Electron Dynamics Driven by Intense Coherent Femtosecond Laser Pulses: Dynamic Interference in Atoms and Photoelectron Circular Dichroism in Chiral Molecules
Since humans have begun to explore nature, they came up with new ways and tools, which have been permanently improved. At some point, those tools allowed to look into the microworld and to study the quantum nature of matter. One of such tools to explore the quantum world is the light amplification by stimulated emission of radiation (laser). Since the first lasers were built almost 60 years ago, their capabilities improved permanently, allowing the study of hitherto-unknown physical phenomena. Two of such phenomena, the dynamic interference and the multiphoton photoelectron circular dichroism (PECD), are the subjects of the present theoretical work. The dynamic interference appears when matter is exposed to intense coherent laser pulses. It is an analogy of the double-slit experiment in time, when two photoelectron wave packets of the same kinetic energy emitted at different moments in time along the pulse superimpose. The resulting interference patterns in the electron spectra are well understood theoretically, but an experimental verification of this effect is still absent. In this work, two open tasks relevant for the theoretical description of the dynamic interference are studied. The first task is to investigate the dynamic interference for systems, which are amenable to experiments at modern laser facilities. The second task is to reinvestigate available theoretical results, which were obtained with simple models, by numerically exact methods. For this purpose, a new method, the time-dependent single center method (TDSC), was developed and tested as a part of this work. The TDSC method solves the time-dependent Schrödinger equation in spherical coordinates for single-active-electron or two-electron wave packets driven in an ionic potential by a laser pulse. It is also used in this work to study the multiphoton PECD in the electron spectra of chiral molecules in the single-active-electron approximation. The PECD is the difference of the angular emission distributions of electrons emitted by chiral molecules ionized by right-and left-handed circularly polarized light, and it consists in the forward/backward asymmetry in the photoelectron emission. The PECD is extensively studied in the one-photon ionization regime, both, experimentally and theoretically. For the multiphoton ionization, many new experiments are available, but a reliable quantitative theoretical interpretation of those observations is still missing. In order to explain available experimental results, in this work, the TDSC method is first tested on the model methane-like chiral system and then applied to study the three- and four-photon PECD in real chiral molecules Camphor and Fenchone.
@phdthesis{doi:10.17170/kobra-2018121761, author ={Müller, Anne Dorothee}, title ={Electron Dynamics Driven by Intense Coherent Femtosecond Laser Pulses: Dynamic Interference in Atoms and Photoelectron Circular Dichroism in Chiral Molecules}, keywords ={530 and Femtosekundenlaser and Interferenz and Elektrodynamik and Chiralität}, copyright ={http://creativecommons.org/licenses/by-nc-nd/3.0/de/}, language ={en}, school={Kassel, Universität Kassel, Fachbereich Mathematik und Naturwissenschaften}, year ={2018-12} }