  High absorption in a wide frequency band has attracted considerable interest
since their potential applications in frequency spectrum imaging systems and
anti-radar cloaking. In this paper, a polarization-independent, ultra-broadband
and omnidirectional terahertz absorber is proposed, fabricated and evaluated.
It is experimentally demonstrated that an over 95% absorption can be obtained
in the frequency range of 0.75~2.41 THz. Attributing to the multi-frequency
destructive interference between the layers and the impedance-matching
condition of the grating, five successive absorption peaks at 0.88 THz, 1.20
THz, 1.53 THz, 1.96 THz and 2.23 THz merged into a ultra-broadband absorption
spectrum.

Optics