Laser Acceleration of Protons from Thin Film Targets

A collimated beam of fast protons, with energies as high as 10 MeV and total number of 109, confined in a cone angle of 40°±10° has been observed when a 10 TW laser with frequencies either ω0 (corresponding to 1 μm) or 2ω0 was focused to an intensity of a few times 1018 W/cm2 on the surface of a thin film target. The protons, which originate from impurities on the front side of the target, are accelerated over a region extending into the target and exit out the backside in a direction normal to the target surface. Acceleration field gradients of ~10 GeV/cm are inferred. The maximum proton energy for 2ω0 can be explained by the charge-separation electrostatic-field acceleration due to vacuum heating. In other set of experiments when a deuterated polystyrene layer was deposited on a surface of a Mylar film and a 10B sample was placed behind the target, we observed the production of ~105 atoms of positron active isotope 11C from the nuclear reaction 10B(d,n) 11C