Theory of the optical Stark effect in semiconductors under ultrashort-pulse excitation

The optical Stark effect is computed for femtosecond excitation of the electron-hole-pair states in semiconductors. The theory is based on the effective Bloch equations for semiconductors and is evaluated for the large detuning, low intensity limit. For the example of CdS, good agreement with recent femtosecond experiments is found. It is shown that the coherent interaction of the pulses and the medium polarization dominates the semiconductor response as long as the pulse duration is of the order of, or less than, the coherence decay time of the medium. (author)