Following her Trial Lecture on “Formulations of time-dependent variational principles for molecular systems”, Dr. Ofstad defended her PhD thesis in auditorium 1.
The external opponents were Professor Ove Christiansen, Department of Chemistry, Aarhus Universitet, Denmark (https://pure.au.dk/portal/en/persons/ove-christiansen(a6653cc1-29c3-420c-a5ab-cb35eed06fab).html), and Associate Professor Ida-Marie Høyvik, Department of Chemistry, Norwegian University of Science and Technology (https://www.ntnu.no/ansatte/ida-marie.hoyvik). The administrative leader of the adjudication committee was Professor Reidar Lund, Department of Chemistry, University of Oslo, and the Chair of Defence was Professor Steven R.H. Wilson, Department of Chemistry, University of Oslo.
Dr. Ofstad’s work was supervised by Researcher Simen Kvaal (main supervisor) and Professor Thomas Bondo Pedersen, both from the Hylleraas Centre for Quantum Molecular Sciences.
Conferral summary
In the thesis, the candidate has worked on time-dependent electronic structure theory in the time domain to describe linear and non-linear optical properties. In connection with this, the candidate has investigated the potential of dynamic orbitals, the ability to model strong magnetic fields, and methods for extracting higher-order response properties.
Main research findings
Within the field of nonlinear optics, nonlinear optical properties are defined as frequency-dependent responses. This definition emerged in the frequency domain, as lasers used in these early experiments emitted monochromatic continuous waves. This led to the development of time-dependent electronic-structure theory predominantly in the frequency domain, using perturbation-theory based response theory.
However, in recent years, advances in computing power and the advent of ultrashort laser pulses have sparked interest in the time-domain for both electronic-structure theory and nonlinear optics. Time-domain electronic-structure theory provides a time-resolved description of light-matter interaction, closely mimicking experiment. Additionally, they offer the advantage of highly nonlinear responses being straightforward to implement.
This thesis contributes to the field of time-domain time-dependent electronic-structure theory for the description of nonlinear optical properties by:
Investigating the potential of dynamic (time-dependent) orbitals for improving the description of nonlinear optical properties, extending a hierarchy of time-domain time-dependent coupled-cluster methods to accommodate strong magnetic fields, and by developing an efficient approach for extracting higher-order response properties.