UC Berkeley

The advent of attosecond pulse duration light sources has enabled the study of fundamental light-matter interactions. Condensed matter systems are of particular interest, as they are often significantly impacted by many body interactions, and thus provide a natural environment for the observation and study of such interactions in the time domain. In this dissertation, an apparatus for extreme ultraviolet (XUV) transient reflectivity is described, and several studies on ultrafast dynamics in solids are performed. In the first chapter, background on ultrafast spectroscopy, light matter interaction, and reflection from surfaces is provided, giving the necessary underpinnings for the subsequent discussion. In the second chapter, the development and capabilities of the constructed XUV transient reflection apparatus are reviewed. Additionally, the static refractive index of germanium (a commonly employed semiconductor), is recovered from multi angle reflection measurements. In the third chapter, femtosecond dynamics in germanium are studied by XUV transient reflection. The results are analyzed and interpreted in the context of the existing optical literature. In the fourth chapter, preliminary attosecond resolved measurements in germanium are presented, and the results are tentatively interpreted in the context of light dressed states. In the fifth chapter, attosecond dynamics of core excitons in magnesium oxide (MgO) are studied. The results are analyzed and interpreted as a light induced modification of excitonic coherence. This body of work is intended to establish XUV transient reflectivity as a technique for study of solid-state systems and to provide example studies in two representative systems, a semiconductor and an insulator.