- We consider a three-level medium with low-frequency separation between the two upper levels. The medium interacts with an external field that induces a coherence between the two upper levels. We analyze the amplification condition for the probe monochromatic optical field in a general nonresonant case. We show that amplification without population inversion arises either at line center or at the sidebands, depending on the sign of the population difference between the upper sublevels. This amplification occurs in a limited range of the coherent pump intensity. 1992 The American Physical Society.