Ion generation in a low-density plastic foam by interaction with intense femtosecond laser pulses

Energetic proton generation in low-density plastic $\left({\mathrm{C}}_5{\mathrm{H}}_{10}\right)$ foam by intense femtosecond laser pulse irradiation has been studied experimentally and numerically. Plastic foam was successfully produced by a sol-gel method, achieving an average density of $10\hspace{0.5em}{\mathrm{m}\mathrm{g}/\mathrm{c}\mathrm{m}}^3.$ The foam target was irradiated by 100 fs pulses of a laser intensity $1\times {10}^{18}{\mathrm{W}/\mathrm{c}\mathrm{m}}^2.$ A plateau structure extending up to 200 keV was observed in the energy distribution of protons generated from the foam target, with the plateau shape well explained by Coulomb explosion of lamella in the foam. The laser-foam interaction and ion generation were studied qualitatively by two-dimensional particle-in-cell simulations, which indicated that energetic protons are mainly generated by the Coulomb explosion. From the results, the efficiency of energetic ion generation in a low-density foam target by Coulomb explosion is expected to be higher than in a gas-cluster target.