Fabrication of anti-reflective micro-structure at terahertz frequency by using Chinese acupuncture needles

A terahertz (THz) anti-reflective structure on a polystyrene layer was fabricated by using a handmade metallic mold comprising a bunch of Chinese acupuncture needles. Polystyrene was spin-coated onto a silicon substrate and then deformed by the mold via a hot-embossing process. The deformed layer yielded gradient refractive index profiles on the substrate. Compared with a common single antireflective layer, we observed an increase of ∼20% in the transmittance. We also observed broader bandwidth properties compared with the single layer structure. The process imposes no substrate limiting, i.e., it can be applied onto various THz device surfaces for antireflection purpose.