Ultra-broadband terahertz absorption by exciting the orthogonal diffraction in dumbbell-shaped gratings

Metamaterials, artificial electromagnetic media consisting of periodical subwavelength metal-based micro-structures, were widely suggested for the absorption of terahertz (THz) waves. However, they have been suffered from the absorption of THz waves just in the single-frequency owing to its resonance features. Here, in this paper, we propose a simple periodical structure, composed of two 90 degree crossed dumbbell-shaped doped-silicon grating arrays, to demonstrate broadband THz wave absorption. Our theoretical and experimental results illustrate that THz waves can be efficiently absorbed more than 95% ranging from 0.92 THz to 2.4 THz. Such an ultra-wideband polarization-independent THz absorber is realized mainly based on the mechanisms of the anti-reflection effect together with the [±1, 0]-order and [0, ±1]-order grating diffractions. The application of our investigation can be extend to THz couplers, filters, imaging, and so on.