Abstract
It is well known that although the group velocity of structured light pulses propagating in vacuum can be subluminal or superluminal, the upper limit of the energy flow velocity is $c$, the speed of light in vacuum. This inequality can be explained in terms of the reactive energy left behind by the fields. Energy and reactive energy densities have been calculated for vector-valued two-dimensional (light sheet) superluminal electromagnetic nondiffractive pulses, as well as scalar-valued and transverse magnetic three-dimensional superluminal and subluminal spatiotemporally localized electromagnetic waves. Emphasis is placed on the physical formation of the reactive energy due to interference of the plane-wave constituents of the structured light waves.
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