Slit manufacturing and integration for the Sentinel-4 NIR and UV-VIS spectrometers

The sentinel–4 spectrometer´s slits are the key components of the ultraviolet–visible (UV–VIS) and the near infrared (NIR) channels for earth observation, with absolute slit width accuracy and variation required as < 0.1 ?m, respectively, and slit planarity < 0.4 ?m peak to valley (P-V). Adapted lithographic structuring techniques as developed for the dry- and wet etching of silicon-on-insulator (SOI) wafers combined with special integration devices for accurate alignment as well as precision optical polishing of the mounting planes of the slit holders together with spring elements can fulfil these requirements. Protected aluminum coating ensures a light tight optical density at wavelengths between 200 nm and 1200 nm, electrical grounding, and chemical protection.