Signal velocity

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The signal velocity of a wave is the speed at which a pulse travels through a medium. The signal velocity is usually defined from the position of half-maximum intensity of the pulse.

For electromagnetic waves such as light, the signal velocity is identical to the group velocity of the wave except when it is travelling through a medium with an absorption resonance close to the frequency of the wave. In this case, the group velocity v_g may exceed the speed of light c, but the signal velocity v_s will always be less than or equal to c.

[edit] See also

• Dispersion (optics)
• Front velocity
• Phase velocity

[edit] References

• Brillouin, Léon. Wave propagation and group velocity. Academic Press Inc., New York (1960).