Influence of phase modulation on the reshaping of ultrashort laser pulses in resonant three-level systems

We present a detailed study of the interaction of ultrashort laser pulses with a resonant three level system (fine structure levels of rubidium). As expected, for low intensities a linear model and for higher intensities a semiclassical model (Maxwell-Bloch) is fully sufficient to describe the observed results. In both cases, however. it is essential to have an accurate knowledge of the incident electric field. i.e., the amplitude and the phase, in order to simulate the interaction process. It is shown that on small time scales the phase modulation of the incident pulse influences the reshaping process during pulse propagation whereas on longer time scales the reshaping is solely governed by the dynamics of the atomic system.