Perturbing an electromagnetic induced transparency within an inhomogeneously broadened transition

This paper reports on the effect a perturbing field on an electromagnetically induced transparency. The studies involve inhomogeneously broadened spin transitions of a nitrogen-vacancy color center in diamond and it is observed that the transparency is unaffected, destroyed or split depending on how the perturbing field is coupled to the system. The observations are explained in terms of doubly driven inhomogeneously broadened 4-level systems.