The population transfer in a ladder-type atomic system driven by linearly polarized sech-shape femtosecond laser pulses is investigated by numerically solving Schr¨odinger equation without including the rotating wave approximation (RWA). It is shown that population transfer is mainly determined by the Rabi frequency (strength) of the driving laser field and the chirp rate,and that the ratio of the dipole moments and the pulse width also have a prominent effect on the population transfer. By choosing appropriate values of the above parameters,complete population transfer can be realized.
Propagation of a few-cycle laser pulses in a dense V-type three-level atomic medium is investigated based on full-wave Maxwell-Bloch equations by taking the near dipole-dipole （NDD） interaction into account. We find that the ratio,γ,of the transition dipole moments has strong influence on the time evolution and split of the pulse:whenγ≤1,the NDD interaction delays propagation and split of the pulse,and this phenomenon is more obvious when the value ofγis smaller;whenγ=21/2,the NDD interaction accelerates propagation and split of the pulse.
