Physical conditions are obtained to make the propagation velocity of a laser pulse and thus the phase velocity of the excited wake be at any desired value, including that equal to or greater than the speed of light. The provision of an active-plasma laser medium with an appropriately shaped pulse allows not only replenishment of laser energy loss to the wake field but also acceleration of the group velocity of photons. A stationary solitary solution in the accelerated frame is obtained from our model equations and simulations thereof for the laser, plasma, and atoms.

• Received 24 May 1993

DOI:https://doi.org/10.1103/PhysRevLett.71.4338