Echelle grating with improved polarization characteristics used for Earth observation

An Echelle-grating specifically developed for the space borne measurement of earth's atmospheric CO2 concentration is presented. It has a line density of ∼170L/mm and is manufactured on a thick crystalline silicon substrate using electron beam lithography. The echelle profile is realized using a highly anisotropic chemical etching process, which stops on the <111> crystallographic planes of the crystal. The established manufacturing process allows perfect linear grating facets with negligible corner rounding of the profile. The important property of showing a low polarization sensitivity of the diffraction efficiency is achieved by a special design and technology for applying the gold coating of the grating which intentionally leaves one grating facet uncoated.