Based on multidimensional particle-in-cell simulations of a short laser pulse interaction with a homogeneous planar target, we perform an optimization study to find the best design parameters for maximizing the number of high-energy electrons generated by a sub-petawatt class laser system for deep gamma radiography purposes. We find that a low-density target with an electron density of 10% of the critical density and a thickness of 240 μm irradiated by a 30 fs 4 J laser pulse can generate 7-nC electron bunches with a mean characteristic energy of 100 MeV.
Electron acceleration has been optimized based on 3D PIC simulations of a short laser pulse interacting with low-density plasma targets to find the pulse propagation regime that maximizes the charge of high-energy electron bunches. This regime corresponds to laser pulse propagation in a self-trapping mode where the diffraction divergence is balanced by the relativistic nonlinearity such that relativistic self-focusing on the axis does not happen and the laser beam radius stays unchanged during pulse propagation in a plasma over many Rayleigh lengths. Such a regime occurs for a nearcritical density if the pulse length considerably exceeds both the plasma wavelength and the pulse width. Electron acceleration occurs in a traveling cavity filled with a high-frequency laser field and a longitudinal electrostatic single-cycle field ("self-trapping regime"). Monte Carlo simulations demonstrated a high electron yield that allows an efficient production of gamma radiation, electronpositron pairs, neutrons, and even pions from a catcher-target.
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