The nonlinear interaction of a four-level atomic configuration in potassium, with ns pump and coupling fields, is numerically investigated. The resonant pump acts on the two-photon transition
causing internally generated emissions in two atomic paths: path-1,
and path-2,
respectively. The coupling laser resonantly excites the single-photon transition
in a Λ-type scheme. A controlled temporal shift and enhancement of the partially coherent cascade emissions of path-2 is obtained. The amplification without inversion mechanism is proposed to explain the lower path-2 emission. It is shown that when the coupling field is delayed from the pump, then an efficient dynamic effect is induced, based on an additional population interplay of states
and
Finally, a novel coherent method for temporally controlling the quasi-stationary population dynamics in a saturated system is proposed, when the driving fields are also delayed. The importance of the present work is related to the fact that the induced coherence (polarisation or energy injection) of the coupling field can be temporally controlled in nonlinear gaseous media.