Laser-driven ion dynamics using multiple ultra-high intensity laser beams

Ion acceleration from foils irradiated by a laser pulse at relativistic intensity is dominated by target rearside electron dynamics of the foil. Simulations show that focusing a second, similar intense laser beam onto the foil, one can produce ion beams with interesting spectral features with respect to angular distribution and higher cut-off energies or can even initiate another acceleration phase depending on the temporal delay. In this contribution, we report on a series of recent experiments adressing the ion acceleration utilizing two ultrashort (30fs), high intensity (10$^{20}$ W/cm$^2$) and high contrast (10$^{-10}$) laser beams. Both beams were focused and spatially overlapped onto 5 micron titanium targets. The main goal was to investigate the impact of temporal delaying of the two laser pulses on the maximum proton and/or ion energy. Extensive studies show an proton energy enhancement by factor 1.5 and clear impact on carbon ion spectra. In addition, we characterize the rearside plasma expansion with a temporal and spatial resolved interferometer (TASRI) and recflectometry using a chirped optical probe to obtain the evolution of electron temperatures and densities in a 20 ps time window for each shot.