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 vg may exceed the speed of light c, but the signal velocity vs will always be less than or equal to c.
[edit] See also
[edit] References
- Brillouin, Léon. Wave propagation and group velocity. Academic Press Inc., New York (1960).
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