Ultranarrow and Wavelength-Scalable Thermal Emitters Driven by High-Order Antiferromagnetic Resonances in Dielectric Nanogratings.

Engineering wavelength-selective thermal emission is a promising technology associated with several advanced applications, including thermal imaging, gas sensing, far/near-field thermophotovoltaics, and so on. However, the majority of reported approaches suffer from low Q-factor emission due to intrinsic loss of metallic components or rely on thick structures like multilayers to ensure unitary emissivity, making it challenging to design compatible high-Q narrowband emitters. In this work, we propose a mechanism to tailor thermal emission by taking advantage of optically induced high-order antiferromagnetic (AFM) resonances in a simple subwavelength 2D Si nanobar. Such AFM modes, stemmed from hybrid magnetic dipoles and high-order Fabry-Perot modes, exhibit both pronounced resonant responses and superior light confinement ability. We first reveal its essential roles in ultranarrowband emission control with a sharp (Q ∼ 400) and near-perfect emissivity available. Especially, the measured angle-resolved emission spectra further indicate that the AFM-induced emission peak, being nearly immune to changes of nanogratings' periods and incident angle, is able to be flexibly engineered in a wide waveband by merely tuning the width-to-height ratio of nanobars. Our work provides a promising strategy to design extremely high-Q thermal emitters possessing robust narrowband performance, large spectral tunability and desirable compatibility with advanced planar nanofabrication techniques, which will be more favorable in practice compared with metallic counterparts. Besides, we anticipate that, the revealed mechanism of high-order AFM modes can also stimulate advanced applications in diverse research communities including but not limited to multipolar physics, nonlinear nano-optics, energy harvesting, etc.