Reinvestigating group-velocity-tunable Bessel-X optical wave-packets

The group-velocity of the Bessel-X optical wave-packet can be controlled by introducing well-designed arbitrarily-axisymmetric pulse-front deformation, which permits realizing superluminal, subluminal, accelerating, decelerating, and even nearly-programmable group-velocities. To better understand the tunability of the group-velocity, the generation methods of this Bessel-X optical wave-packet and the mechanisms of the tunable group-velocity in both the physical and the Fourier spaces are investigated. We also studied the relationship with the recently-reported space-time optical wave-packet, and the group-velocity-tunable Bessel-X optical wave-packet is a subsection of the space-time optical wave-packet.