In this study, we investigate the effects of realistic laser features in 3D Particle-in-Cells simulations. We show that the full reproduction and understanding of experimental trends are only possible when both the experimental intensity distribution and the reconstructed wavefront are taken into account in the simulations. Besides, the performances in terms of electron acceleration and X-ray emission are strongly degraded compared with a case using a Gaussian laser.
In an experiment performed at the Advanced Laser Light Source (ALLS) facility at INRS-ENT, the emission of synchrotron radiation far beyond the theoretical dephasing or depletion lengths was found. With 3D Particle-in-Cell simulations, we show that this increase of radiation originates from the coupling between two distinct causes: the effect of the laser aberrations and a transition to a PWFA regime after the laser depletion. In our study, the experimental laser wavefront is reconstructed from intensity distributions in different planes. It is used together with the experimental intensity distribution to initialize the laser beam in the simulation, such that the realistic and imperfect laser features are taken into account. It is shown that a quantitative agreement between experimental data and simulations requires to use these realistic pulse features instead of a Gaussian fit for the envelope and a flat wavefront. Moreover, performances on the electron acceleration and the synchrotron X-ray emission are strongly degraded by non-Gaussian features, even keeping constant the total laser energy. A drop on the X-ray photon number by one order of magnitude is found and some trends found in the experiments, such as the growing of the X-ray signal with the plasma length, can only be retrieved in simulations with realistic pulses. This suggests the limitation of using Gaussian beams in the simulations and puts forward the interest of improving the quality of the focal spot in the existing laser systems.
|Are you a student?||Yes|