在通常的Λ型三能级系统中，耦合场和探测场分别与一对光学跃迁能级发生相互作用，使探测吸收曲线上出现线宽极窄的电磁诱导透明(Electromagnetically Induced Transparency,EIT)特性。本文采用调谐耦合场同时激励两个基态精细结构能级与激发态能级之间的跃迁，使系统同时呈现EIT和自发诱导相干凹陷两种特性，甚至出现EIT增益现象。详细讨论了耦合场调谐过程中探测吸收曲线的变化规律。研究结果表明:本系统中EIT和自发诱导相干凹陷之间存在相干作用，而且当调谐耦合场的激发频率满足一定条件时，它们之间的相干作用变得很显著，使EIT上出现增益现象。

Electromagnetically induced transparency (EIT) with extremely narrow spectral width is obtained in a well-studied lambda three level system where a coupling field and a probing field interact with two optical transitions. By tuning coupling field, it excites the transitions between two ground state hyperfine levels and excited state level. In this paper, both EIT and spontaneous radiation induced coherent dip can be obtained, and even the gain is observed to superpose to the EIT window. By discussing the behaviors of probing field absorption profiles under the effect of the tuned coupling field, it can be seen that there are quantum interference and coherence between EIT and spontaneous radiation induced coherent dip, and the coherence becomes remarkable when the excitation frequency of the coupling field satisfies certain conditions.