Nonlinear theory of noninversion lasers of an open three-level system

A nonlinear theory of a noninversion laser of an open three-level system based on electromagnetically induced transparency is given. In this noninversion laser model, a nonselective pumping mechanism is used for obtaining lasing gain such that the population in the lower lasing level is always larger than a half of the total population no matter whether the driving field is on or off. In the lasing region, there is no direct pumping to the upper level. The conditions for the existence of a nontrivial and stable laser field are obtained. The dependence of the laser intensity on the intensity of the driving field and the ratio of the two decay rates from the upper level has been obtained, and the ways to obtain a large laser field have been studied.