Doctoral Dissertations


“Fundamental atomic processes such as collision-induced ionization are of relevance in many scientific fields. Describing these reactions can still pose a substantial challenge due to the well-known “few-body problem”, which entails that there is no analytical solution of the equations of motion for systems of more the 2 mutually interacting particle. Novel experimental tools and advancements in theorical methods enable to obtain detailed information on atomic dynamics providing insight into both, the phase as well as the amplitude of the quantum-mechanical wave functions of the particles. In this project, we developed experimental techniques studying multi-photon ionization of lithium in femto-second laser fields. A lithium target is prepared either in the polarized 2p (m = +1) state or in the unpolarized 2s ground state. The target is ionized in the laser field by the absorption of two, three, or four photons, and the energy and angular distributions of the emitted electrons are measured. For these relatively simple systems, several fundamental features are observed: First, polarizing the atoms before ionizing them changes the symmetry of the reaction and shifts in the photo-electron angular distributions are observed. This symmetry breaking process is called Magnetic Dichroism, and we explained it by the interference of partial waves with asymmetric distribution of magnetic sub-levels in the final state. Second, the experimental spectra are revealing violations of the lowest-order perturbation theory even at very low laser intensities, where this theoretical method is typically believed to describe the process well. This indicates that in many situations more advanced descriptions are required. And third, the simultaneous measurement of the ionization from the 2s and 2p states enables to extract final state phase information in a very intuitive way using a “double-slit” picture. The new results show very clean and fundamental realizations of quantum mechanical effects, and they help to improve our understanding of mechanisms and symmetries in light-matter interaction”--Abstract, page iv.


Fischer, Daniel

Committee Member(s)

Schulz, Michael, 1959-
Parris, Paul Ernest, 1954-
Jentschura, Ulrich D.
Madria, Sanjay Kumar



Degree Name

Ph. D. in Physics


The experimental material presented here is based upon work supported by the National Science Foundation under Grant No. PHY-1554776. The theoretical part of this work was funded by the NSF under grants No. PHY-2012078 (M.D. and N.D.) and PHY-1803844 (K.B.), and by the XSEDE supercomputer allocation No. PHY-090031. at the Pittsburgh Supercomputing Center.


Missouri University of Science and Technology

Publication Date

Fall 2021

Journal article titles appearing in thesis/dissertation

  • Magnetic dichroism in the few-photon ionization of polarized atoms
  • Two-path interference in the resonance-enhanced few-photon ionization of atoms


ix, 70 pages

Note about bibliography

Includes bibliographic references.


© 2021 Bishnu Prasad Acharya, All rights reserved.

Document Type

Dissertation - Open Access

File Type




Thesis Number

T 11934

Electronic OCLC #