Prepulse-induced changes in ion acceleration direction: Insights from TNSA regime experiments and simulations at PHELIX

We present an experimental and simulation-based study on ion beam deflection in laser-matter interactions conducted at the PHELIX facility. The experiment was performed using a main pulse (1053 nm, 500 fs) reaching peak intensities of ∼1.5×1021 W cm−2, and a pre-pulse (1053 nm, either 1 or 3 ns) with an intensity ranging from 6.4×1013 to 1.2×1015 W cm−2. The laser was incident on a 5 μm thick carbon foil under an angle of 25° relative to the target normal. Systematic variation of the pre-pulse delay (0–3 ns) revealed significant target deformation effects, leading to ion beam deflection and a reduction of the ion cutoff energies with increasing delay between the pre-pulse and the main pulse. The pre-plasma dynamics were characterized using side-view interferometry in combination with a synchronized picosecond probe beam. Hydrodynamic simulations with FLASH-2D were adapted to match the interferometric measurements by adjusting laser energy and focus size. The simulations confirm that the observed beam deflection originates from pre-pulse-induced target deformation and expansion. Our results demonstrate that ion beam directionality can be controlled via pre-pulse parameters, providing a pathway for optimizing laser-driven ion acceleration schemes. These findings highlight the importance of precisely adapted pre-plasma conditions in high-intensity laser-plasma interactions and their impact on acceleration dynamics.