  The dynamics of magnetic fields with amplitude of several tens of Megagauss,
generated at both sides of a solid target irradiated with a high intensity (?
1019W/cm2) picosecond laser pulse, has been spatially and temporally resolved
using a proton imaging technique. The amplitude of the magnetic fields is
sufficiently large to have a constraining effect on the radial expansion of the
plasma sheath at the target surfaces. These results, supported by numerical
simulations and simple analytical modeling, may have implications for ion
acceleration driven by the plasma sheath at the rear side of the target as well
as for the laboratory study of self-collimated high-energy plasma jets.
