Superluminality in Gaussian beams

On the basis of Rayleigh-Sommerfeld vectorial diffraction formulas, we show that the radiation from a pulsed Gaussian planar source propagates at a slightly superluminal group velocity beyond the Rayleigh distance, in agreement with a recent prediction from the approximate paraxial theory of diffraction. Moreover, superluminality can be sizably enhanced up to velocities 1.5% faster than c (speed of a plane wave in vacuum) by diminishing the diameter of the source down to one wavelength. (C) 2002 Elsevier Science B.V. All rights reserved