arXiv:0710.4388 · Optics Letters

Resolving the wave vector and the refractive index from the coefficient of reflectance

V. U. Nazarov, Yia‐Chung Chang

Published Oct 4, 2007• 14 citations

Abstract

We resolve the existing controversy concerning the selection of the sign of the normal-to-the-interface component of the wave vector k(z) of an electromagnetic wave in an active (gain) medium. Our method exploits the fact that no ambiguity exists in the case of a film of the active medium, since its coefficient of reflectance is invariant under the inversion of the sign of k(z). Then we show that the limit of the infinite film thickness determines a unique and physically consistent choice of the wave vector and the refractive index. Important practical implications of the theory are identified and discussed.

DOI: 10.1364/ol.32.002939

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Comment on “Resolving the wave vector and the refractive index from the coefficient of reflectance”

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In a recent Letter, the reflectance coefficient was used to resolve the sign choice of the wave vector and refractive index in active media. We argue that such a coefficient loses its physical meaning for active media (at real frequencies) when the field amplification is limited only by gain saturation. In this case, the amplitude reflectance coefficient leads to fictitious noncausal reflected fields when the backward Fourier transform is used.

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Reply to comment on “Resolving the wave vector and the refractive index from the coefficient of reflectance”

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We reinterpret our earlier letter [Opt. Lett.32, 2939 (2007)] to demonstrate that the resolution it gives to the problem of the sign of the wave vector and the refractive index is valid for active media without instabilities but invalid otherwise.

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