Development and application of extreme ultraviolet light sources - harnessing novel geometries of high-harmonic generation and using photoelectron spectroscopy to study nanoparticle dynamics

High-harmonic generation (HHG) is an extreme nonlinear optical process, in which visible femtosecond laser light is coherently upconverted to produce ultrashort pulses of extreme ultraviolet (EUV) or soft x-ray radiation. In this thesis, I describe both the development of new HHG sources and the application of HHG to study nanoparticle structure and dynamics. In the first section of this thesis, I discuss the development of novel geometries of HHG that enable the production of EUV light with controllable polarization. In these geometries, either two driving lasers or two highharmonic sources are combined to give greater control over the HHG process and the resulting HHG beams. In addition to control over the polarization state, the specific geometry can have significant ramifications on the macroscopic physics or phase matching of HHG and therefore substantially modify the experimental conditions at which HHG is optimized as compared to traditional singlebeam HHG. In the second section of this thesis, I will discuss using photoelectron spectroscopy to study the electronic structure and dynamics of nanoparticles. Using a nanoparticle aerosol source we were able to introduce nanoparticles of varying compositions into a photoelectron spectrometer. I will describe several experiments studying first the electronic structure and coupling of excitons in quantum dots (semiconductor nanocrystals) and then the properties and dynamics of hot electrons in nanoparticles with a wide array of compositions - ranging from ionic crystals to nanodroplets of organic liquids. The findings presented in this thesis will guide future efforts to extend the capabilities of EUV sources, develop nanoparticle-based devices, and understand how highly excited electrons behave in unconventional and previously inaccessible materials.