PHYSICS OF RELATIVISTICALLY SELF-FOCUSED LASER PROPAGATION IN PLASMA
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The capabilities and achievable intensities of laser systems has grown by leaps and bounds in the past several decades especially since the development of chirped pulse amplification, and the typical behavior of such light has diverged greatly from the well-understood linear optics to new highly nonlinear optical regimes. This has opened the door to a plethora of new phenomena and applications including long-distance filamentation, high harmonic generation, and many varieties of laser-plasma acceleration. Of particular interest to this dissertation is the physics of relativistically self-focused laser pulse propagation through plasma such as during laser-wakefield acceleration. The objective of this dissertation is to optimize relativistically self-focused laser pulses in plasma for kHz laser wakefield acceleration, investigate the emergence and role of spatio-temporal optical vortices in relativistic filamentation, and to further isolate and analyze the interaction between such vortices and plasma. We demonstrate the ability to accelerate electron bunches up to 15 MeV using few-cycle, mJ-scale pulses at a kHz repetition rate by taking advantage of relativistic self-focusing in near-density hydrogen plasma. Laser polarization is shown in both particle-in-cell simulations and in experiment to affect the energy spread, charge, and divergence of accelerated electrons through CEP-driven asymmetric driving of the wakes; we find that circular polarization resulted in the most monoenergetic and collimated electron beams. Furthermore, we investigate the emergence of spatio-temporal optical vortices that arise in relativistic filamentation/self-focused propagation in plasma using particle-in-cell simulations and compare them with non-relativistic filamentation. We find that these vortices are fundamental features of such propagation and mediate the intrapulse flow of energy during filamentation. Lastly, we isolate these spatio-temporal optical vortices (STOVs) and examine their propagation in plasma in the linear regime. As these vortices are known to carry transverse orbital angular momentum, we use particle-in-cell simulations to directly track the evolution of angular momentum in both the fields and particles during the STOVs’ propagation in plasma. Consistent with our group’s previously derived analytic theory, STOVs share angular momentum with the medium in a polariton structure.