UC Berkeley

Laser-plasma accelerators have the potential to be the foundation for the next generation of compact particle accelerators and radiation sources. These devices produce plasma structures with accelerating fields orders of magnitude greater than those in conventional accelerators. In order to drive laser-plasma accelerators, high-intensity laser pulses are required. The laser pulses are focused down to sub-millimeter spot sizes near the plasma accelerator entrance to reach the required intensities. In these regions located close to the accelerator entrance, the laser intensities exceed the damage threshold of conventional optics. This prevents optics from being placed near the accelerator entrance and limits the ability to manipulate laser pulses in that region. One potential solution is the use of plasma optics, which are already ionized and therefore can operate at the high laser intensities present.This work discusses experimental development and implementation of various plasma optics--plasma mirrors, plasma channels, and plasma lenses--for control of relativistic laser pulses in laser-plasma accelerators. Plasma mirrors are an overdense plasma generated by the ionization of solid target that reflects an incident laser pulse. Plasma mirrors can be used as the final turning optic to compactly couple the drive laser pulse into a plasma accelerator. Compact coupling is especially relevant for setups that stage together multiple accelerators, each driven by an independent drive laser, to sequentially inject new laser energy to achieve higher energy gain. In this work, plasma mirrors produced by ionization of a tape target are characterized for their performance on a petawatt-class laser. The surface quality and pointing stability were measured and improved to suitable levels in preparation for the commissioning of the second beamline on the BELLA laser at Lawrence Berkeley National Laboratory. Plasma channels are cylindrical plasma structures capable of guiding intense laser pulses over many diffraction lengths. In this work, plasma channels are formed through optical-field ionization and used to guide laser pulses from the BELLA laser. The laser guiding and electron acceleration was studied. A novel gas jet design was used to allow for control over the plasma channel length. This allowed for direct measurements of the laser evolution as it propagated through the channel. Dark-current-free accelerator operation was achieved, and electrons were accelerated up to 10 GeV. Plasma lenses also utilize plasma channels but operate in a mismatched regime where the laser pulses undergoes spot size oscillations as they propagate through the channel. These spot size oscillations have the potential to enable laser spot size control at the entrance of a plasma accelerator. This work examines the effects of short plasma channels on laser propagation and evolution under various channel conditions. Particle-in-cell (PIC) simulations were performed alongside experiments, aiming to improve the understanding of the observed laser evolution.