The coherent interaction of femtosecond laser pulses and thin CdSe and GaAs samples is investigated experimentally and theoretically. Oscillatory structures in the differential probe transmission around the exciton resonance and around the pump frequency are observed when the probe pulse precedes the pump. Comparison with theory attributes the oscillations to the coherent coupling between the light field and the electron-hole transitions in the semiconductor. For nonresonant excitation, the oscillatory structures around the exciton are identified as the early stages of the optical Stark effect.

• Received 6 August 1987

DOI:https://doi.org/10.1103/PhysRevLett.59.2588