Figure 1: Spatial energy distribution of laser-accelerated proton beams.
From: Direct observation of prompt pre-thermal laser ion sheath acceleration
(a) The accelerating laser pulse is tightly focussed by an off-axis parabolic mirror (OAP) under oblique incidence (δ=45°, p-polarization) onto a 2-μm thick titanium foil target, and proton emission is recorded with stacks (about 15 layers covered with aluminum) of RCF. In front of the off-axis parabola a half-wave plate (λ/2) can be inserted to change the laser polarization. The reconstruction of the particle number per energy for horizontal slices of the RCF dose distributions (see Methods) indicated with the black arrows yields the angularly resolved proton energy spectrum shown in (b). The dashed black line represents the centroid of the angular distribution. Scaled trajectories for protons reaching 70% of the maximum energy (black solid line) at different final deflection angles (α) are added.
