UC Berkeley

The creation of attosecond pulses using high harmonic generation (HHG) to produce extreme ultraviolet light (XUV) pulses has enabled table-top core-level spectroscopy in both the gas and solid phase. Because HHG relies on a near infrared (NIR) driver pulse to create the XUV radiation, it is readily incorporated into pump-probe transient absorption and photoelectron spectroscopy experiments, giving way to measurements with unprecedented temporal resolution. The ability of attosecond XUV pump-probe spectroscopy to study solid state semiconductor materials allows for the interrogation of carriers on the timescales where a separation between electronic and lattice dynamics can occur. This will have far reaching implications addressing the fundamental carrier physics that govern the next generation of hot carrier charge transfer devices, which are at the forefront of photocatalytic and electronic device development.

In this dissertation, a literature review of XUV transient absorption on solids using HHG is presented in Chapter 1. This chapter details the progress from femtosecond experiments on metal-oxide thin films to attosecond time-resolved experiments on semiconductors. In Chapter 2, the design and construction of the attosecond transient absorption apparatus capable of studying ultrafast dynamics in both solid state and gas phase samples using a near infrared (NIR) pump and an extreme ultraviolet (XUV) probe is presented. Chapter 3 presents transient absorption experiments done on germanium thin films, which measure both electrons and hole dynamics simultaneously in a single measurement. These results are supported by work from a theory collaboration. in Chapter 4, preliminary work on silicon germanium alloys is presented. While the results need further confirmation by additional experiments and characterization, it is clear that signals from hot carrier relaxation are present. Chapter 5 presents a theoretical investigation of a future experiment on silver nanoparticles using a velocity map imaging (VMI) device. The key feature of this theoretical study is the identification of a metric to follow the near-field of the plasmon, isolated from the electric field of the exciting laser pulse.