Proton Acceleration Driven by High-Intensity Ultraviolet Laser Interaction with a Gold Foil

Proton acceleration induced by a high-intensity ultraviolet laser interaction with a thin foil target was studied on an ultra-short KrF laser amplifier called LLG50 in China Institute of Atomic Energy (CIAE). The ultraviolet laser produced pulses with a high-contrast of 10 9, duration of 500 fs and energy of 30 mJ. The p-polarized laser was focused on a 2.1 µm gold foil by an off-axis parabola mirror (OAP) at an incident angle of 45 ^? . The laser intensity was 1.2×10¹⁷ W/cm² . The divergence angle for proton energy of 265 keV or higher was 30 ^?, which was recorded by a CR39 detector covered with 2 µm aluminum foil in the target normal direction. The maximum proton energy recorded by a CR39 detector covered with a 4 µm aluminum foil was 440 keV, and the proton energy spectrum was measured by a proton spectrometer. The ultraviolet laser acquires a relatively lower hot electron temperature, which can be ascribed to the proportional relationship of Iλ ², but a higher hot electron density because of the higher laser absorption and critical density. Higher electron density availed to strengthen the sheath electric field, and increased the proton acceleration.