Propagation of high intensity short resonant pulses in potassium vapor

Intense pulses, with area>π propagating through short optical depths of a resonant atomic vapor, have been shown not to reshape. We show theoretically that although the main part of the pulse is unchanged for short propagation distances (αl), the area theorem is nonetheless obeyed in such cases via the formation of a long tail, oscillating in time, produced by free induction decay from the excited atoms. We measure the light in the intensity of such a tail and show that the vapor density dependence of the tail intensity and oscillating structure are in qualitative agreement with theoretical predictions.