechanisms, manifest dominantly in ultrafast transient effects that, experimentally, can appear as a typical Kerr-type (instantaneous) nonlinearity. It is shown that one cannot invoke an adiabatic elimination for the polarization equation on femtosecond time scales. The present self-consistent theory successfully explains recent experimental measurements without recourse to parametrized equations. The possible role of non-Markovian relaxation is also discussed.