Laser ion acceleration by a near-critical density target

Protons having energies up to 3.8 MeV are experimentally generated by the p-polarized, 45 fs, ∼1019 W/cm2 laser pulse interacting with a near-critical plasma cloud produced by the irradiation of the amplified spontaneous emission (ASE) pedestal at an intensity of ∼1013 W/cm2 onto a 7.5-μm-thick polyimide foil target. The emission angle of the high-energy protons is shifted away from the target normal toward the laser-propagation direction of 45 deg. The mechanism which explains the proton generation from the near-critical plasma cloud is discussed using the two-dimensional (2D) particle-in-cell (PIC) simulation