Coherent control of negative refraction based on local-field enhancement and dynamically induced chirality

This paper studies the electromagnetic response of a coherently driven dense atomic ensemble to a weak probe.It finds that negative refraction with little absorption may be achieved in the presence of local-field enhanced interaction and dynamically induced chirality.The complex refractive index governing the probe refraction and absorption depends critically on the atomic density,the steady population distribution,the coherence dephasings,and the frequency detunings,and is also sensitive to the phase of the driving field because the photonic transition paths form a close loop.Thus,it can periodically tune the refractive index at a fixed frequency from negative to positive values and vice versa just by modulating the driving phase.Moreover,the optimal negative refraction is found to be near the probe magnetic resonance,which then requires the electric fields of the probe and the drive being on two-photon resonance due to the dipole synchronisation.     

电磁感应双光子带隙的产生和控制

基于电磁感应透明技术, 通过求解原子的密度矩阵方程和电磁场的传输矩阵方程, 研究了被行波场和驻波场共同耦合的一个四能级冷原子介质的稳态光学特性, 发现在特定参数下能够产生一个几乎完美的双光子带隙结构, 在这两个光子带隙对应的频率区域内反射率都均匀地超过95%. 通过改变耦合场的强度和频率, 可以方便地调节这两个光子带隙的位置和宽度. 这一双光子带隙结构可用来实现全光路由和全光开关, 有望在全光信息网络中获得应用.