Abstract

The optical response of semiconductors on an ultrafast (femtosecond) time scale is significantly affected by many-particle interactions of the excited electrons and holes. These interactions can be divided into two classes. The coherent exchange interaction, which reflects the Pauli principle of the charge carriers, is a nonlinear interaction that involves the Coulomb interaction between the carriers. Secondly, the incoherent effects are scattering processes between the carriers or between carriers and phonons. Both classes of interactions have been investigated in recent years on the basis of the semiconductor Bloch equations, which generalize the optical Bloch equations for N independent two-level atoms in several aspects. The coupling of these levels due to the mean-held Coulomb interaction leads to excitonic and coherent exchange effects. Beyond this so-called Hartree-Fock approximation, one obtains screening and momentum and energy relaxation, which are taken into account on different levels of sophistication. Finally, band-structure effects become important if the dependence of the optical response on tire light-field polarization has to be determined.

© 1994 Optical Society of America