Intrinsic symmetry relations are obtained for components of optical susceptibility tensors of a nonabsorbing linear medium with the nth-order frequency dispersion (n = 1, 2, ...) and time-varying optical characteristics. They are used to find analytical expressions for all components of the energy–momentum tensor of the electromagnetic field of the waves propagating in the medium. In the case of the second- and higher-order frequency dispersion, formulas for electromagnetic field energy and momentum densities have, apart from the known additional terms, new terms involving time derivatives of medium optical susceptibility components.
Ryzhikov et al. (Wed,) studied this question.
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