On 12 December, Vytautas Bubilaitis successfully defended his PhD thesis titled “Spectral Characteristic of Molecular Aggregates at Various Intensities of Optical Fields“. Supervisor - Prof. Dr Darius Abramavičius.
Wishing Dr Vytautas every success in his future career and in the achievements that will shape the future.
Molecular aggregates are versatile systems showing unique electronic excitations and excited state dynamics. Functionally, they are employed by Nature in photosynthetic light harvesting and energy funneling. In specific conditions, the aggregates are formed from synthetic dye molecules thus making a unique playground for design and studies of various quantum phenomena depending on the nature and the number of coupled chromophores. To understand, predict and control their optical properties in various spectroscopy experiments, theory and simulations must be developed and coordinated.
In this thesis, the highly nonlinear effects in nonlinear absorption, pump-probe and 3rd-5th order 2DES spectra of chromophoric aggregates are considered. Spectra are calculated by utilizing nonlinear exciton equations with exciton-exciton annihilation terms for various optical field intensities. We describe how the inclusion of exciton-exciton annihilation terms into nonlinear exciton equations affects the 2D electronic spectra at various levels of wave-mixing. Also compare several factorization types for nonlinear exciton equations for a linear chromophore aggregate from low to high excitation field intensities by calculating the simplest possible absorption spectrum. And study, by calculating pump-probe spectra, the behavior of nonlinear exciton equations solutions with exciton-exciton annihilation terms for J aggregate when restricting the calculations to subsets of excitons.