Relativistic plasma photonics : polarisation control and higher-order mode generation in laser-solid interactions

Bacon, Ewan

Thesis

Relativistic plasma photonics : polarisation control and higher-order mode generation in laser-solid interactions

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Creator

Bacon, Ewan

Rights statement

Strathclyde Thesis Copyright

Awarding institution

University of Strathclyde

Date of award

2026

Thesis identifier

T18167

Person Identifier (Local)

202058747

Qualification Level

Doctoral (Postgraduate)

Qualification Name

Doctor of Philosophy (PhD)

Department, School or Faculty

Department of Physics

Abstract

This thesis reports on experimental and numerical investigations of relativistic plasma photonic effects arising from the interaction of high-intensity (> 1018 W/cm2) laser pulses with solid targets. The work focuses on two themes: the production of frequency-doubled light with higher-order spatial mode structures and the control of the polarisation state of light transmitted through ultra-thin (tens of nanometer) targets. The first investigation explores how aperture targets can be used to generate intense second-harmonic light with structured spatial profiles. Two- and three-dimensional EPOCH simulations identify the target thickness and aperture diameter that maximise conversion efficiency, with the resulting mode shape shown to depend on the laser polarisation. Further improvements were achieved using tapered apertures matched to the convergence angle of the incoming beam. The second study examines practical challenges in producing 2ωL light with aperture targets. Simulations using EPOCH and FLASH are used to explore the effects of plasma forming within the aperture and small misalignments of the laser beam arising from spatial jitter. Both reduce conversion efficiency, but jitter is shown to have more influence, and possible strategies to minimise it are discussed. The third investigation is based on experimental campaign with the Gemini laser, testing the generation of 2ωL light from aperture targets. Measurements of transmitted ωL and generated 2ωL are compared with simulations, confirming that beam jitter and focal-spot quality strongly influence conversion. The results demonstrate the importance of stabilising pointing and preserving high-quality Gaussian beam profiles in future experiments. The final study explores changes to the polarisation of light transmitted through ultra-thin (tens of nanometer) targets irradiated by intense pulses, using the Vulcan laser. A secondary, lower-intensity pulse was used to pre-expand the targets, altering transmission. An unexpected relationship between transmission and polarisation was observed. Comparisons with analytical models suggest that spatio-temporal variations in the transmitted light, combined with diagnostic sub-sampling, explain this effect. These findings highlight the importance of capturing the full transmitted beam when diagnosing polarisation in ultra-thin target experiments. Overall, the research demonstrates how target design, laser stability and diagnostic precision together determine the effectiveness of relativistic plasma photonic control.

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