Pre-plasma shaping via picosecond laser contrast: A hybrid simulation study of proton acceleration in TNSA

We investigate the impact of picosecond-scale laser temporal contrast on proton acceleration via target normal sheath acceleration (TNSA) using a hybrid simulation framework. The initial laser–target interaction and pre-plasma formation in aluminum foils of varying thicknesses (0.25–1 μm) are modeled using fluid-based approach with the MULTI-fs code. These pre-plasma profiles serve as inputs for particle-in-cell (PIC) simulations performed with the Smilei code, which model the main pulse interaction and subsequent proton acceleration. Simulations are carried out for the ATLAS laser system operating in both high- (10−10) and low-contrast (10−8) modes. The results reveal that low-contrast pulses, with longer pre-pulse durations (∼20 ps); produce more extended pre-plasma regions, enhanced volumetric heating, and increased hot-electron generation. These effects lead to stronger sheath electric fields and proton cutoff energies up to ∼45% higher than those achieved under high-contrast conditions. Optimal acceleration is obtained with 0.5 μm thick targets under low-contrast irradiation, offering a balance between structural integrity and efficient energy coupling. Our findings emphasize the pivotal role of laser temporal contrast and target thickness in tailoring ion acceleration, with implications for advancing TNSA-based applications.