【作者】 赵文丽；

【导师】 林圣路；

【作者基本信息】 山东师范大学 ， 原子与分子物理， 2004， 硕士

【摘要】 强场中原子光吸收谱的强共振特性已引起人们的多年的关注。这种现象涉及高里德堡态原子结构和极端条件下物质抗磁性、电子关联及运动规律等基本问题。半经典闭合轨道理论由于具有物理图像清晰、应用范围广泛等特点被普遍用来解释原子或离子在强外场中的光吸收现象，成为实现联结经典理论和量子理论的重要桥梁，并且是研究和发展量子混沌概念的一个典型实例。 在过去一段时间里，人们已对H~-、H以及碱金属原子在各种外场中的振荡特性作了广泛的研究，不仅从各个角度验证了半经典闭合轨道理论的正确性，而且发展了回归谱学、标度律、能级统计学等方法。近年来，含时外场的吸收谱特性已引起人们的广泛关注，因为含时外场在科学实验以及实际应用中是普遍存在的。原子处于含时振荡场(射频场)中时，由于受到非稳恒场的作用，闭合轨道的出射角、入射角、周期、经典作用量都将发生改变，增加了问题的复杂性，产生了新的调制现象。另外，如果外加的激发脉冲不是连续脉冲而是单脉冲或双脉冲时，也将出现不同的吸收谱。由于光吸收谱的计算过程与脉冲的宽度存在一定的关系，所以闭合轨道理论不能直接应用，必须进行适当的修改。 在本课题中，我们以Li原子为例，利用半经典闭合轨道理论结合含时微扰方法分别给出了Li原子在正弦振荡场以及脉冲场中的吸收谱，分析其振荡特性。主要进行了以下几方面的工作： (1) 在半经典闭合轨道理论的基础上，用微扰论讨论了振荡射频场中里德堡原子的吸收谱。把闭合轨道理论推广到外场与时间相关的情况，并且研究了相应的标度变换谱——回归谱。计算表明：射频场的振幅和频率对于吸收谱的回归强度都有很大的影响，但是影响的规律与方式是不同的。射频场的振幅越大，吸收谱的总回归强度减弱的越厉害。对于某一标度作用量，在该场的频率的某些特定值处，吸收谱的回归强度不被减弱。这些性质将在第三章中详细讨论。 (2) 计算了Gaussian型单脉冲激光对于吸收谱的影响。结果表明对于单脉冲来说，咏宽越小，吸收谱的振荡越弱，即回归强度越弱。寸吹士学位论文摘要 (3)计算lJi里德堡原子体系的双脉冲激发率(或激发态布居)，证实了脉冲的相位对原子波包之间的干涉起着很重要的作用。另外还研究了双脉冲激光对原子吸收谱的影婀，结果表明，双脉冲更进一步减弱了吸收谱的振荡振幅。 在I_i里德堡原子这一研究领域中，前人的研究仅限于电磁场与时间无关的情况，对十·含时场存在的情况，这是首次进行研究。对于利用短脉冲研究里德堡波包动力学，不文只是进行了初步的探索。我们的工作既是对半经典理论的推广，又是对该理论的验讨一和完善。另外，因为Li原子体系是一个在实验上可以被测量的体系，所以从另一方面来说，我们得到的结果对于实验研究具有重要的参考意义，同时也有助于对更复杂的体系，如He、q体系开展研究。 沦文共分为五章。第一章为综述，主要从总体上介绍了半经典闭合轨道理论的要点及其发展1第二章介绍了闭合轨道理论在射频场中的应用，给出了经过射频场作用以后的吸收谱。第三章引进标度律和回归谱的概念，讨论振荡场振幅以及频率对回归强度的影响。第四章研究激光单脉冲对光吸收谱的影响。第五章研究激光双脉冲激发的波包运动规律，讨论了双脉冲对光吸收谱的影响。更多还原

【Abstract】 Strong resonance structures of photoabsorption spectra of atoms in external fields have attracted much interest in recent years, since they involve many basic questions such as high Rydberg atoms’ structure, the matter diamagnetism in extreme conditions and electron correlation, etc. Semiclassical closed-orbit theory has been extensively used to explain the photo-absorption spectra of atoms in external fields due to its clear physical picture and wide availability. It has been proved to be a powerful tool for studying the quantum manifestations of classical chaos and a typical example for understanding the conception of chaos.In the past years, closed-orbit theory has successfully been applied to H~, H as well as to the highly excited states of the alkali metals atom in various external fields, the validity of the closed-orbit theory has been fully confirmed, and the recurrence spectroscopy, scaling property and energy statistics have also been developed. In recent years, Absorption properties of atoms in Time-dependent oscillation external field (radio frequency field) have been noticed because it is universal that many scientific experiences and applications involve time-dependent fields. However, when takes time-dependent field into account, the initial and final angles, the period of each closed orbit and the classical action will change which make the problem complicated because the effect of radio frequency field. New modulation phenomena are produced then. In addition, when the external laser pulse is not continuous but limited single pulse or double-pulse, closed-orbit theory cannot applied at first hand and must be modified because of the relationship of the calculational precision of photoabsorption spectra and the pulse width.In this submitted work, we take Li system for example and use both semiclassical closed-orbit theory and time-dependent perturbation method to study the photoabsorption spectra of Li in a radio frequency field and laser pulse field and analyze those properties respectively. The main work is as follows:(1) Using perturbation theory based on semiclassical closed-orbit theory, we discuss the photoabsorption spectra of Li Rydberg atom in radio frequency field. We extend closed-orbit theory to the instance of time-dependent external fields and also study corresponding scaled variable spectra ?recurrence spectra .The results show that the amplitude and frequency are both affect recurrence strength greatly, but the rule and pattern of the effects are different. The more large amplitude of the oscillation field is, the more it weakened the recurrence strength. While recurrence strength are not weakened at some special frequencies. These properties will he discussed at length in the third chapter.(2) We calculated the effect of the Gaussian-shaped single pulse laser on the absorption spectra. The results show that the smaller the pulse width, the weaker the oscillation is.(3) We calculated the population of double-pulse population of Li atom and the results prove the important role of the pulse phase difference in the interference of Rydberg wave packets. Double-pulse laser decreases the amplitude of oscillation in photoabsorption spectra much more.In the case of Li Rydberg atom, different from the formers’ works, which are approached the atoms only in the time-independent electric and magnetic fields, this thesis study the photoabsorption spectra in time-dependent fields. For the study of Rydberg wave packet dynamics using laser pulses, this thesis is still in the beginning stage. Our work are not only the extension but also the validation and supplement for the original closed-orbit theory. Moreover, our results possess an important insight for experiment research and for theinvestigating of the systems that are more complicated, such as He and 0. systems, etc.This thesis is divided five chapters. The first chapter is summarization, which chiefly introduces the development of semiclassical closed-orbit theory. The second chapter introduces the application of closed-更多还原