Fig. 2: Results of experiment and interpreting simulations.

Cut-off proton energy (a) and energy conversion efficiency (b) as a function of the thickness of planar SiN foils (black) and the spatial period of microwire array (MWA) targets (red), from experiments (solid dots) and simulations (solid lines). The conversion efficiency from laser to protons (kinetic energy > 1 MeV) is obtained from the radiochromic film (RCF). Here the high conversion efficiency for 0.2 μm results from more complicated mechanisms thus is excluded from comparison. The error bars are defined by standard deviation from the mean of different shots. It should be noted that the calculation of conversion efficiency takes into account the laser energy measured in each shot. The light-gray shadings represent the scope of cutoff energy or conversion efficiency that planar targets involve. c Proton spectra obtained from RCF stacks (scattered points) and Thomson parabola spectrometer (TPS, dashed lines) for 1 μm SiN foils, and MWA targets with three periods of 1.3, 2.3, and 3.3 μm, respectively. The horizontal error bar marked for p = 3.3 μm as the last sheet of RCF stack changed color in this shot. The inset of (c) is the simulated proton spectra.