# Laboratoire Collisions Agrégats Réactivité - UMR5589

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

## Influence of wave-packet dynamics on the medium gain of an atomic system

A sequence of two femtosecond pulses - a strong driving -polarized pulse and a weak propagating -polarized pulse - excites resonantly the transition of an atomic system. Strong interference effects take place in the system between absorption and emission paths leading to a substantial amplification of the sigma pulse. We study the influence of the fine structure on the medium gain when the contribution of the off-resonant level is taken into account. A drastic reduction of the medium gain is obtained. This effect is explained within the bright-state–dark-state formalism where the strong driving pulse creates a wave packet that can be trapped in a state - the bright state - leading to a significant reduction of the gain for the sigma pulse. Finally, we also show that periodical gain dependence with the driving pulse energy exhibits a significant change in its period value (compared with expected Rabi oscillations).

Voir en ligne : Phys. Rev. A 76, 045805 (2007)