The challenges of broadband performances within a compact imaging spectrometer: the ELOIS solution

ELOIS VISWIR is a science-grade, smallsat compatible, pushbroom hyperspectral payload covering the entire VISWIR spectral range (400-2450 nm) with over 200 contiguous 10 nm wide spectral bands. Its unique all reflective optical design enables covering a 70 km swath with 35 m ground sampling distance (GSD), while guaranteeing high imaging performances across the full field of view. At the core of the instrument, the spectrometer formula expands upon AMOS’ state of the art Offner-based ELOIS VNIR long-slit spectrometer [1], including key features such as built-in slit de-magnification, and the use of a fine-tuned freeform diffraction grating enabling the appropriate compensation of the optical aberrations affecting the fast, F/2.1 focal plane. Besides its excellent imaging performances and advanced control of distortions, the ELOIS VISWIR delivers unparalleled throughput in a single optical chain thanks to the inclusion of leading-edge technical solutions including a broadband multi-blazed freeform diffraction grating, a variable dichroic beam-splitter plate, and high efficiency order sorting filters. In this paper, we discuss these key ingredients in the optical design of the ELOIS VISWIR spectrometer and report the optical performances of the manufactured optical components.