The speed at which the energy of a wave travels.
- ‘Essentially, the group velocity of the wave must fall to zero at that location, dropping in such a way that there is sufficient time for the damping to dissipate all of the wave's energy before it gets to that point.’
- ‘He counters that when a beam passes between positive- and negative-index media the group velocity is negatively refracted.’
- ‘Even when the phase velocity is faster than light, the group velocity should be slower.’
- ‘The group velocity dispersion induced by optical elements in the fluorescence path was measured using white light generated by 800-nm pulses in the same flow cell tilled with water.’
- ‘These numbers indicate a group velocity for these structures of approximately 1% of the speed of light in free space.’