Terahertz-Wave Antireflection Coating on Ge and GaAs with Fused Quartz

In the terahertz-wave region, fabrication of an antireflection (AR) coating is difficult because it must be as thick as several tens of micrometers, which is far thicker than that used in the optical region. We discuss a lapping method for fabricating an AR layer with a desired thickness for terahertz-wave optical devices. To demonstrate this method, we glued a thin fused-quartz plate to a surface of an undoped Ge or GaAs wafer and polished it to a thickness of one-quarter wavelength. This reduced the reflectivity of the AR surface to 1/720 of the reflection of an uncoated surface, as expected from optical theory.