Observations of fast protons above 1 MeV produced in direct-drive laser-fusion experiments

Fast protons greater than or similar to1 MeV have been observed on the 60-b eam, 30 kJ OMEGA laser [T. R. Boehly , Opt. Commun. 133, 495 (1997)] at an intensity I similar or equal to 10(15) W/cm(2) and a wavelength lambda = 0. 35 mum. These energies are more than 5 times greater than those observed on previous, single-beam experiments at the same I lambda (2). The total ener gy in the proton spectrum above 0.2 MeV is similar to0.1% of the laser ener gy. Some of the proton spectra display intense, regular lines which may be related to ion acoustic perturbations in the expanding plasma. (C) 2001 Ame rican Institute of Physics.