Abstract
By integrating wave-type analysis and fluctuation-dissipation theorem, the enhancement of photon tunneling distance in near field thermal radiation through metallic nanopatterns with/without dielectric structures is theoretically studied. When metallic patterns are in the immediate proximity of the conductive emitter, substantial thermal electric enhancement at surface plasmon frequency is observed between the metallic patterns and the emitter when the periodicity of the thermal electric field along the emitter surface is around integer times of the period of the metallic patterns. The mechanism of field amplification is similar to Fabry–Perot type resonance between two reflecting surfaces. The strong thermal electric field from resonance allows long-distance photon tunneling observed in near field radiation at a ∼5 μm separation distance when the same metallic patterns are placed on the collector surfaces. This value is nearly 50 times longer than that with bared emitter surfaces. This long-distance photon tunneling can also happen at a broader range of parallel wavenumbers (i.e., not determined by the period of the metallic patterns) at the surface plasmon frequency when the periodic metallic patterns' sizes are different each period. However, increasing the range of parallel wavenumbers in long-distance photon tunneling with this approach can reduce the strength of photon tunneling. The reduced tunneling strength can be brought up by attaching high refractive index dielectric resonators on top of the metallic patterns. The dielectric resonators on top of the metallic patterns show additional Mie-type resonance when displacement current is induced at the interface between the metallic patterns and the high refractive index dielectric. The higher intensity long-distance photon tunneling with a broad range of parallel wavenumbers can be valuable in harvesting the high intensity and high quality near field radiative energy with engineering feasible micron level vacuum gaps.
