Abstract

Two essentially different mechanisms are known for inversionless amplification. The first is based on coherent population trapping, while the second is connected with the existence of quantum interference effects among dressed states of the coupled atom-field system. Previous investigations of four-level atoms with Raman pumping have emphasized the existence of noninversion lasing by way of the first mechanisms and have interpreted the gain as a result of a population inversion between dressed states. In this case the quantum interference generally hinders the amplification process. By extending this analysis to a broader range of parameters we find that the second mechanism can also become effective. The purpose of this presentation is to show that four-level atoms with a Raman pump can generally support both amplification mechanisms and to define the conditions under which either process may dominate.

© 1992 Optical Society of America