MetaTel: Ongoing work on a meta-material sub-THz telescope for Earth observing

We report on ongoing technology development activities in the build and testing of a refractive telescope composed of metamaterial Gradient Index (GrIn) lenses based on photolithographic meshes. This concept is tailored for Earth Observation, and more precisely limb-scanning in the sub- THz bands addressing emission lines between 50 and 190 GHz. A single GrIn lens design which includes in-built anti-reflection coating layers, allows us to produce sufficient refraction to allow an optical design of a set of compound lenses to create the first THz range telescope fully composed of metamaterials. First lens prototypes have been built and tested spectrally and spatially and compared to analytical models showing good agreement. Prediction of telescope performance is discussed as well as future developments.