Effects of spontaneously generated coherence on transient process in a<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>Λ</mml:mi></mml:math>system

Abstract

Due to interaction with the vacuum of the radiation field, near-degenerate lower levels in a $\ensuremath{\Lambda}$ system have an additional coherence term, the spontaneously generated coherence term. In this paper, we investigate the effects of this kind of coherence on the transient process in the presence of a weak probe and a strong coherent field, with or without an incoherent pump. We find that the transient gain (absorption) properties can be dramatically affected by the spontaneously generated coherence. The transient gain can be greatly enhanced due to the effect of spontaneously generated coherence, and the transient absorption can be completely eliminated just by choosing the proper relative phase between the two fields.