We demonstrate a technique for investigation of a strongly perturbed atomic system, which is an extension of standard radio-frequency spectroscopy. Analogous to "relaxation in the dark" experiments, this technique allows a reconstruction of the population distribution of the unperturbed atomic state by observing the rf spectroscopy signal after an abrupt switch-off of the perturbing light. The evolution and relaxation dynamics of the individual magnetic sublevels is investigated. Experimental observations are supported with numerical modeling based on a full density-matrix calculation performed in the presence of spin-exchange collisions and homogeneous relaxation.