Dispersion forces inside metallic waveguides

TL;DR

This paper investigates how the size of a metallic waveguide influences the dispersion energy between dipoles, revealing a transition from exponential decay to free-space behavior depending on the distance and waveguide dimension.

Contribution

It introduces a scale set by the waveguide dimension that differentiates retarded and quasistatic dispersion interactions, extending understanding of dispersion forces in confined geometries.

Findings

Dispersion energy transitions from exponential decay to free-space form.

Waveguide dimension a determines the interaction regime.

Implications for Casimir effects in dense media within waveguides.

Abstract

We consider the dispersion energy of a pair of dipoles embedded in a metallic waveguide with transverse dimension $a$ smaller than the characteristic dipolar wavelength. We find that $a$ sets the scale that separates retarded, Casimir-Polder-like, from quasistatic, van der Waals-like, interactions. Whereas in the retarded regime, the energy decays exponentially with inter-dipolar distance, typical of evanescent waves, in the van der Waals regime, the known free-space result is obtained. This short-range scaling implies that the additivity of the dispersion interactions inside a waveguide extends to denser media, along with modifications to related Casimir effects in such structures.