Subluminous phase velocity regions of an accurately described Gaussian laser field and laser-driven acceleration

Abstract 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 /( kw 0 ) 2 ), where V ϕm is the phase velocity of the wave, c is the speed of light in vacuum, w 0 is the beam width at focus. This feature gives a reasonable explanation for the mechanism of capture and acceleration scenario.