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Title: Control of nonlinear laser pulse propagation in plasma with strong magnetic fields
Author: Wilson, Thomas Cunningham
ISNI:       0000 0004 8509 5060
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2020
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We examine nonlinear laser pulse dynamics in plasma, encompassing both transverse and longitudinal envelope effects, in isolation and when coupled by the plasma. This is underpinned by an interest in how strong magnetic fields, aligned along the laser axis, modify these processes. In the presence of a strong magnetic field, such that the electron cyclotron frequency is on the order of the laser frequency, there is dramatic modification to the laser-plasma interactions, with the electron motion under left circularly polarised light remaining weakly-relativistic-like at laser intensities typically associated with fully-relativistic behaviour. Conversely right circularly polarised light sees the opposite effect, with the laser-plasma interactions becoming nonlinear at much lower light intensities. This affects all processes underpinned by relativistic motion of the electrons, chiefly self-focusing and self-compression. Such processes are studied in detail for both unmagnetised and magnet ised plasma, and the results are compared. We find that not only does an external field alter the relativistic response of the electrons, but it also modifies the laser group and phase velocities, making the pulse shape of interest to the envelope dynamics. We apply this to study spherical compression of a laser pulse, wherein the pulse dimensions reduce symmetrically towards a single cycle. This process results in greatly amplified single-cycle pulses in the lambda-cubic regime, which may peak at over 100 times the initial laser intensity. Finally, the process by which a fully relativistic pulse may amplify an existing magnetic field is examined. We find that while this effect is known of for Laguerre-Gaussian light, it can also occur for linearly polarised light. The pondero motive effect of the laser, and the external field trapping particles which would otherwise escape, bends their trajectories such that a self-sustaining azimuthal current forms. This current scales with both laser intensity and plasma density, and may produce fields of up to 10 kilotesla. We offer that this work may be of interest for the manipulation of low-power or long-wavelength lasers in underdense plasma, the generation of single-cycle pulses for high-harmonic generation and the generation of localised,quasistatic ultra-intense magnetic fields.
Supervisor: McKenna, Paul ; Sheng, Zhengming Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral