X-ray absorption spectroscopy with an X-ray free electron laser : nonlinear and ultrafast effects in solids
Abstract/Contents
- Abstract
- X-ray absorption spectroscopy provides element-specific information about local electronic structure through the photon energy and polarization dependence of the X-ray absorption coefficient in the vicinity of core-to-valence resonance energies. When using circular polarization, this technique also provides magnetic sensitivity through X-ray magnetic circular dichroism. With the advent of X-ray free electron lasers, it has become possible to perform high resolution X-ray absorption spectroscopy studies with femtosecond time resolution and intensities high enough that nonlinear X-ray effects are important. In this dissertation, we describe our development and use of X-ray magnetic circular dichroism absorption spectroscopy at the Linac Coherent Light Source X-ray free electron laser at SLAC. After describing the implementation of this technique, we briefly describe its application to studies of ultrafast optically-induced magnetic and electronic dynamics in a few magnetic metals of current technological interest. Next, we present X-ray-intensity-dependent measurements of X-ray absorption near the Co L3 edge of Co/Pd magnetic multilayers. The polarization-dependent intensity of the Co L3 absorption resonance changes significantly with increasing incident X-ray flux. These changes depend on the pulse length and photon energy content of the incident X-ray pulses. For monochromatic 40 fs duration X-ray pulses with fluences near the sample melting threshold, the fluence-dependent changes in resonant X-ray asborption are attributed to decreased population of the Co valence states below the Fermi level, and increased population of the Co valence states above the Fermi level. They can be accounted for by reshuffling of electrons from below the Fermi level to above the Fermi level caused by inelastic scattering of photoelectrons and Auger electrons. In this experiment, we also observe a decrease of the X-ray magnetic circular dichroism strength with increasing X-ray intensity, which can be attributed to X-ray-induced demagnetization within the X-ray pulse duration. With wide bandwidth X-ray pulses of about 5 fs and 25 fs duration and fluences many times the sample melting threshold, we observe even stronger fluence-dependent X-ray absorption changes. Some of the observed changes can be assigned to stimulated resonant inelastic X-ray scattering. This constitutes the first observation of this effect in a solid. Our studies pave the way for more sophisticated nonlinear X-ray measurements of solids which are envisioned to provide new insight into their properties.
Description
| Type of resource | text |
|---|---|
| Form | electronic resource; remote; computer; online resource |
| Extent | 1 online resource. |
| Place | California |
| Place | [Stanford, California] |
| Publisher | [Stanford University] |
| Copyright date | 2018; ©2018 |
| Publication date | 2018; 2018 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Author | Higley, Daniel Jeremy |
|---|---|
| Degree supervisor | Reis, David A, 1970- |
| Degree supervisor | Stöhr, Joachim |
| Thesis advisor | Reis, David A, 1970- |
| Thesis advisor | Stöhr, Joachim |
| Thesis advisor | Huang, Zhirong, 1968- |
| Degree committee member | Huang, Zhirong, 1968- |
| Associated with | Stanford University, Department of Applied Physics. |
Subjects
| Genre | Theses |
|---|---|
| Genre | Text |
Bibliographic information
| Statement of responsibility | Daniel Jeremy Higley. |
|---|---|
| Note | Submitted to the Department of Applied Physics. |
| Thesis | Thesis Ph.D. Stanford University 2018. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2018 by Daniel Jeremy Higley
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
Also listed in
Loading usage metrics...