TRANSIENT QUASI-PARTICLE DYNAMICS

Electrons in semiconductors photo-excited by short intense pulses have typically all characteristic times, tile pulse duration: the Rabi fre quency and the excitation lifetime comparable, approximate to 100 fs. We analyze the possibility of introducing ''quasiparticles'' (excitati ons whose propagators obey the semigroup property) into tile quantum d escription of the photo excitation, selecting the case of disorder all oy scattering, and the renormalized Born approximation. The light-indu ced part of the electron self-energy persists over times comparable to the pulse leading to substantial memory effects near the one-photon r esonance. If only the dark self-energy is retained, good auxiliary qua siparticle propagators result, which can be used to treat the scatteri ng integral of the quantum optical Bloch equations.