Terahertz antennas and related optical components

Millimeter- and submillimeter-wave imaging systems for astronomy, planetary, and Earth science applications are increasingly moving towards large focal plane arrays. The relatively long wavelengths together with focal ratios encountered imply mm-sized pixels, and when one considers arrays with a hundred to thousands of pixels, we have to deal with optical elements of quite substantial size. In many applications, geometry makes lenses far more attractive than mirrors, and since cryogenic detectors are invariably employed, ground-based systems as well as testing of space-based systems require vacuum windows 10s of cm in diameter. Especially at shorter wavelengths, very low loss materials are required since the thickness of lenses and windows is substantial, reaching several cm. Crystal quartz can be used in some cases, but available diameters are limited to 12 cm. The anisotropy of the material can be harmful in many situations as well.