Coherent Multidimensional Spectroscopy: Development of Efficient Data Acquisition and Analyses of Quantum Dot 2D Spectra

Sammanfattning: Coherent multidimensional spectroscopy (CMDS) is the most complete nonlinear optical technique based on the interaction of multiple short laser pulses with matter. It has grown to play a significant role in studies of optoelectronic materials and pigment protein complexes. In this work we apply CMDS to investigate electronic excitations and their dynamics in semiconductor nanocrystals, so called quantum dots (QDs). We also apply modern sparsed sampling algorthms to speed up the data collection in the multidimensional experiments. We test the new methods on CMDS experiments on photosynthetic light harvesting complexes. In CMDS spectral information is spread in multiple, typically two, dimensions. Such 2D spectra depend on time providing information about dynamics of the processes, both coherent and incoherent. The 2D view enables disentangling spectral features and dynamics which otherwise would be left “behind” the simple 1D spectra and thereby not visible in simpler low-dimensional representation. In this thesis, we focus on the dynamics and data acquisition of CMDS from five aspects: the excited state dynamics in CdSe QDs at 77 K studied via two-color 2D spectroscopy; the quantum beating of CdSe QDs using 2D electronic spectroscopy (2DES); quantum size effects of CdSe QDs in CMDS; electron-phonon coupling in perovskite nanocrystals, and sparse sampling in the CMDS implemented via the theory of compressed sensing. Specifically, we characterize the details of the relaxation dynamics of CdSe QDs through two-color 2D Spectroscopy. The beating 2D signal was analysed in terms of coherent LO-phonons of CdSe QDs. Besides, the correlation between the excited state energies and the size of CdSe QDs due to the quantum confinement is also analyzed at 77 K via the 2DES. The phonon coupling with excitons and free carriers in perovskite nanocrystals is characterized. Finally, the compressed sensing theory is used to reconstruct the fluorescence detected 2D spectra of the photosynthetic LH2 complexes.