A uv-pump x-ray-probe beamline developed for high time resolution measurement and control of photochemical reactions
File(s)
Author(s)
Lee, Jacob
Type
Thesis
Abstract
Over the last 40 years, ultrafast laser spectroscopy has allowed the transient nuclear dynamics of a vast range of photochemical reactions to be observed. However, study of the first few fs electronic dynamics remains out of reach. Much ground has been covered with the creation of attosecond x-ray pulses from high harmonic generation (HHG) and x-ray free electron lasers (XFELs), however the challenge remains with the observation of valence electronic dynamics on the same few-femtosecond timescale. Many of the iconic reactions such as the ring opening of small molecules, photosynthesis, light harvesting in solar cells and vision occur on this timescale. Here, a beamline capable of capturing electronic dynamics is presented. This is achieved by developing pump pulses from resonant dispersive wave (RDW) emission in hollow core waveguides. This is proved capable of producing sub-5 fs pulses continuously tuneable from the deep ultraviolet to the visible. This is combined with isolated attosecond probe pulses from HHG which can measure atomic specific dynamics at energies beyond the C K edge. These two pulses constitute a spectroscopic technique with which valence dynamics can be measured with unprecedented temporal resolution. How the flux and cut-off of the high harmonics have been improved is reported, along with the absorption measurements at several atomic edges. The development of the RDW emission is reported, including its tuneability, pulse energies, delivery method, and pulse durations. The impressive sub-fs stability between each arm is reported. The ability to deliver targets in gas/vapour, solid and liquid/solution phase is presented. Proof of this technique's ability to measure ultrafast photochemical dynamics is given with the x-ray absorption spectroscopy of the photofragmentation of dimethyl disulphide (DMDS). Future plans for this experimental technique include studying the fast ring opening of cyclohexadiene and thiophene with an order of magnitude better resolution than previously reported.
Version
Open Access
Date Issued
2024-06-15
Date Awarded
01/04/2025
License URL
Advisor
Marangos, Jon
Sponsor
Engineering and Physical Sciences Research Council
Publisher Department
Department of Physics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)