Phase control of light amplification without inversion in a<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>Λ</mml:mi></mml:math>system with spontaneously generated coherence

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 effects of spontaneouly generated coherence on inversionless gain in the presence of a weak probe, a strong coherent field, and an incoherent pump. We find that the inversionless gain stems from both spontaneously generated coherence and dynamically induced coherence, but the former contributes more to the inversionless gain. In particular, we can modulate the inversionless gain just by changing the relative phase between the two fields.