Improved Energy Scaling and Coupling in High-Repetition Laser-Driven Proton Acceleration

Laser-driven ion sources have attracted significant interest due to their potential for compact, high-gradient acceleration and their suitability for a range of applications. Many of these—including radioisotope production, inertial confinement fusion, radiation damage studies, and FLASH radiobiology—require a stable, high-flux proton source with energies above 10 MeV. In this work we report proton acceleration up to 25 MeV from liquid water sheet targets irradiated at 3.3 Hz by 3 J, 30 fs laser pulses in a ~19,000-shot campaign conducted with the L3-HAPLS laser at ELI Beamlines. Target thickness and laser pulse shaping scans reveal enhanced coupling and an improved scaling law exceeding classical TNSA predictions. Time-of-flight, Thomson parabola, and scintillator imager diagnostics demonstrate stable operation over thousands of shots, while laser reflection and transmission measurements correlate shot-to-shot coupling with proton energy and flux. These results demonstrate robust, application-relevant proton acceleration and advance understanding of coupling physics in ultrafast laser-plasma interactions.