Thesis

Optimisation and measurement of bremsstrahlung and synchrotron radiation in ultra-intense laser-solid interactions

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Awarding institution
  • University of Strathclyde
Date of award
  • 2025
Thesis identifier
  • T17281
Person Identifier (Local)
  • 201887863
Qualification Level
Qualification Name
Department, School or Faculty
Abstract
  • This thesis reports on experimental and numerical investigations to optimise and measure bremsstrahlung and synchrotron x-ray production in ultra-intense lasersolid interactions. The aim of the work is to better understand the processes behind the generation of synchrotron and bremsstrahlung x-rays within laser-solid interactions and to be able to resolve and differentiate between x-ray distributions from such interactions. This study also significantly advances understanding of a key diagnostic for measuring x-ray emission in these interactions. First, a numerical investigation of the influence of laser focal spot size, focusing geometry, and pulse energy on bremsstrahlung and synchrotron x-ray production is presented. PIC simulations indicate that bremsstrahlung emission is highly dependent on pulse energy, whereas synchrotron production is highly spot-size and intensity dependent. An increase in synchrotron photon numbers with small spot size is attributed to greater holeboring for higher laser intensities, as there is a larger volume within which electrons can interact directly with the laser fields Building on this, an experimental investigation of the influence of laser focal spot size, focusing geometry, and pulse energy on electron and bremsstrahlung x-ray production is reported. While the data do not strongly indicate a focusing geometry effect, electron and bremsstrahlung production is found to be highly dependent on pulse energy. This is consistent with the previous numerical results. Finally, the focus moves to the development of x-ray diagnostics which would enable improved measurements of the x-ray spectrum. Measurements of bremsstrahlung x-rays for laser intensities up to 3 × 1021 Wcm−2 were analysed. Such laser intensities were achieved through the use of F/1 focusing plasma optics which enabled higher intensities to be reached than otherwise achievable with the Vulcan laser. Through analysis of these measurements and extensive PIC and Monte Carlo modelling, an existing absorption-based x-ray spectrometer is characterised. It is found that there is a high degree of uncertainty in spectral deconvolution with the current spectrometer design, and several improvements are designed and numerically tested. Additionally, through analysis of the total x-ray spectrometer signal and analytical modelling, with comparison to Cu Kα x-ray measurements, our results suggest the presence of lower fast electron temperatures than many published electron temperature scalings predict. This highlights a critical challenge: the combined effects of low-resolution detector design and unexpected physical behavior complicates x-ray measurements in the high-energy part of the spectrum. Consequently, this thesis work underscores the need for more focused efforts on improving signal-to-noise ratios in this region, for example, through dual-spectrometer designs, to better measure high-energy x-rays.
Advisor / supervisor
  • Gray, R. (Ross) J.
  • Neely, David
  • McKenna, P. (Paul)
Resource Type
DOI
Date Created
  • 2024

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