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arXiv · 0812.1521

Causality-based criteria for a negative refractive index must be used with care

P. Kinsler·M. W. McCall
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Abstract

Using the principle of causality as expressed in the Kramers-Kronig relations, we derive a generalized criterion for a negative refractive index that admits imperfect transparency at an observation frequency $ω$. It also allows us to relate the global properties of the loss (i.e. its frequency response) to its local behaviour at $ω$. However, causality-based criteria rely the on the group velocity, not the Poynting vector. Since the two are not equivalent, we provide some simple examples to compare the two criteria.

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P. Kinsler, M. W. McCall. 2008-12-08. Causality-based criteria for a negative refractive index must be used with care. https://doi.org/10.1103/physrevlett.101.167401

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