# Laboratoire Collisions Agrégats Réactivité - UMR5589

Université Paul Sabatier - Bat. 3R1b4 - 118 route de Narbonne 31062 Toulouse Cedex 09, France

## Application of propagation effects in atomic vapours for the shaping of ultrashort pulses

The studies of coherent control experienced a considerable development during this last decade. The successful progress in the technology of « pulseshapers » which modify on request the spectrum of the laser pulses, allowed the control of various physical and chemical processes. However, these devices do not remain useful in picosecond and VUV domains because of the narrower spectrum width of the former and high frequency range of the latter. Additionally, these devices are of passive type and cannot introduce new frequency components in the spectrum. We review in this paper an alternative method using the re-shaping phenomena xperienced by an ultrashort pulse as it propagates through an optically dense atomic medium. We specially focus on the situation of atoms driven by an additional strong pulse that modify drastically and in a controllable way the optical response of the medium allowing the re-shaping of the propagating pulse.