Observation of wide-angle impedance matching in terahertz photonic crystals

Reflection due to impedance mismatch at interfaces of different materials is undesired in many THz applications including THz communication, spectroscopy and imaging. In this work, we theoretically and experimentally demonstrate a type of THz photonic crystals exhibiting wide-angle impedance matching property with free space. The reflection as well as the reflection-induced Fabry-Perot resonances are efficiently suppressed in a relatively broad spectrum. A sample is fabricated using high-resistance silicon and polyethylene terephthalate films. By using THz time domain spectroscopy, we have clearly observed high transmittance and suppression of Fabry-Perot resonances for a wide range of incident angles (0 degrees-60 degrees) and a relatively broad spectrum (0.26-0.55 THz) in both polarizations. Our work opens a general approach for improvement of transmission and imaging quality in THz spectroscopy.