COHERENT INTERBAND EFFECTS IN QUANTUM KINETICS

The quantum kinetics of a laser pulse exciting electrons and holes int eracting with LO-phonons is studied in [1] within the generalized Kada noff-Baym approximation, but the spectral Green functions are approxim ated by damped free propagators. After including the Hartree-Fock cohe rent terms due to the bare Coulomb interaction, oscillations (''quantu m beats'') of the incoherently summed polarization with the LO-phonon frequency have been found in [2]. Here we include the Coulomb Hartree- Fock terms as well as the optical pump field selfconsistently for both the spectral and particle functions. This procedure takes the phonon- assisted transitions and excitonic effects fully into account. Our cal culations in three-dimensional and particularly in two-dimensional sem iconductors show an enhancement of the coherent ''quantum beat'' effec ts in the incoherently summed polarization. Further we show that these quantum beats are well resolved in the photon echo signal.