Resonant Thermal Infrared Emitters in Near- and Far-Fields

Although optical resonators are widely used for controlling and engineering thermal radiation, what has been lacking is a general theoretical framework to elucidate the thermal emission of optical resonators. We developed a general and self-consistent formalism to describe the thermal radiation from arbitrary optical resonators made by lossy and dispersive materials like metals, with the only assumption that the resonators have a single predominant resonance mode. Our formalism derives the fundamental limit of the spectral thermal emission power from an optical resonator and proves that this limit can be achieved when the mode losses to the emitter and the absorber (or far-field background) are matched, and meanwhile, the predominant resonant mode is electrically quasi-static. By efficiently calculating the resonant modes using the finite element methods, our formalism serves as a general principle of designing the arbitrary optical resonator thermal emitters with perfect or maximized emission in both near and far-fields.