We study the generations of dark resonance and electomagnetically induced transparency (EIT) effects in the fourlevel system with two coherent fields coupling the transition from upper level to a pair of ground levels and a lower excited state. The quantum interference between two excited pathways results in double-dark resonances and doubletransparency holes with adjustable frequencies driven into the absorption spectrum in the atomic system. A clear analytical explanation for our numerical results is presented. It is shown that the relation of detunings of two coherent fields plays an important role in the generations of the coherent population trapping and EIT effects.

We investigate the absorption spectra of weak probe filed for a four-level system and demonstrate that the quantum interference between the two excited pathways can result in very narrow resonances, double-ransparencies and gain without inversion. The features and origins of these effects are discussed.

提出一双光场作用下的四能级系统，并对四能级模型的共振荧光谱作了详尽的研究。原子的共振荧光谱随Ra-bi频率的变化展示出能级的ac-Stark分裂，且在很大参量范围内光谱具有这一特性。但当只有一个激发通道时不产生ac-Stark分裂。在一定的条件下原子的共振荧光谱出现了两条黑线（dark line）。可以认为ac-Stark分裂的产生是多通道量子干涉的结果。利用缀饰态理论对ac-Stark分裂给出很好的解释。

我们报道了钠原子分子系统有惰性气体氩原子参与的碰撞能量转移过程。观察到了由此而产生的分子单重态和三重态的紫区受激辐射。实验结果表明，氩原子参与的碰撞能量转移过程在适当的氩气气压下起到了有利的作用，但过高的气压会使布居的粒子数减少，起到荧光淬灭效应。我们利用瞬时速率方程拟合了实验结果，得到了部分相同的变化规律。

The B2Σ+_X2Σ+(0,0) and (1,0) bands of Tin between 410.3 and 427.3 nm were recorded using high resolution laser induced fluorescence (LIF) spectroscopy and these bands have been rotationally analysed. No rotational perturbation was detected in the (0,0) hand, however, four rotational perturbations have been found in the (1,0) hand. These per-turbations could be ascribed to a 4Σ+ perturbing state interacting with the B2Σ+ state. Least-squares fits of the line positions observed yielded molecular constans for the v=0 and 1 level of the B2Σ+ states, and the per-turbing 4Σ+ state.