【作者】 孔令波；

【导师】 詹明生；

【作者基本信息】 中国科学院研究生院（武汉物理与数学研究所） ， 原子分子物理， 2007， 博士

【摘要】 激光场与原子相互作用时,激光诱导的原子相干和量子干涉将改变原子介质的色散和吸收性质,这些改变会在基础物理学研究和实际应用中导致很多有意义的现象,比如相干布居囚禁(CPT)、电磁诱导透明(EIT)、无反转激光(LWI)、光脉冲群速度的慢光速及超光速传播、光存储、弱光相干非线性光学和量子信息处理。本篇博士论文从实验和理论上研究了原子介质中激光诱导的量子相干效应,整个工作可概括为四个部分:1.搭建了一套新的磁光阱(MOT)装置,优化了真空系统、光学设计和磁场线圈,实现了计算机时序控制。在磁光阱中得到了4×108个冷原子,冷原子云团的直径约为3mm。整个磁光阱装置性能稳定,布局简单紧凑,为研究冷原子中的原子相干和量子干涉效应提供了一个好的实验平台。2.研究了交叉耦合效应,即一个强的激光场同时耦合两个或三个能级跃迁。在冷原子级联型系统中实验观察到了激光场交叉耦合导致的多窗口电磁诱导透明现象。提出了在四能级Λ型系统中利用交叉耦合增强三阶克尔非线性效应的新方案,指出该模型可被用来形成超慢光速传播的暗光孤子。3.实验研究了被两个强激光场驱动的多能级87Rb原子在室温下所表现出的亚多普勒效应。窄的吸收、透明和增益谱线出现在多普勒增宽的吸收谱中。基于四能级N型模型,通过解析和数值计算理论分析和解释了实验观察到的现象。在无多普勒增宽的冷原子中,我们提出四能级N型系统能够完全消除线性和非线性吸收损失,而同时得到大的三阶非线性折射率。4.在新实验系统上进行了双色电磁诱导透明实验,利用频率调制谱的方法测量了双色EIT的色散曲线。在双色场耦合基础上,设计实验在冷原子中观察到非共振耦合情况下的弱光四波混频信号,测到的转换效率为18%。更多还原

【Abstract】 When an atomic medium is driven by laser fields, the induced atomic coherence and quantum interference may modify the dispersive and absorptive properties of the atomic medium and leads to a variety of interesting phenomena for fundamental studies and practical applications, such as coherent population trapping (CPT), electromagnetically induced transparency (EIT), lasing without population inversion (LWI), subluminal or superluminal light propagation, light storage, coherent nonlinear optics at low light levels and quantum information processing. This thesis presents the experimental and theoretical studies of laser induced quantum coherence effects in rubidium atoms, and the whole work can be summarized to the following three parts:1. We have set up a new magneto-optical trap (MOT) apparatus with the vacuum system, optical design and magnetic coils being optimized, the number of the trapped cold atoms is about 4×108, the diameter of the cold atom cloud is about 3mm. The time sequence of the experimental process is controlled by computer programming. This new MOT apparatus is very compact and stable. It’s a good experimental platform for the study of laser induced quantum coherence effects in cold atoms.2. We studied the cross coupling effect via two or three transitions coupled simultaneously by one strong laser field. We experimentally demonstrated that this multi-coupling could cause multi-window EIT in a cascade system. We proposed applying cross talk among optical transitions to enhance the third Kerr nonlinearity in a four-levelΛsystem, and we found this system could be used to form slow dark optical solitons.3. Sub-Doppler spectral resolution has been studied in Doppler-broadened multi-level 87Rb atoms coherently coupled by two strong laser fields. Narrow spectral features of absorption or gain were observed in the center or sides of the Doppler-broadened absorption profile. Analytical and numerical calculations based on a four-level N type model were presented to explain the experimental results. We found this four-level N-type system could obtain large third nonlinear index of refraction with vanishing linear and nonlinear absorption in cold atoms.4. We studied the bichromatic electromagnetically induced transparency in our new MOT system. The dispersive curve of bichromatic EIT was measured by frequency-modulation spectroscopy. Based on the coupling of the bichromatic field, we observed a large four-wave mixing signal in cold atoms under non-resonance condition, the measured maximum conversion efficiency was about 18%.更多还原