Modulational instability in atomic vapors

We report an experimental, numerical, and analytical study of the near resonant propagation of a laser pulse through an atomic vapor. In the nonlinear regime probed, the light pulse develops frequency sidebands whose positions are, in first approximation, solely dependent on the maximum Rabi frequency of the system, in a fashion very similar to that observed in optical fibers. This modulational instability dictates the temporal reshaping of the laser field and finally results in pulse splitting.