Source-size measurements and charge distributions of ions accelerated from thin foils irradiated by high-intensity laser pulses

We report on measurements of source sizes and charge state distributions of ions accelerated from thin foils irradiated by ultrashort (100-300 fs) high-intensity (16 × 10¹⁹ W/cm²) laser pulses. The source sizes of proton and carbon ion beams originating from hydrocarbon contaminants on the surfaces of 5 μm thick aluminum foils were investigated using the knife-edge method. For low-energy protons and low-carbon charge states, the source area was found to exceed the focal spot area by a factor of 10⁴. For the determination of charge state distributions, sandwich targets consisting of a 25 μm thick tungsten layer, a 2-nm thin beryllium layer, and again a tungsten layer whose thickness was varied were used. These targets were resistively heated to remove the light surface contaminants. Peaked energy spectra of oxygen and argon ions corresponding to the equilibrium distribution after propagation through matter were observed.