级联三能级锂分子的电磁感应透明和暗荧光
Electromagnetically induced transparency and dark fluorescence in a cascade three-level Lithium molecule
摘要：
利用光学-光学双共振（OODR）光谱技术在级联三能级双原子锂系统中观察到了电磁感应透明（EIT）和暗荧光。当强耦合激光将中间态$A^{1}Σ^{+}_{u}(v=13, J=14)$耦合到$^7Li_2$的上态$G^{1}Π_{g}(v=11, J=14)$时，由于弱探测激光通过基态$X^{1}Σ^{+}_{g}(v=4, J=15)$和激发态$A^{1}Σ^{+}_{u}(v=13, J=14)$之间的共振跃迁进行调谐，因此来自$A^{1}Σ^{+}_{u}$和$G^{1}Π_{g}$态的荧光急剧减少。强耦合激光使得光学厚介质对于探测跃迁是透明的。此外，当两个激光器都调谐到共振时，来自高能级$G^{1}Π_{g}(v=11, J=14)$的荧光也是暗的，这意味着分子被捕获在基态。利用密度矩阵方法模拟了开放分子三能级系统在强耦合场和弱探测场作用下的响应。在稳态条件下得到了解析解。我们在线形分析中加入了转动能级的磁次能级（M）简并，并报道了$|M|$依赖的线形分裂。理论计算与实测荧光光谱符合得很好。我们发现，即使当耦合场失谐远离共振时，相干性也显著保持。
英文摘要：
We observed electromagnetically induced transparency (EIT) and dark fluorescence in a cascade three-level diatomic Lithium system using Optical-Optical Double Resonance (OODR) spectroscopy. When a strong coupling laser couples the intermediate state $A^{1}Σ^{+}_{u}(v=13, J=14)$ to the upper state $G^{1}Π_{g}(v=11, J=14)$ of $^7Li_2$, the fluorescence from both $A^{1}Σ^{+}_{u}$ and $G^{1}Π_{g}$ states was drastically reduced as the weak probe laser was tuned through the resonance transition between the ground state $X^{1}Σ^{+}_{g}(v=4, J=15)$ and the excited state $A^{1}Σ^{+}_{u}(v=13, J=14)$. The strong coupling laser makes an optically thick medium transparent for the probe transition. In addition, The fact that fluorescence from the upper state $G^{1}Π_{g}(v=11, J=14)$ was also dark when both lasers were tuned at resonance implies that the molecules were trapped in the ground state. We used density matrix methods to simulate the response of an open molecular three-level system to the action of a strong coupling field and a weak probe field. The analytical solutions were obtained under the steady-state condition. We have incorporated the magnetic sublevel (M) degeneracy of the rotational levels in the lineshape analysis and report $|M|$ dependent lineshape splitting. The theoretical calculations are in excellent agreement with the observed fluorescence spectra. We show that the coherence is remarkably preserved even when the coupling field was detuned far from the resonance.
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