Heavy ions with energies up to $430\pm 40\mathrm{MeV}$ have been measured from laser-solid interactions at focused intensities of up to $5\times {10}^{19}\mathrm{W}/{\mathrm{cm}}^2$. Observations of proton emission indicate significant structure in the energy spectrum as well as an angular emission profile which varies with energy. Two qualitatively different components of ion emission are observed: (i) a high-energy component which is likely generated by a combination of “Coulomb explosion” and acceleration by the space charge force from hot electrons which escape the plasma, and (ii) a lower-energy component which forms a ring likely created by magnetic fields in the ablated plasma.

• Received 9 November 1999

DOI:https://doi.org/10.1103/PhysRevLett.85.1654