Light-Matter Interaction of Molecules with Intense Ultrashort Laser Pulses

Over the last few decades, laser technology has greatly advanced resulting in high intensity
ultrashort laser pulses operating at many frequencies, which have made a huge impact in the
field of Atomic, Molecular and Optical Physics. As a result of these advances, new phenomena
have been discovered and studied in atoms such as high harmonic generation, multiphoton and
above-threshold ionization, among many more. While methods have been developed to study such
phenomena, such as the strong-field ionization, and the tunneling ionization models, these models
fail to properly describe the interaction between high intensity ultrashort laser pulses and molecules
due to their complex multielectron nature, and extra degrees of freedom.
In this thesis we apply time-dependent density functional theory, optical Bloch equations, and
Floquet theory to study the interaction of high intensity ultrashort laser pulses with molecules in the
context of high harmonic generation, strong field ionization and nonadiabatic electron localization.
Based on our numerical results we analyze new features in high harmonic spectra of molecules such
as the ellipticity of generated harmonics in CO2, as previously measured in experiments, and the ++
appearance of Mollow sidebands in the respective spectra of N2 and C2H4 . We also consider the modification of harmonic spectra by the interaction of two linearly polarized pulses and two circularly polarized pulses interacting with molecules. We then look into the effects of a laser induced coupling of orbitals in the context of ionization and show that as a result of the coupling, ionization contributions from inner shell orbitals are greatly enhanced. We also consider how the addition of a second linearly polarized pulse affects the ionization of molecules. Lastly, we study the effects of electron localization via the laser induced coupling of orbitals for the interactions between molecules and lasers in the context of time-dependent density functional theory and Floquet theory.
Year of Publication
Academic Department
Department of Physics
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Date Published
University of Colorado Boulder
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