Wiener chaos expansion method for thermal radiation from inhomogeneous structures

The Wiener chaos expansion method provides a direct approach to accurately compute the thermal radiation from arbitrary structures. Here, we further extend this method to the structures with a permittivity or temperature inhomogeneity. The inhomogeneous Wiener chaos expansion method treats the two kinds of inhomogeneities with the same governing equation and thus provides a systematic solution to the radiative spectra. Compared to the traditional approach that approximates the thermal radiation from an inhomogeneous structure by the superposition of contributions from its quasihomogeneous subparts, our method calculates the thermal radiation from the entire inhomogeneous structure simultaneously and thus improves the time efficiency. We validate the method against the traditional approach and apply it to study the near-field radiative heat transfer between two gold nanorods with different temperature profiles, from which a four-time tunability is demonstrated at the plasmonic resonance.