Coherent processing of a light pulse stored in a medium of four-level   atoms
  It is demonstrated that the properties of light stored in a four-level atomic system can be modified by an additional control interaction present during the storage stage. By choosing the pulse area of this interaction one can in particular continuously switch between two channels into which light is released. 
A. Raczynski, J. Zaremba and S. Zielinska-Kaniasty