Interaction simulations

The interaction between the laser-generated proton beam and the aluminum foil was modeled using a two-dimensional Monte Carlo code and using for the proton stopping power a model as indicated in ref.³⁹. We have inserted into the code the proton source as obtained in the same experimental conditions and as measured during the shots (an example of proton spectrum is shown in Fig. 5C). The laser-generated proton beam was modeled as the projection of a proton point source with diverging rays at a certain distance, in order to have a proton source of diameter 50 µm. This was modeled similar to what found in ref. ⁵ and considering the laminarity of the beam as indicated in ref.⁶

The divergence half-angle of the proton rays (α) has been adjusted depending on the considered proton energy as obtained in ref.⁴⁰. Within the opening angle, all particles were uniformly distributed. Several simulations were run in order to find the most suitable distance in order to identify the optimum distance between proton source and the second gold target for catalyzing the above-described process.