Stretcher and Amplifier Design for the LPA Drive Lasers ANGUS and KALDERA

Abstract

Laser-plasma accelerators (LPAs) are a promising technology to build compact and cost-efficient accelerators for a variety of applications. To realize this promise, the reliability and long-term stability of the accelerated electrons have to be improved. Much of this improvement relates to the stability of the drive laser. Apart from improving passive stability, increasing the repetition rate of the laser from a few Hz to >100 Hz, enables the use of active stabilizations, that can account for many lower frequency contributions from e.g. mechanical vibrations and air-fluctuations. The overarching goal of the thesis is to develop setups for the Ti:Sa CPA TW-class laser systems ANGUS and KALDERA, that allow for a stable laser performance and acceleration of high-quality electrons. To improve the long-term stability of the ANGUS laser, a new, more stable front-end, based on optical-parametric chirped-pulse amplification (OPCPA) was built. This thesis reports on the design, alignment and characterization of the stretcher, that was required to integrate the OPCPA front-end into the laser system. The design goal was to achieve a stable and tunable stretcher and to minimize the angular chirp of the output beam by alignment with a three-color-laser. The characterization of the stretcher and its implementation into the laser system, which led to the compression of pulses to 31 fs with sub-percent pulse duration stability will be presented. With KALDERA a >100Hz repetition rate LPA drive laser is currently being developed on DESY campus. To withstand the >100W average power in the final pulse compressor, multi-layer dielectric (MLD) gratings need to be used. This thesis reports on the development, setup and characterization of a two-transmission grating, two-pass Oeffner stretcher, that matches such a MLD compressor. Using this stretcher, compression to sub-30 fs pulse lengths at Ti:Sa wavelength in an out-of-plane compressor with MLD gratings could be demonstrated for the first time. The characterization of the output pulses showed the viability of the stretcher and compressor concept for the KALDERA laser and other future high-average power, TW, fs laser systems. To efficiently seed the final amplifiers, a Booster amplifier is required for the KALDERA laser. The designed three-pass Ti:Sa amplifier provides 0.5-1mJ output energy and sub-percent energy stability. The stretcher and the Booster amplifier successfully seed the KALDERA multi-pass amplifiers to saturation, enabling sub-0.5% energy stability in the final amplifier stage.