Pointing of laser-accelerated proton beams

Small fluctuations in the acceleration sheath change the pointing of a proton beam accelerated from the rear side of a laser irradiated thin aluminum foil. The proton acceleration was produced with 40fs pulses of a Ti:sapphire laser at an intensity of approximately 1019W∕cm2. This observation has been made with a high spatial resolution Thomson spectrometer. The proton beam pointing has appeared stable in the energy range between the high energy cutoff (3MeV) and 50% of this value. Deviations of the beam position at lower energies changes in a range of 0–3mrad. The recorded pictures show wiggled and continuous proton traces which imply a release of the proton beam from the acceleration zone with a velocity chirp.