Interaction between radiation and quantum systems with relaxing sublevels

A theoretical analysis is given of the propagation of resonance radiation in a medium with relaxing sublevels. When the time constants of changes in the optical field are comparable with the relaxation times, the relaxation of sublevels gives rise to several special features in the behavior of steady-state π pulses. The analysis explains several effects observed in various experimental situations, including the spectral "hole burning" effect.