We present results from a laser-driven proton acceleration experiment performed at the JETI 40 laser system in Jena, Germany. Here, we investigated the influence of the position of water micro-droplets relative to the laser’s focus along the polarization axis on the maximum kinetic energy of accelerated protons, either for a steep plasma gradient or an additional pre-plasma. The first case was realized by frequency doubling the laser pulses of the JETI 40 which drastically increases the temporal intensity contrast while for the latter case an additional pre-pulse was introduced. The highest proton energies were achieved when the droplets were irradiated under grazing incidence without a pre-plasma. Two-dimensional Particle-in-Cell simulations show that in this case hot electrons were confined near the droplets’ surface due to self-generated electromagnetic fields. This confinement of electrons enhances the electric field responsible for proton acceleration. The laser-plasma interaction was observed and controlled using the few-cycle optical probe of the JETI 40 system.
|Working group||Laser-driven ion acceleration|