Unipolar half-cycle pulse propagation in an amplifying three-level medium

The propagation of a unipolar half-cycle pulse through a layer of a non-equilibrium three-level resonant medium with different energy-level schemes is studied theoretically. It is shown that in such a case initial unipolar pulse gets gradually transformed into a bipolar one due to the formation of oscillating tails at the trailing edge of the pulse. Depending on the specific energy-level scheme both amplification and absorption of a leading half-cycle field burst can take place with the propagation distance. At the same time in all cases the conservation rule of the electric area is obeyed, although the unipolarity degree of the pulse always decreases over its propagation in the medium layer.