Development of high-average-power laser plasma accelerators driven by industrial Yb lasers

Abstract

Over the past two decades, laser plasma accelerators (LPAs) have emerged as a groundbreaking technology with immense potential for electron acceleration. Their ability to sustain exceptionally high accelerating gradients, on the order of 100 GV/m, and provide electron bunches with only few femtoseconds duration, promises a compact, cost-effective solution for numerous industrial, commercial, and medical applications. Yet, to transition from experimental setups to practical applications, it is crucial to enhance their robustness, reliability, and repetition rate. In this context, industrial-quality Ytterbium:Yttriumaluminium-garnet (Yb:YAG) lasers present an ideal, economically-efficient option, thanks to their inherently small quantum defect, high slope efficiency and high average power. This thesis explores the feasibility of using industrial Yb:YAG lasers as drivers for plasma accelerators. Typically, these lasers deliver pulses of relatively long duration, extending to the picosecond-level. However, to excite a plasma wave, femtosecond durations are usually required. Hence, the temporal compression of the laser output to a few optical cycles is the first critical aspect under analysis. To address this challenge, an efficient double multi-passcell (MPC) post-compression scheme is employed, achieving the highest-ever compression factor to date for a 10 mJ-level pulse. In addition to the driver laser, the plasma source plays a key role in the laser-plasma interaction, shaping the plasma density profile. Therefore, an extensive analysis of the most common sources for high-average-power LPA is presented. To overcome the limitations usually faced, a novel microfluidic source is proposed with unique capabilities for precise tailoring of the plasma profile along the laser axis, at the μm level. Its exceptional finetuning ability is demonstrated through a pioneering Bayesian optimisation tool, combining fluid dynamics and particle-in-cell simulations. This novel optimisation approach holds the promise to significantly boost the performances of LPA, particularly in application oriented scenarios. Finally, the post-compressed laser output is used to demonstrate, for the first time, a plasma wakefield driven by an industrial Yb:YAGlaser. The laser-plasma interaction is thoroughly analysed and a clear path towards the first industrial-laser-drivem electron acceleration is presented.