[en] By taking account of the high-order corrections to the paraxial approximation of a Gaussian beam, it has been verified that for a focused laser beam propagating in vacuum, there indeed exists a subluminous wave phase velocity region surrounding the laser beam axis. The magnitude of the phase velocity scales as V_φm∼c(1+b/(kw₀)²), where V_φm is the phase velocity of the wave, c is the speed of light in vacuum, w₀ is the beam width at focus. This feature gives a reasonable explanation for the mechanism of capture and acceleration scenario