中文摘要：

利用求密度矩阵稳态解的方法得到了一般泵浦和衰变情况下A型开放三能级原子系统在强相干光作用下无反转激光的条件。我们证明初始泵浦率和能级间自发辐射率的反转代替了稳态布居数的反转，共同促进了无布居数反转光放大，而且只要前两者之一满足就可以实现无反转光放大。然后利用求解简化原子模型波函数解析解的方法，描述了原子演化使得光场放大的过程，解释了量子干涉在三能级原子无反转激光中的作用。

英文摘要：

The LWI operation condition for an open A-type three level atomic system is obtained by solving the steady-state density-matrix equation with the system being driven by a strong coherent field while the inherent pumping rate and decay rate being arbitrary. It is shown that the inversions of inherent pumping rate and spontaneous decay rate replace the inversion of population, and together help to realize lasing without population inversion. Furthermore, the LWI can be realized if just either one of the two inversions is fulfilled. A schrodinger equation of three-level atomic system with appropriate conditions is analytically solved to explain the qu.antum interference process that leads to LWI.