Ultra-narrow terahertz perfect light absorber based on surface lattice resonance of a sandwich resonator for sensing applications

Perfect light absorbers have attracted much attention because of their potential applications in solar cells, thermal imaging, material detection, bio-sensing, and others. However, it is extremely difficult to obtain the ultra-narrow bandwidth of a perfect light absorber in the terahertz region. Herein, an ultra-narrow terahertz perfect light absorber based on the surface lattice resonance of three stacking layers, namely a square resonator, a dielectric spacer, and a metallic film, is reported. A resonance absorption peak with bandwidth of 0.0200 THz and absorption rate of 98.86% is realized. The absorption performance of the device can be controlled by employing different sized (unit) periods and dielectric spacer thicknesses. Particularly, the device bandwidth can be decreased by reducing the dielectric layer thickness. At a certain thickness, a resonance peak with a bandwidth of only 0.0067 THz is achieved. This peak is very sensitive to the surrounding refractive index. The large sensitivity (2.58 THz per refractive index) and simultaneous ultra-narrow bandwidth lead to an ultra-high figure of merit (385.07), making this a promising light device in terahertz detection and sensing.