Infra Red lens polishing for high performance applications

This activity aims to develop processes to polish InfraRed (IR) optical lenses made of typical IR materials such as ZnSe, ZnS, Si of spheric and aspheric shape down to a surface roughness of 1 nm RMS or below.

SWIR and IR optical lens materials are difficult to machine, since often they are based on micro-crystalline or crystalline substrates which makes them also brittle and difficult to polish. SWIR spectrometer optics for CarbonSat, Sentinel 5 or NISP (Euclid) for instance are highly critical with respect to straylight performance. For mass and volume reasons the optical design of the camera of the spectrometer is based on lenses (Si, ZnSe, ZnS). Those IR lenses have large refractive indices and surface roughness values (current state of the art roughness communicated by industries working on the CarbonSat parallel study, are 2nm RMS for spherical and 4 nm RMS for aspherical IR lenses) which generate straylight levels an order of magnitude higher than regular glass lenses. An improvement in polishing quality of IR lenses is therefore needed. The core of the activity shall be the process refinement/development on a series of samples based on different IR materials. The samples shall be polished to a roughness level of 1 nm RMS or below and tested.