【作者】 卜凡阁；

【导师】 樊锡君；

【作者基本信息】 山东师范大学 ， 理论物理， 2008， 硕士

【摘要】 原子相干效应是相干电磁场与原子相互作用的结果。关于原子相干效应的研究在量子光学领域具有重要的意义,这一研究是近年来物理研究的热门课题之一。相干控制的研究不仅有重要的理论意义,而且在量子光学、非线性光学、量子信息和光通讯等领域内都有重要的应用价值。原子相干可以导致很多有潜在应用价值的物理现象,如:相干粒子数捕获,电磁感应透明,无反转激光,光量子信息的存储与处理等。而在众多的原子相干现象中,无粒子数反转激光(Lasing Without Inversion简称LWI)引起了研究人员更大的兴趣和特别的重视。因为传统的激光器都是在有粒子数反转的条件下工作的,然而,实现粒子数反转对传统激光器来说具有很多限制条件,限制了激光器的近一步发展。无粒子数反转激光作为一种不同于传统激光产生方式的新型激光产生机制,可以在应用传统激光理论和方法很难甚至不可能产生激光的高频光谱区(X-射线甚至γ-射线区)产生激光,因此开展对无粒子数反转激光的研究不仅对光物理基础研究有重要意义而且具有巨大潜在的应用价值。本文首次提出了开放的准Λ型四能级原子系统,并对此系统中无反转激光和光学性质相干控制的理论进行了研究。主要讨论了自发辐射诱导相干(SGC)及探测场和驱动场之间的相对位相对无反转激光增益、色散及系统粒子数差的影响。本论文共分四章。第一章综述,阐述了几种典型的原子相干效应并在此基础上着重介绍了无粒子数反转激光产生的基本原理、无粒子数反转激光和相干控制的研究意义并对当前无粒子数反转激光的研究现状进行了介绍。第二章提出了开放的准Λ型四能级系统模型,并给出了存在自发辐射诱导相干(SGC)效应下的密度矩阵运动方程。然后利用系统定态数值解从不同方面着重研究了自发辐射诱导相干(SGC)对无反转激光增益的影响。研究结果表明,通过调节SGC的强弱可实现从吸收到无反转激光的转换并显著提高无反转激光增益;表示SGC效应的两个因子p1和p2的变化对无反转激光增益的影响程度有较大的差别。我们还发现,相同条件下开放系统可得到远大于相应封闭系统的无反转激光增益;而且在无泵浦场的情况下,开放系统仍然可以得到探测场的无反转放大,而相应封闭系统只能呈现对探测场的吸收。第三章从不同角度分析了探测场和驱动场之间的相对位相Φ对探测场增益(吸收)以及粒子数差的影响。研究结果表明:通过对相对位相的控制,可以实现探测场无反转增益和色散的周期性放大和减弱,并能得到无吸收高色散;同时发现Φ=α的色散曲线与Φ=α+π/2的增益曲线相似;在探测场共振条件下,适当调节相对位相,可以使无反转激光(LWI)增益达到最大。本章还研究了粒子注入和退出速率的变化对位相相关的LWI增益的调制作用。第四章总结了本论文的主要研究成果,并对在开放的准Λ型四能级原子系统的进一步研究工作提出了建议。更多还原

【Abstract】 The atomic coherent effect is a result of the interaction between the electromagnetic field and atom. The study for the atomic coherent effect has an important research value in the quantum optics field, and is one of the physical hot subjects in the recent years. 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 effects have multiple potential applications in many aspects, for example electromagnetically induced transparency (EIT), lasing without inversion (LWI) and optical quantum information storage and processing. Among numerous phenomena of atom coherence, lasing without inversion (LWI) has received tremendous attention. As a new method of producing laser, LWI can obtain laser light in spectral domains, e.g. the x-ray evenγ-ray range, where conventional methods based on population inversion are not available or are difficult to implement, so LWI has wide application prospects.We at first put forward a model of an open quasiΛ-type four-level atomic system and we studied the lasing without inversion and coherent control of optical properties in the system. Then we investigated the effect of spontaneously generated coherence and the relative phase on the gain、dispersion and population differences.This paper consists of four chapters.In Chapter 1, we explained the significance for studying coherent control and LWI, and showed the basic principle of producing LWI. We introduced the simply current research state of coherent control and LWI.In Chapter 2, we gave the model of an open quasiΛ-type four-level atomic system and investigated the effect of spontaneously generated coherence on the gain of lasing without inversion from different respects by using the numerical calculation results of the system in the steady state. The study results show that, the switching from absorption to lasing without inversion (LWI) and the enhancement of the LWI gain can be realized by adjusting the strength of SGC; varying of the two factors p1 and p 2 which represent the SGC effect will produce remarkable different influence on the LWI gain. We also find that, the LWI gain is much larger in open system than that in the corresponding closed system; moreover, when the incoherent pump field is absent, the LWI gain can be obtained in the open system but can’t in the closed system.In chapter 3, the effect of the relative phaseΦbetween the probe and driving fields on gain and dispersion from different aspects in an open quasiΛ-type four-level system by the numerical solution of the steady state is investigated. The results show that by adjusting the value of the relative phase the LWI gain and dispersion can be periodically amplified and attenuated; High dispersion (refractive index) without absorption can be achieved; The dispersion curve corresponding toΦ=αis similar to the gain curve corresponding toΦ=α+π/2; When the probe field is on resonance, the largest lasing without inversion gain can be obtained by adjusting the relative phase. The effect of the atomic exit and injection rates on the LWI gain for different values of the relative phase was also studied.In Chapter 4, we summarized the main research results of the paper, and we put forward a suggestion to the further research work of the open quasiΛ-type four-level atomic system.更多还原