【作者】 孙建锋；

【导师】 李永放；

【作者基本信息】 陕西师范大学 ， 光学， 2002， 硕士

【摘要】 处于激发态原子的自发辐射是场和物质相互作用的一个基本问题，它导致了许多重要的现象，如：光电设备的量子噪声、有限激光线宽等。因此很长一段时间以来，人们一直想通过某种方法来抑制或消除自发辐射。由于激发态原子的自发辐射速率正比于激发态和基态的电偶极矩以及原子所在空间的各个模式的密度。因此人们可以通过两种方式对自发辐射进行修正。第一，我们可以通过改变原子所处的“环境”从而达到改变自发辐射的目的。把激发态的原子放置在我们所要求的环境中去，如光子晶体和共振腔等，这样可以通过改变共振频率附近区域的电磁场的模式来实现对自发辐射的改变；第二，近年来人们又可以通过不同路径之间的量子干涉来实现对自发辐射的控制，这种方法引起了越来越多的重视。并相继在理论和实验上发现了许多由量子干涉引起的物理效应，如自发辐射的抑制和猝灭、超窄谱线、电磁感应透明、无粒子数反转激光等。 本文提出了一双光场驱动下的梯-型四能级模型：中间两个近简并能级|2＞、|3＞和基态能级|1＞通过频率为ω₀₁相干光场相耦合，同时频率为ω₀₂相干光场耦合从能级|4＞到中间两能级|2＞、|3＞的跃迁。其中能级|2＞和|3＞之间以及能级|4＞和|1＞之间是偶极禁戒的。在这个系统中存在着两对由自发辐射导致的量子干涉干涉通道，因此它大大的丰富了量子干涉的内容，这在相关文献中还未见报道。 本文对所提出的这一新的四能级物理模型，从多角度研究讨论了双光场作用下系统的共振荧光光谱、弱探测场的吸收光谱，并用缀饰态理论对其物理机理作了详细的分析和讨论得到的主要结果如下： （1）在共振激发时Rabi频率Ω_3，4的大小不影响系统电磁感应透明的产生，但可使得零吸收谱的线宽变窄，从而得到超窄电磁感应透明。当离共振激发时，Rabi频率Ω_3，4的大小则直接影响电磁感应透明的产生。不同的激发方式也可改变电磁感应透明的位置。只有在适当的条件下才会产生电磁感应透明，且可实现了无反转增益。 （2）在梯-型四能级系统中，当p₁（能级|2＞-|1＞和能级|3＞-|1＞跃迁的自发辐射偶极矩关联度）越接近于1时，它对共振荧光谱的影响越大。但当p₁=1时，系统没有辐射，粒子被完全捕获。当取p₁=0.999时，随着电偶极矩关联度p₂（能级I4）12＞和能级＊＼！3＞跃迁的自发辐射偶极矩关联度)的增加，共振荧光谱的中间的峰的线宽逐渐变窄。特别是当pl＝pZ二0．999时，共振荧光谱中出现了一条超窄谱线。电偶极矩关联度pl．2的大小不影响各个峰的位置。 p)我们利用密度矩阵的实部和虚部（ImM＊和ReMJ讨论了能级I3＞到能级11＞跃迁的吸收线型和色散线型。我们发现量子干涉效应直接影响着梯－型四能级系统中吸收线型和色散线型的变异，中间两能级的间隔对系统增益的产生有不可忽视的作用。 K）在梯－型四能级系统的模型中，我们讨论了激光线宽和多谱勒效应对量子干涉效应的影响。通过理论和数值分析，我们可以看出，激光线宽破坏了相干布居捕获，因此不能产生完全的电磁感应透明，并对粒子的分布有展宽作用。由于多谱勒效应的存在，能级I4＞没有出现粒子数捕获。能级间隔凸的增大可直接导致量子干涉效应的作用降低，从而造成了能级4＞粒子数的增加。更多还原

【Abstract】 Quantum interference has attracted more and more interestsin recent years. The interaction of an excited atom with the vacuum results in the spontaneous emission of the radiation. This radiation has an isotropic distribution in space which leads to a Lorentzian profile and its linewidth in the frequency domain are proportion to the Einstein spontaneous decay rate. It is responsible for many important physical phenomena such as quantum noise of an optoelectronic device and the limited laser linewidth and so forth. For a long time, people have desired to find an approach by which spontaneous emission rate of an excited atom can be depressed or cancelled. Since the spontaneous emission are directly related the electronic dipole moment and the environment where the atom is placed, therefore, there are two ways to modify the spontaneous emission of an atom. By placing an excited atom in a confined environment such as a photonic crystal and a resonance cavity, on the one hand, spontaneous emission can be controlled by tailoring the density of the electromagnetic modes of the environment in the neighborhood of the resonant frequency. On the other hand, the cancellation of spontaneous emission of an excited atom can be obtained via quantum interference between different atomic spontaneous decay pathways. Furthermore, this method has been attracting a lot of attention.In this paper, we take the Ladder-configration of a four-level atom into account. We calculated numerically several important phenomena result from the quantum interference such as ultra-sharp spontaneous spectra and absorption spectra, EIT, CPT etc. This paper is organized as follows. Part one is an introduction. In part two, the basic theory we used has been given. In part three, the model is presented and the formula for the numerical calculation are developed. And then we discuss the physical phenomena caused by quantum interference as follows. The conclusions are summarized in part five.inThrough our numerical calculation, we obtained several useful results in our model. First, we investigate the ultra-sharp EIT and find that the Rabi frequency of upper coherent field does not affect the occurrence CRT but the width of the CRT, then discuss the modification of absorption and dispersion profile, after that we study the effects of two pairs of pathways on the spontaneous emission spectra and the absorption spectra. Finally, we take the laser width and Doppler effect into account and find that the laser width destroys the quantum interference effect.更多还原