Abstract

In a two-level medium, the condition for amplification is population inversion. The simplest scheme in which inversionless amplification occurs is a three-level medium. It was shown recently that a trichromatic field can be amplified by a three-level medium without population inversion if the low-frequency (LF) coherence exceeds some critical value.¹ The question that we address here is how to generalize the two-level amplification condition when one or both levels are split into a number of sublevels.

© 1991 Optical Society of America