INTERBAND QUANTUM KINETICS WITH LO-PHONON SCATTERING IN A LASER-PULSE-EXCITED SEMICONDUCTOR .1. THEORY

Nonequilibrium Green's function theory is employed to derive with the use the generalized Kadanoff-Baym ansatz quantum kinetic equations for the interband polarization and the densities of electrons and holes. These equations are valid in the regime of ultrafast spectroscopy, where that usual Boltzmann kinetics with its individual energy-conserving collisions no longer holds. The memory kernel of the retarded quantum kinetic equations is determined by retarded and advanced Green's functions. It is stressed and explicitly shown by numerical solutions in an adjacent paper that these Green's functions have to be approximated consistently with the coupling to phonons.