A collimated beam of fast protons, with energies as high as 10 MeV and total number of 10~9, confined in a cone angle of 40°+-10°has been observed when a 10 TW laser with frequencies either ω_0 (corresponding to 1μm) or 2ω_0 was focused to an intensity of a few times 10~(18) W/cm~2 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 2ω_0 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 ~(10)B sample was placed behind the target, we observed the production of ～ 10~5 atoms of positron active isotope ~(11)C from the nuclear reaction ~(10)B(d,n)~(11)C.
展开▼
