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 109,duration of 500 fs and energy of 30 mJ.The p-polarized laser was focused on a 2.1 μm gold foil by an of-axis parabola mirror(OAP) at an incident angle of 45°.The laser intensity was 1.2×1017W/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 Iλ2,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.