Coherent interactions and femtosecond pulse propagation in semiconductors

The optical response of semiconductors on an ultrafast (femtosecond) time scale is significantly affected by many-particle interactions of the excited electrons and holes. In this paper we address three aspects: (1) coherent excitation dynamics in systems of different dimensionality, (2) signatures of memory effects in dephasing processes, and (3) pulse propagation effects. First, we show that the influence of the coherent exchange interaction, which modifies the external field and increases the effective Rabi frequency, is similar in bulk and quantum-well systems but is reduced in thick quantum wires. Secondly, we study incoherent effects. To determine the non-Markovian character of dephasing processes in a two-pulse scenario, we propose the use of chirped pulses. The theoretical results were obtained with a Gaussian memory function that models dephasing due to electronphonon scattering. Finally, the influence of exchange and correlation effects on the pulse propagation is discussed for both noninverted semiconductors and semiconductor amplifiers. The problem of long-distance propagation is addressed, and, in particular, recent results are presented for a gain-absorption compensation; these results indicate the possibility of long-distance propagation of light pulses in amplifiers.