Research Papers in Physics and Astronomy


Date of this Version



Published by American Physical Society. Physical Review Letters 84, 4108 (2000). Copyright © 2000 American Physical Society. Permission to use.


A collimated beam of fast protons, with energies as high as 1.5 MeV and total number of ≳109, confined in a cone angle of 40°±10° is observed when a high-intensity high-contrast subpicosecond laser pulse is focused onto a thin foil target. The protons, which appear to originate from impurities on the front side of the target, are accelerated over a region extending into the target and exit out the back side in a direction normal to the target surface. Acceleration field gradients ∼10 GeV/cm are inferred. The maximum proton energy can be explained by the charge-separation electrostatic-field acceleration due to “vacuum heating.”

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