UC Berkeley

Laser-plasma interactions have become a rapidly growing area of modern plasma physics and an important subfield of it is laser-plasma acceleration. Using high-intensity lasers, one can drive a plasma structure with electric-field gradients three orders of magnitude higher than the gradients found in traditional, radio-frequency accelerators. This promises to enable great technological advances in medicine, spectroscopy, and experimental particle physics, as well as to open up new avenues of studying matter under extreme conditions.

An important aspect of laser-plasma acceleration is how the transverse electromagnetic field of the laser affects and drives an accelerated particle via longitudinal waves in the plasma. To understand how the laser interacts with the plasma, it is necessary to understand that the transverse characteristics of the laser dictate its longitudinal propagation dynamics. The transverse radiation field of the laser pulse can be described in various ways and decomposed into bases of orthogonal modes. The presence of multiple higher-order modes, copropagating through the plasma, leads to mode beating. Likewise, these modes propagate at different velocities through the plasma and are susceptible to nonlinear interactions with the plasma to varying degrees.

The primary objective of this thesis is to understand how higher-order laser modes interact with the plasma and with one another. In this work, we discuss the detrimental consequences that mode beating may have on a laser-plasma accelerator and how higher-order modes can be filtered out using specially designed plasma structures. Also discussed is how higher-order mode content can be controlled and utilized to shape and control the wakefields. These ideas are extended to the concept of the plasma undulator as a plasma-based light source. Lastly, we discuss how nonlinear effects can excite higher-order mode content as path to understanding laser pulse break up into multiple filaments.