Intensified proton and carbon ion flux from femtosecond laser driven plasma source

Abstract

Ion acceleration from aluminium foils irradiated with a 30 fs laser pulse of ∼1020 W/cm2 intensity at an incidence angle of 45° was investigated. Laser intensity contrast enhancement by a factor of 100 resulted in a nearly 7 and 30 times increase in proton and carbon ion flux, respectively, while their maximum energy remains almost unchanged. More than 1013 protons and 1014 carbon C4+ ions per MeV bandwidth per steradian solid angle were measured. Simulations, being in a good agreement with the experimental findings, have revealed that the difference in proton emission between the low and high contrast cases is a narrower angular distribution of protons at high laser pulse contrast. In the low contrast scenario, the plasma density gradient increases the hot electron divergence, leading to the reduction of particle flux in a fixed solid angle. The analytical model verifies the concept of the theoretical limit of particle flux. These results open up the possibility for further optimization of the laser driven bright source of energetic particles.