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Attosecond Transient Absorption of Solid-State and Phase-Change Materials Attosecond Transient Absorption of Solid-State and Phase-Change Materials By Marieke Faye Jager A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Chemistry in the Graduate Division of the University of California, Berkeley Committee in charge: Professor Stephen R. Leone, Co-Chair Professor Daniel M. Neumark, Co-Chair Professor Eric Neuscamman Professor David Attwood Fall 2017 Attosecond Transient Absorption of Solid-State and Phase-Change Materials Copyright 2017 by Marieke Faye Jager Abstract Attosecond Transient Absorption of Solid-State and Phase-Change Materials by Marieke Faye Jager Doctor of Philosophy in Chemistry University of California, Berkeley Professor Stephen R. Leone, Co-Chair Professor Daniel M. Neumark, Co-Chair 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. 1 To my family i Contents List of Figures ................................................................................................................................ v List of Tables ............................................................................................................................... vii Table of Acronyms ...................................................................................................................... vii Acknowledgements .................................................................................................................... viii Chapter 1. Introduction .............................................................................................................. 1 1.1 Ultrafast and attosecond spectroscopy ................................................................................. 1 1.1.1 The Pump-Probe Technique ........................................................................................... 1 1.1.2 High harmonic generation .............................................................................................. 3 1.1.3 Isolating Attosecond Pulses: Gating Techniques ........................................................... 4 1.1.3 Applications of attosecond pulses and pulse trains ........................................................ 5 1.2 Core-level Spectroscopy and Electron Correlation in Solids ............................................... 6 1.2.1 Electronic structure of solids .......................................................................................... 6 1.2.2 Core-level transitions in solids: X-Ray Absorption ....................................................... 7 1.3 Ultrafast processes in semiconductors and strongly correlated materials ........................... 8 1.3.1 General ultrafast processes in semiconductors ............................................................... 8 1.3.2 Ultrafast processes in strongly correlated materials: the insulator-to-metal phase transition .................................................................................................................................. 9 Chapter 2. Experimental apparatus for attosecond transient absorption of solids ............. 12 2.1 Introduction to the Apparatus ............................................................................................. 12 2.1.1 Purpose and Motivation ................................................................................................ 12 2.1.2 Experimental overview ................................................................................................. 14 2.2 Custom Diagnostics and Capabilities Introduced .............................................................. 15 2.2.1 Optical Static Transmission Measurements ................................................................. 15 2.2.2 XUV Static Absorption Measurements ........................................................................ 16 2.2.3 Spatial and Temporal Stabilization for 48-Hour Measurements .................................. 17 2.2.4 Sample Raster Scanning and Rotation.......................................................................... 19 2.3 Heat Transfer in VO2 Thin Films ........................................................................................ 20 2.3.1 Experimental Measurements ........................................................................................ 20 2.3.2 Simulations ................................................................................................................... 21 2.3.3 Conclusions .................................................................................................................. 25 ii Chapter 3. Few-Femtosecond Extreme Ultraviolet Transient Absorption of the Insulator- to-Metal Phase Transition in Vanadium Dioxide .................................................................... 26 3.1 Introduction ......................................................................................................................... 26 3.1.1 Motivation .................................................................................................................... 26 3.1.2 Background Information............................................................................................... 27 3.1.3 Experimental Scheme and Measurement Details ......................................................... 28 3.2 Static Spectrum Measurements and Simulations ................................................................ 32 3.2.1 Static Spectrum Measurement ...................................................................................... 32 3.2.2 Atomic Multiplet Simulations ...................................................................................... 33 3.3 Transient Absorption Measurements .................................................................................. 34 3.3.1 Transient Absorption Measurement Details ................................................................. 34 3.3.1 Transient Absorption Measurement Results................................................................. 35 3.3.2 Dynamics in the Insulating and Metallic Phases .......................................................... 36 3.3.3 Discussion of Results .................................................................................................... 39 3.4 Supporting Information ....................................................................................................... 41 3.4.1 Sample Characterization ............................................................................................... 41 3.4.2 in Situ Pulse Characterization....................................................................................... 43 3.4.3 Data Analysis and Fitting Methods .............................................................................. 45 3.4.4 Fluence Dependence ..................................................................................................... 47 Chapter 4. Optical Design of an Endstation for Attosecond-Pump Attosecond-Probe Experiments ................................................................................................................................. 49 4.1 Introduction to the Project .................................................................................................. 49 4.1.1 Motivation and Project Goals ....................................................................................... 49 4.2 Required Capabilities and Overview of Optical Elements.................................................. 51 4.2.1 Required Capabilities ..................................................................................................
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