Pilot study of synchronization on a femtosecond scale between the electronic gun REGAE and a laser-plasma accelerator

Laser wakefield acceleration (LWFA) is a novel technique to accelerate charged particles. Acceleration is achieved by a high-power laser pulse transmitting a gas target where electrons and ions form a strong wakefield with gradients up to 100 GVm^-1. Hence, the size of the laser-plasma accelerator (LPA) is significantly smaller compared to conventional radio frequency (RF) accelerators, because its accelerating gradients are 3 orders of magnitude higher. At present, electron beams generated by LWFA do not satisfy all requirements to make them directly usable for applications such as LPA driven free-electron laser (FEL). Pointing stability and relatively high energy spread are the major limiting factors. Typically, plasma electrons are self-injected in the plasma wake which is created by a high-power laser. There is a lack of control for the injection process and there is no direct access for diagnostics. In order to overcome these challenges and better understand the overall LWFA process, external injection experiments are planned at Deutsches Elektronen-Synchrotron (DESY) in the framework of the Laboratory for Laser and beam-driven plasma Acceleration (LAOLA) collaboration. Thus, well characterized and ultrashort (< 10 fs) electron bunches from the conventional RF accelerator Relativistic Electron Gun for Atomic Exploration (REGAE) will be injected into the laser driven plasma wake. This approach allows to reconstruct and map the plasma wakefield by post diagnosing the injected electron bunches by measuring the energy spectra of it for different injection times. To conduct such a pump-probe type of experiment, synchronization with fs accuracy is required between the electron bunches from REGAE and the high-power driver laser. Two main aspects of the laser synchronization are presented in this thesis. First, a detailed experimental investigation of the conventional, fast photodiode based direct conversion laser-to-RF synchronization setup and its limitations are given. Second, an advanced Mach-Zehnder modulator (MZM) based laser-to-RF synchronization setup has been successfully developed and tested. The conceptual design, a mathematical analysis, tolerance studies and experimental evaluation is presented. Electron beam-based measurements have been performed at REGAE where MZM based laser synchronization achieved a factor of 10 performance improvement in terms of amplitude-to-phase modulation (AM-PM) conversion compared to the previously used conventional photodiode based laser synchronization setup. This setup has been employed to phase lock the REGAE photo-injector laser with excellent long term timing drift performance of 31 fs peak-to-peak over 43 h and a short term timing jitter of 11 fs rms.