What is your thesis about?
"My thesis focuses on the theoretical study of photoionization, which is the process of atoms absorbing light and releasing electrons. Specifically, I investigate multiphoton ionization, where atoms release electrons after absorbing many photons from the light field.
These bursts can be as short as a few femtoseconds (quadrillionths of a second) or even attoseconds (quintillionths of a second). In my thesis work, I primarily examine noble gas atoms, such as helium or neon, that are exposed to extreme-ultraviolet light while also being influenced by an infrared light field. The extreme-ultraviolet light transfers energy to the atoms, causing them to eject electrons. At the same time, the presence of the infrared light field affects the
dynamics of the process, either by probing or disturbing the behaviour of the atoms and the outgoing electrons.
By delving into the theoretical aspects of photoionization and studying the response of atoms to different types of light, I aim to enhance our understanding of the fundamental interactions between light and matter. I hope that my research will provide insights into the intricate processes that occur at the atomic level when light interacts with atoms, contributing to the broader field of atomic physics."
Why did you choose this particular topic?
"I chose this topic because it combines theoretical work, computer simulations, which suited my background in engineering physics where I specialized in computational sciences. The opportunity to engage in both pen-and-paper analysis and computational modelling was intriguing to me. Additionally, the active collaborations between theory and experiment in Lund and the vibrant global community surrounding this topic were highly valued and served as a great source of inspiration throughout my thesis work."
What is the most important result from your thesis?
"The thesis presents several significant findings that have the potential to inspire future research. In our fourth paper, we investigated periodic population transfer, known as Rabi oscillations, between the ground state and an excited state in helium. Utilizing a free-electron laser at FERMI, we directly probed these dynamics in the energy domain. Surprisingly, we observed that ionization occurred from both the excited state and the ground state to a similar degree, challenging previous assumptions and opening up new avenues for exploration."
Another noteworthy result is the prediction of laser-assisted dynamical interference. This phenomenon occurs when an electron, ejected from an atom under the influence of a strong infrared field, interferes with itself at two different times due to the impact of the infrared field on atomic potentials. While similar interference has been previously studied theoretically using only the ultraviolet field, our research has revealed the crucial role of the assisting laser field. These findings shed light on the intricate dynamics of photoionization and offer valuable insights into the behaviour of atoms under the influence of intense light pulses. They expand our understanding of the underlying principles and phenomena governing these processes, paving the way for further investigations and potential applications in the field of attosecond science."
What do you hope your thesis will lead to?
"I hope that the implemented theoretical framework, known as surface methods, that allows the study of photoelectrons and which we have used to study the photoionization of atoms, will be applied to more complex systems such as molecules. I also hope that the theoretical predictions will lead to new interesting experiments."
What will you do when you have finished your dissertation?
"In the near future, the surface methods are now being prepared for release under a permissive license. My next employment will involve implementation of science in society, and I am happy to see how the understanding of the physics of attosecond science grows and look forward to see technology form based on this knowledge."
Why is it important to do research?
"Applied or basic, it expands our ideas of what is possible."
Dissertation
Mattias Bertolino defended his thesis on the 26 of May. It is titled:
"Applications of time-dependent configuration-interaction singles for photoelectrons in attosecond and free-electron laser sciences"
Mattias Bertolino's thesis is available at the Lund University Research Portal
Paper IV: S. Nandi et al., Observation of Rabi Dynamics with a Short-Wavelength Free-Electron Laser, Nature 608, 7923 (2022).
Link to the article on Nature´s website
Paper VI: M. Bertolino, S. Carlström, J. Peschel, F. Zapata, E. Lindroth, and J. M. Dahlström, Thomas--Reiche--Kuhn Correction for Truncated Configuration-Interaction Spaces: Case of Laser-Assisted Dynamical Interference, Phys. Rev. A 106, 043108 (2022).