Ultra-narrow-band terahertz absorber based on gold and silicon stacked structure

In this paper a perfect THz absorber with nearly unity peak absorbance (>99%) and less than 1% full width at half maximum bandwidth based on an insulator-metal-insulator-metal structure composed of high reflective metallic films and silicon slabs are demonstrated. Thanks to the introduction of top silicon layer, the incident terahertz field can tunnel through the initially perfect reflective top gold film and be strongly absorbed at the Fabry-Perot resonance supported by the bottom metal-insulator-metal substructure. Most surprisingly, the FP resonant absorption peak can be infinitely narrowed with no degradation to the peak absorbance. The perfect absorption (>99%) and ultranarrowband width make the terahertz absorber promising in terahertz plasmonic devices such as filter, narrowband THz emitter, etc.