Proton Acceleration by High-Intensity UV Laser Irradiation with Thin Foils

Abstract

Proton acceleration experiments using an intense ultraviolet laser were conducted for the first time. The laser system produced pulses having energies of up to 750 mJ at a wavelength of 248 nm with a temporal duration of 400 fs. Thin copper foils of 4 μm were used as targets, and the maximum intensity on the target was 1.3 × 10¹⁸ W/cm². The highest energy of protons was 700 keV, which was observed when the laser beam was ppolarized and was incident on the target at an angle of 30°C . Fast electrons were generated by vacuum heating or resonance absorption because of the polarization dependence. These protons were accelerated in the target normal direction, which is suggestive of the target normal sheath acceleration mechanism (TNSA).