Abstract.A theoretical study of the nonlinearity reduction in a four-level system of potassium, atom in the presence of a strong nanosecond laser field, which excites the transition 1/2 1/2 4S 6S ↔ with two photons, is presented. It is shown, that the destructive quantum interference between the laser field and the internally generated radiations results in a linear response of the atomic path-1 ( 1/2

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We numerically study the conditions under which a memory is induced in a sample of potassium vapor by a two-photon partially-truncated excitation field detuned from resonance. We assume a four-level atom and solve numerically the appropriate equations observing the time dependence of the coherence 12 in order to determine the region of the proper parameters: two-photon detuning, the external field intensity, and the atomic density. Subsequently we investigate the stability and the 'read-out' process of the optical free induction memory.