Effects of laser prepulse on proton generation

Prepulse is a major issue for laser generation of protons, often limiting the performances of laser sources. Here, we show the use of prepulse (<1013 W/cm2, ns duration) to actively manipulate the proton beam direction. Under oblique high-intensity irradiation (≈1019 W/cm2, ps duration) of the thin foil target, and for low prepulse intensities, the proton beam is directed away from the “unperturbed” target normal. Observations are discussed in terms of target normal sheath acceleration, in combination with a laser-controllable shock locally deforming the target surface.