High-transparency polymer-silicon nano-particle composites for broadband anti-reflection of terahertz waves

Antireflection coatings for silicon optics that work in the terahertz (THz) band were demonstrated. Highly resistive intrinsic silicon nano-particles produced by the laser pyrolysis method were dispersed in a polymer solution and formed refractive index-controlled composites. The silicon nano-particles exhibited THz-wave transmittances as high as that of bulk silicon. The refractive indexes of the composites increased as the density of nano-silicon particles in the polymers increased. A two-layer antireflection coating was fabricated on a silicon wafer. The measured amplitude transmittance exceeded 90% at frequencies from 0.7 to 1.5 THz, and corresponded to the calculated transmittance.