2019/05/15 by Josep Llosa, Llosa, Josep, F. Salvat +1
Engineering · Physics and Astronomy · #30E15 #30E20 #78A99 #Classical Physics (physics.class-ph) #FOS: Physical sciences #Mathematical Physics (math-ph) #Optical Polarization and Ellipsometry #Optical and Acousto-Optic Technologies #Photonic and Optical Devices
paper · pdf · doi:10.48550/arxiv.1905.06069
openalex publication_date 2019/05/15 · openalex created_date 2022/07/29 · openalex updated_date 2026/07/28
We extend Kramers-Kronig relations beyond the optical approximation to dielectric functions that depend not only on 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 extension is applied to some microscopic models for the dielectric function and is compared with previous generalizations. The results derived here also apply to general theories of isotropic linear response in which the response function depends on both wave number and frequency.