激光场线宽对四能级原子系统相干效应的影响

Influence of Laser-Field Linewidth on Atomic Coherence Effect in Four-Level Atomic System

采用密度矩阵方程,在引入激光场线宽的条件下,计算了N型四能级原子系统中介质对探测场的吸收。结果表明:耦合场线宽的引入,消弱了四能级原子相干,对抑制吸收有增强作用,对增强吸收有抑制作用,即耦合场线宽的引入导致了退相干。控制场线宽的引入,在电磁感应透明中削弱了四能级原子相干性,降低了共振吸收,增强了光透明;在电磁感应吸收中,控制场线宽的增加使谱线中心两侧的吸收增强,削弱了谱线中心的吸收增强,从而使四能级系统的电磁感应吸收转换为电磁感应透明。

Using density matrix equation, the absorption of the probing field in N-type four-level atomic system with three coupling laser-fields under introducing laser field linewidth is calculated. The results indicate that the coupling-field linewidth abates the atomic coherence in four-level system, which enhances absorption to absorption inhibition and inhibits absorption to absorption enhancement. The coupling-field linewidth leads to decoherence. The results also indicate that the controlling-field linewidth abates the atomic coherence in four-level system, reduces absorption and enhances light transparency in electromagnetically induced transparency. The increase of controlling-field linewidth enhances absorption of the both sides absorption of the spectral line centre in electromagnetically induced absorption, while abates the absorption enhancement of the spectral line centre. So the electromagnetically induced absorption in four-level system switchs to the electromagnetically induced transparency.