Ultrathin Film Broadband Terahertz Antireflection Coating Based on Impedance Matching Method

Broadband antireflection coatings for terahertz (THz) components are extremely important in the application of THz technology. We present an in-depth materials study on the broadband antireflection design based on the concept of impedance matching. Several selected conductive materials are tested and compared. They can all be used as THz broadband antireflection coatings regardless of their nature of conductivity. We provide a facile method to approximately predict the impedance matching condition for various conductive materials based on their dc real conductivity. The theoretical predications are in good agreement with experimental results and published data. Doped metal oxides or polymers are recommended as good candidates for fabricating antireflection coating in THz range. The thickness-independent dc real conductivity enables better control on individual tuning parameter-film thickness. Given a substrate, THz transmission in antireflection coating has a theoretical upper limit which is further reduced with non-negligible imaginary conductivity.