Femtosecond-laser-fabricated periodic tapered structures on a silicon substrate for terahertz antireflection.

In this research, terahertz (THz) antireflective structures tapered with several profiles (linear, exponential, Klopfenstein) were modeled for high-resistivity silicon and theoretically evaluated using a high-frequency electromagnetic field simulation (HFSS). Their antireflective characteristics are greatly affected by the profiles. One-dimensional periodic tapered THz antireflective structures with different profiles were also fabricated on high-resistivity silicon using femtosecond laser processing. Their antireflective characteristics were experimentally evaluated by standard THz time-domain spectroscopy and modeled by HFSS for reference. The experimental results are in good agreement with the simulations, which showed that the Fresnel reflection reduces to almost zero over a band broader than 1 THz.