Optically levitated targets as a source for high brightness x-rays and a platform for mass-limited laser-interaction experiments
Author(s)
Giltrap, Samuel
Type
Thesis
Abstract
Targets on the scale of the wavelength of an irradiating laser have the potential to couple
very strongly to ultra-short high-intensity laser fields through transient plasma resonances and Mie-like scattering processes, these targets are expected to absorb a significant fraction of the laser energy producing highly energetic x-rays and ions. Compared to bulk targets irradiated under similar conditions, mass-limited micro-targets are predicted to emit significantly higher x-ray photon energies as well as providing an enhancement to the ion acceleration fields. Optical levitation of microtargets enables a new class of experiments, with substantial modification of the charge up and
neutralisation dynamics of a laser-plasma.
Optically levitated targets (10micro-𝑚 droplets of silicon-based oil and ~100micro-𝑚 shells of silver coated glass) were characterised as both an x-ray and ion source. Experiments at low intensity (I ≅
10E17Wcm−2) found a symmetric x-ray source in the 10 - 20micro-𝑚 size range, significantly smaller than comparable stalk mounted targets. This experiment also measured a two-temperature x-ray spectrum with electron temperatures of 0.6KeV and 2.3KeV.
Experiments at the Vulcan facility RAL demonstrated levitated targets displayed a significantly increased front surface ion acceleration when compared to planar targets, with ions reaching energies of ~34M𝑒V whilst planar targets irradiated at a factor of 9 higher intensity produced ~12M𝑒V. The ion distribution from the droplet is found to have a weak preferential direction following the laser propagation axis, compared to planar targets which produce a tight beam emitted normal to the target surface. Several electromagnetic pulse (EMP) diagnostics were fielded; the levitated targets showed no EMP above the noise level of the detector (~40 V/m), stalk mounted targets showed significantly higher signal.
very strongly to ultra-short high-intensity laser fields through transient plasma resonances and Mie-like scattering processes, these targets are expected to absorb a significant fraction of the laser energy producing highly energetic x-rays and ions. Compared to bulk targets irradiated under similar conditions, mass-limited micro-targets are predicted to emit significantly higher x-ray photon energies as well as providing an enhancement to the ion acceleration fields. Optical levitation of microtargets enables a new class of experiments, with substantial modification of the charge up and
neutralisation dynamics of a laser-plasma.
Optically levitated targets (10micro-𝑚 droplets of silicon-based oil and ~100micro-𝑚 shells of silver coated glass) were characterised as both an x-ray and ion source. Experiments at low intensity (I ≅
10E17Wcm−2) found a symmetric x-ray source in the 10 - 20micro-𝑚 size range, significantly smaller than comparable stalk mounted targets. This experiment also measured a two-temperature x-ray spectrum with electron temperatures of 0.6KeV and 2.3KeV.
Experiments at the Vulcan facility RAL demonstrated levitated targets displayed a significantly increased front surface ion acceleration when compared to planar targets, with ions reaching energies of ~34M𝑒V whilst planar targets irradiated at a factor of 9 higher intensity produced ~12M𝑒V. The ion distribution from the droplet is found to have a weak preferential direction following the laser propagation axis, compared to planar targets which produce a tight beam emitted normal to the target surface. Several electromagnetic pulse (EMP) diagnostics were fielded; the levitated targets showed no EMP above the noise level of the detector (~40 V/m), stalk mounted targets showed significantly higher signal.
Version
Open Access
Date Issued
2017-10
Date Awarded
2024-02
Copyright Statement
Creative Commons Attribution NonCommercial Licence
License URL
Advisor
Smith, Roland Adam
Sponsor
Engineering and Physical Sciences Research Council
Atomic Weapons Establishment (Great Britain)
Publisher Department
Physics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)