Storage of light: A useful concept?
  We show both analytically and numerically that photons from a probe pulse are not stored in several recent experiments. Rather, they are absorbed to produce a two-photon excitation. More importantly, when an identical coupling pulse is re-injected into the medium, we show that the regenerated optical field has a pulse width that is very different from the original probe field. It is therefore, not a faithful copy of the original probe pulse. 
M.G. Payne (Georgia Southern University, Statesboro, GA) L. Deng   (Electron and Optical Physics Division, NIST, Gaithersbur...