A Green's function formalism of energy and momentum transfer in fluctuational electrodynamics

Radiative energy and momentum transfer due to fluctuations of electromagnetic fields arising due to temperature difference between objects is described in terms of the cross-spectral densities of the electromagnetic fields. We derive relations between thermal non-equilibrium contributions to energy and momentum transfer and surface integrals of tangential components of the dyadic Green's functions of the vector Helmholtz equation. The expressions derived here are applicable to objects of arbitrary shapes, dielectric functions, as well as magnetic permeabilities. For the case of radiative transfer, we derive expressions for the generalized transmissivity and generalized conductance that are shown to obey reciprocity and agree with theory of black body radiative transfer in the appropriate limit.

► Proof relating DGFs to radiative transfer and thermal non-equilibrium vdW forces. ► Applicable to objects with arbitrary size and shapes. ► Generalized energy transmissivity is expressed as surface integrals of DGFs. ► Derived blackbody radiation transfer formula from generalized transmissivity. ► Fluctuational electrodynamics explanation of the view factor.