First Laser-Accelerated Ion Observations From the Omega EP Laser at 1000 J in 10 ps

The efficient generation of ion beams using short intense laser pulses has many applications including active interrogation, providing a temporally-precise perturbation source for ICF capsule implosions, and providing a hot spot for ion fast ignition schemes. All applications benefit by improvements in the laser-to-ion conversion efficiency. For example, ion fast ignition fusion which promises order-of-magnitude reduction in laser driver energies, requires a conversion efficiency of order 10{\%} to avoid the short-pulse lasers from becoming impractically large and expensive. Presently, ion acceleration at the shortest pulse lengths (\textit{$\tau $}$_{pulse} \quad <$ 1 ps) has been limited. For integrated fast ignition experiments short-pulse laser energies in excess of 10's of kJ will be required necessitating longer pulse lengths on the order of \textit{$\tau $}$_{pulse} \quad \ge $ 10 ps. There is a lack of experimental data in this pulse length regime. For the first time the OMEGA EP laser has been focused onto small foils with 1000 J in 10 ps to produce proton beams up to nearly 50 MeV with high efficiencies. Results of ion energy and conversion efficiency as a function of target size, target thickness, and intensity will be presented.