Quantum-kinetic theory of excitonic hyper-Raman gain

We present a quantum-kinetic theory of hyper-Raman gain due to excitons in semiconductors coherently driven with femtosecond pulses. We observe strong deviations from the stationary picture. The gain region is not simply a mi rror image of the exciton, and saturation effects emerge for large fields. The complex interplay of excitons, continuum states, Coulomb interaction, d ynamic aspects and quantum-kinetic features is discussed. The numerical res ults are in good agreement with recent measurements [Phys. Rev. Lett. 79, 3 716 (1997); phys. stat, sol. (b) 206, 71 (1998)].