Fig. 1. Proton maximal energy as a function of laser power the on target (triangles: snow target experimental and simulation results)^[8–10]; other shapes: different targets and laser facilities)^[11].

Fig. 2. Snow morphology images. Images (a) and (c) are SEM and optical pictures of snow micro-columns without nucleation centers. Images (b) and (d) are SEM and optical pictures of snow micro-columns with nucleation centers.

Fig. 3. Schematics of the experimental setup.

Fig. 4. Line broadening of hydrogen for different time delays between the pre-pulse and the main pulse: (a)  ns, (b)  ns, (c)  ns.

Fig. 5. Mean electron density as a function of the delay after the interaction of the pre-pulse with the snow target.