Spectral control of near-field thermal radiation via photonic band engineering of two-dimensional photonic crystal slabs.

In this paper, we numerically investigate a method to obtain narrow-bandwidth near-field thermal radiation spectra by using two-dimensional (2D) photonic crystal (PC) slabs. Our examination reveals that near-field thermal radiation spectra can be artificially controlled via the photonic band engineering of 2D-PC slabs, where the radiation is enhanced in a range of frequencies of the flat bands and suppressed inside the photonic bandgap. By designing a thermal emitter with a 2D-PC slab of appropriate thickness, and by adjusting the gap between the emitter and the absorber, we can implement narrowband near-field thermal radiation that overcomes the far-field blackbody limit in the near-infrared range. Further, its linewidth is as small as Δλ = 0.14 µm.