Unphysical artifacts are responsible for molecular orientation with   half-cycle pulses
  Sub-cycle electromagnetic pulses in the Terahertz region are considered to be one of the best ways to orient molecules. The simplest option corresponds to half-cycles pulses in the sudden regime, for which the pulse duration is much shorter than the rotational period. However, no experimental demonstration exists so far. We argue that this kind of molecular orientation is an unphysical artifact that arises from a constant component of the electric field that is not a solution of Maxwell's equations, and therefore cannot propagate with the pulse. We present calculations based on Floquet theory that prove this claim. 
Juan Ortigoso
physics.chem-ph