Ultra-Broadband THz Antireflective Coating with Polymer Composites

Abstract

Abstract:Achieving an ultra-broadband range is an essential development direction in terahertz techniques; however, a method to cover the full terahertz band by using a highly efficient antireflection (AR) coating that could greatly increase the efficiency of terahertz radiation is still lacking. It is known that structures possessing a graded-index profile can offer a broadband AR effect, and such structures have been widely used, especially in the visible range. In this paper, first, we tuned the refractive index of a cyclo-olefin polymer (COP) by using a TiO 2 dopant, and a polymer-TiO 2 composite with a refractive index of 3.1 was achieved. We then fabricated a surface-relief structure with a graded-index profile by using a hot-embossing method. The structure on the silicon substrate can provide an excellent AR effect, but the working band is still limited by its scale of sag and swell. To obtain an ultra-broadband AR effect, we then proposed a flat six-layer structure; a graded-index profile was obtained by casting epoxy-TiO 2 composites in the order of a high index to lower indices. With a very well controlled refractive index and thickness of each layer, we achieved an AR effect of <2% in the ultra-broadband of 0.2-20 THz.

Two-dimensional terahertz spectroscopy of condensed-phase molecular systems

“…Unwanted reflections from the back surface of beamsplitter plates can be suppressed by antireflection coatings. [53][54][55][56] Another solution is to use the beam splitter under Brewster's angle for p polarization and add a metallic coating on one side for the required reflectivity. 57 Wire grid polarizers consist of parallel thin metallic wires.…”

In-situ deposition of oxidized porous metal nanoparticles on the surface of picosecond laser-induced micro/nano structures: A new kind of meta-surface equipped with both super-hydrophobicity and anti-reflectivity

“…] when the light beam propagates from medium "1 ′′ to medium "2", where the n i and k i are the real part and imaginary part of the refractive index of the medium, respectively, and i is the medium number. In this regard, reducing the difference between the refractive indices of the two media is an effective method to decrease the surface reflectance, which is called as gradient refraction effect [41].…”

Study of 3D-Printed Dielectric Barrier Windows for Microwave Applications

“…The almost reflectionless transmission of a linearly polarized wave can be achieved for the Brewster-angle disk; however, this output suffers from an inefficient use of space, which may be especially important for divergent wave beams and some distortion of the transverse field structure [9]. Polymers can be mixed with nanoparticles to produce a multilayer dielectric coating [10]. Metamaterial devices and gradient index photonic structures are also used to reduce reflection [11].…”