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The velocity of propagation of electromagnetic energy for a monochromatic plane-wave field in a causally dispersive dielectric, medium with absorption as described by the Lorentz model, is considered within the framework of Poynting’s theorem. A general, rigorous expression for the energy-transport velocity in a Lorentz medium with multiple-resonance frequencies is derived. From this rigorous result, an approximate expression for the energy velocity is obtained that is in a form that is independent of the medium model and so is likely to be applicable to general dispersive media.
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Oughstun et al. (1988) studied this question.
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