Quantum kinetics of femtosecond four-wave mixing in semiconductors

We calculate the transient degenerate four-wave mixing signal with ultrashort laser pulses within the self-consistent formulation of the quantum kinetics of electrons and holes in a semiconductor interacting with longitudinal-optical (LO) phonons. Our numerical calculation shows that the integrated four-wave mixing signal as a function of the delay time shows an effective exponential decay, which, however, is modulated by an oscillation with a characteristic energy given by ωLO[1 + (me/mh)]. This peculiar quantum beat is caused by the interference of the interband polarization components, which are connected through a LO-phonon transition in the conduction band.