Figure 2

Exemplary images of the laser-droplet interaction for four different delays between probe and main pulse arrival T₀ are shown in (a). The orange arrows point at the probe light which is focused by the transparent droplets before the laser arrives at T₀ − 0.2 ps. The main laser illuminates the central droplets from the left. In (b) the maximum proton energy is shown as a function of the position of the droplets relative to the laser focus position along the polarization axis. The black squares are averaged values with standard deviation of 10 consecutive shots taken at each position, except for x = +16.25 μm (11 shots), x = +18.75 μm (9 shots) and x = −16.25 μm (15 shots). The whole scan consists of 165 consecutive shots between x = −18.75 μm and x = +18.75 μm. Every single shot is used in the calculation of the mean values and the corresponding standard deviations. Shots with no signal at or above the Thomson parabola’s low energy threshold of 0.4 MeV were included as 0 MeV in the calculation of the mean values and standard deviations. Red dots and blue triangles represent the highest and lowest proton energies of the different positions, respectively. If the blue triangle at one position represents a value higher than 0 MeV, all of the shots taken at this certain position, for example at x = 11.25 μm, produced a signal on the Thomson parabola’s MCP. Since the droplets’ absolute positions relative to the laser pulse in the x-axis could not be measured directly, it was estimated from the symmetry of the scan. Details about the error bars along the x-axis can be found in the Supplemental Material. (c) Shows exemplary images of the illuminated droplet’s expansion for different positions 150 ps after the arrival of the main laser pulse.