Type
Text
Type
Dissertation
Advisor
Weinacht, Thomas C. | Schneble, Dominik A. | Dawber, Matthew | Bergeman, Thomas | Baumert, Thomas.
Date
2016-12-01
Keywords
Physics | femtosecond laser, strong-field ionization, velocity map imaging
Department
Department of Physics
Language
en_US
Source
This work is sponsored by the Stony Brook University Graduate School in compliance with the requirements for completion of degree.
Identifier
http://hdl.handle.net/11401/76659
Publisher
The Graduate School, Stony Brook University: Stony Brook, NY.
Format
application/pdf
Abstract
In this thesis, work is presented on molecular strong-field ionization, during which an electron is removed from polyatomic molecules in the presence of strong laser fields. This is a process which is the basis of a number of experimental techniques to uncover electronic dynamics in atoms and molecules on the femtosecond and attosecond timescale. ’Strong’ refers to an electric field strength which leads to a response from the system which can not be modeled perturbatively. These fields can be easily produced in the focus of femtosecond laser radiation, as is done in this work. With the use of velocity map imaging of the photoelectron in coincidence with the fragment ion, multiple ionization–dissociation pathways can be distinguished. It is shown that as opposed to early attempts to model the process, multiple low-lying states are populated in the ion, and also the signatures of multielectron dynamics are revealed. By changing the laser pulse duration from 30 fs to below 10 fs, control is demonstrated over which quantum states of the ion are populated. It is also shown that for pulses shorter than 10 fs (which is a timescale below the shortest vibrational period in molecules), ionization pathways that involve motion of the nuclei are almost completely shut off. Finally, the origin of electrons with <1 meV kinetic energy is discussed. A two-step model is proposed for creating the electrons: the first step is population transfer to high-lying excited states of the neutral molecule by the laser field; the second step is ionization. Different ionization mechanisms are examined and their viability is checked against available data. | In this thesis, work is presented on molecular strong-field ionization, during which an electron is removed from polyatomic molecules in the presence of strong laser fields. This is a process which is the basis of a number of experimental techniques to uncover electronic dynamics in atoms and molecules on the femtosecond and attosecond timescale. ’Strong’ refers to an electric field strength which leads to a response from the system which can not be modeled perturbatively. These fields can be easily produced in the focus of femtosecond laser radiation, as is done in this work. With the use of velocity map imaging of the photoelectron in coincidence with the fragment ion, multiple ionization–dissociation pathways can be distinguished. It is shown that as opposed to early attempts to model the process, multiple low-lying states are populated in the ion, and also the signatures of multielectron dynamics are revealed. By changing the laser pulse duration from 30 fs to below 10 fs, control is demonstrated over which quantum states of the ion are populated. It is also shown that for pulses shorter than 10 fs (which is a timescale below the shortest vibrational period in molecules), ionization pathways that involve motion of the nuclei are almost completely shut off. Finally, the origin of electrons with <1 meV kinetic energy is discussed. A two-step model is proposed for creating the electrons: the first step is population transfer to high-lying excited states of the neutral molecule by the laser field; the second step is ionization. Different ionization mechanisms are examined and their viability is checked against available data. | 85 pages
Recommended Citation
Sandor, Peter, "Molecular Strong Field Ionization viewed with Photoelectron Velocity Map Imaging" (2016). Stony Brook Theses and Dissertations Collection, 2006-2020 (closed to submissions). 2545.
https://commons.library.stonybrook.edu/stony-brook-theses-and-dissertations-collection/2545