  One-photon and Raman type interactions between two-level atoms and
narrow-band light are considered. We give some exactly solvable models of these
processes when only one-photon Fock states are involved in the evolution.
Possible application of these models for generation and transformation of
entangled states of the W-class, some of which demonstrate hierarchy structure,
are discussed. Finally, we consider preparation of entangled chains of atomic
ensembles.
