Proton acceleration in two-species targets irradiated by an ultra-intense femtosecond laser pulse

This paper presents results of two-dimensional particle-in-cell simulations of proton acceleration at the interactions of a 130 fs, linearly polarized laser pulse of intensity from the range 10²¹ –10²³ W/cm², predicted for the ELI (Extreme Light Infrastructure) lasers, with thin hydrocarbon (CH) or hydride (ErH3) targets. It is shown that for the targets of the areal density σ > 0.1 mg/cm² and laser intensities below 10²² W/cm² a higher efficiency of proton acceleration is achieved for hydride targets. However for the highest, ultra-relativistic laser intensities (~ 10²³ W/cm²) considerably higher proton energies and proton beam intensities are achieved for thin (σ ≤ 0.1 mg/cm²) CH targets. In this case, at short distances from the irradiated CH target (< 50 um), the generated proton pulses are very short (< 20 fs), and the proton beam intensities and the proton current densities reach extremely high values, > 10²¹ W/cm² and > 10¹² A/cm², respectively, which are much higher than those attainable in conventional accelerators. Such proton beams can open the door for new areas of research in nuclear physics and high energy-density physics as well as can be useful for materials research.