Attosecond Transient Absorption of Solid-State and Phase-Change Materials
Attosecond science, utilizing short bursts of extreme ultraviolet light, has opened up a fascinating new field of ultafast light-matter interactions, where dynamics in atomic, molecular, and solid state systems can now be followed on the timescale of electron motion. In this dissertation, applications of attosecond pulses toward performing transient absorption spectroscopy experiments on complex electron-correlation-driven processes in material systems are described. In the first chapter, a brief overview of ultrafast spectroscopy, attosecond pulse production, and light-matter interaction in the extreme ultraviolet is provided, which offers the necessary breadth and background for the detailed case study that follows, on the insulator-to-metal phase transition in vanadium dioxide.
The origin of the bandgap in vanadium dioxide, which is not predicted to exist under conventional single-particle band theories, has been explained as the result of either electron correlation or structural distortion. The goal of the experiments presented herein is to use transient absorption spectroscopy with attosecond pulses to characterize the timescale of this process and gain a mechanistic understanding of how it occurs. Because vanadium dioxide is heat sensitive, an apparatus had to be specifically tailored to this type of experiments, and it is described in the second chapter. The results and analysis, including extreme ultraviolet static and time-resolved measurements on both the insulating and metallic phases, are described in the third chapter.
The second half of this dissertation describes the design and construction of a new vacuum endstation to perform attosecond-pump attosecond-probe measurements, which was constructed and tested at Berkeley and installed at a high power attosecond beamline at the University of Central Florida. Ray tracing simulation and design considerations for the optical layout are described in the fourth chapter, and design of the vacuum endstation, diagnostics, and preliminary experiments and testing can be found in the fifth chapter.