UC San Diego

With the advent of petawatt-class laser facilities, laser intensities reach unprecedented levels enabling novel and efficient regimes of secondary particle and radiation beams. A regime involving relativistic transparency of dense plasmas and the generation of a Megatesla-level azimuthal magnetic field is shown to be promising for generating energetic electrons and collimated gamma-ray beams. This dissertation focuses on the above regime to explore the acceleration mechanism of electrons, to optimize the gamma-ray yield, to examine the application to two-photon pair production, and to investigate the feasibility of magnetic field detection.

First, we investigate direct laser acceleration in the presence of a strong azimuthal magnetic field. Test-particle models are built to explain the enhanced acceleration. The magnetic fields mitigate electron dephasing and allow an efficient acceleration over a short distance. We then report the important role of the laser phase velocity on electron confinement in this acceleration regime.

We investigate the emission of collimated gamma-ray beams from laser-irradiated channel targets through three-dimensional kinetic simulations. We find a strong power scaling of conversion efficiency into MeV-level photons. The electron-positron pair production via two-photon collisions directly benefits from such a power scaling. We explore two schemes of generating pairs through the linear Breit-Wheeler process: colliding two gamma-ray beams and colliding one gamma-ray beam with blackbody radiation. The strong power scaling boosts the pair yield to the level of 100 000.

Our research on the hollow-channel regime corroborates the robustness of prefilled channels. Due to the influence of ion motion, electrons acceleration and photon emission degrade in hollow channels. With a broader angular spread of gamma-ray beams, the pair yield in hollow channels is shown to be less efficient.

At last, we examine the feasibility of detecting Megatesla-level magnetic fields. We choose XFEL beams to detect magnetic fields, based on the magnetic field inducing a polarization rotation via the Faraday effect. A setup of structured targets with a prefilled channel which mitigates the reduction of rotation caused by relativistic transparency is necessary to achieve rotations that exceed 0.1 mrad. A study on laser focusing configurations suggests there is flexibility regarding laser intensities.