Theoretical study of non-relativistic electron dynamics under intense laser fields

SFA;ATI;HHG;TDSE;Physics

Long, Zijian

University of Waterloo

关键词: SFA;    ATI;    HHG;    TDSE;    Physics;   

Others  :  https://uwspace.uwaterloo.ca/bitstream/10012/6604/1/Long_Zijian.pdf

瑞士|英语

来源: UWSPACE Waterloo Institutional Repository

【 摘 要 】

Strong field approximation (SFA) is the most important approximationin the analytical theory of intense laser matter interaction.Basedon SFA many analytical theories have been developed such that abroad spectrum of strong field physics phenomena can be described.The central idea of SFA-based theories is to approximate theelectron propagation in the continuum by the Gordon-Volkovwavefunction - a well studied analytical solution to the time-dependent Schr;;{o}dinger equation where the electron is driven by thelaser field only. This approximation captures some of the essentialfeatures of strong-field physics, but at the same time causes several problems in the theory. In this thesis a comprehensive study of the SFA hasbeen presented. We introduce the SFA in both the length gauge and thevelocity gauge. The adequacy of SFA has been discussed by comparing the theory to the numerical solution tothe time-dependent Schr;;{o}dinger equation (TDSE). The numerical method of solving TDSE ispresented as a separate chapter.In order to obtain a betterunderstanding of the applicability of SFA-based theory, we tested the major approximations in the theory by usingthree different models: the zero-range potential, the hydrogen atom andthe hydrogen molecular ion. The accuracy of the method of steepest descent (MSD)and other major approximations in the analytical theory havealso been examined. Targeting at the generalization ofthe SFA-based theories, several extensions and improvements of SFAhave been proposed. We will review them in detail and bring theminto unity.One of the most successful aspect of the SFA-based theories is todescribe and decompose electron dynamics into components such thatidentification of different physical processes becomes possible. Forinstance, the direct ionization and non-sequential double ionizationbear clear definitions only within the SFA-based framework. Thephysical interpretation becomes more straight forward due to thefact that there is a close connection between the quantum orbitaland classical trajectory. The MSD is amathematical tool to bridge the quantum orbital and the classicaltrajectory in an SFA-based theory. We will discuss MSD within asystematic framework so that the higher order asymptotic expansionterms can be obtained in a straight forward way.After gaining substantial understanding of the SFA and the MSD we developeda graphic user interface (GUI) software that is capable ofcalculating strong field ionization rates, photo-electron spectraand high harmonic generation spectra. The software interface andalgorithms have been presented in the thesis. Sample calculationswere done and compared with the previously obtained results.In the last chapter of the thesis, we further developed the theory todescribe a two-laser ionization scheme where one laser is chosento be resonantly coupled two real states and the other is a strongfew-cycle laser pulse. We demonstrate the periodic dependence of thetotal ionization on the appearance time of the strong few-cyclelaser pulse. In the case of few-cycle pulses with lower intensity,we observed side-bands in the photoelectron spectrum, whoseintensity vary periodically with the appearance time of the pulse.We show that our extended theory is able to explain these phenomenaadequately.