[en] Using 3D test particle simulations, the characteristics and essential conditions under which an electron, in a vacuum laser beam, can undergo a capture and acceleration scenario (CAS). When a₀ ∼> 100 the electron can be captured and violently accelerated to energies ∼> 1 GeV, with an acceleration gradient ∼> 10 GeV/cm, where a₀ = eE₀/m_eωc is the normalized laser field amplitude. The physical mechanism behind the CAS is that diffraction of the focused laser beam leads to a slowing down of the effective wave phase velocity along the captured electron trajectory, such that the electron can be trapped in the acceleration phase of the wave for a longer time and thus gain significant energy from the field