We report on the transverse refluxing of energetic electrons in mass-limited foil targets irradiated with high intensity (1 × 1019 W cm−2), picosecond laser pulses. It is shown experimentally that the maximum energies of protons accelerated by sheath fields formed at the rear and at the edges of the target increase with decreasing target size. This is due to the modification of the sheath field by the energetic electrons which spread laterally along the target surface and reflect from the edges. In addition, it is shown that this transverse refluxing of energetic electrons can be used to tailor the spatial-intensity distribution of the proton beam by engineering the shape and size of the target.
Observation of proton modulations in laser–solid interaction