Coherent, ultrashort IR, UV and X-ray sources for ultrafast spectroscopies
File(s)
Author(s)
Avni, Timur
Type
Thesis
Abstract
I present development of experimental and computational tools for the enhancement of UV pump, X-Ray probe transient absorption spectroscopy (TAS) experiments. Tunable, optimised and well characterised pump and probe pulse sources are critical for these spectroscopies. A 60 fs, 1.5 mJ, 1400 nm pulse is broadened in a tensioned flexible hollow core fibre and characterised with an SHG-FROG. This is used to generate tunable pump pulses in the 250 - 450 nm range using resonant dispersive wave (RDW) emission in a hollow core fibre, with additional apparatus outlined to spectrally filter and characterise the pulses.
Additionally a variable-length cell is constructed to optimise high harmonic generation (HHG) flux. The anticipated harmonic flux from the source is calculated using a (3+1)D SFA code, and a simplified modelling schema is presented for running large parametric scans without the need for costly simulations. These results are put in the context of other recent work in the literature for scaling HHG with pulse energy, gas pressure and interaction length.
The interaction of high peak intensity laser pulses with a liquid jet is also explored, and HHG in the liquid phase is modelled with comparison to recent experimental results. Both investigations here extend the SFA code used for simulating gas phase HHG to account for the effects of a high density medium on both the driving laser and the emitted harmonics.
The ionisation dynamics in the liquid phase are examined, electron scattering rates are found to agree well with literature, and we characterise the formation of a plasma mirror at the jet’s surface. Good agreement is also found between the modelled and experimental HHG in the liquid phase, giving new insight into scattering cross-sections for low energy electrons in liquids, and adding to the limited literature on the mechanics of liquid HHG.
Additionally a variable-length cell is constructed to optimise high harmonic generation (HHG) flux. The anticipated harmonic flux from the source is calculated using a (3+1)D SFA code, and a simplified modelling schema is presented for running large parametric scans without the need for costly simulations. These results are put in the context of other recent work in the literature for scaling HHG with pulse energy, gas pressure and interaction length.
The interaction of high peak intensity laser pulses with a liquid jet is also explored, and HHG in the liquid phase is modelled with comparison to recent experimental results. Both investigations here extend the SFA code used for simulating gas phase HHG to account for the effects of a high density medium on both the driving laser and the emitted harmonics.
The ionisation dynamics in the liquid phase are examined, electron scattering rates are found to agree well with literature, and we characterise the formation of a plasma mirror at the jet’s surface. Good agreement is also found between the modelled and experimental HHG in the liquid phase, giving new insight into scattering cross-sections for low energy electrons in liquids, and adding to the limited literature on the mechanics of liquid HHG.
Version
Open Access
Date Issued
2023-12-12
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)