Fig. 4: 3D PIC simulation of a cascaded proton accelerator based on the irradiation of two μ-bars.
From: Ion acceleration from micrometric targets immersed in an intense laser field
Each μ-bar was irradiated with a 25 fs long, 60 mJ laser pulse at a 45∘ angle of incidence. The second pulse follows the first one with a Δt = 200 fs delay. a Snapshots of the transverse component of the electric field (Ey) are shown in a red-to-blue color scale, with the electron density overlaid in green and the space-averaged energy of protons in a color scale. At t = 240 fs, protons that were emitted from the first μ-bar are observed to be further accelerated by the sheath of the second μ-bar to energies above 8 MeV. b The resulting differential proton energy spectra from the simulation shown in (a) compared to simulations with shorter (Δt = 190) or longer (Δt = 210) delays between the two pulses. The spectra are also compared with those resulting from the irradiation of a single μ-bar with a 25 fs long laser pulse of 60 or 120 mJ.
