运用密度矩阵方程,研究了在外加相干耦合场作用下呈现可调谐多透明窗口的准Λ型 四能级系统。数值计算结果表明:通过调节外加相干耦合光场的拉比频率强度,该系统可以三重、双重、单重 电磁诱导光透明现象,并在缀饰态表象中给出了定性解释;在三重电磁诱导透明中,透明窗口的位置和吸收峰值 可以通过调节外加相干耦合场的失谐量来进行控制。每个透明窗口在吸收最低时都伴随着高折射率,因此在 此介质中能实现超光速传播。

Using density matrix eqution, the absorption and dispersion properties of a Λ-type four-level system driven by coherent fields are investigated. The result obtained by means of numerical method indicates that by adjusting the intensity of Rabi frequencies of the coherent field in the steady state, three, double or single electromagnetically induced transparency (EIT) can appear explicitly in this system. And the explanations of these phenomena are given by using the dressed states. In the three EIT, the location of transparent windows can be manipulated by controlling the detuning of the driving field. What’s more, it is also found that the medium shows a large refractive index at each transparency window, and the group velocity of the probe laser can be enhanced.