Propagation of Few-Cycle Pulse Laser in Two-Level Atom Medium

By comparing the numerical solutions of Maxwell-Bloch equations beyond and within the slowly-varying envelope approximation and the rotating-wave approximation for the propagation of few-cycle pulse laser in a resonant two-level atom medium, we found that both the Rabi flopping and the refractive index, and subsequently the carrier and the propagation velocity of the few-cycle pulse, are closely connected with the time-derivative behaviour of the electric field. This is because of the Rabi flopping is such that soliton pulse splits during propagation and that a shorter pulse propagates faster than a broader one.