Fig. 1. Experimental setup. The laser (λ = 800 nm) was focused by an off-axis parabola (f/7.5) at an angle of 45° to the target. It produced up to 400 mJ in 45 fs with peak intensities ∼2 × 10¹⁸ W cm⁻².

Fig. 2. Proton beam traces from the front surfaces of Perspex (top), Mylar (center), and CD₂ (bottom) targets. The images show the wiggling of the beam with the target at the best focus, (a) without a pre-pulse and (b) with a pre-pulse.

Fig. 3. (a) Laser pre-pulse contrast at various Pockels cell settings. (b) A typical proton (H⁺) energy spectra recorded for a pre-pulse on a Perspex target showing the 1-MeV cutoff.

Fig. 4. Two-dimensional PIC simulation results. (p_2,p₁) plots of proton ions at various times: [(a) and (b)] without a pre-pulse and [(c) and (d)] with a pre-pulse.