The Petawatt laser at Lawrence Livermore National
Laboratory (LLNL) has opened a new regime of laser matter
interactions in which the quiver motion of plasma electrons
is fully relativistic with energies extending well above
the threshold for nuclear processes. In addition to ∼few
MeV ponderomotive electrons produced in ultra intense laser-solid
interactions, we have found a high energy component of
electrons extending to ∼100 MeV apparently from relativistic
selffocusing and plasma acceleration in the underdense
preformed plasma. The generation of hard bremsstrahlung,
photonuclear reactions, and preliminary evidence for positron-electron
pair production will be discussed.