We present a study of electromagnetically induced transparency(EIT) under the excitation of a 100% amplitude-modulated(AM) coupling field.The EIT feature is associated with a Λ type three-level configuration where a coupling and probe field couples two separate optical transitions and it is well-known that the spectrum of the swept probe field gives a simple single transparency feature induced by the single mode coupling field.It is shown that when a 100% AM coupling field is applied,there is an EIT doublet and the separation of the EIT doublet can be controlled by the modulation frequency of the coupling field.Our result implies a new way of manipulating EIT resonance and opening more than one EIT windows.
We present the spectral line narrowing effect in a Λ three-level atomic system where one transition is coupled by a coupling laser and the narrow feature is observed by probing the other transition with a weak laser. As coupling laser detuning increases the electromagnetically induced transparency resonance is observed to evolve into electromagnetically induced absorption resonance with sub-natural linewidth. The linewidth of the narrow spectral feature is studied as a function of coupling laser detuning and the atomic system parameters. The result is explained using density matrix density equation in the dressed-atom picture.
ZHANG Lian-shui YANG Li-jun LI Xiao-li ZHUANG Zhong-hong GUO Qing-lin
