Achieving optimal acceleration conditions in direct laser acceleration of electrons

Electron acceleration using high-power lasers in plasmas is a promising source of energetic electrons for a wide range of applications. While laser wakefield acceleration (LWFA) offers significant potential for producing monoenergetic beams suitable for future colliders or high-resolution x-ray imaging, the direct laser acceleration (DLA) mechanism can generate electron bunches with total charges in the hundreds of nanocoulombs and laser-to-electron conversion efficiencies on the order of tens of percent [1,2]. These uniquely dense bunches are particularly well-suited for generating high-brilliance betatron gamma-ray beams or for producing secondary particles such as positrons and neutrons via solid converters.

We propose an optimisation strategy for the DLA regime aimed at maximising the cut-off energy of accelerated electrons. This approach involves identifying the optimal combination of laser power, focusing geometry, and plasma density to enhance the efficiency of energy transfer from the laser to multi-GeV electrons. Our strategy is validated using quasi-3D particle-in-cell simulations performed with the OSIRIS code, demonstrating excellent agreement with the derived energy scaling.

Furthermore, we show that multi-petawatt lasers can produce gamma-ray photons with brilliance up to 1022 photons / mm2mrad2s 0.1% BW at energies of tens of MeV [3]. Finally, we demonstrate that DLA-generated electron bunches can be used to create neutral pair plasmas spanning several skin depths, opening new opportunities for laboratory studies of kinetic plasma physics phenomena.

[1] Babjak et al., Phys. Rev. Lett. 132, 125001 (2024) 
[2] Babjak et al., New J. Phys. 26, 093002 (2024)
[3] Babjak and Vranic, arXiv:2502.06744