Two-pulse interference and superluminality

International audience; We examine how the interference of a coherent light-pulse with its slightly time-delayed copy may generate a pulse nearly identical to the original one and ahead of it. The simplicity of this 2-pulse system enabled us to obtain exact analytic expressions of the pulse distortion, valid for a wide class of pulse shapes. Explicit results are given for the pulses usually considered (gaussian, hyperbolic secant) but also for more realistic pulses of strictly limited duration. We finally show that the efficiency of the 2-pulse system is comparable to that of the other superluminal systems, at least for the pulse advancements actually demonstrated in the optical experiments.