Kramers-Kronig relations beyond the optical approximation
Year: 2019
Type: preprint
Abstract: We extend Kramers-Kronig relations beyond the optical approximation, that is to dielectric functions $\varepsilon(q,\omega)$ that depend not only on the frequency but on the wave number as well. This implies extending the notion of causality commonly used in the theory of Kramers-Kronig relations to include the fact that signals cannot propagate faster than light in vacuo. The results we derive do not apply exclusively to electrodynamics but also to other theories of isotropic linear response in which the response function depends on both wave number and frequency.
Source: arXiv (Cornell University)
Institution: Universitat de Barcelona
Language: English
Subfield: Atomic and Molecular Physics, and Optics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2946048718