相干原子介质中的超慢光传播及电磁感应成像
文献类型：学位论文
| 作者 | 王春芳 |
| 学位类别 | 博士 |
| 答辩日期 | 2009 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 韩申生 |
| 关键词 | 电磁感应透明 相干操控 梯度折射率介质 电磁感应成像 多普勒加宽 |
| 其他题名 | The propagation of the ultr-slow light and the electromagnetically induced imaging in the coherence atomic medium |
| 中文摘要 | 物质的光学性质和光学过程的相干控制研究是当前国际上光学研究重要而活跃的前沿领域之一。相干控制的研究不仅有重要的理论意义，且在量子光学、非线性光学、量子信息和光通讯等领域内都有重要的应用。原子相干现象和量子干涉效应在很多方面都具有潜在的应用价值。利用相干光场与多能级原子作用过程中的量子干涉效应，可以显著地改变原子介质的光学特性，产生许多有趣且重要的现象。 作为量子干涉效应的典型代表，电磁感应透明（EIT）受到人们的普遍关注。 而与此相关的课题也得到广泛研究。其中，慢光传播及停止现象更是近年来物理学界的研究热点。然而，我们注意到慢光在原子相干介质中传播的横向空间效应并没有引起多大的重视。 因此，本文首先介绍光场与原子介质相互作用的半经典理论，并回顾了EIT效应研究的发展过程，以及利用EIT介质的特性，在非线性效应和量子效应方面开展的一系列研究工作。 然后从光束传输的空间效应出发，主要研究了原子相干介质中的超慢光传播问题。我们发现相干原子介质中可形成光学图像，通过对光学系统调控,可实现这些图像的变换和存储。主要内容包括： 1．研究了光束在电磁感应透明（EIT）介质中的焦移现象。在特定的光学环境下，利用相关近似，可将EIT介质的极化率表达成梯度结构，从而得到EIT介质中的光束传输规律。论了EIT介质光学系统中的横向光学传输特性。结果表明，与通常梯度折射率介质（GRIN）不同，EIT介质具有较好的操控性。重点讨论了通过调控介质的各项指数，达到更为便捷地控制入射光在介质中的焦移。此外，分析表明，通过调整介质的某些参数，可缩小实际焦点处的光斑半径。 2．冷原子介质设计成一种可调控的成像装置。当电磁感应透明（EIT）条件得到满足，且控制光场为高斯光束时，则原子介质可变为一种实时可调的二次折射率介质。在我们所研究的光学系统中，EIT介质充当着一个成像光学元件的作用。利用Collins公式，我们可得到探测光的在原子介质中的横向空间场分布及物体在介质中的成像位置的解析结果，并将该结果与数值模拟结果进行比较。结果表明，利用经典方法得出的解析解与实际结果存在一定误差，但可以更直观地表达介质中的成像特性。此外，讨论了如何提高介质中像的可见度。并提出，输出面上的图像受控制光场的影响很大，这为光学信息处理提供了一种潜在的可能应用。 3．究了多普勒（Doppler）加宽介质中的自感应成像现象。分析表明，在电磁感应透明（EIT）条件下，常温下的三能级$\Lambda$原子介质中也能产生自成像。详细讨论了温度对自成像位置及成像质量的影响。 数值模拟结果显示，随着温度的升高，自成像所在位置线性地远离物所在位置，成像质量也随之下降。 4．通过"矩"的方法，研究了慢光在受高斯光束驱动的电磁感应透明（EIT）介质中的偏折现象。本文从解析和数值两种方法出发，均证实了慢光在该原子介质中的偏折现象。结果表明，当信号光进入EIT原子介质后，在一般衍射之前，会有一段可观察的光线偏折现象。另外，耦合光强度对偏折现象及信号光的束宽影响也是本文的内容之一。 |
| 英文摘要 | The study of coherent control of optical properties and optical courses is one of the most important and active research front fields in international optics nowadays. The study of coherent control has not only an important theoretical value, but also wide application prospects in many fields, such as quantum optics, nonlinear optics, quantum information and optical communication, etc. In addition, atomic coherence and quantum interference effects have multiple potential applications in many aspects. Coherent light interacting with multi-level atoms can lead to quantum interference in the amplitudes of optical transitions. In this way the optical properties of a medium can be dramatically modified, leading to many interesting and important phenomena. As the most typical quantum interference, electromagnetically induced transparency (EIT) effect has attracted great attention and the related research subjects also have been investigated extensively. Among these subjects, the phenomena of the propagation and stopping of the slow light are the focus these days in the field of physics. While we notice that, there is few attention focus on the transverse spatial effect of the slow light in the coherence atomic medium. So, after introducing the Semiclassical Theory of the interaction between the light and atoms, we reviewed the velopment of the research works on EIT effect, as well as its applications on nonlinear and quantum effects used by the Properties of EIT medium. Then start from the spatial effect of the slow light, we mainly studied the propagation of the ultr-slow light in the coherent atomic medium. We find that, there will be self-imaging formed in the medium, which could be transformed and stored. The main innovative and important results are: 1. By approximating the index distribution of a medium with electromagnetically induced transparency (EIT) as a gradient index (GRIN), propagation laws in the medium with EIT can be obtained. Transmission properties in an optical system with an EIT medium are analyzed. The results show that, unlike the case in the ordinary GRIN medium, the refractive index of EIT medium has the better controllability. Consequently, discussions are focused on how to conveniently manipulate the focal shift of the input in the EIT by means of controlling the index of the medium. Additionally, the speckle radius on the location of the actual focus can be diminished by adjusting some parameters in the EIT medium. 2. Under the circumstance of a Gaussian control field, the cold atomic medium with electromagnetically induced transparency (EIT) turns out to be the special medium with the quadratic index distribution which is controllable online. In our study, the optical system occupies a portion of the EIT medium which acts as an imaging device. With the help of the Collins formula, the analytic expression for the spatial distribution of the probe field in the cold atomic medium is obtained as well as the location of the imaging. Compare with the numerical results, though the analytical results have some differences with the numerical, the former can give the imaging information in a more intuitive way. The methods for improving the visibility of the imaging are proposed in this paper. Moreover, we also show that the shapes of the images on the output are strongly influenced by the intensity of the control field, which provides a potential optical processing method 3. Under the condition of electromagnetically induced transparency, self-imaging in three-level -type atoms at normal temperature is studied. The influences of the temperature on the position of the self-imaging and the corresponding imaging quality are discussed in detail. Numerical results show that, with the increase of the temperature, the location of the self-imaging linearly moves away from the original object, and the self-imaging quality decreases. 4. With the moments formalism theory, we study the deflection of the slow signal light in the cold atomic media, which is under the condition of the Gauss control laser and electromagnetically induced transparency. The deflection is testified by analytic and numerical methods. Results show that, as the signal light propagating in the medium, there would be an observable deflection before the general diffraction. Influence of the coupling intensity on deflection phenomenon as well as the beamwidth of the signal light in the medium is also investigated in this work. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15273]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 王春芳. 相干原子介质中的超慢光传播及电磁感应成像[D]. 中国科学院上海光学精密机械研究所. 2009. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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