Improved Pulse Characteristics and Power Scaling of Drive Lasers for Laser-Wakefield Acceleration

Laser-wakefield acceleration (LWFA) is a promising, emerging technology for future accelerator-based X-ray light sources, which are essential tools in various fields of science, industry and medicine. In laser-wakefield acceleration, an intense laser pulse drives a plasma wave that supports high accelerating field gradients. This allows electrons to be accelerated over distances that are orders of magnitude shorter than in conventional radio-frequency-based particle accelerators. Driving high-brightness, accelerator-based X-ray sources requires lasers with a peak power around 100TW, and well-controlled pulse properties, since of the quality of the accelerated electron beams is sensitive to the properties of the driving laser pulse. For LWFA to become truly competitive with current radio-frequency-based accelerators, the stability and pulse quality of the lasers must be further improved, and their repetition rate must be increased from the current few Hz to the kHz range, thereby raising the average power to the kW level. The challenges that need to be solved to achieve this lie in the design of the laser amplifiers, the pump lasers for those amplifiers, the final pulse compressor of chirped pulse amplification systems, and an overall improvement of the pulse quality and stability in all sub-components of the laser.This thesis outlines a path towards future high repetition rate LWFA drivers by studying these challenges throughout the amplification chain of Ti:sapphire-based lasers. This starts with the generation of the seed pulse, which largely determines the properties of the final, fully amplified pulse. To deliver high quality seed pulses, a laser front-end based on optical parametric chirped pulse amplification (OPCPA) is presented. The technology can deliver pulses with high temporal contrast and flexible spectral properties, which make it an attractive option for seeding Ti:sapphire amplifiers. However, achieving high beam quality and stability is challenging for OPCPA. A thorough experimental and theoretical study of the saturation dynamics of OPCPA, and the use of advanced control methods, allow to combine these features and as a result, the present an OPCPA system exhibits both, unprecedented long-term stability and excellent spatio-temporal pulse quality.Further, the thermal management of high average power Ti:sapphire amplifiers is investigated, leading to a conceptual design for a Joule-level amplifier that will provide a high quality beam for the first 100Hz operation of a high energy laser wakefield accelerator. For future scaling to kHz repetition rates, the thesis further studies the high average power frequency doubling of ytterbium:doped multi-core fiber lasers, a highly scalable technology, which is a potential solution for providing the 10 kW- level average power pump beams required for future 100 TW, 1 kHz Ti:sapphire laser systems.Finally, the thermal limitations of gold-coated pulse compression gratings are studied, where absorption in the gold coating can cause thermal deformation of the gratings. A custom numerical model is developed to show that this deformation can degrade the spatio-temporal quality of the compressed pulses already at the few-Watt level, and as a result, other grating technologies will be required in future multi-kW drive lasers for laser-wakefield acceleration