Optical investigation to minimize the electron bunch arrival-time jitter between femtosecond laser pulses and electron bunches for laser-driven plasma wakefield accelerators

Plasma based particle accelerators driven by either lasers or particle beams are most probably the future of the particle accelerators technology. In a laser driven plasma based particle accelerators a stable synchronization of the electron bunch and of the plasma wake field in the range of less than 2 fs is necessary in order to optimize the acceleration. For this purpose we are developing a new shot to shot feedback system with a time resolution of less than 1 fs. As a first step, stable THz pulses are generated by optical rectification of a fraction of the plasma generating high energy laser pulses in a nonlinear lithium niobate crystal. It is planed that the generated THz pulses will energy modulate the electron bunches shot to shot before the plasma to achieve the time resolution. In this contribution we systematically investigate the influence of the optical properties as well as the theoretical description of the THz generation on the conversion efficiency of the generation of short THz pulses. We compare different approximations for the modeling of the generation dynamics (full second order calculation or first order slope varying approximation SVA) and of the dielectric function (linear approximation of the dispersion relation, influence of the free carries generated by the pump adsorption and their saturation, decreasing of the pump intensity) in order to investigate the importance of a detailed description of the optical properties.