Antireflective broadband micro structure at terahertz range by a hot deformation

We fabricated an antireflective structure on a polystyrene (PS) at terahertz (THz) frequency by using a hot-emboss method. Polystyrene was spin-coated onto a silicon substrate and then deformed by using a metallic mold comprising a bunch of Chinese acupuncture needles. The transformed layer yielded gradient refractive index profiles on the substrate which can reduce the surface reflection effectively. The samples were evaluated by a terahertz time-domain spectroscope system. Compared with a bare silicon substrate, we observed an increase of ~30% in the transmittance. We also observed broader bandwidth properties compared with a single-layer antireflective structure.