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# Under-Dense Laser-Plasma Interactions in Relativistic Optical Vortices

• Author / Creator
Longman, Andrew M
• In the ever-evolving field of high-intensity laser interactions with matter, many approaches have been taken to control and enhance laser-plasma interactions. An alternative, and potentially beneficial approach to further controlling laser-plasma interactions comes from spatial structuring of the laser phase. In this thesis, we explore high intensity ($>1\\times10^{18}Wcm^{-2}$) structured light that carries orbital angular momentum (OAM) via a helical wavefront, also known as an optical vortex (OV). These beams have the unique property of carrying unprecedented amounts of angular momentum, even when linearly polarized. Coupling of this OAM to a plasma is of great interest for the generation of strong axial magnetic fields, particle guiding, enhanced radiation, and gaining an additional control parameter in the laser plasma interactions. We introduce the concept of an off-axis spiral phase mirror for the mode conversion of ultra-fast high-intensity laser systems, and demonstrate the highest intensity OAM optical vortices to date. Diffraction models of the high-intensity OV's are developed analytically and then approximated using Laguerre-Gaussian basis functions for both symmetric and asymmetric modes. The interaction of high-intensity OV's with single electrons and plasma is explored analytically, numerically and experimentally. We show that linearly polarized OAM coupling to single electrons and plasma occurs from nonlinear mechanisms, and can be used to accelerate particles and enhance the laser-plasma interactions. We explore both numerically with particle in cell (PIC) simulations and experimentally new modes of relativistic self-focussing, wakefield acceleration, betatron radiation, and magnetic field generation in the presence of an OAM pulse. We find that angular momentum is indeed coupled to the electrons and that the critical energy of the emitted betatron spectrum is increased with an increase in beam OAM. Additionally, we demonstrate in realistic full scale 3D PIC simulations kilo-Tesla magnetic field generation from the inverse Faraday effect and characterize the spatial extent and temporal duration of these fields.

• Subjects / Keywords
Spring 2021
• Type of Item
Thesis
• Degree
Doctor of Philosophy
• DOI
https://doi.org/10.7939/r3-9hzf-1449