General theory of electromagnetic fluctuations near a homogeneous surface, in terms of its reflection amplitudes

TL;DR

This paper presents a general theoretical framework for calculating electromagnetic fluctuations near homogeneous surfaces using reflection amplitudes, applicable to various materials and conditions, aiding interpretation of near-field experiments.

Contribution

It introduces new general expressions for electromagnetic fluctuations based solely on surface reflection amplitudes, applicable to all homogeneous materials including layered systems and metamaterials.

Findings

Derived formulas for near-field electromagnetic fluctuations.

Established symmetry properties of reflection matrices.

Applicable to all temperatures and material types.

Abstract

We derive new general expressions for the fluctuating electromagnetic field outside a homogeneous material surface. The analysis is based on general results from the thermodynamics of irreversible processes, and requires no consideration of the material interior, as it only uses knowledge of the reflection amplitudes for its surface. Therefore, our results are valid for all homogeneous surfaces, including layered systems and metamaterials, at all temperatures. In particular, we obtain new formulae for the near-field region, which are important for interpreting the numerous current experiments probing proximity effects for macroscopic and/or microscopic bodies separated by small empty gaps. By use of Onsager's reciprocity relations, we obtain also the general symmetry properties that must be satisfied by the reflection matrix of any material.