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A Study of Dynamic Properties of the Rydberg Wave Packet Generated by a Short-pulse Laser in External Fields

Author: LiYing
Tutor: LinShengLu
School: Shandong Normal University
Course: Atomic and Molecular Physics
Keywords: Semiclassical closed-orbit theory Time-dependent perturbation Short-pulse laser Rydberg wave packet Autocorrelation function.
CLC: O562
Type: Master's thesis
Year: 2006
Downloads: 24
Quote: 2
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Abstract

In atomic physics, the field of quantum control of electronic wave packet in Rydbergatoms has burgeoned since the nineties of the twentieth century. A common element ofwork in this field is to use short laser pulses to create an electronic wave packet consistingof series of high Rydberg states. Wave-packet states in Rydberg atoms are a matter ofcurrent experimental and theoretical study due to their usefulness for studying theclassical limit. As the rapidly development of laser and locked-phase pulse technology, theinterplay of Rydberg atoms in external fields and a short-pulse laser has become animportant measure. Various theories and experiments about mutual-interference controlhave produced along with the above development, such as pump-probe technique,locked-phase pulse technology and Rydberg wave-packet interferometer which associateswith semiclassical theory. Wave-packet states in Rydberg atoms is the radial wave packetexcited with a short laser pulse under without external fields present. The wave packetmoves along its almost-classical trajectory in short time. However, after a long while, theevolution of the wave packets will become extraordinary complex because wave packetsmay split and recombine coherently during their propagation. The dynamic properties ofwave packets in real atomic systems, therefore, are quite complicated. The use of wave packet dynamics to analyze the quantum mechanical systems is alsoan increasingly important aspect of the study of the classical-quantum interface. Theautocorrelation function is a quantity that reflects the underlying dynamics of the wavepacket. Furthermore it is an experimentally measurable quantity. Consequently how tocalculate autocorrelation function in these systems becomes an urgent theoretical problem.There have many methods to calculate the autocorrelation function. The apparent methodfor the computing the autocorrelation function is first to represent the wave packet of timet as the superimposition of high exited eigenstates and then to evaluate the overlapintegral. In practice, however, only a few special cases can use this method. Anothermethod is time-dependent semiclassical propagation, in which the wave packet isrepresented by a sum of little train of waves, and these wavelets are propagated directly.This method has been used to obtain the autocorrelation function of a stadium system.In this thesis, we study the autocorrelation function for atoms or ions in external fields.The results prove that the autocorrelation function can be written as a sum of modifiedGaussian terms whether the wave packet is generated by a single-pulse laser or adouble-pulse laser. Each modified Gaussian term comes from a parent oscillation in theoscillator-strength density and is characterized by a set of parameters including its centerposition, height, width, delayed time and other properties.For the study of H Rydberg wave packet dynamic properties using Rydberg atoms inexternal fields and a short-pulse laser, this thesis allows us further exploratorydevelopment on the base of the anterior work. Our work are not only the extension butalso the validation and supplement for the primitive closed-orbit theory. Our resultspossess an important insight into experiment research and the investigating of the systemsthat are more complicated, such as He and alkali metals atoms systems, etc.This submitted work consists of five chapters. The first chapter is the introduction,which displays briefly the development of semiclassical closed-orbit theory and wavepacket dynamics theory, that the reasons why we choose the subject and the main workwe have done are also mentioned. The second chapter presents the physical picture of theRydberg wave packet in external fields and several methods which are used to calculatethe autocorrelation function of Rydberg wave packet. We also quote the concept of scaledlaw in this chapter. In chapter three we express the autocorrelation function in terms of anintegral involving the oscillator-strength density and the Fourier transform of theshort-pulse laser and derive the general formula for the autocorrelation function of foratoms and ions in external fields by using semiclassical closed-orbit theory combinedwith time-dependent perturbation theory. In chapter four, we take H Rydberg atoms inmagnetic field for example and use the formula which we derived in chapter three tostudy the time dependence of the absolute value of the autocorrelation function, insingle-pulse laser instance. We discuss the effect of the pulse width on the autocorrelationfunction. In the last chapter, we respectively discuss the effect of time delay and laserphase parameter on the autocorrelation function, in double-pulse laser instance.

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