Fig. 2: Target density scan for a circularly-polarized helical beam.
From: Electron acceleration from transparent targets irradiated by ultra-intense helical laser beams
a–c Electron density ne normalized to the critical density nc for three different target densities (\({n}_{\max }=2.5{n}_{{{{{{{{\rm{c}}}}}}}}}\), 1.0nc, and 0.5nc), shortly after laser pulse transmission (t = 48.3 fs). d–f Normalized amplitude of the longitudinal electric field, ∣e∣∣Ex∣/mecω, for the same three target densities also at t = 48.3 fs. g–i Density of accelerated electrons for the same three target densities at t = 248.3 fs. j–l Time evolution of the energy distribution for forward-moving electrons selected using the same criterion as that used for Fig. 1c, with εk = (γ − 1)mec2. In panels (a–i), the quantities are shown in the (x, y)-plane at z = 0. Panels (a), (d), (g), and (j) correspond to a target with \({n}_{\max }=2.5{n}_{{{{{{{{\rm{c}}}}}}}}}\); panels (b), (e), (h), and (k) correspond to a target with \({n}_{\max }={n}_{{{{{{{{\rm{c}}}}}}}}}\); panels (c), (f), (i), and (l) correspond to a target with \({n}_{\max }=0.5{n}_{{{{{{{{\rm{c}}}}}}}}}\).
