Fig. 4: Optimal regime of electron acceleration at normal incidence and comparison with a plane-polarized Gaussian beam.
From: Electron acceleration from transparent targets irradiated by ultra-intense helical laser beams
a–e Electron data from a simulation where a target with \({n}_{\max }=0.5{n}_{{{{{{{{\rm{c}}}}}}}}}\) is irradiated by the helical beam. f–h Electron data from a simulation where the same target is irradiated by a plane-polarized Gaussian beam that has the same peak power of 3 PW. a, f Electron density ne normalized to the critical density nc during laser pulse transmission. b, g Areal density at t = 238.3 fs calculated by integrating ne along x. e Density of electrons accelerated by the helical beam at t = 238.3 fs. The vertical dashed lines mark the region shown in (b). c, h Electron energy distribution at t = 398.3 fs for different divergence angles \({\theta }_{\perp }={\tan }^{-1}\left({p}_{x}/\sqrt{{p}_{y}^{2}+{p}_{z}^{2}}\right)\). The distribution in (c) is calculated for ∣y, z∣≤5 μm, whereas the distribution in (h) is calculated for ∣y, z∣≤14 μm. d Electron energy distribution along the x-axis at t = 398.3 fs for the case with the helical beam, where εk is the kinetic energy. Only the electrons with ∣y, z∣≤5 μm are shown. i Electron spectra (t = 398.3 fs), where the red curve shows electrons with ∣y, z∣≤5 μm in the simulation with the helical beam and the black curve shows electrons with ∣y, z∣≤14 μm in the simulation with the Gaussian beam.
