中文摘要：

介绍了新近发展的求解原子在弱电磁波扰动下的受激跃迁的非微扰方法，详细计算并讨论了一种特殊情况．非微扰结果在微扰条件下退化为含时微扰论的结果，但克服了后者在近共振区明显不合理的缺陷．根据非微扰结果，电偶极跃迁的选择定则在短时间内近似成立，但长时间后禁戒跃迁的概率与允许跃迁可相比拟．

英文摘要：

An introduction is presented to a recently established nonperturbative approach to the transitions between atomic states induced by weak electromagnetic waves. A special case of the general solution is calculated and discussed in detail. Results of the nonperturbative approach reduce under perturbation condition to those obtained by the time- dependent perturbative method, but overcome the difficulty that the perturbative results are obviously unreasonable in the near resonant region. According to the nonperturbative solution, the electric-dipole selection rules are approximately recovered for short time. For large time, however, probabilities for forbidden transitions may become comparable with those for allowed ones.